Butterflies don't use a straw to drink: fluid uptake in butterflies with split mouthparts

Over 95% of Lepidoptera, the second largest order of insects, use a proboscis that acts as a conduit for transporting fluids from pools and liquid films to the gut. Fluid uptake mechanisms are often related to a drinking straw, partially due to the resemblance in gross structure of the proboscis and the action of the sucking pump in the head to induce fluid rise. Recent studies suggest that capillary pull and hydrophilic/hydrophobic dynamics facilitate feeding on liquids. The purpose of this study was to determine if the sucking pump is necessary for fluid rise and feeding in butterflies with an elongated proboscis. We used four feeding treatments with Painted lady butterflies (Vanessa cardui) to test the hypothesis that fluid rise is independent of the sucking pump and a sealed proboscis, which consisted of treatments of varying amounts of the proboscis separated and fed a 20% sucrose solution with green food coloring. Butterflies were subsequently dissected and inspected for the presence of food coloring. Our results suggest that butterflies can feed with split proboscises; however, the amount of fluids in the crops differed among butterflies of different feeding treatments.