Spatial Variation in Cocoon Yield in Tropical Tasar Silkworm: An Influence of Insect-Predators and Pathogens

Abstract

Tropical tasar silkworm is a polyphagous silk spinning insect, endemic to India. The silkworms are commercially reared on field-raised host plants, which are geographically contiguous with the wild silkworm fauna. Ecologically, the silkworm is r-selected and evolved with complex survival strategies. Naturally, the population regulated by the interactions between host and natural enemies and their dynamics due to tri -trophic interactions. Hence, understanding the effect of biotic and abiotic factors on silkworm is most critical for increasing the productivity of the cocoons. The cocoon yield trends at different locations are an indication for local specific problems and requirements for specific technological interventions. Cocoon yield obtained at different locations during 2015 to 2017 was analysed for variation in cocoon yield. Further, predator dynamics and incidence of silkworm diseases were also measured to know their impact on silkworms. The results revealed that the highest cocoon yield was recorded in Chhattisgarh (59.97) and West Bengal (54.57) and lowest was in Maharashtra (34.92) and Madhya Pradesh (37.80). Average cocoon yield in Jharkhand and Odisha was 40.18 and 43.30, respectively. Based on the tukeys HSD test, the highest cocoon yield per dfl was recorded at Bilaspur and Pali. The next highest was recorded in Sundergarh, Boirdadar, Patelnaga and Bastar. The significant changes in the predator's population were recorded before and after brushing of the silkworm. Highest incidence was recorded during 1 st , 2 nd and 3 rd instar silkworm and reduced in the subsequent stages. Correlation studies indicated that there was a strong positive linear relationship between silkworm mortality and predator population. Similarly, the silkworm mortality due to disease-causing pathogens was 53.70 %, 26.75 % and 10.90 % during the first crop and 29.27%, 12.10 % and 9.70 % during the second crop in Jharkhand, Madhya Pradesh and Chhattisgarh, respectively. The study showed that the spatial variation in cocoon yield wasinfluenced by the sporadic occurrence of insect-predators and disease-causing organisms at critical stages of rearing.