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Research suggests plants and predators might work together to control aphids

Carmen Blubaugh, an assistant professor in Clemson University’s plant and environmental sciences department, is involved in a study that addresses how plants mediate interactions between predators and prey. The study took place in organic broccoli fields on 52 mixed-vegetable farms in Washington, Oregon and Idaho over a period of two years.

“Plants create toxins that defend against pest insects, such as aphids,” Blubaugh said. “When aphids attack plants, the plants release chemical compounds that tiny parasitoid wasps can smell. The wasps use these odors to track down the aphids and kill them, protecting the crops.”

To examine natural suppression of aphid pests, Blubaugh counted aphids and caterpillars on broccoli plants at the 52 sites and sampled parasitoid wasps using a backpack insect vacuum. After performing the survey, researchers followed up with experiments where they directly manipulated the presence of aphids and caterpillars then measured how fast they grew and how many aphids were eaten by parasitoid wasps.

Blubaugh and her colleagues found that other pests, such as caterpillars, can change the odors released by plants. When caterpillars fed on the same plants as aphids, it was more difficult for the wasps to locate aphids and reduced natural pest suppression.

“Hopefully, this study will help us learn more about how to harness and optimize pest-control services provided by beneficial insects.” Blubaugh, said. “In the past, plants have been bred for appearance, taste, quality, yields and so on, but someday soon, plants may be bred so that they have better chemical defenses and produce strong, reliable signals to attract predators when pests attack.”

Aphids are major insect pests of beans, broccoli, cabbage, southern pea and other crops. These pests are described as soft-bodied “plant lice,” about 1/16th to 1/8th of an inch long, they usually are green although some species are yellow, pink, brown or black. Aphids feed on plant sap with their piercing-sucking mouthparts. They reproduce very rapidly and can quickly reach numbers that cause damage. Their feeding results in distorted or curled and stunted growth.

Aphids are most prevalent on small plants during cool, dry weather. Heavy populations of aphids can stunt plants by withdrawing large volumes of plant juices and delaying maturity.

The insects have several natural enemies, including parasitic wasps, ladybird beetles (ladybugs) and their larvae and green lacewing adults and larvae. Their natural enemies tend to keep aphid populations under control except in cool weather.

Blubaugh is the lead author of an article related to the study: Dual-guild herbivory disrupts predator-prey interactions in the field (http://bit.ly/AphidStudy). It is currently online and will appear in the April 2018 issue of Ecology, the flagship journal of the Ecological Society of America.