Alterations in carbohydrate and fatty acid levels of Lymantria dispar larvae caused by a microsporidian infection and potential adverse effects on a co-occurring endoparasitoid, Glyptapanteles liparidis.

Infection of Lymantria dispar host larvae by the entomopathogenic microsporidium Vairimorpha sp. has a negative impact on the performance of the endoparasitic braconid Glyptapanteles liparidis. To investigate possible causes for this effect, we studied to what extent nutritional host suitability is altered by the microsporidium. Therefore, we analyzed carbohydrates and fatty acids in host larvae after Vairimorpha infection and/or parasitism by G. liparidis. Trehalose levels were significantly reduced in the hemolymph of infected hosts. After day five post infection, it was detected only in traces. Four to six days later, the glycogen resources were depleted in infected larvae. Parasitism by G. liparidis, on the other hand, led to increased hemolymph trehalose levels during the early endoparasitic phase but to a significant decrease at the end of its larval development. No effect of parasitism on the glycogen content was ascertained. Hemolymph levels of the fatty acids analyzed, such as palmitic, stearic, oleic, linoleic, and linolenic acid, were significantly reduced in microsporidia-infected L. dispar. Vairimorpha sp. develops as an intracellular parasite in the fat body of the host larva and synthesis of trehalose and fatty acids may be disturbed. Moreover, microsporidia may also harness metabolites or energy produced by host cells. We conclude that the microsporidia-induced decrease in hemolymph carbohydrates and fatty acids adversely affects growth and development of parasitoid larvae. Copyright 2002 Wiley-Liss, Inc.