Susceptibility of different life stages of the European cherry fruit fly, Rhagoletis cerasi, to entomopathogenic fungi

The effects of six fungus isolates on the mortality of different life stages of the European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), were assessed in a series of laboratory experiments to find an isolate suitable for biological control. In a first step, the effects of fungus treatments on mortality, mycosis and fecundity of adult flies at a concentration of 10(7) conidia/ml were evaluated. All fungus isolates caused mycosis but virulence varied considerably among the isolates. Beauveria bassiana and Isaria fumosorosea caused 90-100% mortality and had the strongest influence on fecundity. Metarhizium anisopliae also induced high rates of mortality, while the pathogenicity of Isaria farinosa was low. The effects of lower conidia concentrations and the influence of the age of flies were assessed in a second step. Higher conidia concentrations generally resulted in a higher mortality. B. bassiana was most efficient at low concentrations. Young flies showed lower mortality rates than older flies but, sub-lethal effects on eclosion rate of eggs were greater in younger flies. Finally, the effects on L-3 larvae were tested: none of the fungus isolates induced mortality in more than 25% of larvae. As L3 larvae and pupae are not susceptible to fungus infection, field control of R. cerasi should be focused on adult flies.