Biological Control

Leonard Coop, Brittany S. Barker, and Joshua Vlach
Revised: 
March 2020

Introduction

Biological control (or biocontrol) is a key component in establishing an ecological and integrated approach to pest management. We define biological control as the decline in pest density as a result of the presence of natural enemies. The degree of pest decline might be in the form of partial or complete pest suppression. We use the terms “natural enemies,” “beneficials,” and “biocontrol agents” synonymously to refer to predators, parasites (or parasitoids), and diseases of pests.

Biocontrol is generally more compatible with organic and sustainable agricultural approaches than pesticide-dependent agriculture, especially when non-selective, broad-spectrum chemistries are used. Biocontrol agents tend to be highly susceptible to non-selective pesticides, so even short or moderate pesticide exposure times may release minor pest insects, otherwise held in check by these natural enemies, to become major pest problems. The term “secondary pest outbreak” is used when this scenario occurs. This reduction in natural enemies can also produce dependence on further pesticide usage and result in a cycle of chemical dependency that has been called a “pesticide treadmill”.

Ideally, natural enemies reproduce on their own and are self-sustaining, they are not harmful to other aspects of the ecosystem, and they can be used in combination with other integrated control tactics. Generalist natural enemies such as most aphid predators can switch readily among alternative food sources. Thus, when target pest numbers are low, the generalist natural enemies may maintain populations locally by consuming other prey species. Specialist natural enemies such as most parasitoid wasps have more restricted food choices, so will leave or die out when prey numbers are low. Natural enemies can be disrupted by chemicals, can struggle in poor habitat with low pest numbers, and may be incapable of suppressing pests below damage thresholds by themselves. In some cases, the benefits of their presence are undervalued because they are difficult to sample or even detect.

Insect pests are susceptible to entomopathogenic nematodes (roundworms) and a variety of diseases caused by pathogens, which include viruses, bacteria, fungi, and protozoa. Natural populations of insect pests are commonly attacked by pathogens, and some pathogens have been mass-produced to use as biocontrol agents (e.g., microbial insecticides).

Thus, natural enemies, especially a combination of generalists and specialists, can be an extremely useful part of pest management programs that recognize and encourage their activity. At the same time, one must keep in mind that biological control agents can have unanticipated effects that may include attacking beneficial and native species. New biocontrol agents increasingly require long-term, stringent evaluations in quarantine to measure their non-target effects and efficacy in controlling the target pest before they may be released. Biocontrol agents that are candidates for introduction may be rejected if, in addition to the target species, they attack native non-pest species. Another risk of introducing new biocontrol agents is the risk of host shifting, in which the agent unexpectedly begins attacking non-target species despite previous efforts to determine its host range.

Types of biological control

In addition to the philosophy of “doing nothing” in order to allow natural biological control to work, there are three principal approaches that involve human intervention:

  1. Classical biological control
  2. Augmentative biological control
  3. Conservation biological control

Classical biological control

Classical biological control is the importation of natural enemies for release and permanent establishment in a new region. In the Pacific Northwest (PNW), we have had very few cases of highly successful classical biocontrol of insect pests, but there have been many successful classical weed biocontrol cases using insects (see the PNW Weed Management Handbook). One successful insect biocontrol agent, the filbert aphid parasite (Trioxys pallidus), was imported from Europe and introduced (in small numbers) by Oregon State University (OSU) scientists in the mid-1980s. Since then, this tiny wasp has spread throughout the growing region and generally maintains the filbert aphid below treatment thresholds. In another case, the spread of and damage by the apple ermine moth (Yponomeuta malinellus), has been greatly reduced by the successful introduction of a wasp parasite (Ageniaspis fuscicollis) in the late 1990s. A cooperative biocontrol program among US Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS), Oregon Department of Agriculture (ODA), and OSU for cereal leaf beetle began in 2000 and was considered successful by 2010. The establishment of the larval parasitoid, Tetrastichus julis (Eulophidae), yielded control below thresholds in some regions of the PNW, especially when combined with altered cultural practices (tillage, irrigation, crop rotation, etc.) and pesticide application. In some cases, 100% parasitism was achieved. A small wasp in the family Eulophidae, Colpoclypeus florus, a native of Europe, has been credited as a major biocontrol agent of leafroller pests such as the oblique-banded and pandemis leafrollers in Washington, and has also been collected in Western Oregon. An egg-larval parasitoid, Ascogaster quadridentatus (Braconidae) was introduced to help manage codling moth, Cydia pomonella, a key pest of apple and pear. The presence of this parasitoid on codling moth has been reported, although the economic success of its introduction is unknown.

