Fruit phosphorus concentration does not affect oviposition preference in the invasive pest Drosophila suzukii

The broad variation in host use among polyphagous insects is well documented but still poorly understood. In numerous pest insects, the proximate mechanisms responsible for variation in oviposition preference among host plants remain to be elucidated Drosophila suzukii is an invasive crop pest that attacks a wide range of host fruits. Females prefer ovipositing on particular fruit media (blackberry, cherry, blackcurrant) that are rich in phosphorus. As phosphorus is known to be involved in female reproduction in insects and Drosophila, phosphorus concentration could drive oviposition preference in D. suzukii. To test the effect of phosphorus on oviposition, we measured the egg-laying preferences of D. suzukii in a choice environment containing 12 media with different concentrations of phosphoric acid (the main molecule that contains phosphorus within fruits). In our assay, D. suzukii female did not prefer ovipositing in media with high phosphorus concentrations. As an experimental control, we verified the previous result of a higher female preference for media made of fruits rich in phosphorus. Two alternative hypotheses could explain our results. A molecule containing phosphorus, but other than phosphoric acid, could drive the preference for phosphorus-rich fruits. Alternatively, one or more molecules that do not contain phosphorus could be responsible for the preference for these fruits. Studying the proximate mechanisms driving host use will ultimately help improve the management of any crop pest.