Enhanced ovicidal activity of an oil formulation of the fungus Metarhizium anisopliae on the mosquito Aedes aegypti

Abstract

The effect of humidity on the activity of Metarhizium anisopliae IP 46 (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) formulated in sunflower oil against Aedes aegypti (L.) (Diptera: Culicidae) eggs was examined. After exposure of eggs at 75% relative humidity (RH) for <or= 25 days, ovicidal activity was not increased by oil-in-water formulated conidia, hyphal bodies or pure-oil formulated conidia, compared with conidia or hyphal bodies prepared in water only. At optimal > 98% RH, eclosion was <or= 13.7% after treatment with oil-in-water formulated propagules in <or= 10% oil, and it was completely inhibited when conidia were applied in pure oil. At 86-100% RH, new conidia were found on eggs treated with oil-formulated conidia and incubated down to 91% RH. Ovicidal activity was still detected at 93% RH and was augmented with increasing humidity and time of exposure of eggs. Eclosion of larvae was distinctly reduced by IP 46 pure-oil formulated conidia after a minimal initial exposure of 3 days at > 98% RH, followed by: (a) a 12-day exposure at 75% RH before submersion in water; (b) a minimal 5-day exposure at > 98% RH and direct subsequent transfer of treated eggs to water, or (c) a minimal daily 20-h exposure at > 98% RH alternating with 4 h at 75% RH for 10 days. We demonstrate that oil-based formulations of conidia of M. anisopliae enhance ovicidal activity at high humidities and conclude that these formulations have potential in the integrated control of Ae. aegypti.

Effects of Metarhizium anisopliae conidia mixed with soil against the eggs of Aedes aegypti

“…Under septic conditions, an effect of the conidial concentrations on aedine eggs can be expected. The ovicidal effect of M. anisopliae against A. aegypti when mixed into soils was obviously reduced in comparison to direct treatments of eggs with conidial suspensions (Luz et al 2007(Luz et al , 2008Albernaz et al 2009;Santos et al 2009). Because in the present study conidia were applied as conidia per unit of soil and were uniformly mixed into the soil, the real dosages to these indirectly exposed eggs were much lower than those delivered by a direct application of fungus to the eggs.…”

“…Whereas the larvicidal and adulticidal activity of M. anisopliae is well documented (Scholte et al 2004a), there is still little information on the ovicidal activity of this and other fungi against A. aegypti. The eggs of this vector were highly susceptible to infection with M. anisopliae IP 46 under laboratory conditions when conidia were applied to eggs arranged on filter paper and incubated at humidities close to saturation (Luz et al 2007(Luz et al , 2008Albernaz et al 2009;Santos et al 2009). The filter paper that is used for oviposition in the laboratory also proved to be a useful substrate for tests on the ovicidal effects of diverse other entomopathogenic fungi in the laboratory (Luz et al 2007).…”

Survival of anopheline eggs and their susceptibility to infection with Metarhizium anisopliae and Beauveria bassiana under laboratory conditions

“…Eggs were treated with water (filled circle) or oil-inwater (empty circle) formulated conidia of M. anisopliae ICIPE-30 at different concentrations or water or oil-in-water only and incubated in soil at >98% humidity and 26±1°C for 10 days Twenty-five eggs of four separate repetitions each were treated with water-formulated conidia (10 5 , 3.3×10 5 , 10 6 , 3.3×10 6 , and 10 7 conidia/cm 2 ), incubated in soil at 26±1°C and >98% relative humidity for 10 days and subsequently submersed in water for 10 days. Values of relative inhibition were obtained by relating eclosion from fungus-treated eggs to control eggs Further, only a handful of publications have investigated the ovicidal activity of fungi against other mosquito genera (Luz et al 2007(Luz et al , 2008Albernaz et al 2009;Santos et al 2009). Because M. anisopliae occurs naturally in soils (Meyling and Eilenberg 2007;Rocha et al 2009), it is plausible that this fungus could act also against anopheline eggs.…”

“…While this has not been previously investigated for anopheline species, B. bassiana, M. anisopliae, and other fungi can infect aedine eggs (Luz et al 2007(Luz et al , 2008Albernaz et al 2009;Santos et al 2009) and also reduce the eclosion of larvae in the laboratory (Luz et al 2007(Luz et al , 2008. For water-formulated M. anisopliae to invade through Aedes aegypti (Diptera: Culicidae) egg shells and to prevent larval eclosion, both high humidity and a 10-day exposure period to this fungus were required ).…”

Biological Control of Dengue Vectors

“…Further work using M. anisopliae found that oil-based formulations can enhance the ovicidal effect (Albernaz, et al 2009). …”