GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) PERFORMANCE IN RELATION TO EGGHATCH AND FEEDING INITIATION TIMES

We investigated performance for groups of gypsy moth that began feedin g during different times in the spring and, thus, coincided with diffe rent levels of host foliage maturation. The study was performed by cag ing groups of newly hatched larvae on host foliage at three different times over a 2-wk period. These times were coincident with the beginni ng of natural gypsy moth egg hatch in the study area, near peak gypsy moth egg hatch in that area, and near the end of gypsy moth egg hatch for that area. At each establishment date, we placed the new groups of larvae onto the same individual trees that we were using to feed the earlier-established groups. Thus, the only host plant characteristics that varied between the groups established on different dates were tho se characteristics related to level of host foliage maturation. The tr ee species we studied were red oak, white oak, bigtooth aspen, and tre mbling aspen. Major findings include the following: larvae placed earl iest had the highest mortality, slowest development times, and lowest larval weights at the end of the season; larvae placed latest had the lowest mortality, fastest development times, highest relative growth r ates early on, and maintained the heaviest larval weights throughout t he season; and effects of the various host species on gypsy moth growt h and survival strongly support host effects seen in our earlier work and the work of others on gypsy moth-host plant interactions. Aspen-fe d insects had the highest larval growth rates at the end of the season and were the heaviest pupae, although aspen-fed larvae had high level s of mortality. Red oak-fed larvae had the best growth rates early in the season and the worst growth rates late in the season.