Susceptibility of larvae and adult females of Aedes aegypti to Metarhizium anisopliae

Concerns about environmental pollution and resistance to synthetic pesticides have lead to rising interest in fungi as candidates for biocontrol agents of mosquito vectors. In most studies fungal infections have been induced by exposure of mosquitoes to various surfaces treated with conidia. Larvae and adult females of Aedes aegypti were exposed to fungal suspensions of three virulent isolates of Metarhizium anisopliae, viz., M34412, M34311 and M81123. Adult female mosquitoes were exposed to filter paper supports previously impregnated with fungal suspensions (in 0.1% Tween 80) at different concentrations (1x10¹⁰, 1x10⁹, 1x10⁸ and 1x10⁷conidia /ml). At higher concentration of 1x10¹⁰ and 1x10⁹ conidia/ml, percent mortality in adult was 95% with M34412 while 87% and 84% with M34311 and M81123 respectively. At lower concentration, it varied from 23.3-36.6% among the three isolates over the 8 days test period at room temperature. The concentration of conidia that resulted in 50% mortality (LC₅₀) mortality were 6.92x10⁸ for isolate M34412, 5.03x10⁹ for isolate M34311 and 8.22x10⁹ for isolate M81123. At a concentration of 1x10⁷ conidia/ml, 3^rd instar larvae of Ae. aegypti were susceptible to the 3 isolates of M. anisopliae with mortality varying from 98.35% in M34412 to 96.7% in M34311 and 95% in M81123 at the end of 7 days. Value of LC₅₀ varied from 5.92x10³ for isolate M34412, 3.49x10⁴ for isolate M34311 and 5.12x10⁵ for isolate M81123. All strains were highly virulent with LT₅₀ ranging from 3.36d to 5.76d for adults and 1.75d to 5.11d for larvae. An exposure time of 4h was sufficient to result in 50% mortality. Although a reduction in the persistence of M. anisopliae against Ae. aegypti was observed, conidia were still effective 4 weeks post application. These results show that M. anisopliae is a potential candidate in integrated vector management programs for control of Ae. aegypti.