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High numbers of Arhopalus in Canterbury

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Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.

From Forest Health News No. 49, February 1996.

Since first arriving in mid-Canterbury in the early 1980's Arhopalus ferus (burnt pine longhorn) can now be found in high numbers in most mid and north Canterbury forests. Assessments in October and November revealed large larval populations particularly in the stumps of logged compartments. A small study in north Canterbury found that based on the emergence holes from the previous flight seasons between 20 and 50 adult beetles could be expected from a stump with a 35-40cm diameter, most of these after just one year of development within the stump. The particular block looked at had 450 stumps/ha which gives a potential of between 9000 to 22000 insects/ha. Work done by Gordon Hosking and John Bain, NZ FRI in the mid-seventies found adult beetles had a male female emergence ratio of around 2:1 with the mean realised fecundity of females being 159. With Arhopalus having a propensity to attack fire damaged pine material the potential number of egg laying females has interesting implications for adjacent mature and semi-mature stands in the event of a large fire and more particularly the time available for recovery of fire damaged trees.

Although much detailed work has already been done by Forest Health, NZ FRI, a small regional trial tracking log degrade caused by larval wood boring has been established in Canterbury. Initial assessments have already indicated that in Canterbury flights of Arhopalus don't appear to occur until mid to late November and that burnt areas are still highly attractive to ovipositing females at least one month after a fire.

Paul Bradbury, MOF, Christchurch

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(Scion is the trading name of the New Zealand Forest Research Institute Limited.)


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