Cigarette tobacco reduces the survival of an invasive parasite that affects Darwin’s finches

Abstract

Invasive parasites are a major threat to biodiversity worldwide, so understanding the factors that control them is necessary to improve the health of affected host species. In the Galápagos Islands, the invasive nest ectoparasite, the avian vampire y (Philornis downsi), is causing up to 100% mortality in nestling Darwin's nches. However, urban nch nests have fewer ies than non-urban nch nests. One explanation is that nches incorporate cigarette butts into their nests, which has been found to decrease nest parasite abundance for other bird species. For our study, we exposed larval ies to cigarette tobacco-treated (concentrated or diluted) or untreated cotton, then characterized pupation success, pupal deformities and success, and adult y eclosure success and size. The in uence of moisture on the effect of tobacco treatment on y health was also determined. Flies reared in tobacco as larvae had lower pupation success, larger pupal volume, and a higher prevalence of pupal deformities compared to control ies, regardless of moisture treatment. Furthermore, we found that tobacco-treated ies had lower eclosure success. In fact, very few tobacco-treated ies survived to adulthood. We also collected nch nests and quanti ed the prevalence and abundance of cigarette butts and abundance of ies in the nests. Although most urban nch nests contain cigarette butts (73%), the mass of cigarette butts was very low and did not correlate with y abundance. Compared to past studies, nch nests require ten times as many cigarette butts to affect y survival. Although tobacco can negatively affect vampire ies, nches likely do not incorporate enough cigarette butts to affect y tness.