30.2 Thursday, Jan. 5 The effect of nectar sugar concentration on the specific dynamic action of the hawkmoth Manduca sexta CONTRERAS, H.L.*; DAVIDOWITZ, G.; University of Arizona; University of Arizona firstname.lastname@example.org
Studies on birds have shown that the cost of processing a meal is higher when dilute nectars are ingested compared to when more concentrated nectars are consumed. Most of the metabolic costs in these studies are associated with the need to warm large volumes of liquid to body temperature. In this study we examined the metabolic cost of processing nectars of different sugar concentrations in nectar feeding ectotherms. Adult Manduca sexta hawkmoths naturally feed from flowers of Datura wrightii and Agave palmeri in the wild, although they have an innate preference for D. wrightii. Flowers from D. wrightii are known to produce a more concentrated nectar (22%) compared to A. palmeri (12%) and therefore, for a specific volume of nectar, provide a higher energy content than A. palmeri. However, the metabolic cost of processing nectar of different sugar concentrations in M. sexta is not known. While M. sexta don’t need to warm their liquid meals, consuming dilute nectars may be more costly to them by imposing additional energy costs on maintaining proper water balance. We predict that M. sexta feed preferentially on concentrated nectar because the cost of processing a concentrated nectar is lower than the cost of processing a more dilute nectar. Therefore the benefits of feeding from a concentrated nectar, like that of D. wrightii, are two-fold: 1. Receive a higher energetic reward; 2. Spend less energy on osmoregulation.