Entomology
"If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos."
- Edward O. Wilson
- Edward O. Wilson
introduction
Entomology is the scientific study of insects, including genetics, taxonomy, morphology, physiology, behavior, and ecology. It is an important subject for all gardeners to dabble in, as it will inform our plant choices, garden culture, and how we treat insects to either encourage or discourage their presence. The origin of the word entomology is Greek, and combines the words for insect (entomon) and study (logia). Some insects have called the earth their home for over 400 million years, and there are an estimated 1.3 million different species (only an estimated 2/3 of which have been officially described). Insects occupy every habitat on earth except for the open ocean. They live in or on animals, plants, soil, wood structures and furniture, streams, lakes, ocean shores, and in stored grain and other food containers. The vast majority of insects have either a neutral or beneficial effect on the world around them. For example, bees and many other insects are considered pollinators to some of our most important crops, and other beneficial insects prey on or parasitize pest insects, using them as a source of food and helping to keep their populations under control. Pest insects can cause serious economic damage by destroying yields both in the field and in storage. About a sixth of the world's food crops are consumed by insect pests, who also carry bacterial, viral and fungal diseases which they transmit to crop plants, livestock, and humans.
The importance of insects to our worldwide biodiversity and functioning cannot be overstated. Many gardeners probably wish that insects were not a part of gardening, as they elicit feelings like fear and uneasiness (or possibly queasiness). The fear of insects, or entomophobia, is a widespread emotion, but it is unwarranted for the most part. As you move through this module, I challenge you to put aside your preconceived notions of these little garden residents, and really open your mind to the idea of welcoming them into your space. This module can serve as a powerful desensitization tool; increasing your knowledge can go a long way in lessening negative reactions to insects.
The importance of insects to our worldwide biodiversity and functioning cannot be overstated. Many gardeners probably wish that insects were not a part of gardening, as they elicit feelings like fear and uneasiness (or possibly queasiness). The fear of insects, or entomophobia, is a widespread emotion, but it is unwarranted for the most part. As you move through this module, I challenge you to put aside your preconceived notions of these little garden residents, and really open your mind to the idea of welcoming them into your space. This module can serve as a powerful desensitization tool; increasing your knowledge can go a long way in lessening negative reactions to insects.
insects and their relativesInsects belong to a group of animals that also includes crabs, lobsters, spiders, and ticks: Arthropods. These creatures have exoskeletons rather than internal skeletons and to grow must go through stages of molting. Entomologists (scientists who study insect life) have defined what characteristics a creature must have in its adult form to be classified as an insect.
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The first requirement is that insects have three body regions, including a distinct head, thorax (which supports both the head and wings), and abdomen. The second is that insects have three pairs of jointed legs. These six legs are connected to the thorax (one pair per segment), and can be specialized for activities like jumping, grasping, or walking.
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The third requirement to be classified as an insect is that an organism must have a pair of antennae. These are attached to the head and are sensory organs that give the insect information about the world around it. The antennae can be short, long, smooth, serrated, or feathered. Insects may or may not have wings attached to their thorax and if they do, they can appear in one or two pairs. Most adult insects have the ability to fly, though some do not. The venation of wings is an important identifying factor for many insect species. Insects are cold-blooded, meaning that their body temperature is externally controlled by the ambient temperature of the environment in which they live. As a result, insects are most active during the warmer months of the year and during the warmer hours of the day. Their rate of development is dependent on temperature, as well; insects go through their various life stages more quickly in the warmer months.
There are many different types of insects though many organisms that most people consider to be insects are not actually insects. Insect relatives include pillbugs (crustaceans), centipedes (chilopods), millipedes (diplopods), snails and slugs (mollusks), and spiders, ticks and mites (arachnids). Although the following organisms are not true insects, they do deserve honorable mentions as insect-like beings. These organisms play important roles in the garden, some as antagonists that destroy plants (and sometimes a gardener's will to continue gardening), and some as important decomposers, pollinators and predators of garden pests.
Arachnids: Mites and Spiders
Arachnids are wingless critters with no antennae, and have two body regions instead of three. The head portion is called the cephalothorax and the posterior is called the abdomen (similar to insect species). Adult arachnids have four pairs of jointed legs attached to their abdomens. Mites are very tiny (many smaller than the period at the end of this sentence), and a hand lens is usually required to see them. Mites are very common garden pests found on fruit and nut trees, vegetable crops, ornamentals, and house plants. They feed on plants using piercing mouthparts that are inserted into the plant host and sucking up liquid cell contents. Because mites are so small, they are usually identified by the damage they inflict on their host plants, such as yellowish stippling (small, light-colored areas) on leaves, general decline of plants, leaf drop, and distortion of leaves, fruit or blossoms.
Arachnids are wingless critters with no antennae, and have two body regions instead of three. The head portion is called the cephalothorax and the posterior is called the abdomen (similar to insect species). Adult arachnids have four pairs of jointed legs attached to their abdomens. Mites are very tiny (many smaller than the period at the end of this sentence), and a hand lens is usually required to see them. Mites are very common garden pests found on fruit and nut trees, vegetable crops, ornamentals, and house plants. They feed on plants using piercing mouthparts that are inserted into the plant host and sucking up liquid cell contents. Because mites are so small, they are usually identified by the damage they inflict on their host plants, such as yellowish stippling (small, light-colored areas) on leaves, general decline of plants, leaf drop, and distortion of leaves, fruit or blossoms.
Mites are very small arachnids.
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Mites have two body segments.
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Mite damage on plant foliage.
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There are two families of mites that cause most of the damage to garden or crop plants in California. The first is known as the tetranychids, which includes webspinning mites as well as brown and red mites. Webspinning spider mites are very common in gardens, and three of the most prominent species in gardens are the Two-Spotted Spider Mite (TSSM), the Strawberry Spider Mite and the Pacific Spider Mite.
Two-Spotted Spider Mite
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Strawberry Spider Mite
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Pacific Spider Mite
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TSSMs and Strawberry Spider Mites are very similar morphologically; the only discernible difference being in the genitalia of males. Pacific spider mites are more green in color, and do not have the abdomen spots that the other two species have. All three of these web-spinning spider mites live in colonies, usually situated on the undersides of leaves. It takes about a week for a generation of mites to grow into adulthood in favorable conditions (hot and dusty). Red mites are also included in the tetranychid family, and the most commonly found garden mites in this group are the Citrus Red Mite and the European Red Mite.
Citrus Red Mite
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European Red Mite
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Red mites congregate on the undersides of leaves.
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The second family of common garden mites are the Eriophyid Mites, which only have four legs (rather than the eight usually found in Arachnids). These mites include Rust Mites, Bud Mites, and Blister Mites. Regularly encountered species include the Fuchsia Gall Mites and the Tomato Russet Mites. These mites cause leaves, flowers or fruit to deform and can cause plants to form galls. Mites thrive in gardens in which insecticides are used, as these chemicals kill mite predators. A garden practice that will lower mite infestations is forcefully spraying plants with water, focusing on the undersides of leaves.
