Patricia Repollet, 2012

University of Puerto Rico Mayaguez

Can grasshoppers reduce herbivory on plants they don't like to eat?

Man and insects have long competed with each other for food resources. When man attempts to control these pests lacking the proper understanding of the system at hand, he sometimes affects untargeted organisms as well as the interactions they are involved in. In this research project, a study of the interaction between a specialist herbivore, the three-lined potato beetle, and a generalist herbivore, the two-striped grasshopper, was conducted to gain a better understanding of the complex interactions that govern natural systems as well as to determine if grasshopper feeding on beetle eggs could potentially limit population size in the three-lined potato beetle. A series of experiments were conducted on the longleaf groundcherry-beetle system to determine: 1) the rate of predation on eggs by natural predators; 2) the possible identity of the main egg predators through video recording; and finally, 3) the circumstances and reasons for egg consumption by grasshoppers by providing eggs alongside both preferred and non-preferred plant hosts. Data obtained revealed that egg mortality increased over the summer (being higher in July than in June); grasshoppers were the main egg predator; clover was the preferred food source (over grass and longleaf groundcherry) but that the availability of a preferred leaf source did not change egg consumption; and that later grasshopper instars consume more eggs than earlier instars. The evidence gathered through this research suggests the possibility that the generalist herbivore could be controlling the population size of the specialist herbivore. The insight into complex interactions between generalist herbivores and specialist herbivore provided through this research could someday prove useful in improving methods of pest control.

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