Entomopathogenic fungi as a biological control for the Greater melon fly Dacus frontalis (Becker) (Diptera: Tephritidae)

Abstract

The Greater melon fly Dacus frontalis is one of the most economically damaging pests of cucurbit fruits in Africa. The aim of this study was to evaluate entomopathogenic fungi for use against D. frontalis and develop better strategies in using these biological agents for integrated fly management. Laboratory experiments were conducted to evaluate the pathogenicity of some commercial biopesticides based on several strains of entomopathogenic fungi against different life stages of the fly. Met52 Granular biopesticide (MET52) based on Metarhizium anisopliae caused the greatest pathogenicity to the adults. Therefore, MET52 was selected for further investigation. Pupal age and an increasing rate of MET52 had no effect on pupal mortality. However, post-emergence mortality increased when the fungus was applied on young pupae. Prior application of MET52 in a granule form caused considerable mortality to larval-pupal stages compared with a drench application. A sublethal effect of MET52 infection, reducing adult reproduction, was found. The fungus was more effective when applied as a granule in soil against emerging adults than as a direct spray against adults. MET52 fungus was able to persist in soil, reducing the adult emergence and subsequent fly population for more than two months after a single application, and also inducing new infections among the fly population. Percentage mortality of untreated females mating with inoculated males was greater than that of untreated males mating with inoculated females. The infection reduced the adult’s reproduction resulting in a considerable reduction in pupae recovered in the fungal treatments. Alone or in combination with MET52 neem had a dose-dependent effect on larval mortality and induced various effects on soil stages and adults of the fly. The efficacy of the fungus increased considerably at low concentration of neem showing the shortest LT50. In field cage trials, baited McPhail traps with yeast hydrolysate enzymatic had the greatest number of D. frontalis. MET52 gave lower adult mortality than insecticide. In conclusion, soil application of MET52 can be a promising effective control of D. frontalis, and can be combined with other control agents providing a possible effective strategy for integrated fly management.