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Biological Control: Greenhouse Pests and their Natural Enemies

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Using beneficial mites to manage thrips and two spotted spider mites in greenhouses.
Using beneficial nematodes to manage fungus gnats and thrips in greenhouses.

Pests and Natural Enemies: Parasites and Predators

Whiteflies

Greenhouse whitefly (Triaulerodes vaporariorum) . This species of whitefly has been controlled effectively for decades in Europe on tomato and cucumber crops by early season inoculative releases of the aphelinid wasp Encarsia formosa. This species is not currently the whitefly of usual concern on flower crops. The main whitefly on flower crops is sweet potato whitefly B-biotype (Bemisia tabaci) formally called the silverleaf whitefly (Bemisia argentifolii).

Encarsia formosa is less effective on tomatoes with hairs because the hairs make it difficult for the parasitoid to detect whiteflies and for the adult females to leay eggs in whitefly nymphs. Adult females lay eggs in whitefly nymphs; larvae emerge from eggs and consume the internal contents of teh whitefly. Larvae eventually pupate and emerging adults creat a circular hole with their mouthparts, which they use to exit from the parasitized whitefly. Adult females also feed on young nymphs. Parasitized whiteflies are black. Encarsia formosa is most effective at temperatures between 70-80F and 50-80% relative humidity. Adults do not fly when air temperature is below 65F and survival is reduced at temperatures greater than 86F. Do not use yellow sticky cards for 3-4 days following release to avoid capturing adults. Most E. formosa are commercially available as pupae glued to paper cards. Suspend the cards in the lower canopy of plants to avoid desiccation from direct sunlight. Adults emerge from the pupae and fly upward. Use E. formosa weekly beginning when whiteflies are first detected. Continue making releases until 80% of the whitefly population has been parasitized. Parasitized pupae are black. E. formosa are very sensitive to pesticides.

Sweet potato whitefly (Bemisia tabaci) and a new biotype of B. tabaci, the Q-biotype, was reported in 2006. This biotype is known to be resistant to a number of commonly used insecticides. This is the principal whitefly on flower crops, especially poinsettias. The commercial strain of Encarsia formosa provides partial control but is insufficient.

Eretmocerus eremicus wasps are used for B. tabaci. They kill whiteflies two ways: parasitism and "host feeding" (acting like a predator and eating whiteflies). E. eremicus attacks both sweet potato B-biotype and greenhouse whiteflies. E. eremicus is sold as pupae glued to paper cards or loosely in sawdust. If using pupae in sawdust, gently pour a portion of the mixture in styrofoam coffee cups, clipped to stakes that are attached to pots or flats. Do not use yellow sticky cards for 4 days after releases. Optimum temperatures are 77-84F. The parasitoid is inactive at temperatures greater than 86F. When scouting look for parasitized whiteflies. Greenhouse whitefly pupae are yellow and sweet potato whtiefly B-biotype pupae are yellow-brown.

Eretmocerus mundus is another parasitioid that only parasitizes sweet potato whitefly B-biotype. This parasitoid is active at a wider range of temperatures than E. eremicus.

Other natural enemies for whiteflies include, Amblyseius swirskii which feeds on whitefly eggs and nymphs and thrips. The predatory ladybird beetle, Delphastus catalinae is not recommended due to cost and requires the whitefly populations to be too high. Beauveria bassiana (BotaniGard, Mycotrol, Naturalis) is an entomopathogenic fungus that is commercially available. Applications must be initiated before whitefly populations are high.

Western flower thrips (Frankliniella occidentalis). Biological control of thrips is more difficult than most greenhouse pests. Western flower thrips and many other thrips species may be suppressed on greenhouse crop by releasing (Amblyseius (Neoseiulus) cucumeris) or predatory bugs (Anthocoridae, Orius spp.).

