Dietary ethanol affects feeding behaviour, flight performance, and mating success in a fruit-feeding butterfly

The evolution of fleshy fruits around 124 million years ago introduced a nutritious resource and drove shifts toward fruit-feeding across the animal kingdom, leading to a variety of adaptations for locating and exploiting this resource. Fruits are inherently dynamic, changing in physical, chemical, and biological properties as they progress from development through ripening to decay. Fruit fermentation produces ethanol, a volatile compound that is simultaneously caloric, intoxicating, and potentially noxious. While the immediate and long-term effects of dietary ethanol are well documented in mammals, and to some extent in insects such as Drosophila , very little is known about its impact on frugivorous butterflies. Although ethanol can serve as a foraging cue for frugivorous butterflies, its ingestion may impair performance and reduce fitness. Here, we examine how dietary ethanol affects ecologically and reproductively relevant behaviours in the Afrotropical butterfly Bicyclus anynana , a species that feeds on fermenting fruits in the wild. We found that butterflies exposed to ethanol-supplemented diets initiated feeding more rapidly, but also spent less time feeding, and they required more stimuli to sustain flight. Moreover, feeding behaviour differed between males and females and between mated and virgin individuals, while flight performance differed between sexes but was not affected by mating status. Given the involvement of flight in male courtship, we also tested the hypothesis that negative effects of ethanol consumption on flight would impair courtship. We found that males fed on ethanol-supplemented diets—particularly young ones—had reduced mating success and took longer to secure a mating. Together, our findings demonstrate that ethanol consumption affects behaviours closely tied to survival and fitness in B. anynana , suggesting that exposure to fermenting resources may impose selective pressures on physiology, behaviour, and reproductive strategies in frugivorous insects.