Pests and Pest Management

"Don't knock the power of a pest. Persistence and stubbornness can be
useful in ​many situations".
- Maria V. Snyder

introduction

Dealing with pests is an unavoidable part of gardening. They see your well-kept landscape as a beautiful bed and breakfast created just for them, and for that reason it's pretty hard to get them to move on once they settle in. At first, these organisms may not make much of an impact, but after time passes and some babies are born, they can start to cause damage to plants, interfering with photosynthesis through lost foliage and inviting accompanying problems like mold and disease. In the page that follows, you'll be learning all about the various common animals and insects that can cause damage to both homes and gardens, as well as how to monitor, treat, and prevent infestations from occurring.
Quick Question: What is a pest?
A pest is any organism that damages or interferes with desirable plants in our fields and orchards, landscapes, or wild areas, or causes damage to homes or other structures. The label also applies to organisms that impact human or animal health such as ticks, mosquitoes, and bedbugs. Pests can either transmit disease or not, but either way are considered nuisances. These organisms can be plants (weeds or parasitic plants), vertebrates (birds, rodents, or other mammals), invertebrates (insects, ticks, mites, and snails), nematodes, pathogens (bacterias, viruses, and fungi), or other unwanted organisms that cause damage to water quality, animal life, or other aspects of the ecological system.
Managing an ecosystem is a herculean task, as it requires constant monitoring and control efforts. Home gardeners can be viewed as ecosystem directors, able to raise and lower the populations of organisms in their spaces through careful intervention with the ultimate goal of maintaining balance. Pest species, whether they be weeds, invertebrates, or vertebrates, are always present in outdoor spaces; there is no ecosystem on our planet that operates completely independently from others. The goal of holistic ecosystem management (also called sustainable integrated pest management) is never to eradicate an entire species but to monitor and use various interventions to mitigate their sometimes damaging effects on the landscape. The lists that follow outline the many types of pests in the home garden.

Weeds

Plant pests are common in every landscape, their main defining factor being that they are unwanted. Any plant can be considered a weed simply depending on how a land owner or horticulturalist categorizes them, but there are many species of plants that are generally considered to be weeds by those who manage formal garden spaces. For more information on these plants, visit the page linked below:

Invertebrates

This group of insects and insect-like organisms frequent urban, suburban, and rural areas, both inside buildings and outdoors in the landscape. They can cause various issues in homes and gardens, from simply being annoying and unwanted to causing damage to plants, buildings, and sometimes humans through bites and stings. Due to their negative effect on the surrounding environment or the damage they do to valuable plants in the landscape, they are considered garden pests.

​Ants
​These small insects are considered pests because they can damage plants directly as well as be protectors of destructive pests like Aphids and Scale insects. Their underground tunnel systems can also disturb plant root systems. Some species can also bite humans.

Aphids
​These destructive garden pests are some of the most famous, as their populations can grow very quickly, and their activities can cause noticeable plant damage. Their feeding can cause stunted growth, yellowing, and leaf curl. They are also vectors for plant diseases and their secretions can cause sooty mold to develop on leaf surfaces, further interfering with plant photosynthesis.

​Beetles
​These organisms can damage plants through their feeding activities. They eat leaves, flowers, and roots, causing problems like skeletonized leaves and stunted growth. They can also tunnel into the trunks and stems of woody plants, creating 'shotholes', 

Cockroaches and Termites
​​These insects cause damage by feeding on plant leaves and flowers, creating holes and ragged edges. They can also pose a contamination risk by spreading bacteria and allergens and can damage garden tools and containers. 

​Fleas
​​Although these pests are not damaging to plants, they are a nuisance for pet owners whose animals spend time outdoors. Fleas can transmit disease or parasites to domesticated animals, and controlling them in the garden can go a long way in protecting furry family members.

Flies
​​​Organisms in this group are referred to as true flies, and can damage gardens through their larval and adult stages, causing issues like root damage and disease transmission. Larvae of some species are adept at burrowing through leaves, which can stunt plant growth and introduce pathogens.

​Grasshoppers and Crickets
​​These organisms can be quite destructive in the garden, especially to crop species. Grasshopper plant damage is typically seen in foliage, appearing as chewed leaves or complete defoliation. They have a special affinity for lettuce, beans, and corn. Crickets are often more focused on consuming roots.

