Studies on the Intraspecific Competition in Dung-Breeding Flies III. Pupal Size and Mortality in Immature Stages under Various Larval Density Conditions in Musca hervei VILLENEUVE (Diptera : Muscidae)

Musca hervei VILL. was reared at thirty-one density levels from 1 to 301 of newly hatched larvae per 50 g cow dung at intervals of 10 larvae. As the density increased, reduction in size of subsequent pupae appeared firstly (at ca. 31 larvae/15 g dung) and progressively reduced up to the level of ca. 191 larvae at which the mean pupal volume was 72.3% less than that at low densities, and the same rate of reductino was seen in both sexes. When the density increaed beyond that level, the reduction could hardly be seen to progress any more, and was replaced by increasing mortalities in both larval and pupal stages. The intensity of the overcrowding affected the sex ratio of the adults emerged, that is, as the larval density became higher than 201 larvae/50 g dung, so much the sex ratio favoured females. From these facts the breeding of this species in a dung pat outdoors was discussed.