Pairs Of Beetles Research Articles

Effect of crowding on oviposition, development and mortality of Cryptolestes ferrugnieus (Stephens) (Coleoptera, Cucujidae)

Laboratory experiments on crowding of the Rusty grain beetle, Cryptolestes ferrugineus (Stephens), were performed at 30° ± 0·5°C and 70° ± 5 per cent r.h. on two culture media, whole-wheat flour and wheat kernels. Oviposition on 0·5 g flour measured over the first 20 days decreased from 6·4 eggs per female per day for 1 pair of beetles per vial to 1·5 for 64 pairs of beetles; on 0·25 g wheat the decrease was from 5·6 for 1 pair of beetles per vial to 0·74 for 64 pairs of beetles. Developmental time from egg hatching to adult emergence on 0·5 g flour increased from 24·0 days for isolated larvae to 87·1 and 86·2 days for initial crowding levels of 32 and 64 larvae per vial, and from 21·2 for isolated individuals to 37·6 days for a crowding level of 32 larvae when prepupae were removed as they formed; on 0·25 g wheat developmental time increased from 28·0 for isolated individuals to 42·3 days for a crowding level of 32 larvae. The combined mortality of larvae and pupae on 0·5 g flour increased from zero for isolated larvae to 93·0 per cent and 96·5 per cent for crowding levels of 32 and 64 larvae per vial unless prepupae were removed as formed when it was only to 37·5 per cent for a crowding level of 32 larvae per vial; on 0·25 g wheat, post-oval developmental mortality rose from 6·2 per cent for isolated larvae to 98·4 per cent at 64 larvae per vial. The deleterious effect of crowding on oviposition, development and mortality was always greater in wheat kernels than in flour. The influence of crowding on the rate of increase of a population in flour is calculated. It is concluded that changes in developmental time caused by crowding produce the greatest alteration in the rate of increase, and that changes in mortality are more important than in oviposition.

Studies in Population Physiology: The Relation of Numbers to Initial Population Growth in the Flour Beetle Tribolium Confusum Duval

Chapman ('28), working with the confused flour beetle Tribolizirn confiusumn Duval, presented evidence demonstrating that a condition of equilibrium, measured in terms of number of individuals per gram of flour, is eventually reached within each population which is approximately uniform irrespective of the environmental size or the initial population density. In table III of his paper, reproduced herewith, he has recorded data, which in addition to supporting his own conclusions, open to experimentation another phase of the problem. Allee ('3I), interested in reviewing the effects of crowding on organisms, has analyzed this data. He shows that for the first periods in the development of the beetle population, namely eleven and twenty-five days, the greatest increase in numbers, in terms of eggs and early instar larvae per female day, comes at the initial population of four, while initial populations of eight or sixteen show a more rapid increase at eleven (lays than that given when only one pair was About this phenomenon, Allee remarks ('3I, P. I8o), This indicates that there is an optimum initial population-medium relationship, which, for certain volumes of medium, is different from that given by the smallest population present. Chapman's original data are presented in table I together with a recalculation to show the rate of increase per female day at all population densities tried. The work to be reported in this paper has been directed towards finding by more extensive experiments whether the initial rate of population growth is usually greater in these beetle populations when more than one pair of beetles is CONDITIONS OF EXPERIMENT