Impact of Metarhizium Anisopliae and Beauveria Bassiana on Bee Pollinators (Hymenoptera: Apidae), and Modelling Their Performance in Bee Colonies

Abstract

Insect pollination sustains the biodiversity of 90% of wild plants, and 75% of crop species for food and nutritional security. Chemical pesticides used to manage arthropod pests constitute a key driver to the unprecedented declines of insect pollinators worldwide. Hence, biopesticides based on entomopathogenic fungi (EPF) are being promoted as safer alternatives. The effects of EPF on insect pollinators have not been investigated in detail for the application in pollinator-resourced crop systems. Thus, this study screened EPF isolates of Metarhizium anisopliae (ICIPE 7, ICIPE 20, ICIPE 62, ICIPE 69 and ICIPE 78), and Beauveria bassiana (ICIPE 284) for their effect on the Western honey bee (Apis mellifera) and African stingless bee (Meliponula ferruginea). The study was undertaken at the international centre of Insect Physiology and Ecology (icipe), Nairobi, Kenya, from November 2019 through February 2021. In the first part of the study, groups of 25–30 bees/cage were exposed to surfaces sprayed separately with six isolates (108 conidial/mL) or sterile water (control) and incubated for 10 days. The exposure assay was replicated four times and repeated twice for each bee species, and conidial acquisition was evaluated on five bees/cage. Apis mellifera acquired more conidia (2.8 × 104–1.3 × 105 colony-forming units [CFU]/bee) than M. ferruginea (1.1 × 104–2.3 × 104 CFU/bee) based on the analysis of variance. Except for ICIPE 7, ICIPE 20 and ICIPE 69 which caused significant A. mellifera mortality (25.8–40.4%) in the first experiment, none of the isolates had a significant effect on either of the bee species according to survival analysis. The isolates are harmless and/or slightly harmful to bees according to the International Organization of Biological Control classification. Bee colonies inherently thermoregulate their hives and, thus, the second part of the study evaluated the performance of six isolates in bee colonies using eight predictive models describing thermal requirements; (minimum....................................................................................................