Effect of glucocorticiod on the growth and development of silkworm Bombyx mori (L).
Hormones can basically influence insect growth, development, metamorphosis, fecundity, and fertility. The exogenous application of ecdysone or their allied forms generally upsets the hormonal titre in the body and results in moulting disorder (Giesultwiz et al., 1980), disrupts normal growth and development (Singh and Russel, 1980) and causes inhibitory effects on reproduction (Thompson et al., 1971; Jalaja et al., 1976; Khan et al., 1990). The invertebrate hormone with particular reference to juvenile hormone and its analogs have been shown to exert profound influence on the growth and development of silkworms. The information pertaining to the effect of vertebrate hormones on invertebrates in general and silkworm in particular is very scanty. A few investigators have made an attempt to investigate into the useful effects of various vertebrate hormones on the silkworm commercial characteristics (Thyagaraja et al., 1985; Bharathi et al., 1987; Karthikeyan et al., 1991). Recent years, the presence and activity of various vertebrate steroid hormones have been demonstrated in life system of many insects (Bhaskar et al., 1983; Bharathi et al., 1984; Shashindran Nair et al., 2002; Miranda et al., 2002). Since the initial study of Mordue, (1967) reported the effect of mammalian corticosteroids on insect growth, development and enhanced production has been extensively studied later by several other investigators (Smith et al., 1968; Rosinski et al., 1978; Gawienoski et al., 1987).
2. MATERIAL AND METHODS
The present work was carried out on "Swarnandhra" silkworm variety of Bombyx mori (L) belongs to the hybrid of APM1 X APS1 (Multivoltine x bivoltine) obtained from National Silkworm Seed Production Centre, NSSP, Central Silk Board, Ministry of Textiles, Govt. of India, Kadiri, Anantapur (Dist.) of A.P., India. Commercially available synthetic glucocorticoid, dexamethasone each tablet of 100 ?g was dissolved in 5ml of distilled water. The silkworms were divided into two groups, first group referred as control fed with normal mulberry leaf and the latter was treated as experimental and fed with dexamethasone sprayed mulberry leaves. Total animal weight, individual organ weights were estimated by gravemetrically by using electronic balance (Sartorios, West Germany).
The tissue somatic indices of these tissues were calculated by using the following formula
TSI = Weight of the tissue (g)/ Weight of the whole larva (g) x 100 = %
The larval weight was significantly elevated in 1st, 2nd and 3rd day of III instar experimental larvae over control. The rate of increase was more in 1st day and minimum in 2nd day with an intermediate change in 3rd day of experimental larvae over control. The larval weight was also increased in all the days of IV instar except 4th day, where there was no significant change in experimental larvae when compared to control. The maximum increase was observed in second day of 4th instar followed by 3rd and 1st day. Significant elevated pattern was observed in the weight changes of V instar experimental larvae in all the days when compared to control. The weight of the larvae was increased in both during before and after moulting stages of III instar when compared to the control. The rate of increase was maximum in after moulting than before moulting stage of experimental larvae over control. The larval weight of IV instar of experimental showed no significant change in before moult, however the after moult stages exhibited significant increase in the weight of the larvae when compared to the control. The maximum reduction in the duration of the instar period was observed in IV instar followed by III and V instars. The whole larval weight was significantly increased in the Dexamethasone treated larvae when compared to the control. The weight of the silkgland was significantly increased in the hormone treated experimental larvae over control. The weight of the bodywall was also significantly increased in the experimental larvae than control. Similarly the weight of the intestine was also significantly increased in the experimental larvae when compared to the control. The TSI was also higher in both silkgland and intestine with no significant change in bodywall.
The investigation was aimed to understand the anabolic effects of the hormone on the morphological, physiological and metabolic changes of the silkworm larvae during different instars. The weight changes were found to be increased proportionately during the hormone treatment from III instar to V instar larvae. The increment in the larval weight after dexamethasone treatment was probably due to a direct physiological effect, which is reflected by increased consumption of the mulberry leaf, seems to be the major factor for the observed weight gain. In addition, the weight gain observed on treatment with dexamethasone might be due to several other reasons. The common application for the weight gain on treatment with dexamethasone can be suggested that the developmental activities of the larvae always influenced by anabolic activities of the metabolism. The results are inconsonant with the earlier reports where the larval weight was shown to be gradually elevated in all instars during different instar periods of the development (Dhinakar et al., 1990). The weight of the larvae, both before and after moulting during III instar period were markedly elevated on treatment with dexamethasone suggesting the activated process of the growth of the larvae. The duration of the III, IV and V instar periods of silkworm larvae were significantly reduced on treatment with dexamethasone hormone, suggesting the hormone might be activating the anabolic process of the metabolism leading to advancement in the completion of each instar period. This observation indicates the possible increase of the organic constituents of the body on treatment with the hormone. The increased organic constituents of the silkworm, Bombyx mori was also observed by earlier investigators on administration of vertebrate pituitary extract (Bharathi et al., 1986). In consistency to the present study increased body weight of V instar larvae was also observed in silkworm on treatment with gonodotropins (Bharathi et al., 1986; Pushparani and Bharathi, 1998) prolactin (Bhaskar et al., 1983; Bharathi et al., 1984), thyroxin (Thyagaraja et al., 1984; Kartekeyan et al., 1991) and other hormetic influence (Shashindran Nair et al., 2002; Miranda et al., 2002). The weight of the larval individual organs and their TSI were markedly higher on treatment with dexamethasone, suggesting the activated process of the growth and development of the larvae along with metabolisms. This can be explained on the basis of the accelerated growth processes, may be due to elevated circulation of growth promoting juvenile hormone in addition to the dexamethasone hormone treatment.
