Linda AÃÆÃâÃâïssaoui and Hamid Boudjelida
Mosquitoes are vectors of many human diseases and cause environmental nuisances. Due to their large geographical distribution and abundance, Culex pipiens and Culiseta longiareolata represent the most important mosquito species in Algeria. The management of these disease vectors using conventional pesticides has failed because of the high reproductive ability, development of insecticide resistance of mosquito species and environmental pollution. These reasons are leading to a search for novel molecules. As so the product Vectobac G that is based on the naturally occurring insecticidal toxin proteins of Bacillus thuringiensis israelensis (Bti) may provide economical control of mosquito larvae. Bioassay was conducted to test the larval toxicity, longevity and mosquito fecundity. The mosquitocidal activity of Bt. Vectobac G was tested at different concentrations, ranging between 5 and 25 μg/l, against the different larval stages (L1-L4) of Culex pipiens and Culesita longiareolata. Bioassays were done on newly moulted larvae under laboratory conditions. The technical material showed a high level of activity with mortality recorded for both treated and following stages and happened after incomplete development. For the same treated series a significant decrease was also recorded in the longevity of the 4th instar and the adult. From a dose-response curve, the LC50 and the LC90 with their confidence limits were determined. The LC50 of 16.21μg/l and 23.98 μg/l and the values of CL90 of 75.85μg/l and 73.31μg/l, were estimated for the both species Cx. pipiens and Cs. Longiareolata respectively. In other experiments the compound was applied at LC50 and LC90 against the fourth instars larvae and its effects was investigated on fecundity of female emerged from larval treated series. The results showed that Bt. vectobac G reduced significantly the laying egg number and the percentage of fecundity.
