Different effects of Drosophila suzukii oviposition and larval activity on fruit rot and mold

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anglais. Understanding symbioses and the selective pressures on symbionts requires elucidating how the different behaviors and phenotypes of hosts affect microbes. When female fruit-flies of the genus Drosophila deposit their eggs, they trigger substantial rots (i.e. the development of yeasts and bacteria) and molds (i.e. the development of filamentous fungi). It is however unknown whether these microbial growths are triggered by female oviposition alone, or necessitate the activity of larvae. We investigated the specific effects of Drosophila suzukii (Diptera: Drosophilidae) female oviposition and larval activity on rot and mold development in fresh, on-plant strawberry and raspberry. To disentangle the effects of egg deposition from that of larval presence some females were mated with sterile males, as occurs when the Sterile Insect Technique (SIT) is deployed. This "sterile treatment" without larvae produced intermediate intensities of rot and mold development, greater than "controls" unexposed to flies, but lower than the "fertile treatment" exposed to fertile flies. The proportions of berries too rotten for market access 3 days post-exposure were however equivalent in the sterile and the fertile treatments. But mold after 3 days was only pervasive in the fertile treatment and on strawberry. These results show specific effects of oviposition and larval activity on the development of yeast, bacteria and molds. The study indicates that when D. suzukii females are present in the field, damages to crops cannot be reduced by the release of sterile males. Instead, the sterile insect technique should be used to prevent population build-up.