• V K K Prabhu

      Articles written in Proceedings – Animal Sciences

    • Hormones in insect behaviour

      V K K Prabhu

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      Hormones play an important role in insect behaviour. These hormones are mainly the neurohormones of the brain and of the corpus cardiacum, the juvenile hormone of the corpus allatum and the ecdysone of the prothoracic glands. These produce either releaser effects or modifier effects. Hormonal modulation of neurophysiological activity controlling various aspects of behaviour, hormonal influence of reproductive behaviour in the male and the female insects, their role in migration, as well as hormonal influence of caste determination and behaviour of social insects, have been discussed.

    • Development, endocrine organs and moulting in the embryos ofDysdercus cingulatus Fabr (Heteroptera: Pyrrhocoridae)

      Mariamma Jacob V K K Prabhu

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      Embryonic development ofDysdercus cingulatus is briefly described. In the embryos, neurosecretory cells become evident in the median, lateral and ventral aspects of protocerebrum 84 hr after egg laying. The corpora cardiaca, the corpora allata and the prothoracic glands arise more or less simultaneously at 78 hr from the dorsolateral wall of the stomodaeum, from the mandibular segments and from the labial segments respectively. Secretory material appears in the brain neurosecretory cells and in the intrinsic cells of the corpus cardiacum at 84 hr and in the nervi corpori cardiaci and aorta at 90 hr. The cells of the prothoracic glands show signs of secretory activity at 90 hr, reaching maximum activity around 96 hr. The corpus allatum appears to be inactive in the embryo. Two embryonic moults appear between 96 hr and 110 hr. Consequence of events suggests that the neurosecretory material stimulates the prothoracic glands including embryonic moulting.

    • Significance of critical developmental stage on starvation induced endocrine mediated precocious metamorphosis inOryctes rhinoceros (Coleoptera: Scarabaeidae)

      A Mini V K K Prabhu

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      Final (3rd) instar larvae of the coconut rhinoceros beetleOryctes rhinoceros were found to undergo precocious metamorphosis when subjected to starvation; the beetles produced as a result were subnormal in size. However, the larva showed this kind of response to starvation only after attaining a certain critical stage of development; otherwise they died after surviving for a varying period, depending on their age. Topical application of the juvenile hormone analogue ‘Kinoprene’ (ZR 777) in sufficient doses at definite periods caused significant delay in the onset of precocious metamorphosis thus suggesting an endocrine involvement. Evidently, starvation might have caused a decrease in JH-titre which in its turn, triggered a chain of events leading to precocious metamorphosis.

    • Nutrient modulation of hormone production: Dietary essential fatty acids, tissue prostaglandins and their probable role in insect reproduction

      V K K Prabhu Mariamma Jacob

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      The essential polyunsaturated fatty acids required by insects in their food appear to be needed for prostaglandinogenesis. Prostaglandins themselves are likely to be widely distributed in insects playing perhaps an hitherto unsuspected important role as in reproduction.

    • Effect of two juvenile hormone analogues on embryonic morphogenesis, histogenesis, endocrines and cuticulogenesis ofDysdercus cingulatus Fabr. (Heteroptera: Pyrrhocoridae)

      Mariamma Jacob V K K Prabhu

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      The effect of topical application of juvenile hormone analogues farnesyl methyl ether and kinoprene (ZR 777) at different doses to eggs immediately after laying, germ band formation and blastokinesis, produced different types of abnormal embryos with varying degrees of derangement of development, most of them ultimately resulting in failure to hatch. Some of the embryos were almost normal but failed to hatch even though they continued to develop inside the chorion and died two days later. On the whole, there was correlation between dose of the analogue applied and mortality rate. Kinoprene was much more effective than farnesyl methyl ether. With given dose, per cent embryonic mortality was more or less the same whether the analogues were applied just after oviposition or germ band formation, but was lesser when applied immediately after blastokinesis. The period just after germ band formation appeared to be most sensitive. Treatments affected the endocrine system. The neurosecretory index was higher in the treated embryos. Prothoracic glands and their nuclei showed considerable enlargement in treated embryos continuing development inside chorion even after their controls hatched. The corpus allatum was smaller in treated embryos and corpora cardiaca were filled with neurosecretory material. Cuticle development was abnormal after treatment.

    • Digestive enzyme secretion during metamorphosis inOryctes rhinoceros (Coleoptera: Scarabaeidae)

      S Sreekumar V K K Prabhu

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      Protease, amylase, lipase and trehalase are present in the larval and adult midguts ofOryctes rhinoceros; cellulase is absent. Invertase is present only in the adult. The presence of trehalase in the pupal midgut suggests that food digestion is not the normal function of gut trehalase. Quantitative studies reveal that protease and amylase in the third instar larvae reach very low levels as the larvae become older and consume little or no food. These two enzymes are not measurable in the non-feeding prepupa and pupa and reappear in the adult with commencement of feeding. Secretion of digestive enzymes is correlated with feeding.

    • Probable endocrine role of midgut tissue in stimulation of digestive enzyme secretion inOryctes rhinoceros (Coleoptera: Scarabaeidae)

      S Sreekumar V K K Prabhu

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      The effect of midgut epithelial extract on digestive enzyme secretion in the third instar larva ofOryctes rhinoceros was studied. Midguts dissected out from third instar larvae were cut at both ends, emptied of their contents, washed in insect saline, ligated at the open ends and incubated in a medium containing extract of 2 midgut epithelia/10 ml incubation solution. In control experiments midgut preparations were incubated in insect saline without midgut epithelial extract. After 30 min of incubation, the contents of the midgut preparations incubated with midgut epithelial extract showed increased secretion of protease and amylase when compared with controls. Digestive enzyme release into gut lumen appears to be due to the action of a hormone present in the midgut epithelium.

    • Stridulation in the coconut rhinoceros beetleOryctes rhinoceros (Coleoptera: Scarabaeidae)

      A Mini V K K Prabhu

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      The coconut rhinoceros beetleOryctes rhinoceros produces different kinds of stridulatory sound under different conditions. Intense stridulations are made quite frequently by the male during courtship and mating attempts. Males also produce characteristic stridulations during aggressive encounters with other beetles, and distress stridulations, when disturbed manually. Females also stridulate, though less frequently. Sexually immature females produce feeble repellence stridulations while courted by males. Gravid females, when confined with males, are found to mimic the courtship and mating behaviour of the males, meanwhile producing intense stridulations resembling male courtship and mating stridulation. This behaviour, presumably has an ovipository motive and, to our knowledge, is the first instance of ‘’pseudomale’ activity to be reported in insects.

      Stridulatory mechanism comprises rubbing of a specialised region along the margin of the apex of the elytron —the pars stridens, against a series of striations —the plectrum, occupying the dorsum of the 7th abdominal tergite. Stridulation is possible with a single pars stridens, either of the left or right elytron, both being identical. No sexually dimorphic difference is apparent in the pars stridens. Plectral structure exhibits sexual dimorphism, being much prominent in the male.

      Wing-locking is necessary to keep the elytra in the stridulatory position. Locking is effected by a longitudinal flange along the median side of one elytron (either the left or right, irrespective of the sex) fitting into a corresponding depression along the other. This differs from the reported cases in other coleopterans in which the flange of the left elytron extends under the right when locked.

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