Exotic bark beetle turns nasty in pine plantations
From the Autumn 2008 edition of Bush Telegraph Magazine.
The tiny Ips bark beetle finds dry drought conditions ideal, which has resulted in an increase in tree mortality. Photos by Dr Angus Carnegie
The exotic North American bark beetle, Ips grandicollis, was accidentally introduced into Australia in the 1940s and was first found in NSW pine plantations in the early 1980s.
In NSW it is generally thought of as a secondary pest, attacking recently-felled logs and trees that have been stressed or damaged, such as by fire, wind or lightning. This tree mortality tends to be to a small number of localised trees.
Ips beetles commonly live and breed in fresh logging debris, and on rare occasions have caused damage to seedlings and young trees established within, or adjacent to, recently logged areas.
However, Ips numbers have recently increased and are now causing large scale tree mortality and have the potential to kill newly planted seedlings.
In several State forests near Tumut and Tumbarumba there has been a population explosion of Ips and it has reached outbreak proportions.
For the first time in NSW, Ips have been associated with large scale tree mortality of drought-stressed pine trees. Trees from eight to 30 years old have been killed.
What has caused this change in beetle behaviour? The prolonged dry condition has made trees susceptible to attack. Climate change may also have triggered optimum conditions for the beetle, giving milder temperatures during spring and autumn, allowing the beetles to breed for longer.
NSW DPI forest health survey unit had mapped plantations by mid-2007 using the Forests NSW Squirrel helicopter. Several thousand hectares were mapped as having some level of damage from Ips.
Remote sensing technology is currently being used to more accurately map the damaged area within Green Hills State Forest, near Tumbarumba, including satellite imagery as well as airborne digital cameras.
Ips beetles are also disrupting the biological control program of another exotic insect, Sirex woodwasp (Sirex noctilio). Sirex attack and kill stressed trees and have the potential to cause large scale tree mortality.
Many years of research in Australia has led to the Sirex Control Strategy, which includes biological control: a group of pine trees are treated (trap trees) to attract Sirex and then the biological control agent (a nematode) is introduced into the trees and this effectively sterilises the wasps. However, in recent years Ips have also been attracted to the trap trees as well, causing problems for the biological control program.
Scientists in NSW DPI, in conjunction with Forests NSW, are currently trialing insect pheromones and synthetic tree compounds to deter Ips from attacking Sirex trap trees.
The fire, in December 2006, that burnt 8500 hectares of the Buccleuch State Forest, near Tumut, saw Ips bark beetle populations increase dramatically to outbreak proportions in the fire-damaged stands, due to ample feeding material of burnt trees and conducive climate conditions.
There is concern that newly planted seedlings established within the burnt areas will be attacked and killed by bark beetles. Scientists from NSW DPI, in conjunction with Forests NSW and Bayer, are trialing a pill that combines an insecticide and fertiliser to manage this problem.
Dr Angus Carnegie - Forest Health Management, Sydney
