THE POLYMORPHIC FORMS OF MELITTOBIA CHALYBII ASHMEAD AND THE DETERMINING FACTORS INVOLVED IN THEIR PRODUCTION. (HYMENOPTERA: CHALCIDOIDEA, EULOPHIDÆ)

Abstract

This parasite occurs in two forms, the typical form and a heretofore undescr. 2d form, which differ from each other both morphologically and physiologically. Type [female][female] parasitize the resting larvae of mud-wasps within cocoons. The first 12 to 20 eggs which a [female] lays upon the host develop in 14 days into 2d-form individuals which remain within the host cocoon and oviposit there. The eggs from this generation, together with the eggs which the original mother continues to lay, all develop on the same host and after 90 days give rise to type-form individuals. After mating, the [female][female] among these individuals leave the host cocoon to seek new hosts. Crosses made between the 2 forms and the experimental transfer of eggs and growing larvae from partially-consumed hosts to fresh hosts and vice versa, demonstrate that the production of one or the other polymorphic form is conditioned solely by trophic factors, and give some insight into the nature of the determination and the time of its occurrence. Individuals intermediate between the 2 forms were obtainable experimentally.