The sex ratio ofBracon hebetorSay at 25°C and 50–60%RHwithAngasta kuehniella(Zeller) as host, was found to be 39% ♀. Numerous females produced male progeny only, when they grew old. This phenomenon is probably due to internal factors. Cannibalism and mortality due to superparasitism favor male survival. The sex ratio rose significantly when females were allowed to feed only on hosts within their webbings, and when mating and oviposition were delayed for a week or more.