Previous PNW classical biocontrol efforts have included programs directed at Russian wheat aphid, orchard leafrollers, larch casebearer, and cherry bark tortrix. Searches for biological control agents for two new invasive pests—spotted-wing drosophila (SWD, Drosophila suzukii) and brown marmorated stink bug (BMSB, Hyalomorpha halys)—were initiated in 2011. Several wasp species that attack SWD were imported from Korea for quarantine, testing, and potential release. The samurai wasp, Trissolcus japonicus, is an egg parasitoid of BMSB that was found established outdoors in Vancouver, Washington in 2015 and in Portland, Oregon in 2016, and it continues to be detected in both areas. As a result of this finding, experimental releases of the parasitoid have begun in Oregon. Orchards may benefit from release of T. japonicas if insects are released in unsprayed areas adjacent to agriculture and in urban sites (Lowenstein et al. 2019). There is good documentation of traits associated with successful introductions of biocontrol agents, with regard to life history traits and other attributes, and applications of these “lessons learned” may improve success rates of this strategy in the future (Kimberling 2004, Abram and Moffat 2018).

Augmentative biological control

Augmentative or supplemental biological control typically involves the mass-production and repeated release of natural enemies to improve their population sizes and effectiveness. This approach is used most often to target slow-moving pests such as mites and aphids, usually in organic agriculture where few disruptive chemicals are applied such as in-home gardens and enclosed spaces (e.g., greenhouses). The two main types of augmentative releases include 1) inundative, whereby large numbers of a species, not necessarily native or able to survive the winter, are released with the goal of short-term biocontrol, and 2) inoculative, whereby a native or climate-adapted species is released for anticipated control after allowing populations to build up over time. The dispersal capability of the natural enemy should be taken into consideration when evaluating its ability to control the target pest. For example, many homeowners have wasted money using ladybug adults to control aphids, only to see them fly away within minutes. If biocontrol agents are native or well-established non-natives, then a release can be directed to augment and improve the rate of natural colonization and control. A non-native biocontrol agent that has limited overwintering success will confer only single-season benefits. Croft and Coop (1998) demonstrated that in cases where pesticides had previously been used to control root weevils that attacked Oregon strawberries, the PNW-native predatory mite Neoseiulus fallacis could be purchased from insectaries and released inoculatively in the early fall to re-establish healthy populations to control the twospotted spider mite, Tetranychus urticae. Another predator mite species, N. californicus, may be purchased in higher numbers and used as an inundative release to provide in-season control, as it is less able to survive cold winters as N. fallacis (Pratt and Croft 2000). Since natural enemies are all specialized to some degree, it’s important to know the pest and which agent(s) are appropriate for the given situation. Table 1 lists some target pests commonly found in home garden and agricultural systems, and their associated commercially-available beneficial organisms. Steps for acquisition and release of biocontrol agents must be planned carefully and followed. Release guidelines depend on knowledge of the biology of the pest and its natural enemy, and the host plant’s influence on both species. Conservation efforts (below) can in some cases enhance the outcome of augmented biocontrol agents.

Conservation biological control

Conservation biological control refers to the manipulation and/or protection of habitat and resources to support and encourage natural enemies in order to increase their numbers and effectiveness. This may include the use and encouragement of the natural enemies’ needs, such as nectar and pollen, alternative hosts, and certain types of non-disrupted habitat. Each of these resources can potentially enhance the fecundity, longevity, and survival of natural enemies.

