Dinesh Kumara*, S. K. Sharana, P K. Mishraa, Ram Kishorea, G. Maheshwarib & N. Suryanarayanaa
aCentral Tasar Research and Training Institute, Piska-Nagri, Ranchi-835 303, India
bSchool of Entomology, St. John’s College, Agra (U.P) India
Received 9th Jan. 2007; Revised 28th Feb. 2007
Abstract : Weight distribution and brain hormone or Prothoracicotropic hormone (PTTH) release timing during fourth and fifth instar larvae of Indian tropical Tasar silkworm, Antheraea mylitta Drury ( Lepidoptera: Saturniidae) both in non-diapause-destined (NDD) and diapause-destined (DD) broods were studied to investigate the variation of frequency distribution of larval weight and also to get an idea about brain programming for initiation of larval moulting. The pattern of frequency distribution of larval weight in NDD and DD brood was found significant in each age group. Body weight of the maximum larvae in age group of day 0 to day 5 were 2.0-2.9 (56.67%), 3.0-3.9 (29.97%), 4.0-4.9 (48.68%), 6.0-6.9 (22.67%), 8.0-8.9 (27.68%) and 9.0-9.9 (30.00%) respectively in NDD generation. DD generation, it was 1.0-1.9 (63.33%), 2.0-2.9 (68.57%), 4.0-4.9 (44.00%), 6.0-6.9 (33.65%), 7.0-7.9 (39.08%), 9.0-9.9 (32.18%), 10.0-10.99(23.00%) in age group from day 0 to 6, respectively. Brain hormone (PTTH) release timing was studied through neck ligation technique. The results reveal that brain hormone release initiated on day 3 in NDD and day 4 in g and above in NDD and 7.0 g and above in DD generation showed the DD larvae. The larvae weighing 8.0 symptom of PTTH release i.e. moulting. However, the proportion of larval population with sign of PTTH release increased with increase in age of the larvae as well as its body weight. It seems that PTTH release is not drily dependent upon critical weight but also on temperature and photoperiod. The generated information will help in further investigation on diapause physiology of the insect.