Effect of entomopathogenic fungus Metarhizium robertsii on non-target organisms, water bugs (Heteroptera: Corixidae, Naucoridae, Notonectidae)

The influence of the fungus Metarhizium robertsii Bischoff, Rehner and Humber on the mortality of four water bug species, Cymatia coleoptrata (Fabricius), Sigara assimilis (Fieber), Ilyocoris cimicoides cimicoides (Linnaeus), and Notonecta reuteri Hungerford, and bloodsucking mosquito Anopheles messeae Falleroni, was investigated under various concentrations of conidia and different treatment types. We found that the mortality of adults of the water bug species was similar or higher than that of A. messeae , with C. coleoptrata and S. assimilis being more susceptible to M. robertsii than N. reuteri , I. c. cimicoides , and the mosquito A. messeae . Treatment with dry conidia at concentrations of 5 × 10 4 and 5 × 10 5 conidia/ml caused higher mortality of the water bug species than did treatment at the same concentrations with conidia in an aqueous suspension. In contrast, higher concentrations (5 × 10 6 conidia/ml) led to higher mortality after treatment with the aqueous suspension, relative to treatment with dry conidia. Our studies showed that water bugs exhibited the classical development of a mycosis with hemocoel colonization, mummification, and conidia formation on cadavers directly on the surface of the water. Possible changes in invertebrate communities in aquatic ecosystems after treatment with Metarhizium are discussed.