Some practices for conservation biological control include:

  • Identification skills. Get to know the beneficial insects and other organisms that frequent your crops and gardens, and find out about the biological control services they provide. A few resources to get you started:
  • Avoid toxic chemicals. Careful use of pesticides and tillage will help to avoid disturbing natural enemies. There are secondary pests that only reach economic pest levels when their natural enemies are disrupted by pesticides that were applied in order to control a different species. Using less toxic and selective controls in the place of broad-spectrum compounds (such as most organophosphates, carbamates, and pyrethroids) can help prevent secondary pest outbreaks. Online databases and listing of pesticide effects on beneficial organisms include:
  • Apply food sprays. These can include as yeast and sugar sprays that attract parasitoid wasps, lady beetles, lacewings, and hoverflies.
  • Manipulate crop and non-crop architecture. Consider changing your farm design in ways that can improve natural enemy activities. For example, wind-break plantings may be used as a barrier to prevent dry, dusty conditions favorable to pest mite flare-ups. Predatory mites that attack these pests may also be inhibited by such conditions. Shelter and alternate hosts can also be supported through methods such as careful rotation, alternate row harvest, and “beetle banks,” which are graded low banks of dense grasses that are placed within a field or in fence row corridors inhabited by appropriate vegetation.
  • Provide insectary plantings. Insectary plantings can provide habitat, alternate prey, and floral resources (e.g., pollen, nectar, nectaries), and include:
    1. Planting within the crop field in strips or smaller blocks
    2. Using perennial and annual border plantings
    3. Planting within hedgerows
    4. Establishing cover crops
    5. Careful management of flowering weeds

We refer readers to several sources for additional information on insectary planting methods (Long et al. 1998, Bugg 1999, Bugg and Waddington 2004, Hogg et al. 2011, SARE 2012, Parker et al. 2013).

As with selecting any new crop management method, choosing insectary plantings for conservation biological control should include consideration of numerous biological, agronomic, and economic factors. To justify the continued use of an insectary planting, the on-site assessment should consider the same factors as the preliminary selection process and include a sampling of pests and beneficials within and surrounding the crop.

Considerations for incorporating insectary plantings
to sustain natural enemies

Timing of flowering

  1. Will the floral resources be present when needed?
  2. Will the flowers attract natural enemies to or away from
    the target pest at certain times?

Characteristics of the natural enemies

  1. What are the relative preferences that key natural enemy
    and pest species have for the different flowers?
  2. What are the different requirements for nectar, pollen,
    shelter, and alternate host food among these key species?
  3. What are the relative foraging ranges and dispersal
    abilities of these key species?

Agronomic considerations

  1. How competitive are the plantings with the crop or
    other weeds?
  2. Do the plantings have the potential to harbor weeds or
    be weeds themselves?
  3. Can the plantings serve as an alternate host for crop
    disease?
  4. Are the plants toxic to any livestock or other local
    animals?

Economic and management considerations

  1. Can the planting be harvested as an additional crop?
  2. What are the costs of seed, establishment, and
    maintenance?
  3. How do these costs compare to other management
    options?
  4. Are the plantings compatible with the main pest
    management plan?

Several studies have measured positive effects of the above practices on biocontrol performance, although efficacy will be case-specific and difficult to quantify due to the complex interactions involved (e.g., see Wyckhuys et al. 2013). However, these practices all make use of the local beneficial species already present in the landscape. These efforts can also enhance natural enemies released in classical and augmentative biological control programs (Colley 1998).

