Christmas beetles are with us again, and it's a big year for this scourge of eucalypt trees.

Clearing for farming and pasture planting has been a huge boon to these beetles with their characteristic metallic shine. As larvae, they spend one or two years underground feeding on the roots of grasses before emerging as adults to feed on leaves of eucalypt trees.

Christmas beetles are responsible for much of the dieback of eucalypts which has occurred along the tablelands of southeastern Australia. They can defoliate whole trees in days.

Trees on farms, open woodland or on the edges of forest are most vulnerable to Christmas beetle attack. Early growth of blue gum and flooded gum have also been affected in plantations established on former pasture sites in coastal New South Wales.

Dr Rob Floyd from CSIRO Entomology said today that the reason there were a lot of Christmas beetles around this year was because of winter rains which softened the soil and enhanced larval survival. "On some trees there are so many they look like cherries on a cherry tree" he said.

"Improved pastures provide an ideal breeding ground for beetle larvae" said Dr Floyd. "The few remaining trees in pasture areas can be totally defoliated within a week. For instance, a 1000 hectare farm with 10 per cent tree cover could produce 450 million Christmas beetles from its pastures. These would have the potential to consume the foliage of four or five times the number of trees on the farm.

"By removing the understorey and density of the woodland we have probably reduced the number of natural enemies of the beetle" said Dr Floyd. "Control is therefore difficult without restoring the original woodland. Chemical pesticides are not cost-effective, except in a limited way on plantations.

"Eucalypt trees, however, have evolved certain characteristics such as terpenoid oils, tannins and phenols in their leaves, partly as a defence against insect feeding" said Dr Floyd.

"Research here at CSIRO Entomology, supported in part by Rural Industries Research and Development Corporation, has found that susceptibility to Christmas beetles varies not only between eucalyptus species and provenances (populations of a species from different regions) but also in individual trees where a single branch can be resistant to attack. These differences are often due to the level of cineole - one of the terpenoid oils - in the leaves.

"Other resistance strategies include a strong capacity to recover after insect attack" said Dr Floyd.

Subsequent research at CSIRO Entomology has focussed on natural resistance and the possibility of selecting resistant varieties of eucalypts to grow on farms in beetle-prone areas.

Dr Floyd said, however, that cost-effective and ecologically sustainable insect control will only be achieved through an integrated approach to pest management.

"We need a range of strategies including planting resistant trees, encouraging regeneration of woodlands, better plantation design and management, biological control, and strategic spraying of biological as well as chemical pesticides" he said.

Biological pesticides are sprays containing fungal or other pathogens (such as nematodes) of the pest species. "They have a great advantage over chemical sprays in that they only affect a narrow range of species and do not leave chemical residues in the environment" said Dr Floyd.

"Selection of trees for cineole content offers good prospects for reducing Christmas beetle attack on eucalypts grown on the tablelands," said Dr Floyd "but the outlook is less promising for growers of flooded gum in coastal regions. Leaves of flooded gum have a very, very low content of oil of any kind, let alone cineole" he said.

Work on insect damage to tree plantations was given a boost this year with the establishment of the Cooperative Research Centre (CRC) for Sustainable Production Forestry in which CSIRO Entomology is a partner.

"Christmas beetles are not the only pests which damage trees," said Dr Floyd. "Autumn gum moths, other beetles, sawfly larvae, stick insects, psyllids, and a range of native vertebrates also cause extensive damage. Further research is therefore vital."

Further information: Dr Rob Floyd 0418 476 527
Jenny Goldie 02-6246-4194