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Effect of heat unit summation on the life period of four lac insect spp.

P.K. Chakrabartya, B.K. Guptaa & Y.D. Mishrab*
aUniversity Department of Zoology, Vinoba Bhave University, Hazaribag 825301
bIndian Institute of Natural Resins and Gums, Ranchi, Jharkhand, India
Received 8th July, 2010; Revised 21st August, 2010

Abstract : The lac insect species of the Genus Kerria are temperature sensitive as almost all post embryonic stages are enhanced with increase in temperature and slow down with diminishing temperature. Due to which the life period has got a good drift from the mean depending upon the temperature faced and some of the species are more affected than others. In case of Kerria lacca, lac entomologists like Negi (1928) and Glover et al. (1932) had reported influence of temperature on different activities of life cycle. Effect of temperature in form of Heat Unit Summation on growth behavior has been demonstrated successfully in different plant species. However, efficacy of the parameter, ‘Heat Unit Summation’ as an indicator of temperature-response has not yet been demonstrated in any insect species. The present study aimed at testing the efficacy of this parameter as an indicator of temperature-response in different species of lac insect viz. K. lacca (Kerr), K. nagoliensis (Mah.), K. chinensis (Mah.) and K. sharda (Mishra & Sushil). It was found that, in case of K. sharda and K. nagoliensis, consistent values of Heat Unit Summation were recorded even under different life periods having different dates of initiation of life cycle. This indicated marked influence of temperature on the duration of life cycle of K. sharda and K. nagoliensis. In case of K. sharda several overlapping generations were observed which can be attributed to thermo sensitivity of the species. However, similar trend could not be recorded in case of other species like K. chinensis and K. lacca. This indicates non significant role of temperature on duration of total life period of these two species.


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