Resources for implementation of biological control

The IPM Practitioner’s 2015 Directory of Least Toxic Pest Control Products. A comprehensive listing of biological control agents and other “least toxic” pest control products for a variety of agricultural, urban, and domestic uses, and their producers and distributors. Bio-Integral Resource Center—https://www.birc.org/Final2015Directory.htm

“Co-managing fresh produce for nature conservation and food safety,” An informative 12-minute video on habitat and biological control made in 2015 by Eric Brennan—https://www.youtube.com/watch?v=zLvJLHERYJI

Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control, by M.L. Flint, M. L, S. H. Driestadt, and J.K. Clark. 1999, 2015. University of California Division of Agriculture and Natural Resources. University of California Press, Oakland, California, USA. Kindle edition available.

Sandhu, H. S. Wratten, R. Costanza, J. Pretty, J. R. Porter, and J. Reganold. 2015. Significance and value of non-traded ecosystem services on farmland. PeerJ 3:e762; DOI 10.7717/peerj.762—https://peerj.com/articles/762.pdf

Oregon Department of Agriculture provides a list of invertebrates approved for importation into Oregon. Except as otherwise provided in rules of the ODA, invertebrate species listed in this list may be imported, possessed, sold, purchased, exchanged or transported within the state without an ODA permit. A permit for the importation, possession, or intrastate transportation of ODA-approved species may be required by the USDA-APHIS Plant Protection and Quarantine program (Form 526)—https://www.oregon.gov/ODA/shared/Documents/Publications/IPPM/OregonApprovedInvertebrateList.pdf

USDA SARE (Sustainable Agriculture Research and Education). SARE supports grant programs, strategies and resources that include protection of biocontrol agents and other beneficials—https://www.sare.org

The Xerces Society. A nonprofit organization formed in 1971 which protects wildlife through the conservation of invertebrates and their habitat. Their focus has expanded beyond native pollinators to include other invertebrate species such as native predators and parasitoids. They have programs to document the impacts of pesticides on invertebrates including biocontrol agents. Xerxes has resources to provide education and training on conservation biological control (e.g., Lee-Mäder et al. 2014) and are very active in the Pacific Northwest. 628 NE Broadway Ste 200, Portland OR 97232 USA; tel: 855-232-6639—https://www.xerces.org

References

Abram, P. K., and C. E. Moffat. 2018. Rethinking biological control programs as planned invasions. Current Opinion in Insect Science 27:9-15.

Bugg, R. L., and C. Waddington. 1994. Using cover crops to manage arthropod pests of orchards: A review. Agriculture, Ecosystems Environment 50:11–28.

Bugg, R. L. 1999. Beneficial insects and their associations with trees, shrubs, cover crops, and weeds. Pages 63–65 in Bring Farm Edges Back to Life! Yolo Country Resource Conservation District, Woodland, California, USA. 105 p.

Colley, M. R. 1998. Enhancement of biological control with beneficial insectary plantings. Master’s Thesis. Oregon State University, Corvallis, Oregon, USA. https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/x633f3882

Croft, B. A., and L. B. Coop. 1998. Heat units, release rate, prey density, and plant age effects on dispersal by Neoseiulus fallacis (Acari: Phytoseiidae) after inoculation into strawberry. Journal of Economic Entomology 91:94–100. http://jee.oxfordjournals.org/content/91/1/94

Hajek, A. E. 2004. Natural Enemies: An Introduction to Biological Control. Cambridge University Press, Cambridge, United Kingdom.

Hogg, B.N., R.L. Bugg, K.M. Daane. 2011. Attractiveness of common insectary and harvestable floral resources to beneficial insects. Biological Control 56:76-84—https://doi.org/10.1016/j.biocontrol.2010.09.007

Kimberling, D. N. 2004. Lessons from history: predicting successes and risks of intentional introductions for arthropod biological control. Biological Invasions 6:301-318.

Lee-Mäder, E., J. Hopwood, M. Vaughan, S. H. Black, and L. Morandin. 2014. Farming with Native Beneficial Insects: Ecological Pest Control Solutions. Storey Publishing, North Adams, Massachusetts, USA.

