Immunodiagnosis of silkworm diseases

Phenotypic and molecular insights into a cypovirus isolated from Antheraea assamensis Helfer (Lepidoptera: Saturniidae) and modelling of its polyhedrin protein structure

Antheraea assamensis Helfer (A. assamensis) or Muga silkworm is popularly known for producing golden silk and endemic to the region of Northeast India. The present work characterizes a cypovirus variant infecting A. assamensis larvae, exhibiting characteristic symptoms of flacherie disease. Scanning electron microscope and transmission electron microscope imaging revealed the presence of polyhedral occlusion bodies (OBs) and virion particles measuring 40-50 nm in size. The cypovirus strain comprised of 10 dsRNA genome segments, which were sequenced, assembled and annotated. The encoded viral proteins from different genomic fragments were studied. The phylogenetic analysis of the RNA-dependent RNA polymerase and polyhedrin revealed a close relationship with the previously classified Antheraea mylitta cypovirus 4. The strain was characterized as Antheraea assamensis cypovirus 4 (AaCPV4) with substantial genomic and proteomic evidence that was previously unexplored. The peptide fingerprints of the polyhedrin protein were analysed in the diseased and healthy silkworm lysate by using LC-MS/MS. The polyhedrin protein of AaCPV4 was modelled by different in silico methods and compared with the previously reported cypovirus strains. The multimeric models of polyhedrin were studied and demonstrated the mechanism of formation of OB geometry. Our study provides new insights into the complete genome of AaCPV4 and its viral proteins, which were previously unknown. The present work will help in understanding the differentiation of CPV4 variants infecting Antheraea species and different host adaptations.

Fecal Transmission of Spodoptera frugiperda Multiple Nucleopolyhedrovirus (SfMNPV; Baculoviridae)

The production of viable nucleopolyhedrovirus in the feces of infected lepidopteran larvae represents a poorly understood route for virus transmission prior to host death. In the present study, we examined the presence of viable virus in the feces of fourth-instar Spodoptera frugiperda larvae infected with the Nicaraguan isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV-NIC). Feces production increased in samples taken at 2 to 6 days post-inoculation but was significantly lower in infected insects compared to controls. Second instars experienced 3.9 to 68.3% of polyhedrosis disease following consumption of feces collected at 2-5 days post-inoculation, which subsequently fell to 29.1% in the 6-day sample. Calibration of the insect bioassay using OB-spiked samples of feces indicated that the concentration of OBs varied between 5.4 × 102 and 4.4 × 105 OBs/100 mg of feces in infected fourth instars. Quantitative PCR analysis of fecal samples indicated the presence of 0 to 7629 copies/mg feces following amplification targeted at the polyhedrin gene. However, no correlation was detected between qPCR estimates of virus concentration and time of sample collection or the quantity of feces collected. The qPCR estimates were positively correlated with the prevalence of lethal infection observed in the insect bioassay, but the correlation was weak and several samples did not amplify. Calibration of the qPCR assay using OB-spiked samples of feces provided estimates that were 5- to 10-fold lower than the insect bioassay, indicating inhibition of the amplification reaction or loss of material during processing. In a greenhouse experiment, 2.5-48.3% of second-instar larvae acquired lethal infection following a 24 h period of feeding on maize plants on which fourth instar larvae had deposited their feces at 3 days and 4 days post-infection, respectively. These findings highlight the potential of OB-contaminated feces as a source of biologically significant quantities of inoculum for virus transmission prior to the death of infected insects and represent an additional contribution to the biological control of lepidopteran pests by these pathogens.

Effect of amino acid fortified mulberry leaves on economic and biological traits of Bombyx mori L

The demand for silk has been increasing day by day but the average silk production is not enough to meet its demand. In this study, we investigated the effect of amino acid supplemented mulberry feed on the biological and commercial traits of Bombyx mori L. (Lepidoptera; Bombycidae). The silkworm larvae at 5th instar stage were taken and fed with fresh and healthy mulberry leaves coated with Alanine, Glycine and Serine in fourteen different combinations. Results of the current study revealed that the average weight of silkworm larvae and the % ratio of silk gland to body weight on day 7 was significantly (P˂0.05) higher in the group fed with amino acid fortified leaves as compared to the control. The commercial traits of larvae fed with amino acid fortified leaves also improved significantly. The larvae fed with Alanine (1 %) treated mulberry leaves showed the maximum cocoon weight, cocoon length, cocoon width, cocoon shell ratio and fibroin content as compared to the control group. It is evident from the results that the amino acid (particularly alanine) coated mulberry leaves have a positive effect on the commercial and biological traits of Bombyx mori (L.).