Finally, it may be concluded that the dexamethasone hormone treatment showed profound influence by elevating growth and development of silkworm larvae and a significant reduction in larval instar period.
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K. Ramesh Babu and M. Bhaskar
Department of Zoology, S.V.University, Tirupati-517 502, A.P., India.
Table--1: Showing the changes of larval weight of III, IV and V instars of control and experimental larvae. Values are the mean of eight individual observations. Mean, [+ or -] SD., + or - indicates the percent increase and decrease over control respectively. "P" denotes the level of statistical significance. N.S. indicates no significant change. S. Name of Day of No. the instar the Weight of the Larvae instar Control Experimental % Change 1 III instar 1 0.038 0.051 +34.21 [+ or -] [+ or -] P<0.001 0.004 0.002 2 0.082 0.094 +14.63 [+ or -] [+ or -] P<0.001 0.006 0.003 3 0.118 0.146 +23.72 [+ or -] [+ or -] P<0.001 0.008 0.011 2 IV instar 1 0.176 0.229 +30.11 [+ or -] [+ or -] P<0.001 0.012 0.017 2 0.336 0.486 +44.64 [+ or -] [+ or -] P<0.001 0.012 0.016 3 0.547 0.718 31.26 [+ or -] [+ or -] P<0.001 0.031 0.035 4 0.672 0.698 3.86 [+ or -] [+ or -] NS 0.038 0.041 3 V instar 1 0.98 1.04 6.12 [+ or -] [+ or -] NS 0.063 0.081 2 1.75 1.96 +12.00 [+ or -] [+ or -] P<0.001 0.090 0.098 3 2.40 2.72 +13.33 [+ or -] [+ or -] P<0.001 0.158 0.169 4 3.00 3.45 +15.00 [+ or -] [+ or -] P<0.001 0.182 0.212 5 3.32 3.73 12.34 [+ or -] [+ or -] P<0.001 0.217 0.228 Table--2: Showing the changes of larval weights in before and after moulting of III and IV instar larvae of control and experimental. Values are the mean of eight individual observations. Mean, [+ or -] SD., + or - indicates the percent increase and decrease over control respectively. "P" denotes the level of statistical significance. N.S. indicates no significant change. Name of S.No. the moult Moulting stage Weight of the larva (g) % Change Control Experimental 1 III Before Moulting 0.118 0.146 +23.72 [+ or -] [+ or -] P<0.001 0.008 0.011 After Moulting 0.097 0.139 +43.29 [+ or -] [+ or -] P<0.001 0.005 0.009 2 IV Before Moulting 0.672 0.698 +3.86 [+ or -] [+ or -] NS 0.038 0.041 After Moulting 0.558 0.686 +22.93 [+ or -] [+ or -] P<0.001 0.028 0.042 Table--3: Showing the duration of the III, IV and V instars of control and experimental larvae. Values are the mean of eight individual observations. Mean, [+ or -] SD., + or - indicates the percent increase and decrease over control respectively. "P" denotes the level of statistical significance. Name of the S.No. instar Duration of instar % Change Control Experimental 1 III 3.00 2.76 -8.00 [+ or -] [+ or -] P<0.001 0.216 0.206 2 IV 4.00 3.66 -8.50 [+ or -] [+ or -] P<0.001 0.281 0.240 3 V 6.33 5.84 -7.74 [+ or -] [+ or -] P<0.001 0.533 0.441 Table--4 : Showing the changes in whole larval weight, tissue weight and tissue somatic index (TSI) in various tissues like Silkgland, Bodywall and Intestine of control and experimental larvae. Values are the mean of eight individual observations. Mean, [+ or -] SD., + or - indicates the percent increase and decrease over control respectively. "P" denotes the level of statistical significance. N.S. indicates no significant change. Name of the Name of the % S.No. tissue parameter Control Experimental Change 1 Whole larval 3.32 3.73 +12.34 weight (g) [+ or -] [+ or -] P<0.001 0.217 0.228 2 Silkgland Tissue weight 0.282 0.358 +26.95 (g) [+ or -] [+ or -] P<0.001 0.011 0.023 Tissue somatic 8.49 9.95 +17.19 index [+ or -] [+ or -] P<0.001 0.352 0.486 3 Bodywall Tissue weight 0.402 0.472 +17.41 (g) [+ or -] [+ or -] P<0.001 0.028 0.031 Tissue somatic 12.1 12.64 +4.46 index [+ or -] [+ or -] NS 1.08 1.15 4 Intestine Tissue weight 0.056 0.071 +26.78 (g) [+ or -] [+ or -] P<0.001 0.005 0.006 Tissue somatic 1.68 1.97 +17.26 index [+ or -] [+ or -] P<0.001 0.10 0.15
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|Author:||Ramesh Babu, K.; Bhaskar, M.|
|Publication:||Bulletin of Pure & Applied Sciences-Zoology|
|Date:||Jan 1, 2006|
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