Dependence of Metarhizium anisopliae on high humidity for ovicidal activity on Aedes aegypti

Eggs of Aedes aegypti, treated topically with Metarhizium anisopliae IP 46, were submitted for up to 30 d to three different moisture regimes at 25 °C: (A) incubated at >98% relative humidity (RH); (B) were held in biphasic humidity regimes with initially increasing exposure times to >98% RH followed by decreasing exposures to 75% RH; and (C) daily alternating exposures to relative humidity of >98% and 75% RH, with increasing exposure times to >98% RH. Quantitative eclosion of larvae from fungus-treated eggs after submersion in water was clearly affected after a minimal 5-d incubation at >98% RH followed immediately by submersion of eggs in water (A) or after up to a total 25-d post-inoculation exposure of eggs to 75% RH (B). Values of 50% eclosion-inhibiting concentrations after 25-d incubation of fungus-treated eggs at >98% RH were 2.8 × 102 conidia/cm2 and 9.8 × 102 hyphal bodies/cm2. Daily alternating humidities for up to 30 d had no clear effect on ovicidal activity (C). Favorable conditions of high moisture for development of M. anisopliae on eggs can be expected during the rainy season but also during drier periods in subterranean breeding habitats.