Effects of the Rearing Host Species and the Host Species Attacked on Performance by Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae)

Two-way factorial experiments were set up to compare the fecundity and longevity of Trichogramma minutum Riley and the percentage emergence and sex ratio of their offspring when reared from the eggs of Ephestia kuehniella Zeller, Sitotroga cerealella (Olivier), Choristoneura fumiferana (Clemens), Manduca sexta (L.) or Lambdina fiscellaria (Guenée) (rearing host species) and attacking the eggs of E. kuehniella, S. cerealella or C. fumiferana (host species attacked). Data were combined across all host species attacked when analyzing the effects of rearing host species and vice versa. There was no significant difference in any of the measured parameters for female T. minutum reared from either E. kuehniella or S. cerealella, but greater fecundity and longevity were recorded for females attacking eggs of E. kuehniella relative to those attacking eggs of S. cerealella. Females reared from E. kuehniella had lower fecundity than those reared from L. fiscellaria, M. sexta or C. fumiferana. Parasitoids had significantly lower fecundity and longevity when attacking eggs of C. fumiferana than when attacking eggs of either E. kuehniella or S. cerealella, and the percentage emergence of the offspring was significantly higher from the latter two host species. Parasitoids reared from eggs of C. fumiferana produced more offspring on eggs of E. kuehniella than on eggs of C. fumiferana. Results from these studies highlight the need to separate the effects of the host species from which the parasitoid is reared from the effects of the host species which the parasitoid attacks. They also illustrate the need to examine reproductive performance against the target species before a comprehensive cost-benefit analysis of a mass-rearing system is made.