Long, R. F., A. Corbett, L. Lamb, C. R. Horton, J. Chandler, and M. Stimmann. 1998. Beneficial insects move from flowering plants to nearby crops. California Agriculture 52:23–26. http://calag.ucanr.edu/Archive/?article=ca.v052n05p23

Lowenstein, D. M., H. Andrews, A. Mugica, and N. G. Wyman. 2019. Sensitivity of the egg parasitoid Trissolcus japonicas (Hymenoptera: Scelionidae) to field and laboratory-applied insecticide residue. Journal of Economic Entomology 112:2077–2084.

Parker, J. E., W. E. Snyder, G. C. Hamilton and C. Rodriguez-Saona. 2013. Companion Planting and Insect Pest Control, Weed and Pest Control - Conventional and New Challenges, Sonia Soloneski and Marcelo Larramendy, IntechOpen, DOI: 10.5772/55044. https://www.intechopen.com/books/weed-and-pest-control-conventional-and-...

Pratt P.D. and Croft B.A. 2000. Screening of predatory mites as potential control agents of pest mites in landscape plant nurseries of the Pacific Northwest. J. Environ. Horticult. 18: 218–223— https://www.hrijournal.org/doi/pdf/10.24266/0738-2898-18.4.218

SARE. 2012 Strategies to enhance beneficials. https://www.sare.org/Learning-Center/Books/Manage-Insects-on-Your-Farm/T...

Wyckhuys, K. A. G., Y. Lu, H. Morales, L. L. Vazquez, J. C. Legaspi, P. A. Eliopoulos, Hernandez, L. M. 2013. Current status and potential of conservation biological control for agriculture in the developing world. Biological Control 65:152–167.

Table 1. Target pests and beneficial organisms often used for augmentative biological control releases

Aphid

(See also soft-bodied arthropods)

predatory midge

Aphidoletes aphidimyza

parasitoid wasp

Aphidius ervi, A. matricariae, A. colemani, Lysiphlebus testaceipes, Trioxys pallidus

big-eyed bug

Geocoris pallens

lady beetle (“ladybug”)

Hippodamia convergens

lacewing

Chrysoperla downesi, C. plorabunda, C. rufilabris

minute pirate bug

Orius insidiosus, O. minutus, O. tristicolor

Armyworm

(See also Butterfly and moth)

braconid parasitoid wasp

Chelonus insularis

Black fly larvae

bacterial endotoxin (Bti)

Bacillus thuringiensis var. israelensis (e.g., Bactimos, Teknar, Vectobac)

Butterfly and moth larvae and eggs of beetle pests in stored grain products, such as almond moth, Indian meal moth, grain weevil

parasitoid wasp

Bracon hebeter

Butterfly and moth eggs and young larvae: beet armyworm, cabbage looper, corn earworm, cutworm, diamondback moth, imported cabbageworm, codling moth and other orchard moths, tobacco budworm

viral pathogen

Nuclear polyhedrosis virus (NPV)

bacterial endotoxin (Btk, Bta)

Bacillus thuringiensis var. kurstaki (e.g., Dipel, Javelin, Attack, Thuricide, Bactospeine, Safer’s Caterpillar Killer), Bacillus thuringiensis var. aizawai (e.g., Certan)

parasitoid wasps of eggs

Trichogramma minutum, T. pretiosum, T. platneri

Codling moth larvae

granulosis virus pathogen

Baculovirus carpocapsae

Flea

parasitic nematode

Steinernema carpocapsae, S. feltiae

Fly (garbage- and manure-breeding)

parasitoids of puparia

Melittobia digitata, Muscidifurax raptor, Muscidifurax zaraptor, Nasonia vitripennis, Pachcrepoideus vindemiae, Spalangia cameroni, S. endius

histerid beetle predator

Carcinops pumilio

Fungus gnat (larvae)

predatory mite

Hypoaspis miles, H. aculeifer

parasitic nematode

Heterorhabditis megidis,

Steinernema carpocapsae, S. feltiae

bacterial endotoxin (Bti)

