Analysis of Drosophila larval feeding response to quinine-adulterated food.

The food responses of Drosophila larvae offer an excellent opportunity to study the genetic and neural regulation of feeding behavior. Compared with fed larvae, hungry larvae are more likely to display aggressive foraging, rapid food intake, compensatory feeding, and stress-resistant food procurement. Omnivores, including humans, tend to avoid noxious or unfamiliar food. Fly larvae avoid bitter substances such as quinine. As an increasing amount of quinine is added to an otherwise palatable liquid medium containing sugar and inactivated yeast, larvae become less likely to consume the tainted food. Larval feeding activity is assayed by scoring the percentage of larvae containing dyed food in a large portion of the midgut. Defensive foraging behavior can be modulated by physiological need and food deprivation significantly increases larval tolerance to quinine. Therefore, the larval response to quinine food and its regulation by hunger provides a useful paradigm for elucidating the genetic and neural regulation of food choice that favors short-term survival. The test described here is designed for quantitative assessment of the motivation of individual larvae to ingest quinine-adulterated food under different energy states. The test is applicable to routine functional testing and larger-scale screening of genetic mutations and biologics that might affect food consumption.