Screening Strains of the Mulberry Silkworm,Bombyx mori, for Thermotolerance

Abstract

A tropical climate prevails in most of the sericultural areas in India, where temperature increases during the summer lead to adverse effects on temperate bivoltine silkworm rearing and cause crop losses. Screening for thermotolerance in the silkworm, Bombyxmori L. (Lepidoptera: Bombycidae) is an essential prerequisite for the development of thermotolerant breeds/hybrids. In the current study, the aim was to identify potential bivoltine silkworm strains specific for tolerance to high temperature. The third day of fifth stage silkworm larvae of bivoltine strains were subjected to high temperature of 36 ± 1° C with RH of 50 ± 5 % for six hours (10:00–16:00) every day until spinning for three consecutive generations. Highly significant differences were found among all genetic traits of bivoltine silkworm strains in the treated groups. Three groups of silkworm resulted including susceptible, moderately tolerant, and tolerant by utilizing pupation rate or survival rate with thermal stress as the index for thermotolerance. Furthermore, based on the overall silkworm rearing performance of nine quantitative genetic traits such as larval weight, cocoon yield by number and weight, pupation, single cocoon and shell weight, shell ratio, filament length and denier, three bivoltine silkworm strains, BD2-S, SOF-BR and BO2 were developed as having the potential for thermotolerance. The data from the present study enhance knowledge for the development of thermo tolerant silkworm breeds/ hybrids and their effective commercial utilization in the sericulture industry.

Screening and classification of mulberry silkworm, Bombyx mori based on thermotolerance

“…With regard to thermal exposure, the 3 rd d 5 th instar larvae were reared in a SERICATRON (Environment chamber with temperature and humidity control) at three different temperatures viz., 32 ± 1°C, 34 ± 1°C and 36 ± 1°C with an exposure duration of six h (10:00-16:00) per d. Fresh mulberry leaves were high temperature conditions. This prompts the commercial exploitation of multivoltine x bivoltine hybrids in India, as they are hardy and ably to survive and reproduce under fluctuating climatic conditions (Kumari et al, 2011).…”

“…However, the attempts to spread bivoltine silkworm breeds / hybrids throughout the sericulture belt of India resulted in extensive crop loss, especially in the hot and humid climatic conditions of tropics (Chavadi et al, 2006). These productive hybrids were vulnerable to varied environmental conditions, as they originated from temperate regions (Kumari et al, 2011).…”

“…Therefore, the estimation of phenotypic changes at high temperature is considered of great importance for sustainable progress in bivoltine breeding (Kumari et al, 2011 …”

“…Intensive and careful domestication over centuries has apparently deprived this commercial insect of the opportunity to acquire thermotolerance (Kumari et al, 2011). This vulnerability is more pronounced in bivoltine breeds compared to multivoltine breeds.…”

“…This vulnerability is more pronounced in bivoltine breeds compared to multivoltine breeds. Thus, among many factors responsible for poor performance of the bivoltine breeds under tropical conditions, the major one is lack of thermotolerance (Kumari et al, 2011). Many quantitative characters decline sharply at higher temperature (Krishnaswami et al, 1973).…”