Probable mechanism of sexual dimorphism in insulin control of Drosophila heat stress resistance

Adult males of Drosophila species (Drosophila melanogaster L. and Drosophila virilis) show a lower tolerance to heat stress compared with females. The present study investigates the effects of RNA interference (RNAi) knockdown of the insulin-like receptor in the corpus allatum of D. melanogaster males on dopamine metabolism and content, heat stress resistance and juvenile hormone metabolism. In male flies, the knockdown of insulin-like receptor in the corpus allatum is shown to change metabolism of juvenile hormone but not dopamine. It is also shown that knockdown of the insulin-like receptor in the corpus allatum results in a decrease of heat stress resistance in females but not males, and that juvenile hormone rescues this decrease. The results suggest that at least one of the ways in which insulin-like growth factors affect heat stress resistance is by successive mediation through juvenile hormone and dopamine, which could lead to sexual dimorphism in the trait.