Bacillus thuringiensis var. israelensis

Grasshopper (nymphs and adults)

protozoan

Nosema locustae

Larvae and grubs that pupate in the soil: cucumber beetles, dampwood termites, flea beetles, root weevils, wireworms

parasitic nematodes of larvae

Heterorhabditis bacteriophora, H. heliothidis, H. megidis, Steinernema feltia, S. carpocapsae, S. riobravis

Grubs in soil such as Japanese beetle, June beetle, and white grubs

bacterial endotoxin (Btg)

Bacillus thuringiensis var. galleriae

Leafminer

braconid parasitoid of larvae

Dacnusa sibirica

Mealybug

lady beetle (“mealybug destroyer”)

Cryptolaemus montrouzieri

Mite: twospotted spider (Tetranychus urticae)

predatory mite

Amblyseius hibisci, A. mckenziei, Galendromus occidentalis, Mesoseiulus longipes, Neoseiulus californicus, N. fallacis, Phytoseiulus persimilis, P. macropilis

predatory six-spotted thrips

Scolothrips sexmaculatus

minute pirate bug

Orius minutus, O. tristicolor

big-eyed bug

Geocoris pallens

Mosquito larvae

predatory fish

Gambusia affinis spp. (only in manmade water bodies or containers that have no connection to natural waterways)

bacterial endotoxin (Bti)

Bacillus thuringiensis var. israelensis (e.g., Dunks, Bactimos, Vectobac, Teknar)

Scale: armored scale, oleander scale, San Jose scale, ivy scale

lady beetle

Chilocorus fraternus

Soft scale: citrus black scale, black/brown hemispherical, nigra scale (See also soft-bodied arthropods)

parasitoid wasp

Metaphycus helvolus

Soft-bodied arthropods: thrips, scale, aphid, spider mite, whitefly, eggs of harmful pests

lacewing larvae (in larval stage)

Chrysoperla downesi, C. plorabunda, C. rufilabris

fungal pathogen

Beauveria bassiana

lady beetle

Chilocorus fraternus, Hippodamia convergens

pirate bug

Orius minutis, O. tristicolor

predatory thrips

Scolothrips sexmaculatus

Thrips larvae (See also soft-bodied arthropods)

predatory mite

Amblyseius cucumeris, A. mckenziei, A. barkeri, A. degenerens

lacewing

Chrysoperla downesi, C. plorabunda, C. rufilabris

minute pirate bug

Orius minutus, O. tristicolor

Wax moth larvae (in honeycombs)

bacterial endotoxin (Bta)

Bacillus thuringiensis var. aizawai (e.g. Certan)

Weevil in landscape plants

parasitoid wasps of larvae

Anisopteromalus calandrae

parasitic nematode

Heterorhabditis heliothidis, H. medidis, Steinernema carpocapsae, S. feltiae, S. riobravis

Whitefly nymph (See also soft-bodied arthropods)

parasitoid wasps of eggs

Encarsia formosa, Eretmocerus californicus

1 Lady beetles include many species in the family Coccinellidae, order Coleoptera.

2 Lacewings include many species in the families Chrysopidae and Hemerobiidae, order Neuroptera.

3 Parasitoid and predatory wasps include a large number of species in families such as Aphelinidae, Aphidiidae, Braconidae, Chalcididae, Crabronidae, Encyrtidae, Eulophidae, Ichneumonidae, Mymaridae, Pompilidae, Pteromalidae, Scelionidae, Specidae, and Trichogrammatidae, order Hymenoptera.

4 Hoverflies include many species in the family Syrphidae, order Diptera.

5 Predatory bugs include many species in families such as Anthocoridae, Lygaeidae, Nabidae, Pentatomidae, and Reduviidae, order Heteroptera.

6 Minute pirate bugs include many species in the family Anthocoridae, order Heteroptera.

7 Big-eyed bugs include many species in the family Lygaeidae, order Heteroptera.

8 Parasitoid Tachinid flies include many species in the family Tachinidae, order Diptera.

9 Bees include many species in families such as Anthophoridae, Apidae, Halictidae, Andrenidae, Colletidae, and Megachilidae, order Hymenoptera.

