THE DELAYED EFFECTS OF CERTAIN CHEMICAL AND MICROBIAL INSECTICIDES ON CULEX PIPIENS (L.) COMPLEX LARVAE UNDER LABORATORY CONDITIONS

This work was conducted to study the effect of two chemical insecticides (chlorpyriphos and methomyl) and the microbial insecticides (biofly and dipel) on C. pipiens larvae during three generations (F₁, F₃ and F₅) with two exposure time (24 or 48 hours, plus continuous exposure until pupation). Meanwhile, their effect on some biological aspects of Culex pipiens (L.) by exposing the 3^rd larval instar to sublethal concentration (L.C.₁₀) under laboratory conditions.
Results indicated that the differences between the means of both larval, pupal mortalities, pupation and adult emergence of C. pipiens for chloropyiphos and mothomyl were highly significant. The interaction effects between chemical insecticides, and both generation & exposure time were highly significant for larval mortality and percentage of pupation, respectively. While no significant differences occurred between the tested generations or exposure time on pupal mortality and adult emergence.
In case of microbial insecticides, the difference between means of both larval, pupal mortalities, pupation and adult emergence for dipel and biofly were highly significant. The tested generations had significant effect on larval mortality and percentage of pupation, while no significant effect on either the pupal mortality or adult emergence was recorded. Exposure time was effective and was found to have high significant effect on previous aspects of C. pipiens. The interaction between chemical and microbial insecticides indicated that microbial insecticides were the more toxic against C. pipiens (L.).
The number of eggs per female and the percentage of hatchability were significantly reduced by chlorpyriphos and methomyl application, while no significant diferences between both compounds was recorded. Also, there were no significant differences among the tested generations on egg-deposition and hatchability percentage.
Biofly and dipel were found reduce egg-deposition and  hatchability percentage significantly. Remarkable differences were found among the tested generations and both egg-deposition and hatchability percentage. The interaction between the chemical and microbial insecticides proved that, chemical compounds were significantly effective on reducing the mean number of eggs laid by C. pipiens females. While no significant differences were recorded on hatchability percentage.