Enemy of the invader: impact of the native ectoparasite Philornis spp. on an invasive bird species, the European starling (Sturnus vulgaris)

Invasive species may be especially susceptible to native parasite infections since invaders have not shared a co-evolutionary history with local parasite species. A recently discovered host-parasite system is the European starling ( Sturnus vulgaris )—botfly ( Philornis spp . ) larvae. The European starling is one of the most successful invasive bird species in the world and has recently arrived in South America. Botfly larvae from the genus Philornis are hematophagous ectoparasites that burrow under the skin of nestlings, or live in the nest material, and can seriously affect host fitness. Most studies regarding Philornis spp. parasitism focus on the effects of Philornis on native hosts or on naïve hosts when Philornis is an invasive parasite. Here, we evaluate the impact of native Philornis spp. larvae on cellular and humoral immunity, hematocrit, morphometrics, and survival of nestlings of the invasive European starling in Argentina. Based on evidence from native hosts and on the relatively recent encounter with this new host species, we predicted that Philornis spp. infestation would result in considerable sublethal and/or lethal effects on starling nestlings, potentially acting as a biological control on the expansion of this invasive species. When nestlings were 4–8 days old, they were measured, inspected for the presence of Philornis spp. larvae, and a blood sample was collected to quantify immune measures and hematocrit. Survival was then monitored until nestlings left the nest. As predicted, parasitized nestlings had lower structural body size and hematocrit levels than non-parasitized ones. In contrast, parasitized and non-parasitized nestlings showed no differences in estimates of cellular and humoral immunity at the age range studied. Furthermore, nestling survival was low and independent of infestation status, suggesting that other sources of mortality are in play. Our results indicate that Philornis spp. infestation has sublethal effects on starling nestlings while further studies are needed to understand whether Philornis spp. has lethal effects on this species.