A novel molecule reduces cocoon production loss in BmNPV-infected Bombyx mori larvae.

Bombyx mori nucleopolyhedrovirus (BmNPV) is a pathogen causing Bombyx mori larval mortality and is also called grasserie disease (Lepidoptera: Bombycidae). Since this viral disease is not fully under control in sericulture, it is necessary to identify agents that can prevent or reduce the infection/proliferation of BmNPV in B. mori culture boxes. Sericultural activity is similar an agriculture, and the loss of cocoon production leads to economic losses. In this research area, we previously reported that the molecule Bm5 inhibits cathepsin activity from BmNPV (V-CATH) and protects infected B. mori larvae from liquefaction processes, limiting the spread of the disease. Here, we evaluated the efficacy of Bm5 in reducing sericultural loss due to BmNPV infection. Assays were carried out with B. mori fifth-instar hybrids immediately inoculated with BmNPV and Bm5 to prevent viral cathepsin action. The biological and productive variables relevant during larval development and cocoon productivity were analysed to verify the effectiveness of Bm5 treatment. Biological and economic parameter data showed that the larval survival rate of the BmNPV-infected and Bm5-treated groups was 35.6% higher than that of the untreated BmNPV group. In addition, the infected BmNPV and Bm5-treated groups showed surviving pupae that produced good-quality cocoons. The α- and β-esterase analysis from the midgut and fat body did not show a change in isoenzyme expression between Bm5-treated and untreated larvae infected with BmNPV. Therefore, the inhibition of viral cathepsin with the Bm5 was shown to be effective in reducing the loss of silk production from BmNPV-infected B. mori larvae. [ABSTRACT FROM AUTHOR]