Fuchsia Gall Mite damage.
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Evidence of Tomato Russet Mites.
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Blister Mite Damage.
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For more information on Mites, including pest control options, check out the following page:
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Quick Question: What is a Gall?
A gall, put simply, is a growth that forms on a plant during the yearly accelerated period of growth (usually around springtime), caused by an increase in growth hormone triggered by an insects' salivary secretions. The gall continues to grow in size as the insect secretes enzymes and feeds on the plant tissues, and will continue to exist after the insect has died. Galls can form on leaves, flowers, and stems. Although they may not be aesthetically pleasing, galls do not actually do much damage to plant heath, and control is not normally necessary. |
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Spiders are larger than mites, and their two body regions are more separated. Though spiders are feared by many, most spiders are completely harmless to humans and are beneficial predators that feed on insects and other small animals by paralyzing them with venom. Most spiders form webs, but others lie in hiding for prey to wander by. Two notable spiders that are poisonous are the Black Widow and the Brown Recluse Spider. Black Widows tend to live in dark, damp places and spin messy webs. These spiders are shiny and black, and have a reddish-orange hourglass marking on the underside of their abdomen.
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Brown Recluse spiders are found primarily in the southeastern United States and have a violin shape on the upper part of their thorax. A commonly encountered non-venomous spider that takes up residence inside homes is the House Spider, which makes its web in corners of rooms.
Black Widow spider.
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Brown Recluse.
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House Spider.
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For more information on spider anatomy, behavior, and species, check out the following page:
Chilopods (Centipedes)
These terrestrial arthropod predators have long antennae and a pair of legs sprouting from each of their flattened body segments. The number of body segments varies from 15 to 191, and is always an odd number. These insect-like organisms are commonly encountered in soil, debris, under rocks or bark, in debris piles, and in rotting wood. Larger centipedes can bite humans using their pincer-like appendages and inject venom in a way similar to that of bee stings. Centipedes are considered to be garden beneficials and act as decomposers, breaking down garden debris and turning it into a valuable source of nutrients for plants and other garden organisms. They are solitary critters, and infestations are very uncommon.
These terrestrial arthropod predators have long antennae and a pair of legs sprouting from each of their flattened body segments. The number of body segments varies from 15 to 191, and is always an odd number. These insect-like organisms are commonly encountered in soil, debris, under rocks or bark, in debris piles, and in rotting wood. Larger centipedes can bite humans using their pincer-like appendages and inject venom in a way similar to that of bee stings. Centipedes are considered to be garden beneficials and act as decomposers, breaking down garden debris and turning it into a valuable source of nutrients for plants and other garden organisms. They are solitary critters, and infestations are very uncommon.
Centipedes have long bodies, made up of many segments, each with one leg on each side.
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Centipedes have varying appearances depending on the species.
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For more information on Centipedes, consult the page linked below:
Crustaceans: Sowbugs and Pillbugs (Woodlice)
When we think of Crustaceans, many picture ocean-dwelling creatures like crabs, crayfish and lobsters, but these animals have land-dwelling relatives, as well. These critters live in soil and breathe through gills, much like their aquatic counterparts. They have segmented, hard outer shells and roll up into balls when disturbed. These organisms feed on decaying plant matter and are most active at night. They will occasionally feed on seedlings, new roots and leaves, fruits (like strawberries), or vegetables (like squash) if plant parts are directly touching soil. These garden friends are frequently blamed for damage caused by other insects, simply because they are numerous in gardens. The main difference between sowbugs and pillbugs is their body shape; pillbugs have a more rounded body shape, whereas sowbugs have a sort of beveled edge around their bodies.
When we think of Crustaceans, many picture ocean-dwelling creatures like crabs, crayfish and lobsters, but these animals have land-dwelling relatives, as well. These critters live in soil and breathe through gills, much like their aquatic counterparts. They have segmented, hard outer shells and roll up into balls when disturbed. These organisms feed on decaying plant matter and are most active at night. They will occasionally feed on seedlings, new roots and leaves, fruits (like strawberries), or vegetables (like squash) if plant parts are directly touching soil. These garden friends are frequently blamed for damage caused by other insects, simply because they are numerous in gardens. The main difference between sowbugs and pillbugs is their body shape; pillbugs have a more rounded body shape, whereas sowbugs have a sort of beveled edge around their bodies.
Sowbug body part diagram.
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Pillbug v. Sowbug body shape.
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Sowbugs are important decomposers.
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For more information on Woodlice, consult the page linked below:
Diplopods: Millipedes
These worm-like creatures have a visible head that support a pair of short antennae. Their bodies are elongated and rounded on top, with two pairs of legs on most of their body segments. They are commonly found in soil, feeding on fungi and decaying organic matter. Millipedes are harmless to mammals.
These worm-like creatures have a visible head that support a pair of short antennae. Their bodies are elongated and rounded on top, with two pairs of legs on most of their body segments. They are commonly found in soil, feeding on fungi and decaying organic matter. Millipedes are harmless to mammals.
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To learn more about Millipedes, consult the page linked below:
Mollusks: Snails and Slugs
At night, snails and slugs become active, and they can be some of the most destructive pests in the garden. More active after irrigation, these organisms move by sliding along mucus or slime trails secreted by their single foot. The most common species in California are the brown garden snail (Cornu aspersum) and the gray garden slug (Deroceras reticulatum), both of which feed on decaying organic matter, seedlings, and low-growing herbaceous material and ripening fruits.
At night, snails and slugs become active, and they can be some of the most destructive pests in the garden. More active after irrigation, these organisms move by sliding along mucus or slime trails secreted by their single foot. The most common species in California are the brown garden snail (Cornu aspersum) and the gray garden slug (Deroceras reticulatum), both of which feed on decaying organic matter, seedlings, and low-growing herbaceous material and ripening fruits.
Gray Garden Slug.
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Brown Garden Snail.
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Snail and slug trails.
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To find more information about snails and slugs, including pest control options, visit the following page:
insect growth and development
The life of every garden insect begins as an egg. Eggs vary in shape, size, color, and the location in which they are laid. For example, in many aphid species, the female carries her eggs in her body and baby aphids emerge from inside her as living insects. Eggs are often tiny, and can be sometimes difficult to spot, but they are a great indicator of future insect population growth. After hatching, as insects grow they will shed their exoskeleton up to six times in a process called molting, where they emerge from an old skin with a brand new (and in many cases, improved) one. The gradual change in form and appearance from juvenile to adult insect is called metamorphosis. There are three categories of metamorphosis: none, gradual (incomplete) and complete.
