Expressional respones of hsp70 genes against abiotic and entomopathgenic stresses in four different noctuid larval species (Lepidoptera: Noctidae)

Heat shock proteins (Hsps) are stress response proteins. In a previous study, host larval Hsp70s were identified as the structural proteins of virions of Heliothis virescens ascovirus 3 h (HvAV-3 h), an insect virus that mainly infects noctuid larvae. To investigate the response of hsp70s,of healthy Mythimna separata, Spodoptera exigua, Spodoptera frugiperda, and Spodoptera litura larvae to various abiotic or entomopathogenic stresses, quantitative PCR was used to detect larval hsp70s expression patterns. Results showed distinct expression patterns of hsp70s in response to different abiotic stresses. Notably, Mshsp70 expression pattern resembled Slhsp70 under most treatments. In healthy larvae, no tissue tropism was observed concerning the relative expression of Mshsp70, Sfhsp70, and Slhsp70. After infection with HvAV-3 h, the expression of hsp70s in all dissected tissues of all tested larval species increased. Significant differences were found in the fat bodies of M. separata, S. exigua, and S. litura as well as in the hemolymph of S. exigua and S. litura. Subsequent silencing of Slhsp70, resulted in a significant decrease in DNA replication levels of HvAV-3 h in S. litura larvae at 24 and 72 h post RNA interference, indicating that Slhsp70 is necessary for DNA replication in HvAV-3 h. These data can provide references for the studying on the stress response of noctuid larvae to different environmental factors.