• A Mini

      Articles written in Proceedings – Animal Sciences

    • 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.

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

      A Mini V K K Prabhu

      More Details Abstract Fulltext PDF

      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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