Inorganic phosphate content 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. The invasive crop pest, Drosophila suzukii, 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 insect species such as Drosophila, it could drive oviposition preference in D. suzukii. Phosphorus is either present as inorganic or organic phosphate in fruits. As the absolute content in macromolecules associated with phosphate in fruits (i.e. proteins and carbohydrates) do not affect oviposition in D. suzukii, we tested for the effect of inorganic phosphate on oviposition preference. We measured the egg-laying preferences of D. suzukii in a choice environment containing 12 artificial media with increasing content in inorganic phosphate (monopotassium dihydrogen phosphate). In our assay, D. suzukii females did not prefer ovipositing in media with high inorganic phosphate content compared to media with lower inorganic phosphate content. As a confirmation, we verified the previous result of a higher female preference for media made of phosphorus-rich fruits (blackberry, cherry, blackcurrant). The higher preference for phosphorus-rich fruits could be driven by macromolecules containing phosphorus (e.g. phospholipids) or by the presence of one or more molecules that do not contain phosphorus, but that happen to be correlated to fruit phosphorus content. Studying the proximate mechanisms driving host use will ultimately help improve the management of D. suzukii and other crop pests.