​Leafhoppers
​These bugs damage plants by sucking their sap, leading to issues like stippling (white spots), yellowing, curling, and distorted leaves. They also leave behind excrement that can cause sooty mold to develop on foliage. They are named for the reaction they have when threatened, which is to hop sideways.

​Mealybugs
​These soft-bodied bugs feed on plant sap that they suck out using their mouthparts. This causes wilting, yellow leaves, and potential plant decline. Mealybugs leave behind sticky excrement that can cause sooty mold to form on leaves, interfering with photosynthesis.

​Mites
​These tiny arachnids damage ornamental and crop plants in the garden by feeding on plant sap Signs of a mite infestation include stippling on leaves, discoloration, and the presence of fine, delicate webbing, especially on the underside of leaves. They can cause leaves to turn yellow and eventually fall off the plant, leading to plant decline over time.

​Moths
​These flying insects are garden pests primarily in their larval stage. Moth caterpillars are voracious eaters, feeding on plant foliage, fruit, and stems. There are many species that are considered pests in gardens, including the Cabbage Moth, Codling Moth, and Gypsy Moth. There are also hundreds of moth species that are commonly called 'cutworms' in their larval stage.

​Sawflies
​These insects are damaging to plants in their larval stage; they cause damage to plants by eating leaves. Adults are harmless in the garden, but their larvae can cause significant defoliation of plants, especially in young trees and shrubs. 

​Scale Insects
​Scale insects are stationary (for the most part), small insects that are oval, wingless, and lack recognizable body parts. They insert their strawlike mouthparts into bark, fruit, or leaves. They are overlooked in the garden, as they often appear as tiny bumps on plant stems, branches, and twigs. Their damage can vary depending on the species, but most can cause at least some damage to, if not kill, their host.

​Snails and Slugs
​These common garden pests are soft-bodied organisms that typically eat decomposing materials. They can, however, in the absence of their preferred foods, wreak havoc on leafy green plants or fruit. Their feeding damage appears as holes in foliage, flowers, and fruits. These organisms are most active at night or on rainy days, and leave behind slime trails.

​Stink Bugs
These bugs are identified by their shape; their bodies resemble small shields. Their common name comes from their defensive excretions of unpleasantly-scented fluid. Some species are beneficial in the garden, others can cause a good amount of damage to plants and fruit.

Squash Bugs
​These garden pests feed mostly on cucurbits like squash and melons, hence their common name. Their feeding activities can cause plants to wilt and die. Fruits that have been fed on will rot away. They are typically slow-moving, but can multiply rapidly.

​Thrips
​These small bugs are slender and have wings. They feed by sucking out plant cell contents, resulting in stippling or silvering of leaf surfaces, commonly accompanied with small black flecks. Certain thrips species are garden beneficials, but some can cause plant decline and eventual death. 

​Whiteflies
​These small, sap-sucking winged insects are a common garden pest, and are often first noticed when a plant is jostled. A cloud of small white flies emerges from their hiding spots underneath leaves, and resettles quickly back onto the same plant. These pests can weaken plants and also transmit plant viruses.

Vertebrates

A vertebrate is an animal that has a backbone. Vertebrates are a diverse group of warm and cold-blooded organisms, including birds, mammals, marsupials and reptiles. The damage caused by these animals is typically more noticeable but less frequent than damage caused by insects or weeds, and typically occurs once fruits are ripened. They can also cause damage to ornamental landscape plants through their digging and foraging activities.

Bats
The only mammal capable of true, self-powered flight, these animals are not typical landscape pests, but can cause some issues around homes and other structures if they decide to roost nearby.

Birds
Both flightless and aerial species of birds are present in many landscapes. Although for the most part these animals do not cause any problems, some of their activities can cause property and agricultural damage, and predatory species can be a danger to domesticated animals.

Cats
These domesticated and wild apex predators are arguably the most destructive to natural ecosystems, and also have the potential to spread disease.

​Deer
​These animals are often seen as beautiful and majestic creatures, but they can also be destructive in landscapes, interfering with crop harvests and feeding on a very wide variety of ornamental plants, as well.