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The life cycle of a grasshopper is an example of a gradual (or incomplete) metamorphosis. The young grasshopper, called a nymph, emerges from its egg looking a lot like an adult grasshopper, the only difference being its size and the fact that it has not yet developed any wings. Many insects go through this incomplete metamorphosis, including Dragonflies, Earwigs, Crickets, Cockroaches, and Mantids. |
Complete metamorphosis is a more complicated process, but also begins with an egg. The egg is the first of four life stages, followed by the larva stage. Larvae are very different in appearance and behavior from their adult counterparts. Some larvae are very destructive (as in moths, butterflies, and flies), and others are actually less destructive than their adult forms (as in cucumber beetles or flea beetles). As larvae increase in size, they molt. Next up is the pupal stage, in which insects are relatively inactive. During this time, insects will encase themselves in a cocoon or other structure or simply hang out exposed on the ground or in vegetation. The adult stage comes after the pupal stage, and after insects have reached this stage they will no longer molt or increase in size. A good rule of thumb for identifying the adult stage is the presence of wings (in winged insect species, anyways).
The egg of a Monarch butterfly.
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Monarch butterfly larvae are called caterpillars, and they have large appetites.
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A Monarch butterfly cocoon.
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An adult Monarch butterfly.
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After reaching the adult stage, the main goal of any insect is to procreate. Some organisms need both male and female individuals to mate in order to create eggs. Other insects, aphids or scale insects for example, engage in parthenogenesis, where female insects produce eggs in the absence of a male partner. The life cycle of development from egg to the production of an egg by the subsequent adult stage is called a generation. Some insects produce one generation each year, others can have several generations produced in a years' time. Cicadas are at the opposite end of the spectrum, with very spaced-out generations; it takes up to 17 years for the next generation to emerge from their eggs and reproduce.
How Insects Feed
Insects feed in two main types of ways: by chewing or by sucking, and the way an insect feeds can change over their lifetime. For example, in butterfly species the larvae have chewing mouthparts that are great for eating plants, but as adults, butterflies have sucking mouthparts for consuming nectar. Chewing insects are equipped with strong jaws, and mandibles with teeth specialized for chewing. These mouthparts allow insects and larvae to consume what they need to grow and molt, and will help them to create holes and tunnels in leaves, twigs, fruits, flowers and stems. Chewing insects cause more visible loss of plant tissue:
Insects feed in two main types of ways: by chewing or by sucking, and the way an insect feeds can change over their lifetime. For example, in butterfly species the larvae have chewing mouthparts that are great for eating plants, but as adults, butterflies have sucking mouthparts for consuming nectar. Chewing insects are equipped with strong jaws, and mandibles with teeth specialized for chewing. These mouthparts allow insects and larvae to consume what they need to grow and molt, and will help them to create holes and tunnels in leaves, twigs, fruits, flowers and stems. Chewing insects cause more visible loss of plant tissue:
Many insects have chewing mouthparts.
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Caterpillars are voracious eaters.
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Chewing damage to fruit.
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Sucking mouthparts are common in insects such as aphids, true bugs, leafhoppers, scale insects, psyllids, thrips, and whiteflies. A stylet (sort of like a probe) is used to pierce plants' outer layers and suck up plant sap inside. This activity can cause injury symptoms to foliage like leaf curling, stunted growth, stippling or yellowing, brown mottling, deformed plant parts, and galls. Some insects with piercing mouthparts will inject a toxic saliva into the plant as they feed, causing dieback from the feeding spot. These insects can unfortunately also carry transmittable microbial plant pathogens (mainly viruses), passing them to each plant they feed on.
An insect with sucking mouthparts.
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Insects with piercing mouthparts can inject saliva into feed sites, causing tissue dieback.
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Insects with piercing or sucking mouthparts can transmit pathogens, like Tobacco Mosaic Virus.
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Insect Breathing and Circulation Most insects breathe through tiny holes in their bodies called spiracles, and do not have true lungs. Spiracles are commonly located on both sides of an insects' body, two on the thorax and about eight on the abdomen of adults, though this varies. Small tubes called tracheae take air from the spiracles and move it to parts of the body where it is needed. Carbon dioxide is expelled back out through the spiracles. Many insecticides work by entering insects' bodies through their spiracles. |
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insect classification and identification
All insects that have been identified and documented are grouped into around 24 orders, each order containing numerous species. These orders are further divided into families, genera and species, and many of the species have common names, similar to the classification of plant life. Identifying insects is sometimes a difficult process, and in some cases it may not be necessary as long as an organism is determined to be either an issue or a beneficial. For example, once a gardener recognizes that they have an aphid infestation, it is not usually necessary to identify exactly which species of aphid has taken up residence (unless they're a particularly curious individual); the treatment protocols are the same. The following orders contain insects that are important in the garden ecosystem:
Blattodea (Cockroaches and Termites)
This order of insects includes cockroaches and recently, termites have been added to this group, as well. Termites were previously in an order of their own, Isoptera, but after genetic and molecular testing they were recategorized. These insects are ancient, having been around for about 275 million years. There are 4,400 species of cockroach (in 500 genera) and 3,000 species of termite (in 300 genera). Most of these critters are outdoor insects, though some have evolved to cohabitate with humans. Cockroaches are not social, but do tend to gather in groups, especially in areas with an abundant food source. They are dark in color, and have segmented bodies (three segments in the thorax and ten segments in their abdomen). Cockroaches have three pairs of legs with claws at the end for gripping and climbing, and their legs have actually been used as blueprints for robotic legs.
This order of insects includes cockroaches and recently, termites have been added to this group, as well. Termites were previously in an order of their own, Isoptera, but after genetic and molecular testing they were recategorized. These insects are ancient, having been around for about 275 million years. There are 4,400 species of cockroach (in 500 genera) and 3,000 species of termite (in 300 genera). Most of these critters are outdoor insects, though some have evolved to cohabitate with humans. Cockroaches are not social, but do tend to gather in groups, especially in areas with an abundant food source. They are dark in color, and have segmented bodies (three segments in the thorax and ten segments in their abdomen). Cockroaches have three pairs of legs with claws at the end for gripping and climbing, and their legs have actually been used as blueprints for robotic legs.
Cockroach.
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Cockroach diagram.
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Different forms of termites in a colony.
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Termites.
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Termites, on the other hand, form colonies with a designated king and queen and sterile workers and soldiers (who are blind for the most part). Termites are pale in color, and have soft bodies with three segments: the prothorax (front segment with legs), the mesothorax (middle of the body, also with two legs), and the metathorax (with a third pair of legs). Most termites cannot fly, but the king and queen can (they are referred to as alates). These insects feed on wood that is in contact with or near soil, building soil tubes to bridge any open-air stretches of their commute. Drywood termites damage buildings, furniture, utility poles, terraces, and piled lumber (really any outdoor or indoor wood). If wood has been treated, termite damage can be resisted, but if the wood stays wet or in contact with soil for long enough and there are termites nearby, they will start to eat it.