Minute pirate bugs (Orius species) tend to establish slowly on bedding plants, and are best used on crops that produce pollen or by releasing them onto flowering ornamental pepper plants that are in flower which serve as a banker plant, attracting the thrips and harboring the predators.  A. cucumeris feed only on the first instar nymphs so must be released early in the crop cycle before thrips populations are high. The predatory mite Ambylseius swirskii, feeds on thrips and whiteflies and has demonstrated to be effective in greenhouse-grown peppers, cucumbers and several ornamental crops. The soil dwelling predatory mite, Hypoaspis miles may feed on thrips pupae in the growing medium in addition to fungus gnat larvae. A single preventative release at planting is generally reommended to supplement above ground releases of A. cucumeris. The rove beetle, Atheta coriaria is a generalist predator that may feed on thrips pupae, along with fungus gnat and shore fly larvae.

Beauveria bassiana (BotaniGard, Mycotrol, Naturalis) is an entomopathogenic fungus that is commercially available. In addition to thrips, these materials may help to manage whiteflies, aphids and mealybugs. The effectiveness varies depending on relative humidity levels at the plant surface, life stage, application rate, crop type and spray coverage, light intensity, season and temperature. Repeat applications are often needed.

For more information, see the fact sheet: Western Flower Thrips, Management and Tospoviruses.

Spider mites (Tetranychus urticae and others). Commercially available predatory mites for two-spotted spider mites include Phytoseiulus persimilis, Galendromus occidentalis, Neoseiulus californicus, and Amblyseius fallacis. Each species requires different environmental conditions.

Phytoseiulus persimilis is the most effective predatory mite for control on two-spotted spider mite. Adults are bright red, pear-shaped with long legs and are larger and more active than two-spotted spider mites. P persimilis is suitable for use in short term crops such as bedding plants. Releases should be made when two-spotted spider mite populations are low or first detected. Two applications, one week apart may be needed. Make releases near infestaions and concentrate releases near localized hot spots. Optimum temperatures around 68F with 75% relative humidity is needed for this mite to be effective. When scouting, check for the presence of live two-spotted mites and eggs. Also look for the predatory mites. They can be observed by shaking plant parts over a white sheet of paper. Pest control materials that have reportedly compatible include, spinosad, pymetrozine, clofentezine.

Fungus gnats (Bradysia spp.)  Options include predacious mites (Hypoaspis miles), entomopathogenic nematodes (Steinernema feltiae), rove beetle (Atheta coriaria) and Bacillus thuringiensis var. israelensis. All are effective if applied before fungus gnat populations are abundant. The growing medium should be moist (not saturated) before applying these natural enemies.

H. miles prefers to feed on first instar fungus gnat larvae and it prey is not avaialble will feed on plant debris and algae. It is important to make releases early in the growing season before fungus gnat populations are high. Applications can also be directed to the soil beneath the benches. Mixing H. miles into the growing media prior to planting decreases survival. When scouting look for reductions in numbers of fungus gnat adults and yellow sticky cards and larvae on potato disks.

S. feltiae is a beneficial nematode that attacks fungus gnat larvae. Nematodes can be applied through a fertilizer injector. it is also helpful to use a small submersible pump to agitate the mixture in a the stock solution so that the nematodes do not settle to the bottom. Remove filters and use a nozzle with large holes. Treat early in the production cycle, just after planting. Use potato disks to monitor for fungus gnat larvae. For pesticide compatibility, see www.beckerunderwood.com

The rove beetle is a generalist predator that feeds on fungus gnat and shore fly larvae. They disperse throughout a greenhouse by flying. Both larvae and adults feed on pests, but also may consume natural enemies such as H. miles. Temperatures of 65-80F and a relative humidity of 50-85% are optimal for survival. Both adults and larvae are difficult to detect by scouting since they tend to hide in cracks and crevices of growing medium. Adults can be observed on the surface of the growing medium with their abdomens raised. Once established in a greenhouse, rove beetles may be present year round. Pesticides dinotefuran and thiamethozam are toxic to rove beetle adults. Rove beetles are compatible with beneficial nematodes.

