Running title : Taste sense in adult butterfly proboscis 2 3 4 Tolerance to fermentation products in sugar reception : Gustatory adaptation of adult 5 butterfly proboscis for feeding on rotting foods

Adult Vanessa indica and Argyreus hyperbius frequently forage on flower 21 nectar, but the former also utilize tree sap and rotting fruits. Compared to flower 22 nectar, these rotting foods are characterized by low sugar concentrations and the 23 presence of fermentation products (ethanol and acetic acid). We suspected that 24 gustatory responses by the receptors on the proboscis might differ in these species. 25 Among the three sugars tested, sucrose elicited the greatest probing (behavioral) 26 responses and was followed by fructose and glucose. A. hyperbius showed higher 27 sugar sensitivity than V. indica in probing responsiveness. In electrophysiological 28 responses of the proboscis sensilla, V. indica was slightly more sensitive than A. 29 hyperbius to glucose and lower concentrations of the other sugars. The sugar 30 reception in A. hyperbius was strongly inhibited by fermentation products, particularly 31 acetic acid at natural concentrations. In contrast, V. indica was noticeably less 32 susceptible to them than A. hyperbius, and its behavioral and sensory responses to 33 sucrose were enhanced by 5–20% (w/v) ethanol. Thus, V. indica not only possesses 34 tolerance to fermentation products but may perceive them as synergists for sugar 35 reception. To utilize rotting foods, such tolerance might be more necessary than high 36 sugar sensitivity. 37