For more information about Cockroaches and Termites, including pest control information, consult the following page:
Coleoptera (Beetles and Weevils)
Beetles are very common in gardens, constituting about 40% of all living insect species worldwide. Most are not considered to be pests, and many species are actually beneficial predators and decomposers in landscapes. For example, the Convergent Lady Beetle is an important predator that controls aphid and mite populations. Beetles engage in complete metamorphosis, have chewing mouthparts, and commonly have two sets of wings: a hard outer pair and a delicate inner pair that is used for flight (though not all beetles are able to fly). Beetles and weevils usually have noticeable antennae, and weevils are differentiated by their noticeably protruding snouts.
Beetles are very common in gardens, constituting about 40% of all living insect species worldwide. Most are not considered to be pests, and many species are actually beneficial predators and decomposers in landscapes. For example, the Convergent Lady Beetle is an important predator that controls aphid and mite populations. Beetles engage in complete metamorphosis, have chewing mouthparts, and commonly have two sets of wings: a hard outer pair and a delicate inner pair that is used for flight (though not all beetles are able to fly). Beetles and weevils usually have noticeable antennae, and weevils are differentiated by their noticeably protruding snouts.
Beetles have two sets of wings.
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Junebugs are a type of beetle.
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Convergent Lady Beetles, or Ladybugs, are beetles, also.
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Weevils look like beetles, but have a protruding proboscis.
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Although most are harmless to garden functioning, there are a few notable mentions of beetles in the pest category (in various stages of development): Flea Beetles, Boring Beetles, Granary Weevils, Wireworms (Click Beetle Larvae), Cucumber Beetles, Vegetable Weevils, and Fruit Beetles are common pests in western home vegetable gardens. For more on different species of beetles as well as information on how to deal with beetle pests in the garden, consult the page below:
Dermaptera (Earwigs)
These organisms go through a gradual (or incomplete) metamorphosis, and have chewing mouthparts. Molting five times in their lives, as adults they are elongated, flattened insects that are characterized by strong, movable forceps on their rear end. Earwigs have two sets of modified wings that consist of a thickened leathery short front pair and membranous hind wings. Their antennae are threadlike and about half the length of the main body. Earwigs can be both pests and beneficials in the garden: they are aphid predators, but do also feed on plant shoots, seedlings, and a handful of dead and live organisms. They are nocturnal and hide during daytime hours in leaf litter, mulch, and bark.
These organisms go through a gradual (or incomplete) metamorphosis, and have chewing mouthparts. Molting five times in their lives, as adults they are elongated, flattened insects that are characterized by strong, movable forceps on their rear end. Earwigs have two sets of modified wings that consist of a thickened leathery short front pair and membranous hind wings. Their antennae are threadlike and about half the length of the main body. Earwigs can be both pests and beneficials in the garden: they are aphid predators, but do also feed on plant shoots, seedlings, and a handful of dead and live organisms. They are nocturnal and hide during daytime hours in leaf litter, mulch, and bark.
An adult earwig.
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A female, nymph and male.
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Earwigs have the ability to fly.
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Earwig nymphs.
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For more information about earwigs, including how to manage them in the landscape, consult the following page:
Diptera (Flies, Mosquitoes, Gnats, Leafminers and Midges)
In this diverse group of insects, members share the characteristics of having a complete cycle of metamorphosis and piercing or sponging mouthparts (chewing when they are in their larval stage). Most larvae do not have true legs or head capsules, and are white and worm-like. Adults are generally soft-bodied and hairy, have compound eyes, and a pair of membranous wings. Mosquitoes are the exception; their larvae have distinct head capsules. The most recognizable member of this group is probably the Common Gray Housefly, which infests homes, livestock barns, or poultry enclosures. Their larvae, called maggots, are commonly found in manure piles and around decaying matter, and flies can produce several generations per year. Many flies and their maggots are considered to be garden pests:
In this diverse group of insects, members share the characteristics of having a complete cycle of metamorphosis and piercing or sponging mouthparts (chewing when they are in their larval stage). Most larvae do not have true legs or head capsules, and are white and worm-like. Adults are generally soft-bodied and hairy, have compound eyes, and a pair of membranous wings. Mosquitoes are the exception; their larvae have distinct head capsules. The most recognizable member of this group is probably the Common Gray Housefly, which infests homes, livestock barns, or poultry enclosures. Their larvae, called maggots, are commonly found in manure piles and around decaying matter, and flies can produce several generations per year. Many flies and their maggots are considered to be garden pests:
Common Gray Housefly
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Cabbage Maggot
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Seedcorn Maggot
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Onion Maggot
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Walnut Husk Fly
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Apple Maggot
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Vinegar Fly (Fruit Fly)
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Spotted Wing Drosophila (Fruit Fly)
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Some of the insects commonly referred to as Leafminers are in the fly family (others fall in the Lepidoptera group alongside butterflies and moths). Adult flies will deposit their eggs inside of leaves, and the larvae that hatch burrow through the leaf while they feed, creating a 'mine'.
Leafminer
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Leafminer damage.
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Leafminer Maggot
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Mosquitoes are members of the Diptera order as well, and are slender, frail-looking flies. The larvae typically live in standing water. Adult females use piercing mouthparts to puncture the skin of mammals and suck out their blood. This action can transmit diseases (like malaria) in humans and other host animals.
Mosquito larvae in water.
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Mosquito.
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A diagram of mosquito body parts.
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Mosquito bites are very itchy.
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There is a species of fly that deserves a special mention here due to its helpfulness in the garden. You may have seen these small flies buzzing around your flowers and thought that they were little bees of some kind, but Syrphid Flies (also called hover flies or flower flies) are actually true flies. Their larvae look like small green to brown slugs or legless caterpillars, and eat aphids in high numbers. It is because of this pest-fighting ability that these flies are very beneficial to gardens.
Syrphid flies look like small bees.
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Syrphid fly larvae eat aphids.
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Syrphid fly anatomy.
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These are also called Hover Flies, due to their ability to hover in place.
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Hemiptera (True Bugs, Leafhoppers, Aphids, Scales, Mealybugs and Whiteflies)
This group has a gradual (incomplete) metamorphosis, and piercing-sucking mouthparts. True bugs have two sets of wings that, when folded, form an X or inverted triangle shape on their back. Their eggs are cylindrical or barrel-shaped, and they produce between one and several generations in a calendar year. Both the adults and nymphs of numerous true bug species are plant-feeding pests, for example Stink Bugs, Lygus Bugs, Squash Bugs, and Harlequin Bugs. Garden plant pests that are true bugs use their sucking mouthparts to retrieve the contents of plant cells, which damages leaves, buds, and fruits. There are also some species that inject toxins into their host plant, causing yellow spots on leaves and ripening fruit.
This group has a gradual (incomplete) metamorphosis, and piercing-sucking mouthparts. True bugs have two sets of wings that, when folded, form an X or inverted triangle shape on their back. Their eggs are cylindrical or barrel-shaped, and they produce between one and several generations in a calendar year. Both the adults and nymphs of numerous true bug species are plant-feeding pests, for example Stink Bugs, Lygus Bugs, Squash Bugs, and Harlequin Bugs. Garden plant pests that are true bugs use their sucking mouthparts to retrieve the contents of plant cells, which damages leaves, buds, and fruits. There are also some species that inject toxins into their host plant, causing yellow spots on leaves and ripening fruit.
