Laboratory and field evaluation of some chemical and biological larvicides against Culex spp. (Diptera: Culicidae) immature stages

Abstract

Efficiency and efficacy of three insecticides i.e., temephos, Bacillus thuringiensis var. israelensis (Bti) and pyriproxyfen against the immature stages of Culex spp. were evaluated under the laboratory and field conditions. LC<inf>50</inf> values for pyriproxyfen, temephos and Bti under the laboratory conditions were 0.00079, 0.0059 and 0.012 mg L^-1, respectively. Under field conditions, temephos was the most effective insecticide, which caused 100% mortality of the larval population followed by Bti (60%), after one week of the first application. However, the mentioned mortality percentages decreased gradually to reach their minimum at the fifth week and then fluctuated to be 74% for temephos and 0.43% for Bti at the tenth week. After the second application at the tenth week, the same trend of temephos and Bti toxicity against larvae was observed. Pyriproxyfen caused 59.77% emergence inhibition against pupal population at the first week and gradually increased to reach 74% at the tenth week. Its effect reached 100% at the eleventh week after the second application and then gradually decreased to 36% at the fifteenth week. The results indicated the needs for decreasing the intervals between the first and the second application of all three insecticides to be 5 days for Bti and three weeks for both temephos and Pyriproxyfen, to keep the population of Culex spp. larvae under control. © 2011 Friends Science Publishers.