Abstract: In the mulberry silkworm, Bombyx mori L., the first developmental marker event, the egg hatching is the most important one for the beginning of successful commercial silkworm cocoon crop. Many external factors such as photoperiod, temperature, humidity etc., directly affect hatching in silkworm. Two popular silkworm hybrids, PM x CSR2 (multivoltine x bivoltine) and CSR2 x CSR4 (bivoltine x bivoltine) were selected for hatching studies. Three photoperiodic conditions, LD 12 : 12, DD and LL were adopted. In combination, three temperature (25, 30 and 35 °C) and three relative humidity conditions (RH, 60, 70 and 80%) were considered for the study. In total, data on hatching patterns, hatching percentage and other related aspects of 2 silkworm hybrids x 3 photoperiodic x 3 temperature x 3 humidity conditions x 5 replications (= 270 individual batches) were recorded and analyzed. Hatching was very distinct, confining to a single day, with PM x CSR2 under LD 12 : 12 condition. Peak hatching occurred at or immediately after ‘lights-on’, taking it as the synchronizing signal. Eggs of CSR2 x CSR4 hatched for two consecutive days, with stray hatching on day-1 and maximum hatching on day-2, indicating circadian control over hatching. Driven under continuous conditions (DD/LL), hatching occurred for 2 days. Hatching was low on the day-1 and high on day-2 under both DD and LL conditions. Further, hatching distribution broadened with decrease in amplitude, indicating ‘damp-out’ or ‘near damp-out’ situation, especially with CSR2 x CSR4 under LL. Thus, B. mori hatching rhythm was circadian, diurnal, taking lights-on as synchronizing signal and followed the ‘gating’ phenomenon.
Keeping ambiguity of presenting 54 chronograms of hatching (for 2 hybrids x 3 photoperiodic conditions x 3 temperature x 3 humidity conditions), data on hatching patterns were computed for circular variables like mean vector (mean f), length of mean vector (r) and angular standard deviation (s) using circular statistics. Mean vector indicated that hatching rhythmic patterns are not much affected by temperature and humidity conditions. However, r and s values varied significantly, indicating that height of peak hatching decreased and broadening of hatching increased under high temperature and low humidity conditions. Hatching percentage was more affected by high temperature and low humidity, decreasing hatching magnitude to below economical hatching. Similarly, high temperature and low humidity implicated in increased number of dead eggs. High temperature resulted in scorching and low humidity in desiccation of silkworm eggs. Results are discussed in terms of contemporary economic hatching in silkworm.
Keywords: Silkworm, Bombyx mori L., hatching, photoperiod, temperature, humidity.
Title: On the implications of temperature and humidity on egg hatching in the commercial silkworm, Bombyx mori L.
Author: P. Narasimhulu, P. Lakshminarayana Reddy, B. Sujatha, K. Lavanya Latha, B. Vinayak Reddy, S. Sankar Naik.
International Journal of Life Sciences Research
ISSN 2348-313X (Print), ISSN 2348-3148 (online)
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