Melatonin and the pea aphid, Acyrthosiphon pisum

Pea aphids, Acyrthosiphon pisum, were fed on artificial diet containing various concentrations of melatonin. Under long-day conditions (16 h light: 8 h dark) their progeny included males and virginoparous/oviparous (asexual/sexual) intermediate females, which normally occur only in short days or around critical night-length. Endogenous melatonin in pea aphids was measured by radioimmunoassay and verified by parallelism with a melatonin standard curve and by thin layer chromatography. However, melatonin titres showed large variations and although they tended to be higher during the scotophase than during the photophase they were not significantly different. The possibility of melatonin being involved in photoperiodism is discussed. (C) 1997 Elsevier Science Ltd.