Stink Bug
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Lygus Bug
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Squash Bug
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Harlequin Bug
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These pests are best removed by hand-picking adults and removing their egg colonies from leaves. There are also some species of True Bugs that are garden heroes, consuming insects that gardeners consider pests. These bugs include Assassin Bugs, Damsel Bugs, Minute Pirate Bugs, and certain species of Stink Bugs.
Assassin Bugs
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Damsel Bugs
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Minute Pirate Bugs
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Squash Bug
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Aphids
Many in the Hemiptera group are small, soft-bodied insects and they can either have wings or not. Aphids are grouped in with true bugs, and have two cornicles (tube-like projections) protruding from their rear end. They can come in many shapes, sizes and colors (including brown, black, green, yellow, and red). Aphids attack a wide variety of crops in California, from vegetables and legumes to stone fruit crops, apples, and ornamentals. In our climate, they can produce numerous generations per year. Some species produce offspring via parthenogenesis, others produce offspring sexually. They are excellent at reproducing either way; an adult female of some species can produce 1,560,000,000,000,000,000,000,000 (1.56 times 10 to the 24th power) offspring over her lifetime.
Many in the Hemiptera group are small, soft-bodied insects and they can either have wings or not. Aphids are grouped in with true bugs, and have two cornicles (tube-like projections) protruding from their rear end. They can come in many shapes, sizes and colors (including brown, black, green, yellow, and red). Aphids attack a wide variety of crops in California, from vegetables and legumes to stone fruit crops, apples, and ornamentals. In our climate, they can produce numerous generations per year. Some species produce offspring via parthenogenesis, others produce offspring sexually. They are excellent at reproducing either way; an adult female of some species can produce 1,560,000,000,000,000,000,000,000 (1.56 times 10 to the 24th power) offspring over her lifetime.
Aphid.
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Aphids birth live offspring.
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Aphid damage.
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Parasitic wasps help to control aphid populations.
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As they feed, aphids cause curled, distorted leaves and sticky honeydew exudates (which causes sooty mold on leaves lower down on the plant). A few aphids can transmit viral diseases as they feed, but for the most part a low to moderate population of aphids can be tolerated in most home gardens. If aphids need to be removed, the most effective way to do so is to simply spray them off of the plant with water. Natural predators of aphids include lady beetles, syrphid fly larvae, lacewing larvae, and parasitic wasps.
Leafhoppers
Leafhoppers are insects that feed on leaf undersides, which causes stippling damage. There are many species of leafhoppers that attack a variety of plants, including ornamentals, turf, beans, cucurbits, potatoes, eggplants, grapes, and apples, and some can spread diseases. For example, leafhoppers are the main spreaders of Pierce's disease of grape vines. They can be tolerated in most gardens, and are very difficult to manage because of their high mobility.
Leafhoppers are insects that feed on leaf undersides, which causes stippling damage. There are many species of leafhoppers that attack a variety of plants, including ornamentals, turf, beans, cucurbits, potatoes, eggplants, grapes, and apples, and some can spread diseases. For example, leafhoppers are the main spreaders of Pierce's disease of grape vines. They can be tolerated in most gardens, and are very difficult to manage because of their high mobility.
Leafhopper.
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Leafhopper nymph.
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Leafhopper leaf damage.
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Pierce's disease.
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Scale Insects
With about 8,000 described species, these are small but mighty pests of many plants, including fruit trees, nut trees, grape vines, and ornamentals. These insects are generally split into two groups: soft scales and armored scales. Soft scales include Black Scale, Brown Soft Scale, Lecanium Scale, and Kuno Scale are larger than their counterparts and have a more convex shape at adulthood. These scale insects excrete honeydew, drawing ants and causing issues with photosynthesis via the development of sooty mold. Armored scale insects, on the other hand, are relatively small, flat, and have a plate-like, hard shell. They do not produce honeydew as they feed. Scales in this group include California Scale, Walnut Scale, and Oystershell Scale. There are a few scales that don't fit into the two categories above, including Cottony Cushion Scale, Sycamore Scale, and Oak Pit Scale.
With about 8,000 described species, these are small but mighty pests of many plants, including fruit trees, nut trees, grape vines, and ornamentals. These insects are generally split into two groups: soft scales and armored scales. Soft scales include Black Scale, Brown Soft Scale, Lecanium Scale, and Kuno Scale are larger than their counterparts and have a more convex shape at adulthood. These scale insects excrete honeydew, drawing ants and causing issues with photosynthesis via the development of sooty mold. Armored scale insects, on the other hand, are relatively small, flat, and have a plate-like, hard shell. They do not produce honeydew as they feed. Scales in this group include California Scale, Walnut Scale, and Oystershell Scale. There are a few scales that don't fit into the two categories above, including Cottony Cushion Scale, Sycamore Scale, and Oak Pit Scale.
Black Scale (Soft)
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Brown Soft Scale (Soft)
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Lecanium Scale (Soft)
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Kuno Scale (Soft)
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California Scale (Armored)
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Oystershell Scale (Armored)
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Walnut Scale (Armored)
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Cottony Cushion Scale
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Sycamore Scale
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Oak Pit Scale
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Scale damage on a houseplant.
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Scale adult interior.
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Adult female scale insects and many immature forms are sessile (immobile), moving only when first hatched or when they are actively molting. When immobile, they may not even be recognized as insects; they look like small bumps, or scales, usually situated at nodes and along branches. Their bodies conceal the eggs of the next generation. Although small, immobile, and seemingly harmless, these insects are some of the most destructive. To rid your garden of these pests, they can be physically rubbed off of plants, revealing the eggs or young insects and by doing so, killing them. If an insecticide spray is used, they should be applied during the dormant season or when scales are newly hatched. Scales can also be controlled through encouraging their natural predators to come around more often, which usually means controlling the ant population that protects them.
Mealybugs
These ovular, segmented, wax-covered insects are common pests of house plants, greenhouse plants, and woody ornamentals. These insects, like aphids and scale, produce honeydew. Mealybugs are related to scale insects.
These ovular, segmented, wax-covered insects are common pests of house plants, greenhouse plants, and woody ornamentals. These insects, like aphids and scale, produce honeydew. Mealybugs are related to scale insects.
Mealybugs.
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A mealybug colony on a leaf.
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Mealybug infestation.
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Mealybug.
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Whiteflies
These insects are found on and around a wide variety of plants, including veggies, ornamentals, and citrus trees. When host plants are disturbed or shaken, these small flies take flight and form clouds of white, tiny, winged adults. Nymphs are legless and excrete honeydew, only moving when they molt. Infestations of host plants usually cause black sooty mold to form on lower leaves, yellowing foliage, and sticky leaves. Whiteflies can transmit viral infections that have devastating effects on vegetable crops. The positive aspect is that these small flies have many natural predators, and can also be controlled using insecticidal soap on the undersides of leaves.
