Heat shock induced changes in the cocoon traits of poly- and bi-voltine silkworm strains of Bombyx mori
Muzafar Ahmad Bhat, Hosaholalu Boregowda Manjunatha
The manifestation of cocoon characters due to heat shock (HS) during the larval stage of poly- (Daizo and Pure Mysore) and bi-voltine (NB4D2 and CSR2) silkworm strains of Bombyx mori was studied. Because, temperature being a major factor that shape distribution of organisms, insects in particular have diverse response to deal with critical temperature and exposure to wide-ranging thermal conditions led to amendment of biochemical and physiological protective mechanisms. To this, different instar larvae of poly- and bi- voltine breeds were subjected to thermal stress and the data generated in respect of cocoon traits were pooled separately for statistical analysis. Interestingly, highest weight of the cocoon was recorded from fifth instar CSR2 larvae HS at 40°C (1.99 g) with an improvement of 44.20% against control (1.38g). But, high rate of response to HS at 40°C was recorded in NB4D2 with an improvement of 46.82% in the weight of the cocoon. Among different instars, the fifth instar larvae of all the breeds HS at 40°C produced good quality cocoon with higher shell weight than control groups. Consequently, although, all instars larvae HS at 35 and 40°C metamorphosed into pupae with better growth than control highest per cent of improvement in it was recorded from fifth instar. However, heat shock temperature of 45˚C was lethal since all the biological and commercial characters were severely affected in all instars. Thus, temperatures of 40°C shall be taken into account to elicit profound response to acquire tolerance to overcome the fluctuated environmental condition, while screening for better parents to develop thermotolerant breeds/hybrids for tropical countries like India.