​Dogs
These beloved companion animals and their wild counterparts have the ability to do a lot of damage in a short amount of time.

Moles
While moles can be a nuisance in the landscape, burrowing in lawns and agricultural areas,  they are generally considered beneficials.

Opossums
Typically omnivorous scavenger animals, these marsupials sometimes feed on agricultural crops and make messes while foraging.

​Rabbits
​These hopping, long-eared garden residents, although loved by some, can cause a measurable amount of damage to crop and ornamental plants.

Raccoons
​These mammals are opportunistic foragers, and venture into urban areas quite often. Although considered somewhat beneficial, they also have the potential to be destructive to landscapes, dangerous to domesticated pets, and can spread disease.

​Rodents
This large group of animals includes Mice, Rats, Voles, Squirrels, and Gophers. These animals, although relatively smaller than other landscape vertebrate pests, can cause significant damage to crop and ornamental plants as well as structures and food stores.

​Skunks
​These burrowing, foraging animals can cause property damage in the form of digging in lawns and forming nests under porches and other structures. 

Sustainable Integrated Pest Management

After perusing the lists above, you may be thinking that protecting your garden is going to take a lot of time and effort. However, if garden cultural best practices are followed and your landscape is kept relatively healthy as a result, it makes it much more difficult for large-scale infestations to occur. Sustainable Integrated Pest Management is a holistic program seeking to provide long-term prevention or suppression of pest problems with minimal impact on human health, the environment, and nontarget organisms in the garden. It is an ecosystem-based strategy focusing on long-term prevention of pests and their associated damage through a combination of tried-and-true techniques such as biological controls, habitat manipulation, modification of cultural practices in the garden, and the use of resistant varieties. A fundamental concept of this program is that some pest activity can be tolerated in the maintenance of a healthy landscape. Broad-spectrum pesticides are generally not used except in dire situations, and even then their use is directed and carefully monitored.
How Does Sustainable Integrated Pest Management (SIPM) Work?
Using the SIPM system, gardeners take actions to keep pests from becoming a problem in the first place, such as growing resistant varieties that can withstand pest attack or engaging in small garden projects, like caulking cracks in concrete or sealing entryways correctly to prevent pest entry. Rather than simply waiting for pests to take hold and then treating with insecticides (or other interventions), SIPM is a preventive system that takes into consideration how a garden functions on a larger scale, and focuses on the ways pests thrive in certain environments. Monitoring garden spaces and correct pest identification are the keystone ideas of this program. The landscape is routinely checked for issues, populations of pest insects are tracked, and there are five major methods employed to control existing insect populations.
Legislative Control
Quarantines are established at the county, state, and federal levels to prevent entry or further spread of pests into designated areas. At the federal level, countries typically have laws, regulations, and executive authorities that govern the control, prevention, and eradication of insect, disease, and weed pests (collectively referred to a plant pests, noxious weeds, and invasive species). These laws empower involved agencies to act at borders, within states, or across jurisdictions in many cases. Each country, state, county, or territory has the ability to regulate the movement and spread of these organisms through unique legislative controls. Examples of federally controlled insects include:
Asian Longhorned Beetle
Emerald Ash Borer
Spotted Lanternfly
Mediterranean Fruit Fly
Physical and Mechanical Control
Physical and mechanical controls are used by landowners on their properties and in some cases by pest control companies and other related organizations. These methods directly trap insects, kill them, or exclude them in some way. Techniques include anything from placing cardboard or paper collars around young transplants to exclude cutworms, handpicking caterpillar larvae from plants, and screening windows to prevent the entry of flying insects into a structure. These effective interventions can be preventative or curative in nature, and do not require the use of chemicals.
Cultural Control
This group of techniques includes modification of normal gardening activities to prevent or reduce pest problems. Examples include planting pest-resistant varieties of vegetables, fruits and ornamentals, rotating crops from year to year to prevent pest population buildup, and maintaining a cover crop of turf or mulch in fruit tree orchards to discourage dust-loving spider mites.
Biological Control
This collection of techniques includes the use, preservation, conservation, and augmentation of parasites, predators, and disease-causing microorganisms (pathogens) to bring about the control of insect pests in the garden. The most important controls are natural enemies that exist in the garden. Every pest insect has some predators, and in many cases, they can keep pest populations in check. Many outbreaks of pests occur because a broadly toxic insecticide was used in the area at some point in the past, which killed both the pests and their natural enemies. Pests, whose populations can rebound more quickly, will start to pop up again before their natural enemies can recover from extermination. Avoiding the use of insecticides can help to preserve the natural balance of pests and predators in the garden. The ability to recognize predators and parasites and the signs of parasitization is a critical piece of knowledge for home gardeners to have.
There are some biological controls that can be purchased for release and use in the home garden. Lady beetles and lacewings can be found for sale in nurseries or ordered online and then released into the garden space. There is also a widely-available insect pathogen called Bacillus thuringiensis (Bt), which can seriously damage populations of caterpillar pests while causing minimal harm to other forms of insect life. There are biologists who specialize in these types of insect pathogen-based biological controls, who travel the world in search of new natural enemies for some of the more aggressive pest insects in California. In recent history, these scientists have imported tiny wasps that parasitize aphids, scales, psyllids, whiteflies, beetles, and other insects.
Chemical Control (Insecticides and Pesticides)
Insect and mite pests can be controlled using products such as insecticidal soaps, horticultural oils, various inorganic substances, botanical compounds, microbial insecticides, and synthetic organic materials. Some are used in advance of a pest infestation and are called preventive treatments, though most are designed to be used after infestation begins (which is when most people notice the pests in the first place). Botanical insecticides are organic insecticides that are derived from plant sources, including pyrethrum (or pyrethrins) and azadirachtin (neem extract). The main advantages of using these products is that they have a short residual activity, a lower impact on non-target organisms, and can be applied up to the day of harvest on edible crop plants. Other safe-to-use pesticides include horticultural oils, insecticidal soaps, and insect growth regulators. Synthetic materials last longer, though they do have the unwanted side effect of being toxic to natural enemies of pests, as well. Due to the toxic nature of many pesticides, special attention should be paid to their correct use.

