A check on parasites of Sirex noctilio
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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. 31, May 1994.
In 1980 Mike Nuttall wrote "introduced parasitic insects may kill 70% of sirex larvae ..." (FRI leaflet no. 47). An opportunity to check on the current situation has occurred in Woodhill Forest north west of Auckland, where a small patch of 8 year old radiata has a number of trees attacked by sirex.
The presence of the nematode in the sirex larvae that are growing inside the trees has already been confirmed by Mike Nuttall. Further work with adult females emerging next summer will confirm whether this is the sterilising strain. This strain can result in as many as 90% of adult females being rendered sterile.
In order to check on parasitic insects convenient lengths of sirex infested radiata have been placed in FRI's insectary. From the dissection of sirex larvae we know that Ibalia leucospoides larvae are present internally. Adult Ibalia will start emerging towards the end of December.
Back in the bush, Rhyssa and Megarhyssa should become busy in spring, laying their eggs on the almost fully grown sirex larvae inside the dead radiata trees. To confirm this, more lengths of radiata will be taken down to the insectary about December of this year and Mike will count the Rhyssa and Megarhyssa emerging in spring of 1995. There is another insect that parasitises sirex larvae, a native called Guiglia schauinslandi that may also emerge. So if all these parasites are present, it's no wonder the poor old sirex loses 70% of its young.
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