Biology of the Fireblight beetle, Acacicola orphana (Erichson) (Coleoptera: Chrysomelidae), a defoliator of Acacia dealbata (Link.)
Creators: name: Simmul, TL
Publisher: name: University Of Tasmania
Year: 2023

description: Acacicola orphana (Erichson) is a winter developing insect that severely defoliates its host trees, Acacia dealbata (Link.) and A. mearnsii (De Wild.). Both adults and larvae feed on green bark and foliage, resulting in damage which may lead to tree death. This study investigates the biology and ecology of A. orphana, focussing on its developmental biology, distribution and host-plant relationships. At the commencement of this project a basic guide to the different stages of A. orphana was established. Developmental biology was examined in the laboratory, where development from eggs to adults was found to require 1266 DD &gt; 4.4 ¬¨‚àûC. Field development studies suggested a lower threshold. Consequently, inaccuracies were observed when laboratory information was used to predict the timing of stages in the field. Management strategies therefore need to be based on field estimates. Natural enemies of A. orphana identified were; a tachinid, Lixophaga sp., a braconid hyperparasitoid, Meteorus sp. and a fungal pathogen, Beauveria bassiana. Fourth instar mortality attributable to the tachinid was up to 17%. Beauvaria bassiana was recovered from adults only and caused up to 12% mortality. Geographical distribution of A. orphana was mapped throughout southeastem Australia. This information was then used to predict the distribution throughout Australia and globally using CLIMEX, a climate modelling package. Global mapping predicted populations could survive in African and Asian countries where some Acacia species (in particular A. mearnsii) are economically important. On the Australian mainland, A. orphana was observed predominantly on A. mearnsii, rather than on A. dealbata, which was its main host in Tasmania. Thus, experiments examining oviposition, larval development and survival between A. dealbata and A. mearnsii were undertaken. Whilst both species experienced similar levels of defoliation in the field, larval development was 25% faster on A. mearnsii. Acacia orphana and its interactions with Acacia dealbata were the main focus of this study. Consumption studies showed final instar A. orphana consumed `0.93 g^-1g^-1day^-1` and the efficiency of conversion was 40%. Initial hypotheses relating to bark feeding behaviour were disproved, with findings that green bark feeding does not occur due to a lack of foliage, nor does it enhance the foliage quality for the next generation of larvae. Further investigations of host-plant interactions involved assessing first instar larval survival and defoliation on four different A. dealbata provenances. General differences in nutrition, colour and fluctuating asymmetry of the trees were also assessed. One provenance experienced significantly less defoliation. Phenotypic differences showed that low foliar nitrogen, low moisture and redder-coloured foliage were related to increased defoliation and larval survival. It was hypothesised that climate and environmental conditions primarily regulate the host-plant interactions of A. orphana.