Pharyngeal stimulation with sugar triggers local searching behavior in Drosophila

Foraging behavior is essential for all organisms to find food containing nutritional chemicals. A hungry fly of Drosophila melanogaster performs local searching behavior after drinking a small amount of sugar solution. Using video tracking we examined how the searching behavior is regulated in D. melanogaster. We found that a small amount of highly concentrated sugar solution induced a long-lasting searching behavior. After the intake of sugar solution, a fly moved around in circles and repeatedly returned to the position where the sugar droplet had been placed. The non-nutritious sugar, D-arabinose, but not the non-sweet nutritious sugar, D-sorbitol, was effective in inducing the behavior, indicating that sweet sensation is essential. Furthermore, pox-neuro mutant flies with no external taste bristles showed local searching behavior, suggesting the involvement of the pharyngeal taste organ. Experimental activation of pharyngeal sugar-sensitive gustatory receptor neurons by capsaicin using the Gal4/UAS system induced local searching behavior. In contrast, inhibition of pharyngeal sugar-responsive gustatory receptor neurons abolished the searching behavior. Together our results indicate that in Drosophila the pharyngeal taste-receptor neurons trigger searching behavior immediately after ingestion.