Juvenile hormone as a causal factor for maternal regulation of diapause in a wasp

Most temperate multivoltine insects enter diapause, a hormonally controlled developmental suspension, in response to seasonal photoperiodic and/or thermal cues. Some insect species exhibit maternal regulation of diapause in which developmental trajectories of the offspring are determined by mothers in response to environmental cues that the mother received. Although maternally regulated diapause is common among insects, the maternal endocrinological mechanisms are largely veiled. To approach this issue, we used the jewel wasp Nasonia vitripennis, which produces non-diapause-destined offspring under long days and diapause-destined offspring under short days or low temperatures. Comparative transcriptomics of these wasps revealed possible involvement of the juvenile hormone (JH) biosynthetic cascade in maternal diapause regulation. The expression of juvenile hormone acid O-methyltransferase (jhamt) was typically downregulated in short-day wasps, and this was reflected by a reduction in haemolymph JH concentrations. RNAi targeted at jhamt reduced haemolymph JH concentration and induced wasps to produce diapause-destined offspring even under long days. In addition, topical application of JH suppressed the production of diapause-destined offspring under short days or low temperatures. These results indicate that diapause in N. vitripennis is determined by maternal jhamt expression and haemolymph JH concentration in response to day length. We therefore report a novel role for JH in insect seasonality.