Molecular characterization and expression analysis of six small heat shock protein genes in Trogoderma granarium during cold and starvation-induced larval diapause

The khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), is a highly invasive pest infesting stored grains, cereal products, and is recognised as a quarantine pest in many countries. Various stressors can instigate prolonged diapause among insect larvae, increasing the challenge of managing infestation. When the environmental conditions become conducive to development, diapause ceases, and the larva progresses on its developmental course. Members of the Heat Shock Protein (HSP) family play a significant role in protecting insects from the impacts of environmental stressors. In this study, six small heat shock proteins (TsHSP19.8, TsHSP20.5, TsHSP20.6, TsHSP20.8, TsHSP21.2, and TsHSP21.3) were identified and characterized in T. granarium. Transcript abundances of TsHSPs were analysed across distinct phases of larval diapause induced by both cold exposure and starvation stress treatments, alongside various developmental stages. The gene expression patterns of TsHSP20.5 and TsHSP21.2 exhibited peak mRNA levels during pre-diapause following the cold treatment, while the greatest abundances of TsHSP19.8, TsHSP20.6, TsHSP20.8, and TsHSP21.3 were detected in the diapause phases. The highest mRNA abundances of TsHSP20.5, TsHSP20.8, TsHSP21.2, and TsHSP21.3 were observed during the diapause phase following the starvation treatment, while it was noted on the first day of the post-diapause phase for TsHSP19.8 and TsHSP20.6. The remarkable levels of TsHSPs during diapause might imply their putative role in cold and starvation survival. Significant expression of TsHSP19.8, TsHSP20.6, TsHSP20.8, and TsHSP21.3 transcripts was observed in adults, suggesting their potential involvement in developmental processes. Understanding the genetic mechanisms involved in the diapause physiology of T. granarium could offer additional insights for the integrated management of this pest.