Melatonin and the pea aphid, Acyrthosiphon pisum

Area of Science:

• Entomology
• Insect Physiology
• Chronobiology

Background:

• Pea aphids (Acyrthosiphon pisum) exhibit distinct reproductive strategies influenced by environmental cues.
• Photoperiodism, the seasonal response to day length, is a critical factor regulating insect development and reproduction.
• Melatonin, a hormone involved in circadian rhythms, is a potential mediator of photoperiodic responses in insects.

Purpose of the Study:

• To investigate the effect of exogenous melatonin on the reproductive modes of pea aphids.
• To measure endogenous melatonin levels in pea aphids under different light conditions.
• To explore the potential role of melatonin in mediating photoperiodism in pea aphids.

Main Methods:

• Pea aphids were reared on an artificial diet supplemented with varying concentrations of melatonin.
• Progeny development and reproductive morph determination were observed under long-day photoperiods (16h light:8h dark).
• Endogenous melatonin levels were quantified using radioimmunoassay and validated with thin-layer chromatography.

Main Results:

• Feeding aphids melatonin under long-day conditions resulted in the production of males and intermediate females (virginoparous/oviparous), forms usually associated with short-day photoperiods.
• Endogenous melatonin levels exhibited significant variation, with a slight, non-significant trend towards higher levels during the scotophase (dark period) compared to the photophase (light period).

Conclusions:

• Exogenous melatonin can induce reproductive changes in pea aphids indicative of short-day responses, even under long-day conditions.
• While endogenous melatonin levels fluctuate and show a trend related to the light-dark cycle, their direct role in mediating the observed photoperiodic effects requires further investigation.
• Melatonin is a plausible candidate involved in the photoperiodic regulation of reproduction in pea aphids.