Development of the solitary larval endoparasitoid Glyptapanteles porthetriae (Hymenoptera: Braconidae) in its host Lymantria dispar (Lepidoptera: Lymantriidae)

The development of the solitary endoparasitic braconid Glyptapanteles porthetriae in gypsy moth larvae of different ages was studied. Host larvae were parasitized during the premolt to the 2nd instar (A-larvae), to the 3rd instar (B-larvae) or to the 4th instar (C-larvae), respectively. The percentage of successfully parasitized larvae decreased markedly with the age of the host at the time of parasitization. When parasitization occurred at the premolt to the second or third instar, parasitoid larvae successfully emerged at rates of 68% and 57%, respectively, in contrast to the 17% from larvae parasitized in the premolt to the fourth instar. In all three groups of parasitized larvae the final host instar was significantly longer than the corresponding instar of unparasitized control larvae of the same age. However, the growth and growth rate of parasitized larvae were reduced compared to control larvae. Due to the extremely low rate of successful development of G. porthetriae in C-larvae, parameters of parasitoid development were only recorded in A and B-host larvae. In both the parasitoid growth was slow during the first instar but rapidly increased during the second instar. Total developmental time of the parasitoid was significantly longer in B-host larvae, and the resultant cocoons were heavier than those that developed in A-host larvae, but proportionally fewer of the offspring were females. Within both groups the female wasps took significantly longer to develop than the males.