PATHOGENICITY OF METARHIZIUM ANISOPLIAE VAR. ANISOPLIAE1 TO MOSQUITO LARVAE

Water samples from various mosquito breeding habitats did not have an effect on the efficacy of Metarhizium anisopliae var. anisopliae isolate E9 when treated in the laboratory against 3rd instar of Culex quinquefasciatus. At the highest dosage rate (5.0 mg), the percent mortality varied from 89.1 ± 4.8 in rice field water to 94.4 ± 4.1 in sewer drainage and open ditch water. In another laboratory test, all field collected instars (89.25% Culex, 8.50% Aedes and 2.25% Psorophora) were found to be highly sensitive to isolate E9. At the 5.0 mg rate the percent mortality ranged from 91.2 ± 2.9 in the 2nd instars to 100.0 in the 3rd instars. There was no significant difference (P = 0.05) in mortality between instars except at the lowest dosage (1.25 mg) where the 4th instar mortality (28.6 ±8.5%) was significantly lower than those of other instars. The LT50 values for the 1st through the 4th instar increased with age and ranged from 1.1 to 1.8, 1.7 to 2.7, and 2.0 to 4.3 days at the 5.0, 2.5 and 1.25 mg dosages, respectively. In a preliminary field test to determine the susceptibility of field collected 3rd instar, up to 97.9 ± 1.8% mortality was recorded at the 800 mg rate.