Effect of azadirachtin on the nutrition, development and biogenic amine levels in the Eastern Death’s Head hawk moth, Acherontia styx (lepidoptera: sphingidae)

Abstract

Previous studies have suggested the involvement of biogenic amines in insect metamorphic events and post-embryonic development. The effect of azadirachtin (AZ), a natural antifeedant and growth-disrupting compound, on the nutrition, development, and biogenic amine contents of the last instar larvae of the Eastern Death’s Head hawk moth, Acherontia styx, was examined. Single doses of AZ, injected into the haemolymph at day 1 post-ecdysis, inhibited food consumption in a dose-dependent manner (ED₅₀ = 0.65±0.08 μg AZ/g body weight), and was found to be highly effective at producing pupal deformities and inhibiting larval growth (0.1–0.2 μg AZ/g body weight range). Biogenic amine contents, namely octopamine (OA), dopamine (DA) and serotonin (5-HT), in the brain and the haemolymph of 4-day- and 8 day-old larvae were analysed using high-performance liquid chromatography (HPLC) with an electrochemical detector (ECD). A dose-response relationship between AZ and biogenic amine contents in the brain and the haemolymph was also established. Low doses of AZ (0.1–0.2 μg AZ/g body weight) caused a dramatic reduction in OA and 5-HT levels in both the brain and the haemolymph. However, higher doses (0.9–1.2 μg AZ/g body weight) were needed to induce a significant reduction in DA levels. The significance of these findings in relation to the possibility of the involvement of biogenic amines in regulating metamorphic events in insects through mediation of juvenile hormone synthesis and/or release is discussed.