Table 2. Flowering plants visited by beneficial insects that can aid biological control conservation efforts

Common name (botanical name)

Beneficial insects

Apiaceae (Carrot family)

Angelica (Angelica)

lady beetle (“ladybugs”), lacewing

Anise (Pimpinella anisum)

parasitoid wasp

Blue lace (Trachymene caerulea)

parasitoid wasp

Caraway (Carum caryi)

hoverfly, minute pirate bug and big-eyed bug, lacewing, parasitoid wasp

Chervil (Anthriscus cerefolium)

parasitoid wasp

Coriander (Coriandrum sativum)

hoverfly, parasitoid wasp, parasitoid tachinid fly

Dill (Anethum graveolens)

hoverfly, lady beetle, parasitoid wasp

Fennel (Foeniculum vulgare)

hoverfly, parasitoid wasp, parasitoid tachinid fly

Lovage (Lovisticum officinale)

parasitoid wasp

White lace flower (Ammi majus)

hoverfly, predatory bug, lady beetle, parasitoid wasp, parasitoid tachinid fly

Wild carrot (Daucus carota)

hoverfly, predatory bug, lady beetle, lacewing, parasitoid wasp

Asteraceae (Daisy family)

Blazing star, gayfeather (Liatrus spp.)

minute pirate bug, big-eyed bug, parasitoid wasp

Chamomile (Anthemis nobilis)

lady beetle

Cosmos (Cosmos bipinnatus)

hoverfly, lacewing, minute pirate bug

Golden marguerite (Anthemis tinctoria)

lady beetle, parasitoid wasp, parasitoid tachinid fly

Goldenrod (Solidago altissima)

soldier beetle, predatory bug, lady beetle, parasitoid wasp

Marigolds, signet (Tagetes tenuifolia)

minute pirate bug, parasitoid wasp

Mexican sunflower (Tithonia tagetifolia)

hoverfly, minute pirate bug

Sunflower (Helianthus annuus and H. debilis)

hoverfly, lady beetle, parasitoid wasp

Tansy (Tanecetum)

hoverfly, lady beetle larvae, parasitoid wasp

Yarrow, milfoil (Achillea millefolium)

hoverfly, parasitoid wasp

Yarrows (A. macrophylla, A. taygetea, etc.)

hoverfly, parasitoid wasp

Brassicaceae (Cabbage family)

Broccoli (Brassica oleracea)

hoverfly, parasitoid wasp

Sweet alyssum (Lobularia maritima)

hoverfly, parasitoid wasp, parasitoid tachinid fly

Globe candytuft (Iberis umbellata)

hoverfly

Mustards (Brassica hirta and B. juncea)

hoverfly, minute pirate bug, big-eyed bug

Dipsaceae (Scabiosa family)

Cephalaria (Cephalaria giganitica)

hoverfly, parasitoid wasp

Dipsacus (Dipsacus spp.)

hoverfly

Pincushion flower (Scabiosa caucasica)

hoverfly, parasitoid wasp

Scabiosa (Scabiosa atropurpurea)

hoverfly

Fabaceae (Legume family)

Alfalfa (Medicago sativa)

bee, predatory bug, lacewing, lady beetle, parasitoid wasp

Clover (Trifolium spp.)

bee, predatory bug, lacewing, lady beetle

Vetch (Vicia spp.)

bee, predatory bug, lacewing, lady beetle

Hydrophyllaceae (Waterleaf family)

Fiddleneck/Phacelia (Phacelia tanacetifolia)

bee, predatory bug, hoverfly

Lamiaceae (Mint family)

Germander (Teucrium spp.)

bee, parasitoid wasp

Polygonaceae (Buckwheat family)

Buckwheat (Eriogonum spp. and Fagopyrum spp.)

hoverfly

See notes for Table 1.