The intrinsic rate of natural increase of Cryptolestes ferrugineus (Stephens) (Coleoptera, Cucujidae)

Abstract

The intrinsic rate of natural increase, r m , of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), was calculated from data obtained in the laboratory on oviposition, developmental time, mortality and sex ratio at 70% R.H. and temperatures from 17.5 to 42.5°C at 2.5°C intervals. At 25, 30 and 35°C additional experiments were done at 40 and 90% R.H. The culture medium was wheat flour plus 5 per cent by weight of wheat germ. The highest value of r m , 1.000 per week, was obtained at 35°C, 90% R.H. and the lowest, 0.021 per week, at 20°C., 70% R.H. No increase was possible at either 17.5°C because no eggs were laid, or at 42.5°C because mortality during the larval and pupal stages was 98 per cent. The value of r m was virtually the same at 70 and 90% R.H., but was always lowest at 40% R.H. at the three temperatures used, the difference being greatest at 35°C. The value of r m at optimal conditions of temperature and humidity was higher than the values recorded for the related species, C. capensis (Waltl), C. pusilloides (Steel & Howe), C. turcicus (Grouvelle) and C. ugandae Steel & Howe. Compared with other species that infest stored products, the value for C. ferrugineus was as high as those recorded for Tribolium castaneum (Herbst) and Oryzaephilus surinamensis L., higher than that of Sitophilus oryzae L. and much higher than any values given for Ptinid beetles. The r m for C. ferrugineus was most influenced by changes in developmental time and least influenced by mortality until limiting conditions of temperature and humidity were approached.