These insects are found on and around a wide variety of plants, including veggies, ornamentals, and citrus trees. When host plants are disturbed or shaken, these small flies take flight and form clouds of white, tiny, winged adults. Nymphs are legless and excrete honeydew, only moving when they molt. Infestations of host plants usually cause black sooty mold to form on lower leaves, yellowing foliage, and sticky leaves. Whiteflies can transmit viral infections that have devastating effects on vegetable crops. The positive aspect is that these small flies have many natural predators, and can also be controlled using insecticidal soap on the undersides of leaves.
Whiteflies.
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Whiteflies and their eggs and young.
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An adult whitefly.
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Whitefly damage.
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Hymenoptera (Bees, Wasps, Sawflies and Ants)
This very large order of insects undergoes complete metamorphosis, and individuals have chewing mouthparts. Most larvae are legless, though sawfly larvae do have true legs. Adult insects have two pairs of membranous wings, and soft or slightly hardened bodies. Many of these insects play important beneficial roles as pollinators, such as honeybees, leafcutter bees and alkali bees. Others are natural predators of pest insects, for example, paper wasps.
This very large order of insects undergoes complete metamorphosis, and individuals have chewing mouthparts. Most larvae are legless, though sawfly larvae do have true legs. Adult insects have two pairs of membranous wings, and soft or slightly hardened bodies. Many of these insects play important beneficial roles as pollinators, such as honeybees, leafcutter bees and alkali bees. Others are natural predators of pest insects, for example, paper wasps.
Honeybees are important pollinators.
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Leafcutter bee.
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Alkali bee.
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Paper wasp.
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For more information on bee anatomy, behavior, and species, check out the following page:
Ants
These insects are generally non-damaging to gardens, though some can cause issues due to the fact that they feed on the honeydew secreted by pest insects and therefore protect them from predators. Some species of ants can also invade homes and cause structural damage.
These insects are generally non-damaging to gardens, though some can cause issues due to the fact that they feed on the honeydew secreted by pest insects and therefore protect them from predators. Some species of ants can also invade homes and cause structural damage.
Ant
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Ant anatomical drawing.
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Ants feed on honeydew.
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Ants form colonies.
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Sawflies
These insects feed on plant matter and are considered to be pests, especially in their larval stage.
These insects feed on plant matter and are considered to be pests, especially in their larval stage.
An adult sawfly.
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Sawfly caterpillar.
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Sawfly damage.
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Sawfly larvae on a pine tree.
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Lepidoptera (Butterflies and Moths)
These insects go through complete metamorphosis. Larvae are commonly worm-like and are voracious feeders with chewing mouthparts. They have three pairs of legs on their thoraxes and leg-like protuberances on their abdomens. Adult insects are soft-bodied and have two pairs of membranous wings that are covered in small scales. Their mouthparts are sucking tubes. The larvae of these insects have many names, including cutworms, loopers, leafminers, skeletonizers, webworms, and borers. A good way to identify which type of larvae you may have is to watch their behavior. Skeletonizers consume leaf material between veins. Many small caterpillars will roll leaves up around themselves to form shelters as a protection from predators. There are also species of larvae that will feed on fruits or nuts, and are generally more damaging than those who eat foliage. Examples of fruit-feeding larvae are the codling moth and corn earworm (tomato fruitworm). The activity of these larvae leave fruits susceptible to fungal and bacterial infections.
These insects go through complete metamorphosis. Larvae are commonly worm-like and are voracious feeders with chewing mouthparts. They have three pairs of legs on their thoraxes and leg-like protuberances on their abdomens. Adult insects are soft-bodied and have two pairs of membranous wings that are covered in small scales. Their mouthparts are sucking tubes. The larvae of these insects have many names, including cutworms, loopers, leafminers, skeletonizers, webworms, and borers. A good way to identify which type of larvae you may have is to watch their behavior. Skeletonizers consume leaf material between veins. Many small caterpillars will roll leaves up around themselves to form shelters as a protection from predators. There are also species of larvae that will feed on fruits or nuts, and are generally more damaging than those who eat foliage. Examples of fruit-feeding larvae are the codling moth and corn earworm (tomato fruitworm). The activity of these larvae leave fruits susceptible to fungal and bacterial infections.
Cutworm damage.
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Looper damage.
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Skeletonizer damage.
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Leafminer damage.
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Webworm activity.
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Borer damage.
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Codling moth larvae.
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Corn earworm.
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Codling moth larvae are the most destructive pest to apples, pears, and walnuts in the state of California, and they will also attack stonefruit crops. For detecting larval issues in the garden, inspect fruits and the undersides of leaves with a hand lens. Some species, like clearwing moth and carpenterworms, will bore into trunks and branches of trees; these spaces are best investigated using a stepladder. Ridding your garden of these pests is a double-edged sword, unfortunately. Exterminating them will rob your garden of the pollinators they turn into, like butterflies and moths, that are essential for good fruit set.
Clearwing moth.
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Clearwing moth caterpillar.
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Carpenterworm.
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Codling moth.
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Neuroptera (Lacewings, Antlions)
This order of insects go through complete metamorphosis and have chewing mouthparts. Adult insects in this group have two pairs of membranous wings that are held over the body when they are landed. Antennae are long. As larvae, they are flattened and alligator shaped. They also have prominent mandibles for chewing. Most species are predators of other insects. The larvae consume aphids, psyllids, mites, other soft-bodied insects, and insect eggs. Because of this appetite, they are sometimes referred to as aphid lions. Green lacewing eggs are easily recognizable, laid at the ends of tall, threadlike stalks attached to leaves. Adults look relatively fragile, and have green to brown transparent wings with a fine network of venation. Their wings are longer than their bodies are.
This order of insects go through complete metamorphosis and have chewing mouthparts. Adult insects in this group have two pairs of membranous wings that are held over the body when they are landed. Antennae are long. As larvae, they are flattened and alligator shaped. They also have prominent mandibles for chewing. Most species are predators of other insects. The larvae consume aphids, psyllids, mites, other soft-bodied insects, and insect eggs. Because of this appetite, they are sometimes referred to as aphid lions. Green lacewing eggs are easily recognizable, laid at the ends of tall, threadlike stalks attached to leaves. Adults look relatively fragile, and have green to brown transparent wings with a fine network of venation. Their wings are longer than their bodies are.
Lacewing.
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Lacewing larvae eating aphids.
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Lacewing larvae.
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Lacewing eggs.
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Antlions
These insects are closely related to lacewings, and feed on ants and other insects. The adults resemble damselflies, but they have softer bodies with knobby antennae.
These insects are closely related to lacewings, and feed on ants and other insects. The adults resemble damselflies, but they have softer bodies with knobby antennae.
Antlion.
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Antlion larvae.
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Antlion eggs.
