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Abstract: Insect damage to production forests has the potential to reduce financial returns by retarding tree growth and causing mortality, however, long-term realised quantification of these losses is rare. In order to help elucidate economic damage thresholds for making spray decisions we capitalised on a natural outbreak of autumn gum moth, Mnesampela privata, in a 2-year-old Eucalyptus nitens plantation. Following the partial chemical control of this insect outbreak we measured the tree growth variables diameter at breast height over bark and height of five differing tree defoliation classes for 75 months following tree damage. At the end of this period a threshold model was fitted to describe the relationship between tree defoliation and realised tree wood volumes. The model revealed that realised stand wood volume was not significantly affected up until defoliation exceeded 60% and then declined sharply after this defoliation level was reached. Further support for this defoliation threshold was evident from multiple comparisons among defoliation classes that showed 50% defoliated trees did not have significantly different wood volume compared to more lightly defoliated trees, but did have significantly greater wood volume compared to trees that were 72% or more defoliated. To determine if the realised differences in wood volume resulted in differences in yield over a plantation rotation the E. nitens growth model NITGRO was used to on-grow trees to age 15 years for a ‘best case’ (type 1 growth response, constant growth rates from last inventory until harvest) and ‘worst case’ (type 2 growth response, divergent growth rates from last inventory until harvest) scenario. The threshold model was then fitted to the outcomes of both scenarios and the economic consequences of defoliation were clearly dependent on the growth function assumed. [Copyright &y& Elsevier]

Abstract The native Eucalyptus leaf beetle Chrysophtharta bimaculata (Olivier) (Coleoptera: Chrysomelidae) has become a pest of the introduced, plantation species, Eucalyptus nitens Maiden in Tasmania, Australia. However, in the field it prefers to oviposit on the Tasmanian native species, E. regnans F. Muell. This laboratory study found that the performance of C. bimaculata larvae was superior on foliage of E. nitens compared with E. regnans . Larval development was 4 days shorter on E. nitens than on E. regnans foliage. Total food consumption per larva and relative consumption rates were about 30% lower while relative growth rates and weight of emergent adults were more than 25% higher on E. nitens than E. regnans . Efficiency of conversion (ECI) of fresh food into larval wet weight was 0.26 on E. nitens compared with 0.14 on E. regnans . Mortality of larvae feeding on E. nitens (23%) was only one third of that on E. regnans (69%), a result of high first instar mortality on E. regnans . Although the amount of foliage consumed per larva was lower on E. nitens (0.23 g vs 0.32 g), the differential mortality meant that the amount of E. nitens consumed per egg batch was 60% more than that of E. regnans . If these results occurred in the field, then the same monitored population of C. bimaculata eggs may result in heavier defoliation of plantation E. nitens than of E. regnans . These data show that the reported oviposition preference of C. bimaculata for E. regnans in the field cannot be explained by selection of host factors related to superior larval performance. [ABSTRACT FROM AUTHOR]

The genus Mycosphaerella Johanson contains many pathogens capable of causing a severe impact on the growth of susceptible eucalypt species. The lack of knowledge about which species are present in Tasmania and their potential risk to the plantation industry prompted this study into the Mycosphaerella species occurring on Eucalyptus globulus and Eucalyptus nitens plantations in Tasmania. A total of 36 plantation and five road verge sites of E. globulus and E. nitens were sampled. Five Mycosphaerella species and three species from associated anamorph genera were isolated and identified in Tasmania; Mycosphaerella nubilosa, Mycosphaerella cryptica, Mycosphaerella tasmaniensis, Mycosphaerella grandis, Mycosphaerella vespa, Coniothyrium ovatum, Sonderhenia eucalypticola and Sonderhenia eucalyptorum. The most frequently isolated species with the highest incidence and severity of infection were M. cryptica and M. nubilosa. These two species appear to have the greatest potential to damage juvenile eucalypt plantations in Tasmania. A link between Mycosphaerella vespa and Coniothyrium ovatum is described for the first time. [ABSTRACT FROM AUTHOR]

Chrysophtharta bimaculata is a serious pest of eucalypt forests in Tasmania. The beetle overwinters as a diapausing adult, but it is poorly documented whether it forms overwintering aggregations or where it shelters. During winter 1992, we searched 386 possible overwintering sites for C. bimaculata in Eucalyptus obliqua forests. Fourteen types of habitat were identified, of which clumps of Gahnia grandis sheltered the greatest mean number of insects (3.31 ± 0.72 insects/plant, n = 65 plants), while bracken fern litter sheltered the least (0.14 ± 0.14 insects/sample, n = 7, 1 m2 quadrat samples). Of the 14 habitat types, all except two (under the bark of eucalypt stags and in G. grandis clumps) were more often unoccupied. Beetles were more commonly found on mature forest edges or in logged and regenerating forests; few were found within mature forests. Our results show that C. bimaculata rarely forms overwintering aggregations of greater than 20 individuals per site, nor does it appear to have a significant pre-diapause dispersal. [ABSTRACT FROM AUTHOR]