Molecular characterization and seasonal expression profiling of circadian clock genes in relation to obligatory diapause in the Sunn Pest, Eurygaster integriceps (Hemiptera: Scutelleridae).

Univoltine insect pests exploiting seasonal crops must synchronize reproduction and diapause with host phenology. The Sunn pest, Eurygaster integriceps, reproduces in spring and enters an obligatory diapause over the summer-winter, yet the role of circadian clock genes in this schedule remains unclear. We asked whether seasonal modulation of core clock genes aligns with generation-specific reproductive versus diapause states in E. integriceps. Using a brain + corpora cardiaca + corpora allata (brain-CC-CA complex) transcriptome and RT-qPCR, we identified five core clock genes (Clock/clk, cycle/cyc, period/per, timeless/tim, cryptochrome 2/cry2), verified hemipteran orthology, and quantified transcript levels in female brain-CC-CA complex collected in January, March, June, and August, representing overwintering, reproducing, and new-generation diapause adults, respectively. Also, ovarian status was assessed by dissection. Most core clock transcripts (per, tim, clk, and cry2) were elevated in March relative to summer diapause, whereas cyc showed a distinct profile with higher levels in January. Per, tim, cyc, clk, and cry2 were significantly downregulated in June and August, indicating transcriptional dampening consistent with seasonal reprogramming of clock-gene transcripts during the refractory phase. In contrast, diapausing adults in January exhibited renewed expression, with cyc reaching its annual peak. This upregulation marks the transition from physiological diapause to quiescence, when the circadian clock enables accurate photoperiod measurement. Such sensory priming is essential for detecting lengthening winter days that cue migration to wheat fields and the onset of feeding and reproductive activity. These findings link seasonal clock gene expression dynamics to diapause, feeding, and reproduction in the Sunn pest's obligatory diapause, highlighting circadian components as potential targets for control strategies.