Efficacy of entomopathogenic fungi against the fruit fly Drosophila suzukii and their side effects on predator and pollinator insects

Abstract
Entomopathogenic fungi (EPF) are insecticide alternatives for pest control. Their ability to easily adhere and quickly penetrate the insect cuticle is a key factor for their selection, which has received too little consideration so far. Here, we evaluated the impact of five EPF on the survival and fecundity of Drosophila suzukii, a worldwide invasive pest of soft-skinned fruits. We assessed the exposure time needed to achieve fly mortality as well as the mortality of two non-target insects: Orius laevigatus and Bombus terrestris, commonly encountered in greenhouses where D. suzukii is the most damaging.
Drosophila suzukii were exposed for 3 hours to a fungal culture from each EPF and survival rates were assessed daily. Beauvaria bassiana was the most efficient EPF, killing over 95% of the flies within 10 days. Additional flies were then exposed to this fungus culture for 10 seconds, 1 minute, 10 minutes and 1 hour. The exposure time impacted the mortality rates: 50% of the flies died within 4 days after a 3-hours exposure to B. bassiana, whereas 6 days were needed to reach the same result with 10 seconds of exposure. Whatever the exposure time, this EPF always needed ten days to be lethal for more than 95% of individuals. Beauvaria bassiana was not lethal for the non-target species.
Thus, B. bassiana is an option to control D. suzukii without harming beneficial insects. Further studies are now needed under real cultivation conditions to assess whether B. bassiana can be included in biocontrol strategies against D. suzukii.