Predation on Gypsy Moth (Lepidoptera: Lymantriidae) Egg Masses by Birds

Abstract

We studied predation of gypsy moth, Lymantria dispar (L.), egg masses in two study areas. In Connecticut, individual egg masses were mapped and examined from February to April. Predation rate, expressed as the mean amount removed from an individual egg mass, increased gradually from 30% in February to 53% in April. The percentage of all egg masses upon which some predation was observed increased from 67% to 89% over the same period. Sixteen of 105 egg masses were completely destroyed. Three species of birds were observed feeding on egg masses in the field. In an aviary study, four out of five bird species fed on egg masses with and without alternative foods. Three species of captive small mammals never ate egg masses. In West Virginia, an exclosure experiment revealed that vertebrate predators accounted for 9.3% of egg mass predation from August to April, whereas invertebrates accounted for only 1.5%. Only 5 of 146 egg masses were completely destroyed. Although it is theoretically possible that mammals were responsible for some predation, the gradual nature of egg removal, direct observations of avian predation, and the fact that no mammal has ever been observed to eat an egg mass in field or laboratory leads us to believe that birds were responsible for the observed predation. We conclude that egg mass predation is a variable but potentially important gypsy moth mortality factor worthy of further study.