An insect-killing nematode is being put through its paces in Irish forests as part of Coillte's drive to use alternatives to insecticides in managing woodlands.
THE WEEVILS IN the woods had better watch out. A tiny worm native to Ireland is being deployed to control a species of weevil that is the most serious pest to forestry in northern Europe.
The insect-killing worm or nematode is being put through its paces in Irish forests by the Behavioural Ecology and Biocontrol Lab in NUI Maynooth. The target of the diminutive worm is the pine weevil (Hylobius abietis), a long-snouted brown beetle with yellow blotches.
Coillte dips or sprays insecticides on seedlings to protect them against this pest. "If we didn't protect the trees, we would suffer 50 to 100 per cent losses from these insects," says Dr Michael Keane of Coillte. The state forestry company replants up to 10,000 hectares annually. Weevils cause needle loss, reduce plant growth and kill trees by damaging bark. "The damage looks like something has been gnawing at the bark, with irregular pieces missing," says Dr Christine Griffin, head of Maynooth's biocontrol lab.
Weevils are attracted to the smell of cut timber and lay their eggs in freshly felled conifer stumps. The weevils mature under the bark. Dr Aoife Dillon at NUI Maynooth has reported that over 100,000 adult weevils can emerge in a single year in one hectare of forest. Dr Griffin says pines in particular produce massive populations. "It seems a better material for the juveniles to feed on, though emerging adults will eat everything - pine, spruce and even hardwoods," she says.
The Maynooth scientists surveyed Irish soils for insect-killing nematodes and discovered a suitable species from Wexford. The species, Heterorhabditis downesi, reduces the number of adult weevils emerging from pine stumps by more than 80 per cent. "We've compared different nematodes and this one is the very best," says Dr Griffin. The biocontrol lab is interested in studying the species' natural occurrence. It was found in sandy coastal soils and is believed to naturally parasitise a beetle called the garden chafer.
Coillte is seeking alternatives to insecticides as part of its certification under the Forest Stewardship Council, a non-profit organisation that encourages responsible forest management. Last summer, Coillte began the first widespread biocontrol project in Irish forests when it sprayed tree stumps with a commercially produced nematode - Steinernema carpocapsae. This nematode, used throughout Europe, was applied to 10 sites; the species from the Maynooth group was used on six.
Nematodes enter pine weevils through natural body openings, though Heterorhabiditis can use a tooth to cut into juvenile weevils. Once inside, the nematodes release bacteria from their gut which proliferate inside the insect. The weevils succumb within two days. "The bacteria convert the insect into a kind of soup and the nematode feeds on the bacteria and digested insect tissue," says Dr Griffin. After four weeks, up to 100,000 nematodes emerge from each dead insect, ready to infect yet more weevils.
Dr Griffin's group is carrying out research funded by the Environmental Protection Agency on the environmental safety of nematodes, focusing on their persistence and effects on other insects. Dr Griffin stresses that the worms pose no risk to people and only attack insects. "They don't spread away from stumps and die off in a couple of years," she says.
Lab work has examined the susceptibility of a wasp that infects the weevil and of longhorn beetles, which are important decomposers of wood. Dr Griffin would like to see H downesi field tested on a larger scale and believes the species has commercial potential. "There are commercial nematode producers interested in it, companies in the UK, the Netherlands, and Germany. There is also possible scope for an indigenous nematode producer."