Chemosterilants for control of reproduction in the eye gnat (Hippelates collusor) and the mosquito (Culex quinquefasciatus)

Abstract

A number of chemical sterilants as well as some antibiotic compounds were evaluated in the laboratory and field for reproduction control in the eye gnat Hippelates collusor (Townsend) and the mosquito Culex quinquefasciatus Say. Reproduction control here denotes the suppression of fecundity. It is achieved either through the reduction in the number of ova produced or a decrease in their viability, or both. The materials were made available to the adult eye gnat as sugar baits, water solutions, deposits on glass surfaces, and also as pupal dips. The chemosterilants were offered as sugar solutions on cotton pads, to the adult mosquitoes. Against larval and pupal stages the chemosterilants were tested as water solutions or suspensions. Metepa applied as a contact chemosterilant for 1 hour at 0.8 ?g/cm2 sterilized both male and female eye gnats. Apholate did not appreciably suppress reproduction when tested by the contact technique. Apholate and metepa also produced high levels of reproduction control when offered in water solutions to gnats of both sexes. Apholate was highly effective at 0.1 per cent in sugar bait, as was Upjohn 14743 (porfiromycin) at safe rates. Olin 53356 at 0.1 to 0.5 per cent in sugar bait yielded complete control of reproduction, while Olin 53264 at 0.01 and 0.05 per cent in sugar bait produced high levels of control. No appreciable control resulted from metepa used for pupal dips. In laboratory screening against adult eye gnats, U-15800 (pactamycin), U-14743 (porfiromycin) and U-4527 gave good control, but this was not true of U-7726 and U-10071 (tubercidin). Olin 53356, Olin 53061, and Olin 53139 produced good to complete suppression, while Olin 53362, and Olin 53247 produced low levels of reproduction control. Eastman Inhibitor HPT at 0.1 and 1.0 per cent resulted in good to complete suppression; Acti-dione Oxime, GC-6936, GC-8993, and Dowco 186 yielded low to moderate levels of control. In the field, female eye gnats (attractant available for females only) were readily sterilized with apholate offered in sugar bait or water solution. Merepa as a contact material also readily sterilized the natural populations of female gnats. Against mosquito larvae, apholate (0.002 per cent water solution) yielded complete control of reproduction in the resulting adults, while metepa at 0.01 per cent water solution gave a very high level of control. Both materials at 0.01 and 0.1 per cent, respectively, yielded good to complete control. Apholate used in this manner proved over 10 times as effective as metepa. Against larvae, none of the Olin series of compounds (with the exception of Olin 53356) showed any appreciable activity, and none was found effective against pupae. U-7726 against larvae suppressed reproduction markedly, U-10071 produced a moderate reduction, while U-14743 resulted in complete control. Results with V-15800 are inconclusive. Sugar baits of Olin 53139, Olin 53356, and Olin 53362, used against adult mosquitoes, completely suppressed reproduction. U-10071 and U-15800, offered as sugar bait to the adult mosquito, yielded a high level of control; with U-14743, control was almost complete. U-7726 was not effective at the concentrations used. In general, the margin of safety between sterilizing concentrations and those causing appreciable mortality was found to be narrow. This would possibly pose some problems in the sterilization of laboratory and field populations of insects. The full potential of chemoscerilants for the control or eradication of insects harmful to humans and animals is not well established as yet. Many more fundamental studies will have to be conducted before these potentially useful compounds can be recommended for the control or eradication of insects.