Movement patterns of an Australian chrysomelid beetle in a stand of two Eucalyptus host species

Summary We examined the movements of Chrysophtharta hectica, a eucalypt-feeding chrysomelid beetle in New South Wales, Australia, in relation to the beetle's sex, age and life-history, and to attributes of its Eucalyptus host plants. Beetle movements within the site were not influenced by beetle age or sex, but may be related to generation. Beetle distributions on the two host plant species, Eucalyptus stellulata and E. pauciflora, were generally clumped. Some of this clumping resulted from preference for E. stellulata over E. pauciflora. Clumping of beetles also occurred within host plant species; some plant individuals were consistently heavily used by beetles over the course of three years. We examined nutritional, spatial and biomass attributes of plants and found plant height and foliage production to be the best predictors of beetle numbers.     

Insect pests of Tasmanian blue gum,Eucalyptus globulus globulus,in south‐western Australia: History,current perspectives and future prospects

Trends in, and potential causes of, insect pest problems of the Tasmanian blue gum, Eucalyptus globulus globulus, in south‐western Australia are reviewed. Historical evidence suggests that insect pest problems of E. g. globulus in south‐western Australia have greatly increased in the last 10 years, which corresponds to a time of rapid expansion of the blue gum industry in the region. Current major establishment pests include the African black beetle, Heteronychus arator, spring beetles, Liparetrus spp. and Heteronyx spp., and the wingless grasshopper, Phaulacridium vittatum. Current major pests of established trees are the Eucalyptus weevil, Gonipterus scutellatus, and chrysomelid beetles, Chrysophtharta spp. and Cadmus excrementarius. The occurrence of these insects on an introduced eucalypt is not unexpected because insect‐rich native eucalypt forests dominate the landscape where E. g. globulus plantations are grown. Insect damage may also be exacerbated because E. g. globulus is grown as a monoculture.     

Phenology of Eucalyptus weevil, Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), and chrysomelid beetles in Eucalyptus globulus plantations in south-western Australia

1 In south‐western Australia, Eucalyptus globulus plantations are defoliated by a complex of beetle species, yet only scant information exists on these species under such climatic conditions. To improve management of these defoliating beetles in the region, canopy fogging and shoot clipping were conducted in plantations between 1999 and 2002 to identify and document the phenology of the beetle species present. 2 Eucalyptus weevil, Gonipterus scutellatus, was the most common and destructive defoliating beetle. Gonipterus scutellatus undergoes one principal generation each year with a lesser second generation or cohort in some seasons, which contrasts greatly with reports of two to four annual generations for the species in other regions. This limited reproduction by G. scutellatus may be due to the limited availability from summer onwards of new flushing foliage, which is essential for feeding and oviposition. 3 Several species of chrysomelid beetles were collected in plantations, but these were present in much lower numbers than G. scutellatus and were only a minor concern. However, some species, such as Chrysophtharta variicollis, appear to be capable of developing short‐lived outbreaks. 4 A diverse suite of natural enemies was fogged from plantations but they were significantly less abundant than defoliating beetles and are not likely to provide significant control of beetles. 5 In terms of managing these defoliating beetles, monitoring and control should focus on G. scutellatus, and be conducted during spring when most damage occurs.     

The effects of elevated CO2 atmospheres on the nutritional quality of Eucalyptus foliage and its interaction with soil nutrient and light availability

 Seedlings of Eucalyptus tereticornis (Smith) were grown under two levels of availability each of CO₂ (352 and 793 μmol mol⁻¹), soil nutrients (1/24 and 1/4 Hoagland’s solution) and light (full and 30% sunlight). Low soil nutrient availability or high light increased the C:N ratio of leaves, leading to lower leaf nitrogen concentrations, higher leaf specific weights and higher levels of both total phenolics and condensed tannins. These results were consistent with other studies of the effect of environmental resource availability on foliage composition. Similar results were observed when the C:N ratio of leaves was increased under elevated CO₂. The changes in leaf chemistry induced by the treatments affected the performance of 4th-instar larvae of Chrysophtharta flaveola (Chapuis) fed on the leaves. Increased C:N ratios of leaves reduced digestive efficiencies and pupal body sizes and increased mortality. Below a threshold nitrogen concentration of approximately 1% dry mass, severe reductions in the performance of larvae were recorded. Such changes may have significant consequences for herbivores of Eucalyptus, particularly in view of projected increases in atmospheric CO₂. Received: 8 January 1996 / Accepted: 26 June 1996     

Inundative release of coccinellid beetles into eucalypt plantations for biological control of chrysomelid leaf beetles

Abstract 1 Inundative augmentative releases of adult coccinellid beetles were assessed for their potential to effectively supplement biological control of outbreak populations of the Eucalyptus leaf beetle Chrysophtharta bimaculata in Eucalyptus nitens plantations. 2 Mixed groups of two species of overwintering coccinellids, Cleobora mellyi and Harmonia conformis, were collected from the field then fed three diets in the laboratory prior to release. Both species were released in the summer into two E. nitens plantations with economically damaging Chrysophtharta populations. 3 Differences between dispersal of coccinellids fed the three diets were slight; beetles brought straight out of overwintering before release were initially slower moving onto trees. 4 Numbers of coccinellids on trees in monitoring plots decreased exponentially with time, and populations had returned to prerelease levels 7 days after release. The number of coccinellids recaptured decreased with increasing distance from the release point with very few coccinellids per tree at 70 m distance. Dispersal of C. mellyi away from the release plot was slower than that of H. conformis. 5 Numbers of coccinellids on trees were significantly related to predation levels of C. bimaculata with a large decrease in the C. bimaculata population to below the economic damage threshold in plots where the numbers of coccinellids were high. 6 The results of this study suggest that inundative release of laboratory reared coccinellids is possible for biological control of C. bimaculata, although it may only be economically viable in small, environmentally sensitive areas.     

Predicting time to peak occurrence of insect life-stages usingregression models calibrated from stage-frequency data and ancillary stage-mortality data

1 Integrated Pest Management programmes often require predictions of peak occurrence of particular insect life‐stages to optimize the timing of population monitoring and control operations. 2 Given a known or estimated starting time for a synchronously developing pest population, predictive models estimated from stage‐frequency data alone can only predict the times of peak occurrence assuming a constant mortality rate across stages. 3 Here, continuation ratio regression models of relative stage frequencies estimated from stage‐frequency data are combined with a stage‐specific model of mortality estimated from ancillary mortality data to allow prediction of time of peak occurrence. 4 To calculate time of peak occurrence new mathematical derivations are given for continuation ratio models. 5 The models are used to predict the time of peak occurrence in degree‐day units for each of the first to third larval instars of the Tasmanian Eucalyptus leaf beetle Chrysophtharta bimaculata (Olivier) (Coleoptera: Chrysomelidae), a serious defoliator of Eucalyptus regnans and E. nitens plantations in Tasmania.