Notes on the Life History and Anatomy of Trichogramma

During the last decade a considerable amount of information has accumulated concerning the biology and utilization of Trichogramma, yet recorded observations concerning the larval stages and the gross internal anatomy of the adult are very limited. Recently the writer investigated the development and morphology of Trichogramma evanescens and T. embryophagum when reared in the eggs of the arctid, Estigmene acraea (Drury). The eggs of this moth are medium sized and contain sufficient food to permit complete development of from one to ten indi-viduals per egg. A number of Estigmene eggs were exposed to parasitism for a period of one hour. They were then held at a fairly constant temperature of about 80 ° F. so that the life cycle required eight days. At intervals a host egg was dissected in aceto-carmine solution in order to determine the state of the parasite. It was found that the egg-incubation period was about 22 hours, and that there were three larval instars. In about 26 hours after hatching the larva passes through two instars and has consumed all of the food material within its host. The larva enters the prepupal stage about 12 hours after ceasing to feed. This stage is characterized by the formation and growth of the milk-white "urate " bodies, uniformly distributed under the derm. It is during this period that the peculiar blackening of the vitelline membrane of the host occurs. ' The length of this period in the case of embryophagum is two days, while in the case of evanescens it is two and one-half days. As the anlage of the adult develops, the urate bodies apparently become enclosed within the developing abdomen. The pupal period occupies about three and one-half days. The last larval skin, as well as the pupal skin, are scraped off from the adult as it emerges through the exit aperture cut in