Incidence and ecological relationships of pupal parasitism by Brachymeria intermedia in new Jersey populations of the gypsy moth

Abstract: Pupal parasitism of the gypsy moth,Lymantria dispar (L.), was monitored in 15 study plots in New Jersey from 1978 to 1988. The predominant parasitoid was a chalcidid wasp,Brachymeria intermedia (Nees), which was found in only six plots. Parasitism was generally observed in the year of or preceding the peak numbers of gypsy moth egg masses. Parasitism exceeded 4% in only one plot. Percentage parasitism was correlated significantly with numbers of egg masses per hectare in the current season and with numbers of pupae per plot in the previous season, suggesting delayed density dependence. A multiple regression analysis found percentage parasitism to be correlated significantly with percentage infection by nuclear polyhedrosis virus, density of male host pupae, and mean minimum temperature in August and March. A canonical discriminant analysis carried out to distinguish study plots with and without the parasitoid was significant. Plots withB. intermedia had relatively higher host populations and defoliation.