Sensitivity of larval and adult crickets (Gryllus bimaculatus) to adipokinetic hormone

Abstract

Total carbohydrate and lipid concentrations in the haemolymph of female and male last instar larvae were high at the beginning and the end of the larval stage but low approximately 24 h after molt. Except during the first few hours of the larval stage, lipids exceeded the sugar content in all ages in both sexes. Injections of 0.3-30 pmol Grybi-AKH into 1-day-old last instar larvae resulted in a dose-dependent mobilization of energy stores in which lipid release was approximately twice that of carbohydrate release. This sensitivity in energy mobilization to AKH remained relatively constant in older larvae, whereas no sugars and only minor amounts of lipids were released in freshly ecdysed larvae. Carbohydrate and lipid concentrations in the haemolymph of adult females and males changed slightly during the first 5 days of adult life, but both decreased with increasing age. Lipids exceeded the sugar content at all ages. Injections of 0.01-30 pmol Grybi-AKH into 2-day-old adults resulted in a dose-dependent release of lipids with approximately 100% increase at 0.3 pmol whereas carbohydrates were only slightly mobilized by 10 and 30 pmol AKH, respectively. At the beginning of adult life as well as in animals older than 10 days, carbohydrate and lipid mobilization was lower than during the intervening ages. One to 4 h of tethered flight induced moderate increase in haemolymph lipids when compared to injection of 10 pmol AKH. AKH degradation in the haemolymph (in vivo) occurred with a half-life of approximately 3 min. In vitro tests indicated that AKH-degradating enzymes were released from the haemocytes.