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Thyroxine-induced haemolymph protein and ecdysteroid increases in the silkworm, Bombyx mori: effect on larval growth and silk production

Thyroxine-induced haemolymph protein and ecdysteroid increases in the silkworm, Bombyx mori: effect on larval growth and silk production

Journal of insect physiology7(2): 153-159

The effect of feeding mulberry leaves treated with thyroid powder on larval growth and cocoon formation was analysed following treatment ofdifferent larval instars. Larvae treated during the second instar only, showed maximal growthalong with other enhanced cocoon characters. This suggests that thyroxine could be usedeffectively for commercial silkworm rearing by treatment at an early stage of silkwormdevelopment. The larval period was shortened by 30-40 h with increased cocoon and shell (silk)weight in all treated groups, reaching 150% in some cases with no loss in silk quality. Anincrease in haemolymph ecdysteroid level was observed during the fourth instar,suggesting that thyroxine in some way affects ecdysteroid metabolism. As compared to controls, wherehaemolymph ecdysteroid levels reached 1.4 ng/microliter during the fourth instar,ecdysteroid levels showed an almost 2-fold increase during the fourth instar when animals were treated with thyroxine from the first through the fifth instar (2.3 ng/microliter) or when treated inthe fourth instar only (2.8 ng/microliter), and a 3.5-fold increase (4.8 ng/microliter) for treatment in thesecond instar only. A peak of haemolymph ecdysteroid was observed on day 10 of the fifth instar for alltreated groups, but not until day 11 for the control group. Thyroxine treatment from the firstthrough the fifth instar caused a 2-fold increase in haemolymph protein level during the first(15.07 microgram/microliter) and second (10.99 microgram/microliter) instars, as compared to controls(7.73 and 5.48 microgram/microliter, respectively). Thyroxine treatment of second or fourth instars alone resulted in a 2-foldincrease in haemolymph protein levels to 12.83 and 13.49 microgram/microliter, respectively,during the fourth instar, when compared to that of the control group (6.20 microgram/microliter). This suggeststhat thyroxine, in addition to affecting ecdysteroid metabolism, also affects protein metabolism.

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Accession: 013213359

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DOI: 10.1016/0022-1910(91)90101-5

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