Impact of thermal stress on lipid profiles and economic traits in cross breed and double hybrid Bombyx mori L.

Abstract

The silkworm, Bombyx mori L., is an economically significant lepidopteran insect that forms the backbone of the global sericulture industry. As a poikilothermic organism, its growth, development, and productivity are profoundly influenced by environmental temperature fluctuations. The present investigation was carried out to evaluate the impact of imposed thermal stress at 35±1 °C on the lipid content of reproductive organs (testis and ovaries) and key economic parameters in two commercially important silkworm hybrids, PM×CSR2 and FC1×FC2, during the fifth instar larval period. Fifth instar larvae were exposed to thermal stress using a BOD incubator at 35±1°C with a cyclic exposure protocol of 15 minutes stress followed by 15 minutes rest, while control batches were maintained at 28±1 °C. Lipid content was estimated using the semi-micro method of Bragdon (1951) [6] modified by Pande et al. (1963) [26]. The results revealed that thermal stress induced significant alterations in the lipid content of both testis and ovaries in the two hybrids, with notable increases observed on the third day of fifth instar in PM×CSR2 (15.29% in testis, 10.03% in ovary) and in FC1×FC2 (8.33% in testis, 14.21% in ovary). Larval weight showed a progressive increase under thermal stress in both hybrids. However, economic parameters including cocoon weight, pupal weight, shell weight, filament length, filament weight, and denier exhibited a predominantly negative trend under the imposed thermal regime, indicating that 35 °C represents a critical threshold temperature that adversely affects the manifestation of productive cocoon traits in both hybrids. The FC1×FC2 hybrid demonstrated comparatively better resilience to thermal stress in certain parameters. These findings underscore the necessity of developing thermotolerant silkworm breeds for sustaining sericulture productivity under changing climatic conditions.