creating an integrated pest management system in the home garden

Sustainable Integrated Pest Management encourages gardeners to select sustainable pest management practices that provide long-term prevention or suppression of pest problems with minimum impact on the overall health of the garden, beneficial organisms, and humans. The main goal is to keep pest populations at manageable levels by using evidence-based, non-toxic methods. The home gardener is the main tool used in any IPM system; they will be doing the most important piece of work to prevent pest infestations: careful monitoring. Creating an IPM strategy is a creative process that brings together knowledge, monitoring, and informed decision-making.
Successful Pest Management Guidelines
There are three basic guidelines to use when implementing a pest control system. The first of these is to identify the problem and determine whether an intervention is warranted. Before a pest can be successfully managed, it must be identified. Plant underperformance can be due to myriad causes, including mechanical damage, under- or over-watering, poor plant placement or soil management techniques, pests, or misuse of garden chemicals among others. Pinpointing the cause of a plant's troubles is difficult, and if problems are incorrectly diagnosed, treatments used in response will not be effective. Home gardeners should familiarize themselves with the basic identification of plant issues, so they can be more informed when the time comes to identify a problem in their landscape.
The second guideline in an IPM process is to select a proper control action strategy. The action or actions taken after a pest is identified as a problem should be chosen with care to cause as little environmental damage as possible. It may not seem like treating a pest in the garden would have a noticeable effect on the larger ecosystem, but it most certainly does. Some gardeners will never apply pesticides under any circumstances and prefer less toxic controls like hand-picking or using water streams to treat infestations. Others may use pesticides, but only those that are naturally-derived like insecticidal soaps, oils or microbials that carry little to no risk of damage to life. As a general rule, the least toxic option should always be chosen. The treatment chosen also must be applied at the correct time to maximize effectiveness. This involves being familiar with the life cycle of the pest to be eradicated, its natural enemies, and its competitors. Interventions should be applied when the pests are at the developmental stage where they are most vulnerable. Actions taken can also be guided by the expert Master Gardeners in your county if help is needed.
Timing is everything when it comes to treating pest infestations in the home garden. For example, the Juniper Twig Girdler is a moth that attacks Juniper and related plants, and for most of the year, they are tunneling beneath the bark of the plant, which protects them from any pest treatments applied. However, their adult moth form is most active in June through the middle of July, and this is when they are vulnerable and their population can be curtailed.
The third and final general guideline for implementing an IPM system is to evaluate the results of the control action(s) employed and develop an ongoing pest management plan for continued control. This step requires close monitoring of the identified pest species and knowledge of what the host plant looks like when it is healthy. Experience with treating a pest within a garden space can inform a gardener about possible future problems, allowing them to make tweaks to their existing program to ensure the issue does not pop up again. When these three guidelines are considered, creating an integrated pest management program for a unique garden space falls into place. A successful IPM system is formed through trial and error, improving on past techniques, and establishing best practices for working in and maintaining the garden.

