Survival of Metarhizium humberi in granular formulations, and activity against Aedes aegypti adults after prolonged storage

Abstract

Interest in mycoinsecticides for integrated mosquito control is high, and a granular formulation of Metarhizium humberi is showing promising results against Aedes aegypti, a vector of important arboviruses in the tropics. Storage conditions will affect shelf-life and the further fitness of mycoinsecticides. Here, two granular formulations with microsclerotia plus conidia or with only conidia were packed loose or fixed on black cloth in bags with ambient or low air pressure and subsequently stored at 25 °C or 4 °C for up to 24 months. Temperature proved to be the most critical factor for extended shelf-life. Both conidia and microsclerotia quickly lost their viability in the first two months of storage at 25 °C. The lower temperature distinctly retarded the decline of viability of propagules and increased shelf-life and activity in A. aegypti adults up to 16 months. The packing method used did not affect shelf-life and enables more flexible use. Often unavoidable suboptimal temperatures remain a major challenge for extended storage of mycoinsecticides that needs to be addressed.