Commonly available natural enemies used for biological control:
Convergent lady beetle, Hippodamia convergens. The adult beetle is orange with six small, black spots on each side and a black area with white markings behind the head. The larva is soft-bodied, alligator-shaped, grey and orange in color with rows of raised black spots. Larvae and adults feed on aphids and other small, soft-bodied insects and mites. Adults also feed on nectar, pollen and honeydew. Development (egg to adult) takes 2 to 3 weeks, and adults live up to several months.
This species occurs throughout North America. In California, adult beetles overwinter in huge aggregations on mountainsides. These are harvested, stored at cool temperatures and shipped to customers in the spring and summer for release in gardens or crops. Unfortunately these releases have limited usefulness because the beetles fly away soon after release. They provide long- term, adequate aphid control only if they reproduce. Female beetles cannot produce eggs until they have fed on prey, and they lay eggs only where prey are abundant. Larvae provide better aphid control.
Suppliers recommend release rates ranging from 1 pint to 1 quart of beetles per home garden, and from 1 gallon of beetles per acre to 1 gallon per 15 acres for larger areas.
Mealybug destroyer, Cryptolaemus montrouzieri. The adult of this Australian lady beetle is a small (3/16 inch), black beetle with orange on the wing tips and behind the head. The larva is covered with white, waxy material and resembles a mealybug. Adult and larval stages feed on above ground mealybug species, but will also consume aphids and immature scale insects. This natural enemy won’t reproduce without large numbers of mealybugs and optimum environmental conditions (72 to 77 degrees F and 70 to 80 percent relative humidity). The mealybug destroyer may not control mealybug infestations during winter months. It is most effective when used for quick reductions of heavy mealybug infestations.
Suppliers recommend releasing one beetle per 2 square feet of planted area or two to five beetles per infested plant. Supplies are often limited because colonies are difficult to maintain.
The lady beetle, Delphastus pusillus, has been shown to suppress sweet potato whitefly infestations. Commercial availability is very limited.
Lacewing. Chrysoperla carnea, the common green lacewing, is the most widely available lacewing species. Chrysoperla rufilabris is an eastern lacewing species that is better adapted for use in tree crops. Green lacewings occur naturally throughout North America. The adult has a delicate, light green body with large, clear, veined wings. Larvae are small, elongated and greyish brown with sickle-shaped mandibles. Eggs are deposited singly on silken stalks. Although C. rufilabris and most other lacewings are predaceous as adults, the adult C. carnea feeds only on nectar, pollen and aphid honeydew, and females cannot produce eggs if these foods are unavailable. Adults fly at night and disperse soon after emerging whether or not ample food is present. Artificial foods (Bug Chow®, BugPro® or Wheast®) may be a useful supplement to natural foods (nectar and honeydew) to attract and concentrate adult lacewings.
Lacewings can be purchased as eggs shipped in a mixture of rice hulls and frozen caterpillar eggs or larvae. Suppliers recommend releasing from one to five lacewing eggs per square foot for gardens, and from 50,000 to 200,000 lacewing eggs per acre in field crops and orchards. Releases are made singly or sequentially at 2-week intervals, depending on the pest to be controlled. The costs of purchasing and releasing such high numbers of lacewing eggs may be prohibitive.
Preying mantid. Several species occur naturally in most of the U.S. In the fall, females produce egg cases that may contain up to 200 eggs. Eggs hatch in the spring. Nymphs and adults are territorial and general predators, feeding on a wide variety of insects, including other mantids. They are not effective in controlling aphids, mites or most caterpillars. Mantids are nearly useless for pest control in gardens because of their feeding habits and high mortality rate. Egg cases of the Chinese praying mantid, Tenodera aridifolia sinensis, are most commonly available for purchase.
Predatory mites. Spider mite predators in the genera Phytoseiulus and Amblyseius are quick breeding, fast moving, pear shaped predators with short life cycles (from 7 to 17 days, depending on temperature and humidity). They are pale reddish and distinguished from twospotted spider mites by their lack of spots, their long legs and rapid movement. Predatory mite eggs are elliptical and larger than the spherical eggs of spider mites. Adults feed on all stages of spider mites, whereas the nymphs feed on eggs, larvae and nymphs.
Phytoseiulus persimilis does best in a temperature range of 70 to 80 degrees F and a relative humidity of 60 to 90 percent. The suppliers suggest releasing from two to 30 predatory mites per plant, depending on the stage and susceptibility of the crop. Some experimentation may be necessary to determine the best release rate and method for specific situations. U.S. insectaries often recommend releasing P. persimilis when one or fewer spider mites per leaf occur throughout the greenhouse. Where spider mite populations are larger, it is a good idea to apply an insecticidal soap or other nonresidual insecticide to reduce the infestation before predatory mites are released. Spot releases and uniform, area-wide releases both are occasionally advocated, depending on the distribution of the spider mite. In Europe, spider mites are sometimes released into the greenhouse at a low rate soon after planting, followed later by the release of predators. This practice allows the predatory mites to become established. In other cases, spider mites and predators are released together early in the season.
Phytoseiulus longipes tolerates temperatures up to 100 degrees F when humidity is high, and tolerates lower relative humidities (down to 40 percent) at lower temperatures (70 degrees F). Amblyseius californicus also tolerates high temperatures (up to 90 degrees F), but consumes mites at a slower rate than Phytoseiulus species and survives better when spider mite numbers are low. Mixed releases of the two predators have been made in greenhouses where conditions and spider mite numbers are variable.
