JoAnne Skelly: Beneficials at work

I learn something new each time I visit Carson High School’s The Greenhouse Project. This week it was which kinds of insects work best in a greenhouse at this time of year.

Pests can be a challenge in the optimum environment of a greenhouse. The climate is warm, with temperatures around 80 degrees on a sunny winter day and low temperatures stable at approximately 50 degrees at night. Couple these lovely temperatures with a delightfully humid environment filled with lush green plants and you have a pest heaven.

Cory King, Greenhouse operations manager and site educator, has been researching which beneficial insects will reduce aphid and thrips infestations.

In August, after repeated crop damage from these pests, he shut the greenhouse down while King and AmeriCorps interns Haley and Tyler emptied it out and cleaned it thoroughly. With the old infested plants gone and hiding places eliminated, most of the pests were gone, too. Beneficial insects are more effective pest management tools when the infestations aren’t out of control.

Not all beneficial insects are created equal. Some won’t lay eggs or survive at this time of year, even in a greenhouse; or won’t work against the particular pests found in our greenhouse. Some eat the pests (predators), others lay eggs in pests and the larvae grow, eating their hosts from the inside out (parasitizers).

King chose Aphidius matricariae, a parasitic wasp and Aphidaletes aphidimyza, a cecidomyiid fly for managing aphids in our greenhouse. The wasp lays her eggs into the aphids. The larvae develop inside the aphid bodies turning them into rigid, golden-brown mummies.

Finally, the adults emerge from the mummies by cutting an exit hole in the top and repeat the egg-laying process. The flies or midges are small (2-3 mm), delicate and mosquito-like. “The midge larvae paralyze each aphid by attacking its leg joints, and then suck it dry, leaving a blackened, collapsed aphid attached to the leaf” (Cornell University). Pretty cool stuff for entomology geeks.

Thrips and fungus gnats also are constant battles in the greenhouse. Dalotia coriaria, a rove beetle that looks similar to a small earwig, and Stratiolaelaps scimitus (Womersley), a soil-dwelling mite, are both voracious predators of these pests.

Beside insect control, the use of beneficials has been a great learning experience for the students who are monitoring pest and prey interactions through hand lenses. We are all discovering more about the insect world.

JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at


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