Canadian Forest Service Publications
Alteration of developmental rate and growth of Choristoneura fumiferana parasitized by Tranosema rostrale: role of the calyx fluid. 1996. Doucet, D.; Cusson, M. Entomologia Experimentalis et Applicata 81: 21-30.
Issued by: Laurentian Forestry Centre
Catalog ID: 16939
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We studied the effect of parasitism by Tranosema rostrale (Brischke) (Hymenoptera: Ichneumonidae) on the developmental rate and growth of its host, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). In the laboratory, T. rostrale completed its larval development in 13–14 days and its prepupae always emerged from 6th instar hosts, irrespective of host age (day 2 of the 4th, 5th or 6th instar) at the time of parasitization. Parasitism by T. rostrale did not affect the developmental rate of C. fumiferana parasitized as 4th instar larvae, but significantly lengthened the developmental period of hosts parasitized as 5th or 6th instars, with a doubling of duration in the latter case. In addition, T. rostrale significantly reduced the growth of its host: the maximum fresh mass reached by larvae parasitized as 4th, 5th or 6th instars was about half that of unparasitized larvae and their dry mass gain varied between 7 and 20% of that measured for their unparasitized counterparts. Parasitism also significantly lowered the production of faeces by host larvae. We examined the possibility that accessory fluids from the female wasp were responsible for the observed parasitism-induced alterations. Calyx fluid (CxF) injected into 6th instar larvae lengthened the time to pupation whereas venom had no effect on development. Although total faeces production was not affected by injection of either fluid, the rate of faeces production was significantly reduced in larvae injected with CxF at 0.5 female-equivalent. Injection of CxF treated with psoralen and UV did not delay pupation of C. fumiferana. These results indirectly suggest that polydnavirus transcription is required for this developmental alteration to be effected.