The Effect of Crowding Upon the Oviposition of Grain-Infesting Insects

The crowding of adults invariably had a depressing effect upon the rate of oviposition in the insects studied here, while egg-fertility was not affected. In unconditioned media, at densities possible in actual populations, the reduction of fecundity was, it appears, entirely a result of competition for the oviposition sites usually for two purposes, viz. oviposition and feeding. That is to say, at such densities the effect of crowding upon oviposition was of a behaviouristic nature. When two species were living in the same environment their mutual effect upon each other's fecundity was more or less dependent upon the degree of identity of the niches for which they were competing. The reduction of fecundity of Rhizopertha by homotypically and heterotypically conditioned media was at first roughly proportional to the degree of conditioning, but after a time the effect of all media was the same. Homo- and hetero-typical conditioning were not radically different in effect. It is believed that conditioned medium operates upon fecundity through ‘poisoning’, and that the effect is upon oviposition rather than, as that of starvation, upon egg-production. When returned to an optimum environment the insects recovered from all the experimental conditions mentioned here: immediately from conditions of overcrowding, more slowly from conditioned media, and more slowly still from complete starvation.