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  A Publication of UVM Extension's Vermont Vegetable and Berry Program

Beneficial Insects for the Greenhouse

by Vern Grubinger
Vegetable and Berry Specialist
University of Vermont Extension

If you're an aphid with a taste for tomato plants, the term 'biocontrol' makes you quiver with fear. You'd rather not think about predators and parasitoids with a voracious appetite for insect pests, especially since their eating habits would qualify them for starring roles in an 'Aliens' movie.

Biological control agents, a.k.a. "good bugs," are important parts of integrated pest management (IPM) in the greenhouse. For them be effective, growers have to monitor their crops frequently for the first sign of insect pests. Once found, a pest must be quickly and accurately identified so appropriate biocontrol species can be purchased while the pest population is still low. If the pest population becomes high, then biocontrols rarely provide satisfactory control because they can't reproduce as fast as the more numerous pests unless one is willing to pour a lot of money into the task. Before and after introducing a biocontrol, pesticides must be avoided or carefully selected so that good bugs aren't killed along with pests.

There are several dozen species of commercially available biocontrols for a wide range of pests, and just a few examples are listed below. Don't be put off by the Latin species names of these good bugs, they'll still work fine even if you can't pronounce their names!

Aphidius of several species are tiny wasps that inject their eggs into the bodies of immature aphids (the nymphs). Aphidius wasps are parasitoids, meaning they reside in their host and eventually kill them. In this case, a wasp hatches inside an aphid and, as it grows, it consumes the aphid's innards. When the food is gone, the wasp cuts a neat exit hole in the backside of the host and emerges, leaving behind a hollow aphid shell, or 'mummy.' Your friendly biocontrol distributor can help you select the species of Aphidius that will work best on the type of aphid pest you may have.

Aphidoletes aphidimyza is a midge that looks like a tiny mosquito. In the immature stage, this guy is a predator, meaning it hunts and consumes prey. The adults fly at night, locate colonies of aphids, and lay their eggs nearby. The eggs soon hatch into fast-moving orange larvae with a hankering for aphid meat. They run after the aphids, bite them on the knees, and inject them with a paralyzing toxin. Then, they literally suck their guts out. On a good day, a single A. aphidimyza larvae can chow down on 50 aphid Slurpies. They eat most all flavors of aphids, except melon aphids.

Many ladybugs are also predators. In the greenhouse, the convergent ladybeetle, Hippodamia convergens, feeds on aphids and spider mites. Ladybugs do not always provide successful, long-term control but they are useful to "knock down" an infestation. These predators are collected in the wild, but availability is good, except during the early summer months when supplies may be sold out. Ladybugs can be stored in the refrigerator for several weeks and released one handful at a time. They are usually thirsty when released, so plants should be misted prior to release. Releasing them in the evening is also important.

Encarsia formosa is a tiny parasitoid wasp used to control greenhouse whitefly. It lays its eggs inside whitefly larvae, which young wasps later consume and kill. Encarsia formosa comes to the grower as parasitized whitefly pupae stuck to small cards. The cards are easy to hang on plants below the canopy, out of direct sunlight. The wasps do best when daytime temperatures exceed 72 degrees and nights are above about 60 degrees. At lower temperatures, and at low light levels, the whiteflies reproduce too fast for Encarsia formosa to control them.

Phytoseiulus persimilis is a predatory mite for control of two-spotted spider mite. This is a case of a fast mite that can run down and eat slower mites. The predator is shipped mixed with vermiculite or bran and must be released carefully by sprinkling a little on every infested leaf. It becomes established in the crop in about one week. Predatory mites prefer moderate temperatures and humid conditions (60 to 90% relative humidity). Spider mite populations have a tendency to explode when it gets hot and dry, so early or preventative releases of Phytoseiulus persimilis are key to success.

Steinernema species and Heterorhabditis species are parasitic nematodes that attack a variety of soil dwelling insect pests. These include the larvae, or grubs, of certain beetles, and weevils. The nematodes enter the pest larvae then they multiply inside their bodies, killing them and then leaving by the thousands, seeking out other susceptible larvae. A moist soil environment is a requirement for success with parasitic nematodes. The nematodes can be supplied in a spray concentrate or a moist granular carrier. Some growers apply them using injector systems or diluting them with water and using a pump sprayer, hose end sprayer, watering can or pail.

Biocontrols can help reduce or eliminate insecticide use in the greenhouse. And although they can be more expensive than chemicals and don't work as fast, they're a lot more fun to use! Biocontrols have been growing in popularity over the past few years as prices come down and growers learn how to use them effectively. This one case where biological warfare is good thing, although aphids may beg to differ.

Sources of biocontrols include:

9664 Tanqueray Ct.
Redding CA 96003
(800) 477-3715

IPM Laboratories, Inc.
Main St.
Locke NY 13092
(315) 497-2063

Koppert Biological Systems, Inc.
28465 Beverly Rd.
Romulus MI 48174
(734) 641-3763

Published/last revised: April 2003
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