ABSTRACT
Cypermethrin is a pyrethroid insecticide with high insecticidal activity, low mammalian toxicity, and biodegradability. The present study aimed to determine the acute toxicity and evaluate the secondary toxic effects of a commercial formulation of cypermethrin on silkworm Philosamia ricini Hutt of Northeast India. The potential genotoxicity of cypermethrin on silkworm hemocyte was examined by comet assay, caspase activation, and annexin V affinity assay. Alteration in nutritional physiology and histoarchitecture of the gut region was evaluated. Additionally, immunotoxicological effect of cypermethrin was studied by phenoloxidase (PO), lysozyme assay, and abundance of circulating hemocytes. The LC50 value at 24-, 48-, 72-, and 96-h exposure period was recorded as 185.96, 105.34, 72.42, and 58.41 µg/liter, respectively. Approximately sevenfold increase in mean comet tail length was observed at 24 h posttreatment with sublethal concentrations of cypermethrin. Cypermethrin also induced apoptosis and activated caspase reaction in silkworm hemocytes. Moreover, a significant decrease in digestive enzyme activity was observed at higher concentrations of cypermethrin. In cypermethrin-exposed groups, alteration in histoarchitecture was also observed in the form of ruptured microvilli and thin, deformed, fused mucous layer. The PO enzyme and lysozyme enzyme activity was also altered with sublethal concentration of cypermethrin. Total hemocyte count was reduced to 10587.10, 10052.30, 9234.30, and 8842.60 per mm3 with 10, 20, 30, and 40 µg/liter, respectively. The results offer new insights into the negative consequences of very low concentrations of cypermethrin formulations on nonmulberry silkworm of Northeast India.
Subject(s)
Animal Nutritional Physiological Phenomena , Apoptosis , Immunity, Innate , Insecticides/toxicity , Moths/drug effects , Pyrethrins/toxicity , Animals , Larva/drug effects , Larva/growth & development , Larva/immunology , Moths/growth & development , Moths/immunologyABSTRACT
Antheraea assamensis Helfer (muga silkworm) is an economically important endemic insect species of North Eastern Region of India. The silkworm is often susceptible to infection by pathogenic bacteria, leads to a disease commonly known as flacherie which causes 40% loss per annum to the silk industry. In this study, we have reported isolation, characterization and pathogenicity assessment of gut-associated bacteria of healthy and diseased muga silkworms. Thirty five bacterial isolates were screened from the gut of healthy and diseased silkworms by morphological observation and biochemical tests. 11 and 5 strains from healthy and diseased silkworm respectively were identified by 16S rRNA gene sequencing and analyzed. Pseudomonas aeruginosa (DRK1), Ornithinibacillus bavariensis (DRK2), Achromobacter xylosoxidans (KH3) and Staphylococcus aureus (FLG1) strains were commonly found in healthy as well as diseased larvae whereas, Bacillus thuringiensis (MK1) was found only in diseased larvae. Survivability analysis was performed with the identified strains by injection and oral administration (10(4)CFU/ml). The immune response of the silkworm against the pathogen was also studied by phenoloxidase and lysozyme enzyme activity assay, total and differential hemocyte count and phagocytic activity of hemocytes. It was observed that S. aureus, P. aeruginosa and B. thuringiensis significantly reduced the survivability of silkworm (p<0.001) hence found highly pathogenic. The lethal concentrations (LC50) values of the pathogenic strains were calculated at different time intervals (24, 48, 72 and 96h) within the range from 1.38×10(2) to 3.63×10(7)CFU/ml. The pathogenic groups demonstrated inhibition of phenoloxidase activity and decreased in total hemocyte count after 48h of infection. However, the lysozyme activity increased significantly in the pathogenic groups compared to the control (p<0.05). Granulocytes and plasmatocytes showed phagocytosis whereas; other types of cells did not show any phagocytic activity. Increasing granulocytes and plasmatocytes counts corroborates the results of phagocytic activity. The present study might be helpful in understanding the disease prognosis and colonization of bacteria causing the disease in muga silkworm.