In unsprayed greenhouses, growers may find adult hunter flies(Coenosia attenuata) and the parasitoid Synacra pauperi on sticky cards. Adult hunter flies are sometimes introduced on new plant material. Hunter flies resemble common house flies. They attack and feed on shore fly, whitefly, leafminer adults and other prey species in flight. Photos of both of these natural enemies can be seen in our photo library.

The soil-borne bacterium Bacillus thuringiensis spp. israelensis (GnatrolWDG) may be used before fungus gnat larval populations are high since it must be ingested to be effective. Applications are more effective on young larvae (1st instar) than mature larvae. Apply weekly until fungus gnat populations decline. BTi is not effective on shoreflies.

Shoreflies (Scatella stagnalis) . The only commercially available natural enemy that may manage shore flies is the rove beetle Athea coriaria.

Aphids (various species). Aphids are susceptible to many natural enemies, both predators and parasitoids. In general parasitoids are more effective than predators in reducing aphid populations, although parasitoids may fail to provide acceptable control under warm conditions when aphid populations tend to increase rapeidly. For information on using biological control for aphids see the fact sheet, Managing Aphids. Biological control options include ladybird beetles (Hippodamia convergens, Adalia bipunctata), green laceing (Chrysoperla rufilabris) the predacious midge Aphidoletes aphididmyza and the entomopathogenic fungus Beauveria bassiana).

Banker plants are often used to manage aphids. Banker plants are used to rear prey that provide a continuing food source for specific natural enemies to ensure that they continue to reproduce. Banker plants for aphids are pots of common rye or winter barley on which colonies of grass-feeding aphid species such as the corn-leaf aphid, or bird-cherry aphid are established. Banker plants are placed along walkways and at the end of the benches. After positioning the banker plants in the greenhouse, Aphidius colemani are ordered if you have green peach or melon aphid. The aphid mummies (parasitized aphids) are released onto the banker plants. A colemani attacks the grass feeding aphid, which is not a pest of most greenhouse grown crops, (except ornamental grasses and other monocots). The bird-cherry aphid is too small for the parasitoid A. ervi to develop, so will not work for that species. Also note that A. colemani is not effective against the foxglove aphid. Aphidoletes aphidimyza is used for foxglove aphid. More information about banker plants is available in the New England Floriculture Guide, see resources.

Leafminers (Liriomyza spp.). The parasites Dacnusa sibirica and Diglyphus isaea are used for control of these pests. Both of these parasitoides are most effective for long-term crops such as cut lowers and stock plants and should be used preventively to manage leafminer populations.

Mealybugs (mainly citrus mealybug, Planococcus citri, and longtailed mealybug Pseudococcus adonidum). It is important to identify mealybugs to species before releasing natural enemies. The parasitoid Leptomastix dactylopii is only effective for citrus mealybug. The predatory ladybird beetle Cryptolaemus montrouzieri is also use to control citrus mealybug, but is less effective for longtailed mealybug.

Scale: Armored (Diaspididae) and Soft (Coccus hesperidum). Biological control of armored an soft scales may be difficult due to the wide range of scale species that may occur simultaneously. Currently, the number of commercialy available natural enemies for control of both armored and soft scale is limited. Chrysoperla spp. (green lacewing) and Rhyzobius lophanthae are two commercially available predators.

Caterpillars Bacillus thuringiensis spp. kurstaki (Dipel, Deliver, Javelin)(Bt) is available that provide satisfactory control for some kinds of caterpillars. Bt is a bacterium that must be consumed by the caterpillar to be effective and through coverage is needed. Caterpillars stop feeding within 24-48 hours after eating the bacterium and die after 3-4 days.

Resources and Reference Materials

Originally Prepared by:
Roy Van Driesche and Mark Hoddle
Greenhouse IPM Program
University of Massachusetts, Amherst
August 1995

Revised in 2011 by Tina Smith
UMass Extension
Greenhouse Crops and Floriculture Program

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