prevention

The methods designed to prevent pest development and spread are called preventive management strategies. These controls are the gold standard in a pest management program, because they reduce pesticide use in the garden. There are three main strategies under this prevention umbrella: choosing and installing resistant cultivars or species, engaging in good sanitary practices, and properly caring for the garden in a way that reduces plant issues overall.
Planting Resistant Cultivars or Species
Reducing pest problems in the garden can be as simple as planting the right species and cultivars for the garden's specific water availability, climate, sun exposure, soil type/texture, and other factors. When plants are described as being pest resistant, it does not mean that they are immune. This term refers to varieties of plant species which exhibit less pest damage than others under similar growing and pest population conditions. These varieties may be less desirable to pests or have physical or chemical properties that repel them or inhibit their development. Other varieties in this group are those that can handle large populations of pests without getting too damaged. Natives are obviously the superstars of resistant plant species, as they have evolved over time to be well-adapted to their landscapes.
Sanitary Practices
These techniques refer to garden cleanliness activities like cleaning up infested or dead plants, reducing populations of pests and pathogens that could infect garden plants, and keeping weeds in check. Similar to the reasons why it is beneficial to keep a clean home, keeping a tidy garden will facilitate the monitoring of pest populations, allow easier access to all areas of the landscape, and discourage issues like mold and mildew. Removing diseased plant parts from their attachment to plants and from the ground around other plantings is an important preventive measure against the spread of pathogens in the garden, and removing weeds from landscapes removes host plants for many pest species.
Proper Cultural Practices
Many issues can be prevented in the garden by simply providing good growing conditions for plants. Avoiding environmental stressors makes the plants healthier overall and more able to resist pest infestation. Even within smaller gardens, there are multiple microenvironments that differ in humidity, heat, and sun exposure; plants should be chosen specifically for these spaces. The correct amount of nutrients should be applied to plants according to their growth rate. When used correctly, fertilizers and waterings promote healthy plant growth and increases plants' ability to tolerate pest damage. By this same line of reasoning, soil should also be fertile and healthy enough to support plant growth. Avoiding overwatering can increase plant health by discouraging development of stem and root diseases.

options for nonchemical control

One of the fundamental concepts of IPM is that a limited amount of pest damage in ornamental and edible plants is acceptable. Produce from the home garden does not have to be as perfect as produce from the supermarket. If the choice comes down to using chemicals or accepting some insect damage on fruit or damage on plants, the non-chemical option should always be chosen. Aligning garden care with responsible use of chemical interventions is of utmost importance. Good garden practices in combination with non-chemical controls can help reduce losses due to pest activity as well as the need to use pesticides in the first place. There are some great options for non-chemical control in the garden, outlined below.
Cultural Controls
These techniques are modifications to normal plant care activities that reduce or prevent pest infestations. Many of these methods will overlap with the efforts of preventive measures.

​Digging, Tilling, and Cultivating
These activities can reduce or eliminate weeds in the garden, as well as expose soil-borne pests to adverse conditions and predators. Deep digging can bury some insects and prevent their eventual emergence from the ground. 

​Crop Rotation
Rotating the location where certain crops are grown can be effective against diseases and insect pests that develop on groups of plants, especially if these pests are unable to travel over long distances. Moving the host crop for these pests will isolate the pests from the crop, and they will eventually starve without a food source. If working in a smaller garden where there is not enough space for crop rotation, change the sequence of plantings in that space; do not plant members of the same plant family in the same location for two seasons in a row.

