Evaluation of Two Insect Growth Regulators (IGRS) As a Feed- Through Treatments against Adults of Culex pipiens L. mosquito

This study was carried out to evaluate the biological effects of two IGRs (Match and Baycidal) on Culex pipiens mosquitoes when fed the adults on sugar solution mixed with 0.1, 0.5 and 1 ppm of each compound. Some delayed effects of these treatments were also determined. The results indicated that the use of each of the tested IGRs caused a reduction in the blood-feeding activity of mosquito female when compared with the controls. The reductions were 18.2, 22.7 and 31.8% by using Match and 25, 27.3 and 36.3% by using Baycidal, respectively, at the tested concentrations. The reduction in biting activity of mosquito females may lead to a decrease in the number of fully engorged females and accordingly affect their reproductive capacity of mosquitoes. The use of Match and Baycidal at the tested concentrations caused a marked prolongation in the time needed for blood meal digestion by C. pipiens females. The prolongation percentages were 44.4, 48,8 and 55.5% by using Match and 51.1, 55.5 and 62.2% by using Baycidal, respectively. Also, treatments caused a reduction in the reproductive capacity. The maximum decreasing in egg production was 30.3% at concentration of 1 ppm of Match. The result showed that the treatment by Baycidal at 0.1, 0.5 and 1ppm led to a remarkable reduction in the egg production by 61.9, 66.1 and 69.2%, respectively and also the hatchability was reduced in the treated females. Subsequent study was carried out to investigate the delayed effect of IGRs Match and Baycidal on the hatched larvae. The result showed that the larval development was gradually inhibited by 17.8, 49.8 and 92.7% by using Match at 0.1, 0.5 and 1 ppm, respectively. On the other hand the larval development was completely inhibited after the treatment of adults fed by 0.5 and 1 ppm Baycidal. The larvae developed till the 2 instar but completely failed in molting to the 3 instar. Subsequent study was conduced on the effect of Match and Baycidal on the longevity of the survived mosquito adults that, the records showed that no significant differences in the mean of adult longevity between treatments and control.