Functional characterization of the adipokinetic hormone in the pea aphid, Acyrthosiphon pisum

Aphids are important plant phloem-sucking pests and detailed knowledge about the hormonal control of their metabolism can potentially contribute to the development of methods for their management. The insect metabolism is predominantly controlled by neuropeptides belonging to the adipokinetic hormone/red pigment-concentrating hormone family (AKH/RPCH). The main goal of this study was to obtain the sequence of AKH transcripts and analyze its expression in all polyphenic female forms of the pea aphid, Acyrthosiphon pisum. The neuropeptide is expressed in the brain of all female forms and in the ovaries of the both (wingless and winged) parthenogenetic forms. The form of active Acypi-AKH decapeptide was confirmed by the LC/MS and + ESI tandem mass spectrometry. The highest relative amount of Acypi-AKH was recorded in winged virginoparae. Furthermore, a potential role of this hormone when directly applied to the aphid was studied as well. Interestingly, no significant increase of trehalose in the wingless virginoparae after application of synthetic Acypi-AKH was detected. Yet this treatment did affect the level of protective polyol (mannitol) and furthermore led to increased activity of the detoxification enzyme glutathione S-transferase. The possible physiological function of AKH in A. pisum under the stress conditions is discussed.