MOBILIZATION OF LIPID AND CARBOHYDRATE RESERVES IN THE MIGRATORY GRASSHOPPER MELANOPLUS-SANGUINIPES

The North American migratory grasshopper Melanoplus sanguinipes Fabric ius (Orthoptera: Acrididae) exhibits heritable variation in predisposi tion to make long-duration flights, and performance of long-duration f light enhances reproductive output. As a first step in understanding t he physiological basis of these phenomena, we examined the mobilizatio n of lipid and carbohydrate reserves during flight and in response to injection of extracts of the corpora cardiaca. Extract of conspecific corpora cardiaca elevates the concentration of haemolymph lipid. Both synthetic locust adipokinetic hormone I (AKH I) and synthetic Locusta migratoria AKH II raise the concentration of lipid in the haemolymph. However, although AKH I is more active than AKH LT in locusts, dose-re sponse curves for the two peptides are similar in M. sanguinipes. Neit her extract of conspecific corpora cardiaca nor locust AKH I affects h aemolymph carbohydrate in this species. Haemolymph carbohydrate and to tal glycogen reserves are diminished by tethered flight; in contrast, haemolymph lipid is elevated by flight. Grasshoppers identified as pre sumptive migrants or non-migrants do not differ significantly in body composition. Total lipid reserves did not decrease measurably after ex tended flight, even though total reserves of carbohydrate do not appea r to be sufficient to maintain the durations of flight performed.