Can facilitation become competition? What happens when two invasive Drosophilid share a resource

Spotted wing drosophila (SWD) (Drosophila suzukii) and African fig fly (AFF) (Zaprionus indianus) are two invasive drosophilids that are significant economic pests. Spotted wing drosophila is a highly impactful pest that can infest ripening soft skin fruits with its serrated ovipositor, while AFF lacks a hardened ovipositor and instead lays its eggs in wounds on the fruit, including ripening figs which have wounds present from pollination. In the US, AFF is also observed in fruit that is infested by SWD suggesting that SWD facilitates the spread of the AFF by damaging fruit. Here, we determined the role SWD plays in facilitating AFF in three common berry crops in the lab. We found that in blueberries, SWD could facilitate AFF and that there is very low infestation of AFF without damage. However, in blackberries and raspberries, AFF was able to infest fruit regardless of whether there was any damage. In subsequent experiments, we tested if there is competition between these two species when infesting the same fruit. We found that success of AFF was influenced by SWD but was dependent on fruit species, and there was little to suggest negative effects of AFF on SWD. Together, these results clarify the intricate dynamics between these two pest species and indicate that invasive species with no prior history of interaction can influence each other’s population dynamics.