Effect of seasonal placement ofCotesia melanoscela (Hym.: Braconidae) on its potential for effective augmentative release againstLymantria dispar (Lep.: Lymantriidae)

Abstract

) biosys, Columbia, MD 21046, USA Cohorts of Cotesia melanoscela (Ratzeburg) (Hymenoptera: Braconidae) cocoons were exposed in the field at three Maryland locations to attack by natural enemies tbr two week periods, then were held in an outdoor insectary until C. melanoscela adult or hyperparasitoid emergence. The timing of placement of the C. melanoscela cocoons in the field had a profound effect on the number of C. melanoscela that survived and emerged as adults in synchrony with the field occurence of susceptible early-instar Lymantria dispar (L.) larvae. The proportion of emerged adults available during susceptible host stages ranged from 1-92 %, depending on dates of release. November or December placements of C. melanoscela cocoons were most effective with 74-92 % emergence of adults during peak periods of susceptible host stages. Spring placements were least effective. The causes of ineffective placement, which varied with location and with date, were program (handling) loss, non-emergence, attack by hyperparasitoids, predation, and C. melanoscela adult emergence at times when appropriate L. dispar life stages would not be present. We concluded that November/December releases avoided natural enemies and promoted appropriate diapause and post-diapause development that enhanced survival and synchrony of adult emergence with host stage susceptibility.