The effects of crowding on the survival, rate of development, size, colour and fecundity ofDysdercus fasciatusSign. (Hem., Pyrrhocoridae) in the laboratory

Abstract

Experiments were conducted to ascertain whether the rearing density ofDysdercus fasciatusSign. affected its rate of development, colour, size, reproduction and general activity. The length of the nymphal and adult life decreased when more than 12 insects were reared per 200-cc. cage. Isolated virgin females and females that eopulated once lived longer than females each kept constantly with one male. Nymphal crowding in adults that were smaller than those reared in isolation and in an excess of males. Nympha derived from crowded parents became red at an earlier age than the progeny of one male and one female per cage. Crowding reduced feeundity when the density of nymphs or adults, either male or female, was increased.The pre-oviposition period and the time interval between successive egg-batches were greater for virgin than for mated females. Infertile eggs were the longest; females allowed to copulate once laid eggs intermediate in size between infertile ones and those laid by females each kept with a male. The number of eggs laid by females isolated throughout life with one male was found to be higher than the number laid by those that were crowded either in the nymphal stages or were crowded with males in the adult stage. When Dysdercu8 was crowded with one or two locusts the number of eggs laid and the number of egg-batches were considerably reduced; amputation or painting the antennae, which caused the Dysdercus to be less active, also reduced egg production but disturbance by mechanical shaking of the container had little effect. These findings are discussed in relation to the ' phases ' of locusts and other insects, and it is concluded that the effects of crowding on D. fasciatus do not completely parallel phase differences in locusts.