Ecological characteristics of the eucalypt-defoliating chrysomelid Paropsis atomaria Ol.

Abstract

This paper reports part of a study of the llfe system of Paropsis atomaria Ol., and deals with the intrinsic properties of the species, e.g. its behaviour, host preferences, reproductive capacity, rate of growth, diapause phenomena, and distribution. The studies reported were made in plantations of eucalypts in the Australian Capital Territory where two generations of the insect are completed annually. Adults which emerge in autumn were found to enter a form of reproductive diapause in response to shortening day-length, and to hibernate in the litter and soil beneath their host trees. In spring and summer, eggs are laid in batches on young shoots, their distribution conforming to that of a negative binomial. The larvae are highly gregarious in all four instars. Their rate of growth and their final weight are influenced, respectively, by temperature and by intrinsic qualities of the foliage upon which they feed. Pupation occurs in the soil beneath the trees. The fecundity of adult females was found to be a function of their size, this in turn being determined by the level of larval nutrition. The average female can mature more than 600 eggs. Although the adults appear competent to fly for considerable distances, the females tend to oviposit on the first suitable tree they encounter following emergence from the soil or litter.