Day length and temperature dependent sex-specific growth and development pattern of tropical tasar silkworm Antheraea mylitta larvae in non-diapausing and diapausing generations

Larval growth and development pattern of Daba bivoltine ecorace of Antheraea mylitta on the basis of green & dry weights, green & dry weight gain in non-diapause-destined (NDD) and diapause-destined (DD) generations along with available photoperiod/day length, relative humidity and temperature was studied. Weight gain was higher during early instars and significantly higher growth rate was observed in the first half of each instar. There was no significant sex-specific variation of green and dry weight was found wit in the same generation. The fifth instar feeding and spinning larvae of diapausing generations sexes had more dry weight than NDD generation. The relative growth rate (RGR) on green weight was always higher in NDD generation than DD generation. The RGR on dry weight basis was higher in I, II & III instars of DD generation, thereafter, this higher trend reversed in subsequent instars as RGR was lower than IV & V instar larvae of NDD generation. The relative loss rate (RLR) of spinning larvae was higher in DD generation. The lowered RGR pattern after III instar of DD generation is indicative of the induction for diapause preparation at the end of third instar which further strengthens during IV and V instar owing to longer larval duration under the affect of available day length/photoperiod, temperature and humidity. In first crop, average day length was recorded to be 13 h 36m, 13h 39m, 13h 24m, 13h 19m, 13h 14m & 13h 12m in I, II, II, IV, V & VSP. The average photoperiod/day length increased from I to II instar, thereafter, it gradually decreased till pupation. The minimum temperature was 24°C and under such conditions all pupae behaved as non-diapausing. In second crop, average photoperiod/day length was recorded to be 12 h 29m, 12h 18m, 12h 04m, 11h 52m, 11h 30m & 11h 10m in I, II, II, IV, V & VSP. The minimum temperature ranged in between 17.00 to 23.40 °C. As the rearing progressed the minimum temperature went down resulting into increased V instar phago and spinning period and under such conditions all the formed pupae behaved as diapausing. Overall larval duration from hatching to Day 0 pupa was higher in diapausing generation (53 days) than first crop (35 days).