Horizontal transmission and persistence of Metarhizium anisopliae in Dacus frontalis (Becker) and the effect of the fungus infection on fly reproduction

The Greater melon fly, Dacus frontalis, is an economically damaging pest of cucurbit fruits in Libya. The ability of Dacus frontalis flies emerging from soil inoculated with MET52 Granular biopesticide, based on a pathogenic fungus, Metarhizium anisopliae, var anisopliae, to induce new infection in untreated flies was investigated. Contaminated adults were able to transmit the fungus conidia to untreated individuals of the opposite sex, resulting in above 30% mortality among females and 15% among males. The impact of MET52 on adult reproductive success in different mating combinations was assessed. The progeny pupation rates were affected by the treatments. The lowest pupal number was produced when inoculated males were paired with untreated females, resulting in a nearly 89% reduction. The persistence of MET52 was assessed in terms of infectivity against larval–pupal stages (measured by calculating adult emergence rate) and adult D. frontalis under laboratory conditions. The fungus reduced the emergence rate and caused mortality in newly emerging adults for more than two months after a single application.

Overall, the MET52 fungus was able to persist in soil, reducing the adult emergence rate and subsequent fly population for more than two months after a single application. In addition, it induced new infections among the fly population and reduced adult reproduction.