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Odonata (Damselflies and Dragonflies)
Damselflies and dragonflies go through a gradual, or incomplete, metamorphosis and have chewing mouthparts. Adults have short, bristly antennae, large eyes and two sets of elongated, membranous, wings. Their bodies are elongated and slender, and have bright colors. All life stages are predators, feeding on mosquitoes, midges, and other smaller insects. Larvae are aquatic. Adult dragonflies hold their wings extended horizontally at rest, and damselflies hold their wings over their backs.
Damselflies and dragonflies go through a gradual, or incomplete, metamorphosis and have chewing mouthparts. Adults have short, bristly antennae, large eyes and two sets of elongated, membranous, wings. Their bodies are elongated and slender, and have bright colors. All life stages are predators, feeding on mosquitoes, midges, and other smaller insects. Larvae are aquatic. Adult dragonflies hold their wings extended horizontally at rest, and damselflies hold their wings over their backs.
Damselfly.
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Damselfly larvae.
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Dragonfly.
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Dragonfly larvae.
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Orthoptera (Grasshoppers and Crickets)
These insects go through a gradual (incomplete) metamorphosis and have chewing mouthparts. Adults are relatively large, hard-bodied, and have two sets of wings. The front wings are hard and leathery, and the second pair underneath are membranous. Insects in these groups sing by rubbing their body parts together. Populations of grasshoppers and crickets build up in foothills and open rangelands, and if grasshoppers migrate to a garden, they can defoliate everything in sight.
These insects go through a gradual (incomplete) metamorphosis and have chewing mouthparts. Adults are relatively large, hard-bodied, and have two sets of wings. The front wings are hard and leathery, and the second pair underneath are membranous. Insects in these groups sing by rubbing their body parts together. Populations of grasshoppers and crickets build up in foothills and open rangelands, and if grasshoppers migrate to a garden, they can defoliate everything in sight.
Grasshopper.
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Grasshopper nymph.
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Cricket.
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Cricket nymph.
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Psocodea (Booklice and Barklice) This order consists of small scavenger insects that feed on fungi, algae, lichen, and organic debris. They are abundant worldwide and have chewing mouthparts and a supportive rod in the center of their mouths that serves to hold their weight as they feed. These insects are soft-bodied with segmented abdomens, and some species have silk glands. They are most commonly detected by the fine, dense webbing that they spin on trunks of host trees, usually Oaks or Pecans. They are not considered harmful; they simply feed on the lichen or algae growing on the tree trunks. Removal involves brushing them away with a broom or spraying them with a garden hose set on high pressure. |
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Siphonaptera (Fleas)
This order of insects goes through complete metamorphosis and has sucking mouthparts. Fleas are wingless, even as adults, and many live their lives as ectoparasites on birds and mammals. Adults have short antennae and flattened bodies, and larvae are tiny, whiteish, and do not have legs. Adults are quick and can jump, sucking and feeding on the blood of their hosts, who sometimes lose their hair as a result. Fleas can carry disease from host to host, and are responsible for the spread of diseases like the bubonic plague and endemic typhus. Larval fleas often live in carpets and feed on decaying organic matter. When controlling fleas, the larvae and adults both need to be taken care of, or the effort will not be successful.
This order of insects goes through complete metamorphosis and has sucking mouthparts. Fleas are wingless, even as adults, and many live their lives as ectoparasites on birds and mammals. Adults have short antennae and flattened bodies, and larvae are tiny, whiteish, and do not have legs. Adults are quick and can jump, sucking and feeding on the blood of their hosts, who sometimes lose their hair as a result. Fleas can carry disease from host to host, and are responsible for the spread of diseases like the bubonic plague and endemic typhus. Larval fleas often live in carpets and feed on decaying organic matter. When controlling fleas, the larvae and adults both need to be taken care of, or the effort will not be successful.
Flea.
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Flea larvae.
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Fleas can cause hair loss.
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A flea anatomical drawing.
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Thysanoptera (Thrips)
These insects have somewhere between a gradual and complete metamorphosis and have sucking-rasping mouthparts. Adults are very small (under a millimeter), slender, and have soft bodies. Long, narrow wings are membranous and each individual has two pairs. Antennae are short. Adults can be a variety of colors, from black to yellow. Some species of thrips are beneficial, feeding on mites and other insects (for example, the six-spotted thrip. Other thrips, like citrus thrips or flower thrips, feed on plant parts and scar leaf and fruit surfaces with their rasping-sucking mouthparts. Damage is mostly cosmetic. They are drawn mostly to citrus, raspberries, grapes, vegetables, and ornamentals, and they can transmit plant diseases as they feed.
These insects have somewhere between a gradual and complete metamorphosis and have sucking-rasping mouthparts. Adults are very small (under a millimeter), slender, and have soft bodies. Long, narrow wings are membranous and each individual has two pairs. Antennae are short. Adults can be a variety of colors, from black to yellow. Some species of thrips are beneficial, feeding on mites and other insects (for example, the six-spotted thrip. Other thrips, like citrus thrips or flower thrips, feed on plant parts and scar leaf and fruit surfaces with their rasping-sucking mouthparts. Damage is mostly cosmetic. They are drawn mostly to citrus, raspberries, grapes, vegetables, and ornamentals, and they can transmit plant diseases as they feed.
Thrips.
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Immature thrips.
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Thrips damage.
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Thrips life cycle.
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Thysanura (Silverfish and Firebrat)
Silverfish and firebrats are well-known household pests that feed on starchy substances including glue, book bindings, starched clothing, paste in wallpaper, curtains, linens, silks, paper, and starchy foods. Adults are wingless and reach about 1/2 inch long, with three tail-like bristles at their rear end. Immature insects resemble adults; they either go through a gradual (incomplete) metamorphosis or none at all.
Silverfish and firebrats are well-known household pests that feed on starchy substances including glue, book bindings, starched clothing, paste in wallpaper, curtains, linens, silks, paper, and starchy foods. Adults are wingless and reach about 1/2 inch long, with three tail-like bristles at their rear end. Immature insects resemble adults; they either go through a gradual (incomplete) metamorphosis or none at all.
Silverfish.
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Immature silverfish.
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Firebrat.
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Firebrat or silverfish damage.
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Insect movement and spread
Many adult insects have wings, allowing them to use flight as their principal means of movement. They can easily spread through the air into areas that were previously not infested. Insects (both pests and beneficials) navigate to new host plants using their ability to follow odors emitted by plants (kairomones), by chemical messages left by the first few insect explorers (aggregation and sex pheromones), or by using their eyes to find the right colors. The insects then lay eggs on the plant, which gives rise to a new generation. Wingless insects can use their legs (or for legless individuals, their body movements) to move from plant to plant or from overwintering or hiding spaces to feeding areas. Many insects are most active at night, so their migration patters may be best observed with a flashlight.
