Lipid mobilization and locomotor stimulation in Gryllus bimaculatus by topically applied adipokinetic hormone

Abstract. Walking activity of 3‐day‐old adult female Gryllus bimaculatus (de Geer) (Ensifera, Gryllidae) was measured over 24 h. A high level of locomotor activity during the scotophase was found, which was two‐ to three‐fold higher than that during the photophase. The titre of lipid in the haemolymph was relatively low 2 h after lights on, increased significantly 2 h after lights off, although, 2 h after lights on in the next photophase, the lipid titre had decreased to the basal level. Topical application of homologous Grybi‐adipokinetic hormone (AKH) (100 pmol in 20% 2‐propanol) led to a significant increase in haemolymph lipids, comparable with the maximal increase caused by injection of AKH (3 pmol in water). Topical application of AKH also stimulated locomotor activity in crickets (maximal stimulation 1.8‐fold with 100 pmol Grybi‐AKH). The results suggest that AKH penetrates the cuticle quickly. It is assumed that AKH stimulates locomotory activity at least in part via the increase of haemolymph lipid titres; however, the stimulation of locomotor activity via a direct neuromodulatory effect of AKH cannot be excluded.