Fitness Effects of Founder Female Number of Trichogramma papilionis Reared on Ephestia kuehniella

Abstract

Trichogramma species (Hymenoptera: Trichogrammatidae) are egg parasitoids of a variety of insect pests, especially Lepidoptera, and are often mass reared in large numbers for use in augmentative biological control. Many issues with captive rearing of parasitoids may impact their effectiveness as biological control agents, including inbreeding and loss of fitness within colonies. The goal of this study was to test the effect of female founder population size on the fitness of progeny of T. papilionis over successive generations and quantify any change in their biological performance. Two parasitoid lines were reared for 10 generations using 1, 2, and 10 inseminated founder females each generation. Fitness parameters were measured in each generation including fecundity (number of eggs per female), emergence rate, and sex ratio, under two different rearing temperatures. Parasitoid founder number did not affect the mean number of eggs per female in T. papilionis over ten generations, but emergence rate and sex ratio were significantly reduced in the lower founder number treatments. These results suggest that establishing laboratory colonies with 10 or more founder females will reduce the likelihood of loss of fitness.