​Changes in Planting or Harvesting Time
Planting or harvesting at the same time each year has the potential to reduce plant damage or keep pests separated from damaging vulnerable parts of the host plant. For example, seed maggot damage and the issue of damping off can be helped by delaying planting until the soil is warm enough for the seeds to germinate quickly.

​Garden Diversification
The aim of intercropping, or growing two more more crops in the same space,  is to diversify host plant populations so that pest problems are reduced. Adding some flowers to a vegetable garden, for example, can increase the activity of natural enemies that will feed on damaging pests.
Mechanical Controls
These techniques reduce insects, weeds, and diseases through using labor such as hand-picking or devices like traps and barriers.
​Preventive Mechanical Devices
These devices assist in excluding pests from various areas of the garden using a number of techniques:
Paper Collars
Placed around plant stems or trunks, these devices prevent damage from pests like cutworms, rabbits, and rodents.
Cheesecloth
Screens made of cheesecloth are used over hot beds and cold frames to exclude insects and other pests.
Mesh Covers
These work for small fruit trees, berry shrubs, tomatoes, and other plants to keep out birds and large insects.
Sticky Barriers
When added to a tree trunk, these materials prevent damage from crawling insects, who get stuck on their way up.​
Reflective Plastic Mulch
Use these devices on soil beneath rows of plants.
Coarse Organic Mulches
These materials do a great job at excluding weeds from the garden.
Landscape Fabric
Although not generally recommended, this material can prevent weeds from sprouting.

​Hand-Picking, Hand-Pulling, and Hoeing
​These interventions are aimed at physically removing pests, and is a very effective control if used regularly. It is an especially effective method when used to curb populations of foliage-feeding pests such as snails and slugs, bean beetles, potato beetles, squash bugs, and hornworms. Weeds can be managed by hand-pulling or hoeing (digging and loosening soil). 

Washing
A fine stream of water under pressure can do quite a good job at getting rid of insect pests, as many that are knocked off of plants are not capable of returning. For example, spider mites, whiteflies, and aphids can be physically controlled by washing them off of leaves. Comparison studies done with several widely-used pesticides indicate that washing performs as well or better than chemical intervention.

Traps
A variety of traps are used to cull populations of pests, including slugs, snails, and earwigs. Low-sided cans or other containers sunk into the soil and filled with an attractant can go a long way in trapping, and in many cases culling, pest populations. Slugs and snail traps should be filled with stale beer, and earwig traps should be filled with vegetable oil with a drop of bacon grease or tuna fish packing water.
Environmental Controls
Environmental controls are physical control methods that include using light, temperature, and other environmental variable manipulation methods to control for pests and pathogens.

Keeping Foliage Dry
Eliminating overhead irrigation in the landscape can ensure that fungal diseases like black spot or powdery mildew do not take hold as easily. Watering at the base of plants is always recommended.

Hot Water Dips
Soak flower bulbs in hot water (warmed to between 140 and 150 degrees Fahrenheit) can effectively control certain bulb pests, such as nematodes, bulb mites, and bulb fly larvae. This method is sometimes called Hot Water Treatment, or HWT. It is a process that must be done with extreme precision, as the margin between killing pests and damaging the bulb is very narrow.

Heat Pasteurization of Growing Media
Small quantities of potting mix can be pasteurized in a conventional oven or microwave oven. Moisten potting mix and allow to bake at 180 to 200 degrees Fahrenheit for about an hour in a conventional oven. To heat it in the microwave, moisten and place in a plastic bag. Heat the potting mix long enough so that it reaches 180 degrees Fahrenheit (which should take around 10-15 minutes). Once it cools, it is ready to store for future use. 

Composting
​This process controls pests and pathogens by using heat to kill them and by creating a healthy environment with beneficial microbes that outcompete or destroy harmful ones. To effectively control pests, especially pathogens and weed seeds, compost must reach and maintain high temperatures (between 131 and 170 degrees Fahrenheit) for several days.

