Development of Composite Eggs in Miastor (Diptera: Cecidomyidae)

Abstract

IN insects, two embryos developing within a common set of egg membranes may originate in several ways: by a splitting of the original embryonic primordium¹; by production of a secondary primordium^2,3; by naturally occurring polyembryony⁴; and by ovarian fusion of oocytes to produce composite eggs^4,5. Oocyte fusions have been reported (or are assumed to have occurred) in several orders of insects^5–9, but detailed embryological studies have been made only in phasmids (Orthoptera)⁵. This report is about the development of composite eggs in a laboratory stock of a paedogenetic parthenogenetic species of Miastor¹⁰. (Imagos are necessary for species determination in Miastor—although this stock has been under continuous observation since 1958, no adult midges have been found.) Fourteen composite eggs were found among some 12,000 eggs examined during investigations of embryogenesis in Miastor. Material consisted of whole mounts of eggs stained with borax carmine, and of sectioned material stained with iron haematoxylin or with Feulgen and fast green. The term “egg” as used throughout refers to the structure composed of the oocyte or embryo, the nurse cells and the surrounding follicle cells.