CYTOGENETIC EFFECTS OF CHEMOSTERILANTS IN MOSQUITOES. II. MECHANISM OF APHOLATE-INDUCED CHANGES IN FECUNDITY AND FERTILITY OF AEDES AEGYPTI (L.)

¹ Department of Biology, University of Notre Dame, Notre Dame, Indiana

1. Two-day-old larvae of Aedes aegypti were reared until pupation in 15 ppm apholate, a commonly used insect chemosterilant. This concentration induced almost complete female infecundity. Ovarian dissections of developing females at regular time intervals were made in order to study the underlying basis of reduced fecundity. Apholate greatly inhibited ovarian development. The follicles in treated females remained small and sooner or later underwent complete degeneration. In some of these follicles a distinction into nurse cells and oocytes never took place. In others, a complete breakdown of the follicular epithelium, nurse cells and oocyte was observed. Rarely, one or more follicles completed development in treated females. Many of these failed to hatch after insemination with normal males. This indicates the induction of dominant lethals in these eggs.

2. Motile sperms were produced by males emerging from larvae treated at second instar stage. The size of the testes in 9-day-old treated males was not greatly different from those of 8-day-old untreated males. Males used in these dissections were not mated with any females. Although conclusive data are not yet available, a lower fecundity in treated males than that of untreated males was indicated. Epithelium of the testes in some treated males showed necrosis. The so-called "male sterility" must result from induction of dominant lethality in motile sperms.

3. Some explanations concerning the mode of action of apholate and the nature of dominant lethals are discussed.