Evaluation of a granular formulation containing Metarhizium brunneum F52 (Hypocreales: Clavicipitaceae) microsclerotia in controlling eggs of Aedes aegypti (Diptera: Culicidae)

ABSTRACT

We evaluated the potential of a granular formulation of Metarhizium brunneum F52 containing microsclerotia (MbMSc granules) for control of Aedes aegypti by targeting eggs. MbMSc granules produced infective conidia within 14 days after application to 2.5 g moist potting soil, producing 5.9 × 10⁵, 2.08 × 10⁶ and 6.85 × 10⁶ conidia from 1, 5 and 25 mg MbMSc granules, respectively. Application of MbMSc triggered premature eclosion of eggs (EC₅₀= 12 mg) with percentages as high as 31 ± 2.9% and 67 ± 4.3% of the eggs treated with 5 and 25 mg MbMSc granules, respectively, after 14 days on moist filter paper. Premature eclosion of eggs started at 3 days subsequent to MbMSc granule application and survival of larvae was significantly reduced for granule treated eggs (74 ± 2.2%, 39 ± 2.0% and 23 ± 4.9% larvae survived for 1, 5 and 25 mg granule treatments, respectively, EC₅₀ = 4.9 mg). When MbMSc granules were applied in moist potting soil with mosquito eggs, rates of 1, 5 and 25 mg of MbMSc granules significantly reduced adult emergence with only 81 ± 2.1%, 47 ± 1.9%, and 34 ± 2.1% emergence, respectively (EC₅₀ = 7 mg). Eggs treated with increasing concentrations of fungal conidia enhanced premature eclosion of eggs with an EC₅₀ = 1.6 × 10⁶ conidia/mL. Our results demonstrate that MbMSc granules are a promising candidate for control of A. aegypti and that fermentative production of Mb F52 microsclerotia as the active propagule has the potential for use for mosquito control.

KEYWORDS:

• Metarhizium brunneum
• microsclerotia
• eclosion
• Aedes aegypti

Acknowledgements

We thank the following individuals for their help in various aspects of this study: M. Doehring for his help on zymographic experiments, A. Thompson for assistance with SEM, K. Zeman, M.Brimberry, and W. Lindquister for assistance with bioassays. In addition, we thank T. Walker of the East Baton Rouge Mosquito Abatement and Rodent Control division for providing eggs of the Rockefeller strain of A. aegypti. The mention of firm names or trade products does not imply that they are endorsed or recommended by the USDA over other firms or similar products not mentioned. USDA is an equal opportunity provider and employer.

Disclosure statement

No potential conflict of interest was reported by the authors.