Effect of gamma-irradiation on some biological activities of the larval stage of the khapra beetle, Trogoderma granarium Everts (Col., Dermestidae)

Abstract: The present study was carried out on the larval stage of the khapra beetle, Trogoderma granarium Everts to determine some biological effects of gamma irradiation at levels between 20 to 100 Gy on various aspects of larval behaviour such as number of moults, developmental time, larval growth, starvation and mortality, pupal promptness in addition to larval density. Larval mortality of 92.5% was obtained by treating with 80 Gy and no larva lived after an exposure of 100 Gy or more. With increasing doses from 40 Gy or more, half of the male and female larvae had six moults as compared with three to five moults in the control. The larval duration increased gradually and reached 40.2 days for male larvae and 44.2 days for female ones at a dose of 80 Gy as compared to 25.2 and 28.3 days, respectively, for the control. Larvae irradiated with 60 and 80 Gy did not feed as much as those irradiated at 20 and 40 Gy or the control group. A negative correlation was observed between increasing dosage levels and reduction in the fresh body weight of larvae. The highest larval starvation of 79.8% occurred at 80 Gy and the least (23.8%) at 20 Gy. Pupal promptness seems to be lower at the higher radiation doses. With 40, 60 and 80 Gy, approximately 69.5, 19.6 and 7.5%, respectively, of the larvae succeeded in pupation compared with 94.6% in the control. High doses of radiation seem to enhance the production of males. An increase of larval density enhances the effects of radiation doses to retard the developmental time, to increase larval and pupal mortality and to reduce adult eclosion.