Cytogenetic Basis of Chemically-Induced Sterility in <i>Culex pipiens fatigans</i> Wiedemann

Abstract

Studies on the potential use of induced sterility in insect control have resulted in the discovery of a large number of chemicals having effect on fertility and fecun dity of many species of insects. While the cumulative effect of these compounds lead to sterility their mode of action at cellular level is not yet clear. Many chemosterilants belonging to aziridinyl compounds, phosphoramides and s-tri azines are known to cause cytogenetic damage in the reproductive or embryonic tissues of insects (LaChance et al. 1968, Morgan 1967, Cline 1968, Reinecke et al. 1969). In addition, a similar damage to the brain cells of Aedes aegypti (L.) has been observed by larval treatment of apholate and hempa (Rai 1964, Sharma and Rai 1969, George and Brown 1967. As a result of these studies a concept has evolved that cytogenetic damage caused by chemicals is some how related to sterility (LaChance et a1. 1968).In our earlier studies, a number of alkylating and non-alkylating chemosteri lants were shown to induce sterility in Culex pipiens fatigans Wied. . The present investigations were, therefore, aimed to elucidate a cytogenetic basis of such chemosterilant-induced sterility in C. p. fatigans by detailed studies involving their effects on somatic, reproductive and embryonic tissues, and on DNA synthesis in the gonads. The present paper deals with the effects of apholate, metepa and hempa on the somatic chromosomes. Materials and methodsThe mosquitoes for the present studies were drawn from a Delhi strain of C. p. fatigans established in our laboratory since 1965 (Pillai and Grover 1969). The chemosterilants employed were as follows: 1) Apholate-2, 2, 4, 4, 6, 6-hexahydro-2, 2, 4, 4, 6, 6-hexakis (1-aziridinyl)-1, 3, 5, 2, 4, 6 triazatriphosphorine, 2) Metepa-tris (2-methyl-l-aziridinyl) phosphine oxide, and 3) Hempa-Hexamethyl phosphoric triamide.Mid-forth instar larvae (65 hrs old) were used for preparing somatic chromo somes of the brain following the squash technique of Breland (1961) modified by French et al. (1962). The karyotype studies were made by employing the modified mammalian chromosome technique of Lewis and Riles (1960) and chromosome measurements were made according to the procedure used by Baker and Aslamkhan (1969). Rapid cell divisions were found to occur in the brain cells of the larvae