Electrophysiological and Morphological Characterization of Contact Chemosensilla in Adults and Larvae of the Butterfly, Atrophaneura alcinous

SIMPLE SUMMARY: In butterflies, oviposition and feeding are induced by the recognition of host plant compounds with contact sensory organs called chemosensilla. Oviposition behavior of the butterfly Atrophaneura alcinous involves detection of two plant compounds—an alkaloid and a monosaccharide—using tarsal contact chemosensilla of the foreleg. Feeding behavior of the adults and larvae involves detection of sucrose, sodium chloride, and other chemicals. We examined the distribution and electrophysiological response of contact chemosensilla in A. alcinous adults and larvae. In adults, tarsal contact chemosensilla were classified into long- and short-type sensilla. Long-type sensilla were distributed widely much more in females than in males, whereas short-type sensilla were found at the edge of the tarsi in a similar manner in both sexes. Long- and short-type sensilla showed different responses to methanol extracts of host plant compounds. Our findings suggest that the adult butterfly discriminates between host plant compounds using long-type sensilla during oviposition and recognizes the taste using short-type sensilla. In the larval mouthparts, contact chemosensilla were present on the maxillary galea and epipharynx. Electrophysiological responses of chemosensilla suggest that larvae can discriminate between host plant compounds. ABSTRACT: Distribution and electrophysiological responses of contact chemosensilla were examined in the Aristolochiaceae-feeding butterfly Atrophaneura alcinous. In adult butterflies, tarsal contact chemosensilla of the foreleg were classified into two groups based on length: long- and short-type sensilla. Long-type sensilla were distributed much more widely in females than in males, whereas short-type sensilla were found at the edge of the tarsi in a similar manner in both sexes. Taste responses of the long- and short-type sensilla to methanol extracts of Aristolochia debilis and Citrus spp. were recorded. Aristolochia debilis extracts evoked spikes with different amplitudes, whereas Citrus spp. extracts evoked spikes with a single amplitude in the long-type sensilla. Short-type sensilla did not respond to either extract. Moreover, we recorded responses to different concentrations of sucrose and NaCl. Results suggest that adult butterflies can discriminate the taste of host plant components from other chemicals using long-type sensilla during oviposition and may recognize diets containing sugar and salts during feeding using short-type sensilla. In the larval mouthparts, there were lateral and medial styloconic sensilla on the maxillary galea and epipharyngeal sensillum on the epipharynx. Electrophysiological responses of these sensilla suggest that larvae can discriminate between host plant compounds.