Abstract
Three experimental groups of adult females of Pyrrhocoris apterus (reproductive brachypterous, diapausing brachypterous, and macropterous with non-diapause type of reproductive arrest) were analysed for their dose dependency of adipokinetic response, sensitivity of the fat body to Pya-AKH and locomotor activity during a 24 hour cycle. The greatest adipokinetic response (lipid elevation after hormonal treatment) was observed in macropterous, lower in diapausing brachypterous and the lowest in reproductive brachypterous females. Macropterous females also exhibited the highest activity of walking, while the lowest locomotor activity was found in diapausing brachypters. Diel changes of adipokinetic response were recorded in all three experimental groups, with maximal response occurring during the day at 6-7 h after the onset of light. On the contrary, the minimal adipokinetic response was found in the night and early after the onset of light. No significant differences in diel rhythms were observed between groups exposed to various day lengths. Diel changes in locomotor activity were found only in reproductive brachypterous females and females of macropterous morph, and showed a diurnal rhythm with only one peak of activity during a 24 hour cycle. In the latter, the rhythmic pattern of walking activity was positively correlated with diel changes of adipokinetic response. This indicates an important role of Pya-AKH in dispersal strategy of macropterous females of this heteropteran.
Highlights
Adipokinetic hormone (AKH) is one of the best known neuropeptides that controls and regulates energy metabo lism in insects
The main aim of this study was to test the hypotheses that (1) adipokinetic response and locomotion of P. apterus exhibit diel rhythms, (2) these rhythms cor relate in time, and (3) the dose-dependent adipokinetic response and diel rhythms in adipokinetic response and walking activity are related to the wing dimorphism and physiological status of the bugs
The analysis of the dose-response effect of Pya-AKH on 10-day-old reproductive and diapausing brachypterous females and females of macropterous morph revealed that haemolymph lipid elevations were dose-dependent in all experimental groups (Fig. 1)
Summary
Adipokinetic hormone (AKH) is one of the best known neuropeptides that controls and regulates energy metabo lism in insects. Many AKHs have been isolated from cor pora cardiaca and characterized in a great number of insect orders (Gade et al, 1997; Gade, 1999; Lorenz et al, 1999), and recently in the firebug Pyrrhocoris apterus, a representative species of the suborder Heterop tera (Kodrik et al, 2000). Almost all of these hormones are octa-, nona- or decapeptides with characteristic struc tural similarities (Gade et al, 1997), and they are grouped into the AKH/RPCH (Adipokinetic Hormone/Red Pig ment Concentrating Hormone) family. The stimulation of walking activity by AKH was recently proven in P. apterus (Socha et al, 1999a, b; Kodrik et al, 2000)
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