I. Entomological and parasitological aspects of vector chemosterilization

Abstract
1. Chemosterilization of mosquitoes, Ae. aegypti, Ae. togoi, A. g. melas, A. g. gambiae and C. p. molestus, allowed to rest for 1–3 hours on deposits of thiotepa, a radiomimetic alkylating agent, at 20 to 40 mg./sq. ft. is highly successful. 2. From detailed studies with Ae. aegypti, sterility of eggs results from the genetic infertility of sperms of treated ♂ ♂ passed to normal ♀ ♀ at copulation, and directly in treated inseminated ♀ ♀, possibly by infertility of ova sometimes; failure in egg production occurs in treated ♀ ♀ and may be immediate in young ♀ ♀ or progressive in successive gonotrophic cycles until, by cytostatic destruction of all the ovarioles in a ♀, oogenesis is no longer possible. 3. Chemosterilant deposits of either tepa, metepa, thiotepa or apholate have remained effective against Musca and Aedes aegypti adults for about 1 month, and against Stomoxys for about 6 months. This is a practical asset, but requires to be understood more fully in terms of persistently toxic low residues. 4. Filaria parasites (Brugia patei) are so severely retarded in their growth in thiotepasterilized Ae. togoi that transmission seems highly improbable, except at a dosage which does not completely sterilize the vector. 5. Transmission of Plasmodium gallinaceum by thiotepa-sterilized Ae. aegypti was reduced by only 25 per cent.; some of the failures in transmission were by gland-positive moquitoes; there was no obvious evidence of more pathogenic mutants of the malaria parasite. 6. Prospects for practical applications of chemosterilization for the control of vectors of disease are discussed in reference to mosquitoes, tsetse and housefly with the conclusion that, apart from the need—which may yet be met—for chemosterilants more acceptable for practical use on toxicological grounds, control policy depends largely on the ecology and behaviour of an insect species and would be easier to devise if better attractant stimuli, particularly for ♀ ♀, could be found. 7. Subject to these considerations, chemosterilization of insects is a promising technique for the control of pests, vectors and vector-borne diseases.