1Silkworm Physiology Laboratory, Central Tasar Research and Training Institute, P.O. Piska-Nagri, Ranchi, India.
2Division of Entomology, Indian Agricultural Research Institute, New Delhi, India.
Growth and related endocrine events in ultimate instars of tropical tasar silkworm, Antheraea mylitta Drury are different in non-diapausing (NDD) and diapausing (DD) generations when larvae were reared under 13h 43 m to 13 h 12 m of day light regimen in decreasing (natural) trend, 20 to 38°C of temperature range and 48 to 85% relative humidity till the end of rearing in NDD and under 12 h 18 m to 11 h 19 m natural photoperiod regimen, 15 to 30°C temperature range and 54 to 91% relative humidity in DD. The growth of tasar silkworm is much faster in NDD than DD generation. RGR on dry weight basis was higher in NDD than DD. NDD ultimate instar show gut purge after attaining a weight of 22 g on day 5 thereafter larvae having lower weight of 17–19 g also gut purge in a synchronised manner, whereas, in DD fifth instars population attaining a weight of 19 g and above on day 7 gut purge in a distributed manner starting from day 9 to day 17. The after effects of PTTH release in NDD generation were prominent during afternoon and in late scotophase periods; later these effects are always visible. In NDD stimulatory effects of PTTH on pupal transformation is generally observed after 24 hours whereas it takes more than 42 hours in DD generation. The second release of brain hormone or PTTH takes place on or after day 13 in NDD and on or after day 22 in DD generation. In the phagoperiod of NDD ultimate instar, sub-oesophageal ganglion had numerous NSCs full of neurosecretory material though these cells were not visible in SOG of DD fifth instar. Ecdysone titre in phagoperiod of ultimate instar was higher during dusk in NDD and during dawn in DD generations. The endocrine events and related behavioural responses are preceded by a larger or smaller peak of ecdysone titre in the haemolymph. The requirements of ecdysone are similar for pupal cuticle formation in both NDD and DD generations. This basic information may form the basis for manipulation of voltinism in this commercially important insect.
Antheraea mylitta, Ultimate instar, Development, Ecdysone titre, Dusk and dawn
