Differential mortality in male and female gypsy moth (Lepidoptera: Lymantriidae) pupae by invertebrate natural enemies and other factors

Pupal mortality in the gypsy moth, Lymantria dispar (L.), caused by invertebrate natural enemies and other factors was monitored at Belleplain State Forest in southern New Jersey from 1983 to 1991. Two methods were used, laboratory rearings of intact pupae field collected during metamorphosis and postseason examination of pupal remains. The introduced chalcidid Brachymeria intermedia (Nees) consistently destroyed higher percentages of male gypsy moth pupae clan female pupae. Ichneumonid parasitism was sometimes higher in male pupae than female pupae. Diptera, mostly Tachinidae and Sarcophagidae, were more likely to emerge from female than male intact pupae, but in the case of pupal remains, emergence from each sex was variable, being significantly higher in male pupae than female pupae for 2 yr, but the reverse in another year. Sex-based bias in predation of gypsy moth pupae by invertebrates, primarily larvae of Calosoma sycophanta (L.), was observed only in 2 yr, when it was slighly higher in male pupae. Incidence of disease was higher in female pupae than male pupae, but desiccation was more likely to occur in male pupae than female pupae. Based on examination of pupal remains, survival of female and male pupae averaged 53.0 and 45.5%, respectively, with marked differences observed in 5 of 9 yr of the study. Because of the sex-based bias in mortality by some invertebrate natural enemies, sex ratios (expressed as percentage of females) of gypsy moth adults were sometimes much higher than pupae. This bias was most noticeable during the outbreak and decline phases of the gypsy moth population cycle