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 short days. The circadian clock is involved in the assessment of daylength as a seasonal cue. After the assessment of daylength, the endocrine effector determines the developmental fate. In some insect species, diapause induction is determined by 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 parasitic jewel wasp Nasonia vitripennis, which produces non-diapause-destined offspring under long days and diapause-destined offspring under short days. Comparative transcriptomics and RT-qPCR revealed possible involvement of the juvenile hormone (JH) biosynthetic cascade in maternal diapause regulation. JH acid methyltransferase (jhamt) was typically downregulated under short days. The haemolymph JH concentration was reduced under short days. RNAi targeted at jhamt reduced haemolymph JH concentration and resulted in deposition of diapause-destined offspring even under long days. In addition, RNAi targeted at circadian clock gene period up-regulated jhamt expression. These results indicate that diapause in N. vitripennis is determined by maternal jhamt expression and haemolymph JH concentration in response to daylength.