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SUMMARY(1) Insects that lay their eggs in groups can influence the success of their offspring not only by selectively laying eggs on hosts of high quality, but also by adjusting the number of eggs that they place on hosts.(2) The oviposition behaviour of females of the pyralid moth, Omphalocera munroei, leads them to vary the number of eggs placed on their food plants in the genus Asimina in such a way as to reduce the impact of within-species competition.(3) Plants with many leaves are more likely to have eggs laid on them, receive larger clutches, and receive more clutches than plants with few leaves.(4) The number of eggs placed on a plant more closely reflects the carrying capacity of the plant when natural mortality rates are taken into consideration than it does the carrying capacity in the absence of mortality.(5) The overall effect of the oviposition behaviour of 0. munroei is to reduce substantially the likelihood that the moth larvae will be forced to abandon the plant before they complete development, thus increasing their chances of survival to reproduction.