Insects have also been known to use air movement to catch a ride to the next host plant. Scales are a great example of insects that take advantage of this system; newborns (called crawlers) are tiny and flat, easily able to catch a breeze. They then settle down in their new host plant and take up residence. These young scales can also catch a ride on the feet of animals or insects. Spider mites can also be carried over long distances by air currents, and can even be blown through screen doors and windows onto indoor plants.
Insects have also been known to use air movement to catch a ride to the next host plant. Scales are a great example of insects that take advantage of this system; newborns (called crawlers) are tiny and flat, easily able to catch a breeze. They then settle down in their new host plant and take up residence. These young scales can also catch a ride on the feet of animals or insects. Spider mites can also be carried over long distances by air currents, and can even be blown through screen doors and windows onto indoor plants.
Bees, like many other insects, use their wings to transport them from plant to plant.
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Other insects, like ants, leave pheromone trails to guide the rest of the colony to greener pastures.
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Wingless insects must walk from plant to plant.
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Many insects are more active and move at nighttime.
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There are also some species of caterpillars which create silken strands that they use to dangle from branches, looking for a new spot on a tree or shrub to feed. They can also transfer to other plants in this way. One of the most significant ways that insects move (and the way they travel the farthest) is through human intervention, most times inadvertent. Plants purchased at nurseries can have insect residents that are transported over longer distances than they normally would be otherwise. For this reason, it is critical that any plant purchased for use in the garden be inspected for signs or symptoms of insect infestation before they are brought home. It is also a good idea to quarantine plants for a while if they are brought from an outside source, to limit both disease and insect spread.
Beneficial attributes of insects
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Insects, although regarded as unwanted visitors for the most part, are not all 'bad'. Out of the around 92,000 insect species we have identified in the United States, about 95% are either good or neutral in their effect. Many garden insects actually play valuable, sometimes critical, roles in landscapes. These garden heroes prey on pest species, and are sometimes called natural enemies, because they eat the bad bugs that will cause damage and invite disease. Examples of predator bugs are lady beetles, lacewings, syrphid flies, and preying mantes. Parasitic insects such as Ichneumon and Trichogramma wasps are also beneficials, stealing food, energy, and life from insects we consider pests.
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Possibly the most important benefit that insects have in our gardens and crop fields is acting as pollinators. These organisms are important in the production of almonds, squash, melons, kiwis, apples, avocadoes, cherries, pears, plums and many other crops. Around 80% of the pollination that we get for our crops comes from beneficial insect pollinators. Insects that live in undeveloped areas are also very beneficial to life on earth. Forest insects help to decompose downed forest trees and make room for new seedlings. Insects can also produce products like wax, honey, propolis (bee glue), royal jelly, pigments used to dye cosmetics and food products, and silk.
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Exotics and invasive pests
There are two more groups of insects that are worth mentioning here: invasive insects and exotic insects. Exotic insects are natives of a different region of the world. Invasives are non-native species that rapidly colonize an area, usually causing damage to the local ecosystem and biodiversity. Exotic pests are commonly transported on nursery plants, on luggage, or in fruits or vegetables transported across borders, and can become invasive because they do not have any natural predators or diseases that are able to limit their numbers. Once established, these populations are very difficult to eradicate, and can cause ecological as well as economic damage. Examples of invasive pests include glassy-winged sharpshooters, Diaprepes root weevils, and light brown apple moths (LBAMs). The importance of engaging in best practices to discourage the spread of these exotic invasives cannot be understated.
Glassy-Winged Sharpshooter.
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Diaprepes Root Weevil.
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Light Brown Apple Moth (LBAM)
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insect distribution
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Fluctuations in insect populations are very common, and can depend on a number of variables, including temperature, rainfall, food availability, and the presence of parasites or predators. Insects can have international spread, or can be regional. Most insects have specific climate and other environmental requirements that make it difficult for them to survive outside of their natural habitat, and this limits their ability to survive, thrive, and spread in foreign areas. The state of California has many different climates, from costal to interior valley to desert to mountainous.
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For example, Argyresthia cupressella (Cypress Tip Miner) is a pest that attacks Arvborvitae, Coast Redwood, Cypress and Juniper trees and shrubs. It is active only in coastal, foggy areas in California, and is not commonly found in the Central Valley, the Sierra, or the mountainous regions of northern California, even though its host plants abundantly grow there.
diagnosis of plant problems caused by insects and mites
Diagnosing plant problems is a difficult process, considering all of the factors that can cause plants to underperform. In many cases, issues are caused by a confluence of variables. For example, drought-stressed trees are often selected for attack by insects, who then further damage the tree. Also, a single pest may cause more than one symptom in a host plant. Aphids can cause twisted or cupped yellowing leaves as well as their proclivity for producing honeydew, causing black sooty mold to form on lower foliage. In the diagnosing of plant problems, there are two categories of indicators: signs and symptoms. Signs are the actual signs of an attacking pest, such as chewing damage to foliage, frass (poop) on leaves and at the base of the plant, eggs, or webs. Symptoms are the reactions of the host plant to the infestation. There is a wide variety of symptoms that plants can exhibit, including leaf discoloration, wilting, gall formation, problems with flower or fruit set, or issues with yield. Knowing which symptoms pests can cause is the first step in diagnosing the cause of plant damage.
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Although some are general feeders, most insects and mites will show some specificity in the selection of their host plants. The first step in identifying a pest is to know which plant or plants they attack. Most reference literature for pest identification is based on the host plant, as well, so having this information is key. |
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Although many issues are caused by insects, it is important to keep in mind that there are also myriad plant diseases that can be caused by other factors, such as soil nutrition, water issues, inadequate sun exposure, or mechanical damage. Additionally, it is important to consider the health of the entire plant, not just one area. For example, wilted leaves may be caused by vascular disease issues, or by a pest attacking the roots. If, in this instance, only foliage is inspected, the real issue will not be identified. |
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If the entire plant has died as a result of damage caused, it is probably not a pest issue. With a few exceptions, insects and mites do not kill their host plants, but diseases will kill plants frequently. Also, in many cases, pest issues are only noticed after the insects have vacated the host plant. If this situation occurs, corrective efforts will not be effective. |
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Looking for signs of feeding can be one of the most effective ways to diagnose a pest problem. Many insects will feed or behave in distinct ways, such as Leafcutter bees, who leave a rounded cut on leaves after they have harvested. |
conclusion
The critters on this page are all part of a larger garden ecosystem that functions to maintain balance. By familiarizing ourselves with the many organisms we share our landscapes with, we can begin to identify where problems exist and where best to put our efforts at pest control. We'll talk about creating an integrated pest management system for home gardens more in the Year in the Garden module.
Resources for Identification
https://ipm.ucanr.edu/PMG/PESTNOTES/index.html
https://bugguide.net/node/view/15740
https://sfbaywildlife.info/species/insects.htm
https://ipm.ucanr.edu/PMG/PESTNOTES/index.html
https://bugguide.net/node/view/15740
https://sfbaywildlife.info/species/insects.htm
