, Volume 6, Issue 1, pp 43-64

Feeding behavior ofRhagoletis pomonella flies (Diptera: Tephritidae): Effect of initial food quantity and quality on food foraging, handling costs, and bubbling

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Abstract

Under seminatural conditions feeding and postfeeding behaviors of individual apple maggot flies, Rhagoletis pomonella(Diptera: Tephritidae), were recorded after flies were presented with yeast hydrolysate or sucrose droplets, varying in either concentration, amount of food solute, or total droplet volume. The objectives were (a) to establish, at a constant level of previous food deprivation, food ingestion thresholds in relation to food quality and quantity and (b) to study the effect of initial food quantity and quality on food handling time and subsequent food foraging behavior. For both carbohydrate and protein substrates, fly foraging time after feeding on a tree branchlet was positively related to total amount of food solute previously encountered on a leaf surface, though largely independent of food volume or concentration. The volume and concentration of food presented, however, significantly affected food “handling” and “processing” time and therefore foraging time. In fact, total branchlet residence time was more closely linked to food handling and processing time than to foraging time. Less time was needed for uptake of liquid than dry food, the latter requiring liquification by salivary secretion and eliciting considerable intermittent cleaning of mouthparts by feeding flies. Similar to the situation in other fluid feeders, uptake time in R. pomonelladecreased with increasing dilution, although below a threshold of a 30% concentration of solute, the rate of nutrient intake decreased rapidly. When the level of dilution and total volume of food ingested were great enough, engorged flies entered extended quiescent postfeeding periods during which they extrude orally droplets of liquid crop contents (“bubbling”). After this they reinitiated feeding, followed by more bubbling and feeding bouts. Multivariate logistic regression analysis suggested that bubbling behavior is determined by liquid food volume and degree of dilution, hunger, and temperature. Although thresholds triggering bubbling decreased with increasing temperature, higher temperature by itself did not result in bubbling behavior. This suggests that bubbling is not primarily a mechanism to achieve evaporative cooling as has been suggested but, rather, a behavior to eliminate excess water, thereby enabling engorged flies to continue feeding on diluted food sources.