Effects of hypervitaminosis of vitamin B3 on silkworm biology.

A high-dose of vitamin B(3) in silkworm diet interrupts larval feeding and normal growth. High mortality of larvae occurs during molting and they cannot complete this process normally. Also the larvae exhibit nicotinamide hypervitaminosis symptoms such as immobility, dyspepsia, darkening of the skin, inability to excrete normally, exerting brownish fluid from anus and swelling of rectal muscles. Maximum larval weights in 1, 2 and 3 g/l treatments were 2.9, 1.6 and 1.2 g respectively, while maximum larval weight in the control was 5.6 g. Larval stage compared to control had increased 18, 26 and 31 days respectively. The concentration increase of uric acid in haemolymph demonstrates the hyperuricemia, while other measured biochemical compounds show significant decrease; sodium and potassium did not change significantly.

PTTH--a potential growth activator in silkworm, Bombyx mori L. for enhancing silk production.

In silkworm, prothoracicotropic hormone (PTTH), directly or indirectly controls silk production and spinning activity along with juvenile hormone (JH). An effort was made to exploit the potential of PTTH by indirectly activating silk gland for increasing silk productivity using short chain synthetic analogues of PTTH. The analogy in action was also established using PTTH extracted from the silkmoth. Different doses of 42 synthetic PTTH analogues, viz., 2.5, 5, 10 and 20ppm and 3.3 mg/ml of PTTH extracted from silkmoth heads were administered orally to V instar silkworm larvae (Race:KAxNB4D2 and PMxNB4D2) at 0-144 hr at an interval of 24 hr. The analysed data showed an improvement of about 14 - 23% in KA x NB4D2 and about 10-14% in PMxNB4D2 in respect of cocoon shell weight on administration of some of the synthetic PTTH analogues. The PTTH extracted from the adult brain also showed similar effect. The structural analogy of synthetic PTTHs (which improved the shell weight) with original PTTH and its probable mode of action in silkworm are discussed.

RH-5992--an ecdysone agonist on model system of the silkworm Bombyx mori.

RH-5992 is a novel synthetic non-steroidal ecdysteroid agonist with a high selectivity towards Lepidopteran species. The effect of ecdysone agonist RH-5992 on larval period, larval weight, silk gland weight and haemolymph protein profile were examined in the model organism, the larvae of silkworm, Bombyx mori. The LD50 values were found to be 16.21 and 12.01 micrograms/larva for 72 and 96 hr respectively. In the present study, three sublethal concentrations of 1/5th, 1/10th and 1/20th of LD50 at 72 hr were selected and applied on the mid-dorsal line of the silkworm B. mori. The maximum mortality of 35% was observed in the group which received the highest (3.2 micrograms/larva) concentration of RH-5992. The mortality rate was found to be dose dependent as well as time dependent. Interesting results were observed in haemolymph profile of the RH-5992 treated larvae as staining intensity of 30 kDa protein decreased significantly whereas the effect was not marked on other major proteins like storage proteins and vitellogenin polypeptides. From the results, it is confirmed that RH-5992 causes changes in larval characters and protein profile of silkworm B. mori. It is proposed that RH-5992 may cause negative effect specifically on reproductive characters like development of ovary and egg production due to decrease in 30 kDa protein.