The Heliothis subflexa caterpillar is a specialist herbivore that eats only the fruit of Physalis plants which include ground cherry, tomatillo and Chinese lantern. H. subflexa's choice of food turns out to have unusual benefits in the three-way struggle between herbivores, their predatory wasps and the plants.

"We know that many plants produce volatile chemicals when chewed on by herbivores and that some of these chemicals attract wasps that parasitize the caterpillars," says Dr. Consuelo M De Moraes, assistant professor of entomology. "However, when we investigated H. subflexa's spit, it did not contain volicitin, a chemical elicitor that signals the plant to produce the volatile chemicals that attract wasps."

H. subflexa somehow does not turn on the plant's defenses.

"The co-evolution of plants, herbivores and their parasitoids is complex," says Dr. Mark C. Mescher, assistant professor of biology. "We do not fully understand how the system is influenced by the interactions of the three players and we need to understand this to develop more environmentally friendly ways to deal with agricultural products and pests."

Thinking the absence of elicitor was related to the caterpillar's food, the researchers fed H. subflexa on a different food source and fed a different caterpillar on Physalis angulata. The Physalis-fed caterpillar did not produce the elicitor either, but H. subflexa, fed on a different food, did produce elicitors.

The researchers report in this week's online edition of the Proceedings of the National Academy of Sciences that the Physalis angulata fruits used "lack linolenic acid." Linolenic acid is necessary to produ
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Contact: A'ndrea Elyse Messer
aem1@psu.edu
814-865-9481
Penn State
7-Jun-2004