The ecology of a natural population of the Queensland fruit fly, Dacus tryoni. I. The parameters of the pupal and adult populations during a single season

Abstract

The ecology of a natural population of Dacus tryoni is being studied at an orchard near Sydney, N.S.W. Changes in numbers observed during a single year are described and discussed. Estimates of pupal numbers were based on the weekly total pupal production of a random sample of the fruit trees in the orchard. Parameters of the adult population were measured by means of mark-recapture sampling and analysed by means of three mathematical models. Discrepancies between some of the estimates of numbers given by these models are explained by extensive adult emergence at those times, and the lower survival factors of the young adults. Evidence for the random sampling of adults is presented. The decline of the population towards the end of the season was brought about mainly by (1) high pupal mortality, (2) cessation of pupal production due to diminution and disappearance of larval food, (3) a marked decline in the number of gravid females, apparently in response to diminishing oviposition sites, and (4) a high rate of loss of young adults, presumably by emigration. There was no evidence of overcrowding.