Soil Solarization
​Soil solarization uses black or clear plastic sheeting to trap the sun's heat, which effectively kills a very wide range of soilborne pathogens, pests, and weeds by raising the soil temperature to lethal levels. Soil is typically irrigated and then covered for 4-6 weeks during the warmest months of the year. The edges of the plastic can be buried or weighted down with rocks.
Biological Controls
​Pest populations in the garden can be balanced through the use of biological controls. These methods harness the activity of a species that reduces the adverse effects of another. The species used to control is typically referred to as a beneficial or biological control agent because they keep pest populations low enough to prevent significant damage. These biological controls can be pathogens, parasitoids, predators, competitive species, or antagonistic organisms. 

Pathogens
This group includes various microscopic organisms, such as bacteria, fungi, and viruses. These agents cause disease in pest insects, mites, nematodes, or weeds. A common example of a pathogen used to control a pest population is the case of Bacillus thuringiensis irsraelensis (Bti). This bacteria kills mosquitoes when dropped in water by creating toxins that damage their digestive system.

Parasitoids
These organisms attack pest species such as aphids, whiteflies, cutworms, or hornworms and spend some of their life cycle with the host. They are typically small wasps or flies that use their ovipositor (stinger) to deposit eggs in or on a host. Eventually, the host dies and the adult insect emerges to start the cycle all over again. These organisms are referred to in groups depending on which stage of the host within which they develop. There are egg parasitoids, larval parasitoids, larval-pupal parasitoids, pupal parasitoids, and adult parasitoids.

Predators
These organisms include a wide range of insects, arachnids, and animals. Predators can be in their larval or adult stage when most effective. They overpower or immobilize their prey and then consume it. For example, lady beetle larvae are voracious consumers of aphids, and in their adult form are effective predators of these garden pests as well.

Competitors
This technique involves adding organisms to the garden that will compete with less desirable ones. These competitors typically include cover crops, which are plants such as grasses and legumes that have been selected and managed to serve as living mulches and outcompete pest weeds. They can also be nonpathogenic soil-dwelling fungi that compete for resources and reduce or exclude populations of plant-pathogenic fungi.

Antagonists
These organisms release toxins or otherwise change environmental conditions so that pest activities or populations are reduced. For example, naturally-occurring soil fungi and bacteria may antagonize nematodes by producing compounds that are toxic to them.
The positive work that each of these groups does in the garden is a naturally-occurring phenomenon in healthy ecosystems. However, broad-spectrum pesticides that kill certain pests as well as their natural enemies can cause an issue called secondary pest outbreak. This occurs when pesticides take out all populations of organisms in a food chain, and pest species repopulate more quickly than their natural predators. For example, the sudden outbreak of an aphid, scale, mite, or whitefly population can occur after a tree nearby has been treated with a broad spectrum insecticide. Unfortunately, the parasitoids and other natural enemies in the general area are killed as well. This trend is one of the main reasons why a sustainable integrated pest management program uses pesticides and other chemical interventions as an absolute last resort.
Conservation strategies that protect populations of beneficial organisms are the most effective at controlling pest populations in the landscape. The first step in conservation is to discontinue use of pesticides, insecticides, and fungicides in the garden. Other conservation methods include:
Keep food sources for beneficial species in the garden. Pollen, nectar, and water are especially important. Include plants in the garden that bloom at various times of the year, and maintain some organic matter in the garden that beneficial fungi and bacteria can use to sustain or increase their populations.
Tolerate small numbers of pests. These pest populations are the main food source for many beneficial natural predators, who will move on to greener pastures when their preferred prey is absent from the landscape. Trap crops can be used to host these pests away from valuable plants in the garden.
Use controls on pest protector organisms like ants, who will interfere with the ability of predators and parasitoids to control certain pests. Ants can be prevented from accessing aphids and scale insects by using bands of sticky material at the base of infected plants.

Augmentation
This tactic involves releasing large numbers of natural enemies, either naturally-occurring or foreign. These natural enemies can be collected, reared, and released back into the environment or purchased and released. These organisms include predatory mites, parasitic nematodes, mealybug destroyers, parasitic wasps, green lacewings, and lady beetles.

resources and references

UC IPM Website
UCIPM: Biological Control
U.S. Regulated Plant Pest Table
​https://californiacitrusthreat.org/
​https://ucanr.edu/sites/ACP/
​https://ipm.ucanr.edu/PMG/PESTNOTES/pn74155.html