THE DIFFERENTIATION OF GONADS IN ANTHONOMUS-POMORUM (L) (COLEOPTERA, CURCULIONIDAE) LARVAE

The single gonad anlage in the first-instar larva of Anthonomus pomoru m (L.) (Coleoptera: Curculionidae) has a form of a solid cylinder encl osed by a basal lamina, covered by the peritoneal sheath. The basal la mina lies on the gonad-envelope made of a layer of flat somatic cells that surrounds a group of dozen or so germ cells and some inner somati c cells. In the second-instar, the gonad anlage is larger and divided into 2 parts connected with a band of somatic cells. Within this cellu lar band, the lumen of the future gonadal ducts (lateral oviducts or s eminar ducts) appear. As a consequence of numerous mitoses, the gonad grows and splits into 2 parts. Each part will form one ovariole in the female or one testicular follicle in the male. In the third-instar la rva, the gonocytes are gathered into several groups that are isolated by thin extensions of the somatic cells. Each part of the freshly divi ded gonad is connected to a tube of a developing gonadal duct. The tub e joins the 2 parts of the gonad and extends towards the end of the ab domen. At the end of the third instar, the mitoses of the gonocytes do not end with complete cytokinesis; as a result, they form clusters of cells connected by the intercellular bridges. The fusomal material th at fills up the individual bridges joins into one structure, forming t he polyfusome. (C) 1997 Elsevier Science Ltd.