Dyeing of textile fabrics is considered to be one of the most polluting industries today, and there is a need to develop green processes that can reduce this pollution. A promising technology that can potentially cleanup the dyeing of silk fibers that are widely used for textile applications would involve the generation of intrinsically colored silk cocoons. This can be achieved by feeding of Bombyx mori silkworm larvae with a modified feed of mulberry leaves containing a sprayed dye solution. This process significantly reduces the need for treating toxic dye effluents that are generated in traditional dyeing processes. In this report, we have evaluated a set of seven different azo dyes that are used in the textile industry for dyeing to produce intrinsically dyed silk. The dyes used in the study had similar chemical structures with systematically varying partition coefficients. The results suggest that while some dyes produced intrinsically colored silk other did not. Careful evaluation of the physical properties of these related azo dyes suggest that the balance of hydrophobic and hydrophilic character is necessary for diffusion of the dye from the alimentary canal of the silkworm larva into the hemolymph and later into the silk glands. The partition coefficient of the dye also determines the preferential association of the dye with either sericin or fibroin protein in the silkworm gland and finally into the cocoon. These insights are extremely important in development of novel dye molecules that can be successfully fed to Bombyx mori silkworm larvae for producing intrinsically colored silk of various colors and shades.

The molecular mechanism involved in BmNPV resistance was investigated using a genome wide microarray in midgut tissue of Indian silkworm Bombyx mori. In resistant race (Sarupat), 735 genes up-regulated and 589 genes down-regulated at 12 h post BmNPV infection. Similarly, in case of susceptible race (CSR-2), 2183 genes up-regulated and 2115 genes down-regulated. Among these, nine up-regulated and eight down-regulated genes were validated using real-time qPCR analysis. In Sarupat, vacuolar protein sorting associated, Xfin-like protein and carboxypeptidase E-like protein genes significantly up-regulated in infected midgut; prominently down-regulated genes were glutamate receptor ionotropic kainite 2-like, BTB/POZ domain and transferrin. Considerably up-regulated genes in the CSR-2 were peptidoglycan recognition protein S6 precursor and rapamycin while the conspicuous down-regulated genes were facilitated trehalose transporter and zinc transporter ZIP1-like gene. The up-regulation of genes in resistant race after BmNPV infection indicates their possible role in antiviral immune response.

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Parasitization of silkworm, Bombyx mori by invasive larva of dipteran parasitoid Exorista bombycis caused upto 20% revenue loss in sericulture. The parasitism was successful by suppressing host immune system however mechanism of immune suppression induced by E. bombycis is unknown which is unravelled here. The infestation induced cytotoxic symptoms in host hemocytes, such as vacuolated cytoplasm, porous plasma membrane, indented nuclei with condensed chromatin and dilated RER. One of the markers of necrosis is cell permeabilization, which can be measured as released lactate dehydrogenase (LDH). LDH level showed significantly (P<0.01) high release into extracellular medium in vitro after exposure of hemocytes to parasitoid larval tissue protein compared with control revealing membrane permeability and loss of cell integrity. At five minutes after exposure, cytotoxicity was 43% and was increased to 99% at 3h. The cytotoxicity is signalled by increased content of hydrogen peroxide (H2O2) causing lipid peroxidation followed by porosity in plasma membrane. A test for lipid peroxidation by measurement of lipid peroxidation breakdown product, malondialdehyde (MDA) revealed significant increase in peroxidation from one to 24 h post-invasion, with maximum at 12 h (P<0.008). Level of reactive oxygen species measured as H2O2 production increased from 6 to 12 h post-invasion and continued to increase significantly (P<0.03) reaching maximum at 48 h. These observations reveal that dipteran endoparasitoid invasion induced H2O2 production in the hemocytes causing cytotoxicity, lipid peroxidation and membrane porosity that suppressed both humoral- and cell-mediated immune responses of hemocytes in B. mori.

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