Thrips predators. Amblyseius cucumeris and A. mckenziei (or A.barkeri) are mites that feed on the western flower thrips and onion thrips. They can also subsist for short periods on pollen, fungi or spider mite eggs. These mites require high humidity and are sensitive to insecticides. They do not produce eggs during the winter, which makes thrips control difficult at that time.
Suppliers recommend releasing large numbers of these predators to control thrips. Rates vary from 10 to 50 predatory mites per week per plant, plus an extra 25 to 100 mites per infested leaf in the greenhouse, until there is one predatory mite for every two thrips. Very little research has been published about these types of releases, but literature from Europe indicates that lower release rates may be feasible. This is not an effective method of vector control for dealing with tomato spotted wilt virus.
Greenhouse whitefly parasite, Encarsia formosa. This is a tiny parasitic wasp. Adults lay eggs during the third and fourth nymphal whitefly stages. Parasitized whitefly nymphs blacken within 2 to 3 weeks and die as the wasp larvae develop inside. Adults also feed on and kill early and late nymphal stages. Encarsia develops best in bright light, 70 to 80 degrees F temperatures and 50 to 70 percent relative humidity. Under these conditions it reproduces faster than whiteflies. Commercially available Encarsia are not effective parasites of the sweet potato whitefly, although adult wasps will feed on and kill the immature stages.
Most U.S. suppliers suggest making releases when fewer than one adult whitefly per upper leaf is found throughout the greenhouse. Releases should be made at 2-week intervals to control immature whiteflies. Release rates range from one to five wasps per square foot or one to eight per plant, depending on plant species and the severity of the infestation. In European vegetable greenhouses, whiteflies are introduced at low levels before the natural enemy is released. Where this approach is not used, parasites must be released at the very first sign of whitefly infestation or on a preventive schedule.
Caterpillar egg parasites, Trichogramma spp. These wasps are extremely small, averaging about 1/4-inch in length as adults. Females lay their eggs in the eggs of moths and butterflies. A few species parasitize the eggs of other insects. Trichogramma larvae develop inside host eggs, killing the embryos. Instead of a caterpillar, one or more adult wasps emerge from the parasitized egg. There are many species and strains of Trichogramma. Some are general parasites but others parasitize only selected species.
Trichogramma wasps are usually released as mature pupae inside host eggs. Adults emerge within 1 to 3 days and live for about 9 days. Releases are timed to correspond with the egg-laying period of the pest, as determined by monitoring. Single or sequential releases at rates of 50,000 to 300,000 wasps per acre per release have been made, but the results have been extremely variable.
Two species available include:
1) T. pretiosum, which parasitizes more than 200 species of caterpillar eggs (though not equally effective against all species); and
2) T. minutum, which controls orchard and forest caterpillars. The size and host-finding ability of Trichogramma is influenced by the way the wasp is reared.
In commercial operations they are reared in the small eggs of the Angoumois grain moth. The parasites produced this way are also small and may not do well at locating eggs of target pests in the field. Parasites reared locally on the eggs of the intended target pest are more likely to provide successful control.
Insect parasitic (entomogenous) nematodes, such as Steinernema carpocapsae, have been mass reared and formulated on sponges so that they can be mixed with water and sprayed onto plants or for treating soil and growing media. Different species and strains of these nematodes have different abilities to kill specific insect pests. Since these organisms are multicellular animals, these products (BioSafe®, Exhibit®, Guardian Nematodes and others) are not regulated by the Environmental Protection Agency). These nematodes are considered to be nontoxic and nonpathogenic to plants and animals.
The juvenile (J3) stage of the nematode is used in these products. Once applied, the nematodes actively seek out arthropods. After successfully gaining entry into the arthropod body, the nematodes’ symbiotic bacteria are injected into the host’s blood to paralyze them. The nematodes then complete their development inside. Use of the nematodes have been more successful in the control of arthropods with restricted movement such as root-feeding weevil larvae. However, they are commonly used to control insect pests such as fungus gnat larvae and sod webworms. Foliar treatments are most effective when applied in the evening or at times when water film remains on the leaf surface for an extended period of time. However, care must be taken with these treatments to avoid promoting disease outbreaks. Effectiveness of applications is dependent upon environmental conditions. Temperature, humidity, soil microfauna and moisture all effect the free-living juvenile stages.
Extracted from T. Henn and R. Weinzieri, 1990
Hunter, C. D. 1994 ed. Suppliers of Beneficial Organisms in North America. California EPA, Dept. of Pesticide Regulation, l020 N. Street, Room l6l, Sacramento, CA 95814-5604; 916/324-4100.
Knutson, A., 1998. The Trichogramma Manual. B-6071. The Texas Agricultural Extension Service, The Texas A&M System, College Station, TX.
Flint, M. L. and S. H. Dreistadt. 1999. Natural Enemies Handbook – The Illustrated Guide to Biological Pest Control. University of California Press, 6701 San Pablo Ave., Oakland, CA 94608-1239.
Henn, T., and R. Weinzieri. 1990. Beneficial insects and mites. Circular 1290. University of Illinois, College of Agriculture, Cooperative Extension Service.
Steiner, M.Y. and D.P. Elliott. 1987. Biological pest management for interiorscape plantings. Alberta Public Affairs Bureau, Publication Services, 11510 Kingsway Ave., Edmonton, AB, Canada T5G 2Y5.
For a listing of available biological control organisms in North America, see Suppliers of Beneficial Organisms in North America from the California Department of Pesticide Regulation (CDPR).
For a report on advances in biological control technology in the greenhouse, request “Biological control of two-spotted spider mite in California greenhouses” and “Biological control of greenhouse whitefly in California greenhouses” from the Bulletin Secretary, University of California Cooperative Extension, 4205 Wilson Way, Stockton, CA 95205.