The Effect of Long‐Term Heat Stress on Performance and Expression of Heat Shock Protein Genes in Parental Lines of the Silkworm Bombyx mori (L.)

The presence of substantial genetic diversity for heat tolerance provides valuable opportunities to develop thermotolerant commercial silkworm hybrids. A total of 15 silkworm lines were evaluated in the spring of 2023. These lines belonged to two groups including 7 Chinese‐shaped lines (IRA2, IRA4, IRA8, IRA10, 32, 104, and 154) and 8 Japanese‐shaped lines (IRA3, IRA7, IRA9, IRA11, 31, 103, 151, and 153). The larvae in the heat treatment group were subjected to long‐term heat stress (38°C for 8 h) starting from the fifth instar. Survivability was assessed by larval mortality during the feeding period (LM1), the spinning period (LM2), and total mortality (TM). The larval and cocoon weights were recorded to measure productivity traits. The expression of some important heat shock proteins (HSPs) was assessed in the selected susceptible and tolerant silkworm lines. The results showed that the spinning stage is more sensitive to thermal stress than the feeding stage. Lines IRA2, IRA7, IRA8, IRA10, 104, and 153, which had better thermotolerance, also had higher cocoon weights. According to the survivability and performance traits, the most susceptible lines were 32 and IRA3, while the most tolerant were IRA2 and IRA7. The gene expression of sHSP19.9, sHSP20.4, HSP70, and HSP90 showed that sHSP20.4 expression was different among the parental lines. All HSP genes were upregulated in the susceptible lines. Therefore, the expression of HSPs may serve as a biomarker to select thermotolerant lines. The introduced heat‐tolerant lines can be recommended for sericulture in semiarid climates or under climate change scenarios.