Studies on the influence of temperature and humidity on biological traits of silkworm (Bombyx mori L.; Bombycidae)
Impact of variations in temperature and humidity on pupation, hatchability and larval mortality of eleven inbred silkworm lines M-101, M-103, M-104, M-107, Pak-1, Pak-2, Pak-3, Pak-4, PFI-I, PFI-II and S-1 was investigated during autumn and spring, 2007-2008 at Sericulture Research Laboratory, Lahore. The experiment was laid out in factorial design with replications and the data was pooled over season. The larvae of 4th and 5th instar were exposed to three temperature regimes (25, 30 and 35 ± 1°C). Significant variations in hatchability, pupation and mortality were noticed due to the effect of temperature and relative humidity on 4th and 5th instar larvae of inbred silkworm lines. The maximum mean values of hatchability (93.15), pupation (93.12) and the lowest mean larval mortality (2.60) was observed at 25°C and 70-80% RH. Lower RH of (55 and 65%) even at 25°C lowered the hatchability and pupation of the silkworm lines and contributed significantly in higher larval mortality. The lowest mean value of hatchability (68.96) and pupation (76.55) was recorded at 35°C and 55% RH while highest larval mortality (11.92) was noticed at 35°C with 55% RH. The results indicate that the mean performance of inbred silkworm lines under various conditions of temperature and humidity was significantly different from each other at various temperature and humidity exposures during 4th and 5th instar. At 25°C with 75% RH, the performance of silkworm lines remained consistent but variations in temperature or humidity for three hours significantly affected all three parameters (hatchability, pupation and larval mortality). The results illustrate that hatchability percentage of M-101(84.98), Pak-2 (84.52), Pak-3 (84.32) and Pak-4 (84.05) and pupation rate of Pak-4 (86.60), Pak-2 (86.08), PFI-I (85.33) and M-101(84.88) was significantly better as compared to other silkworm lines. The mean values of larval mortality observed in Pak-2 (5.56), Pak-3 (5.76), PFI-I (6.03) and M-107 (6.20) showed significantly lower mortality. The lower relative humidity level (less than 65%) is not conducive for seed cocoon production even at the optimum temperature of 25°C. The study clearly underlines the importance of optimization of environmental conditions during larval rearing in relation to seed cocoon production. The investigations strongly recommend that temperature and relative humidity in the range of 25-26°C and 70-80% respectively are mandatory for excellent results of egg hatchability, pupation and survival rate (low larval mortality). The results also emphasize that Pak-2, Pak-3, Pak-4, PFI-I, M-101 and M-107 showed better potential for seed production and commercial exploitation.
Key words: Sericulture Pakistan, silkworm rearing.