Submission Date


Document Type

Paper- Restricted to Campus Access




Dr. Cory Straub

Committee Member

Dr. Kathryn Goddard

Committee Member

Dr. Richard Wallace

Department Chair

Dr. Kathryn Goddard

Project Description

Alfalfa, Medicago sativa, is one of the most important forage crops in the world. The potato leafhopper, Empoasca fabae, is the primary pest of alfalfa in Northeast USA. A secondary pest of alfalfa is the pea aphid, Acyrthosiphon pisum. Farmers traditionally use chemical insecticides to manage pests of alfalfa. However, insecticides can be detrimental to environmental and human health. Therefore, finding ways to reduce insecticide use through alternative pest management strategies is an important aspect of agricultural ecology. One alternative pest management strategy is host plant resistance, which involves the genetic manipulation of a plant to make it less desirable to pests. Alfalfa has been bred to have glandular-trichomes, which may cause it to be partially resistant to the potato leafhopper. I examined the effects of leafhopper-resistant alfalfa on the potato leafhopper, pea aphid, and predatory insects. In an open-field experiment, leafhopper-resistant alfalfa resulted in a reduction in leafhopper intensity, an increase in pea aphid intensity, and had mixed effects on predatory insects. I conducted a microcosm experiment to explore the possible mechanisms by which aphid intensity increases in leafhopper-resistant alfalfa. The results suggested that the higher aphid-intensity in the leafhopper-resistant alfalfa is caused, at least in part, by a competitive release from the primary leafhopper pests. Thus, leafhopper-resistant alfalfa appears to be an effective way to control the potato leafhopper, but control of the primary leafhopper pest may release pea aphids from competition and promote outbreaks of this secondary pest.


Research funded by US Department of Agriculture, National Institute of Food and Agriculture, Ursinus College Summer Fellows Program, Ursinus College FUTURE Program, and Howard Hughes Medical Institute.