Changes in eucalypt architecture and the foraging behaviour and development ofAmorbus obscuricornis(Hemiptera: Coreidae)

Abstract

AbstractField surveys, manipulative field experiments and laboratory studies were employed to study the behaviour and development of a large coreid,Amorbus obscuricornis(Westwood), in response to changes in the architecture/foliar quality ofEucalyptus(Myrtaceae) hosts in Tasmania, Australia. Following tree decapitation and subsequent regrowth,A. obscuricornisnymphs were only associated with coppiced hosts. Eucalypts coppiced naturally by wild fire were found to carry significantly more nymphs than non-coppiced conspecific hosts. In contrast, adultA. obscuricorniswere found on both coppiced and non-coppiced hosts. The foliar quality of coppiced hosts was superior to that of non-coppiced hosts; being softer, having a higher moisture content and a lower C/N ratio. Field collected fifth instar nymphs were heavier when collected from coppice vs. noncoppice; but in bagged shoot experiments second instar nymphs gained less weight on coppice than non-coppice. It is suggested that because coppice is softer the shoots may deteriorate (i.e. wilt) more quickly than non-coppice shoots. Through different exposure regimes, it was confirmed that first instar nymphs need only water to ecdyse, while feeding is initiated in the second instar. Differences in the nutritional requirements of first and second instar nymphs were reflected in their behaviour. First instar nymphs did not discriminate between conspecific hosts on the basis of whether they were coppiced or not, whereas second instar nymphs preferentially chose coppiced conspecific hosts. The findings of this work are discussed in the context of the plant vigour and resource regulation hypotheses.