CRC Forestry - CRC for Forestry

Executive summary
The total area of plantations of Eucalyptus globulus and E. nitens in southern Australia has grown
considerably over the last few decades. This has led to predictions of increasing insect pest
problems. Accordingly the following research questions were investigated:
1. Are the damage levels from insect herbivores in eucalypt plantations increasing?
2. Are the current significant insect herbivores of E. globulus/nitens plantations the same species
as in the past?
3. Have new insect herbivore species recently emerged as pests?
4. Are the insect herbivore species evenly distributed throughout the plantation estate?
5. Are insect herbivore species that have recently emerged as problems in eucalypt plantations
expanding their range?
National and regional datasets on insect herbivory were assembled from the Green Triangle, southwest
Western Australia (WA) and Tasmania. Data was collated on insect damage between 2000 and
2010 for most species, but for some species data went back as far as 1990. Over time, the survey
effort and methodology is unlikely to have been very consistent among regions and even
companies, and this compromised the quality of the data. Nevertheless, the data are still important
as they are the only historical account of patterns of insect pests in E. globulus/nitens plantations.
There was little evidence that damage caused by insect herbivores in eucalypt plantations has
increased over time. Insect herbivore records classified as causing severe damage across Australia
correlated with the area of new plantings of young trees but not with time. The lack of increase in
damage by insect herbivores over time might be due to:
� improved site surveillance and control of establishment and post-establishment pests,
resulting from a better understanding of the biology of insect species, including location and
timing of insect swarms
� improvements in silvicultural practices, such as better site selection, site preparation, weed
control and nutrient application, as well as the use of improved tree genetics
� colonisation of plantations by natural enemies residing in native vegetation
� reduced spraying of plantations with broad-spectrum insecticides, thereby conserving natural
enemies.
Some of the currently significant insect herbivores of E. globulus/nitens plantations are the same
species as in the past. Some of the species that have been recognised previously as pest species have
inflicted a lower level of damage more recently, while some new pest species have emerged.
There was strong evidence that the total number of species of insect herbivores that caused tree
damage in eucalypt plantations increased initially with the expansion of the eucalypt plantation
estate and over time, but then reached a fluctuating equilibrium.
Within regions, few insect herbivore species were found evenly throughout the plantation estate.
Each region had its own suite of species causing damage to eucalypt plantations. Some species were
restricted to certain sub-regions, possibly due to climatic constraints.
CRC for Forestry Technical Report 216: November 2011
Are insect herbivores in eucalypt plantations a worsening problem? v