Farm Forestry New Zealand
PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Gypsy moth response – eradication essential for notorious pest
from Biosecurity Issue 48, December 2003.
Immediately following the discovery of a trapped male gypsy moth (Asian strain) in Hamilton in late March 2003 (Biosecurity 43:4), MAF implemented response actions.
The gypsy moth is regarded internationally as a high impact pest causing major environmental and economic damage throughout many parts of the world. It defoliates trees and MAF perceives it as a very serious threat to New Zealand’s forest and horticultural industries, indigenous flora, ornamental trees and urban parks. MAF has recognised the threat posed by gypsy moth for many years and as a result has established end to end biosecurity systems to reduce the risk.
Caterpillars can kill trees
The caterpillar stage of the moth’s life cycle is responsible for the damage the pest causes, eating the leaves of trees in the spring. As they grow and reach maturity, the individual caterpillars consume tremendous amounts of leaf material. In outbreak situations, when their numbers get high enough, the caterpillars are capable of completely stripping the leaves off host trees over wide areas. Repeated defoliation can eventually kill trees.
DNA profiling
On discovery of the male moth, DNA profiling confirmed that its origin was Japan and it was of the Asian biotype, Lymantria dispar ssp. praeterea. The probable source of entry into Hamilton was via an egg mass, transported on an imported used car or container. The last lines in this defence are surveillance and response.
Contingency arrangements
Initial activities were based around the gypsy moth contingency plans developed by Forest Research for MAF. This involved ground searching around the site where the moth was trapped, deployment of traps baited with a chemical sex attractant and invoking of a Controlled Area. These actions were aimed at delimiting the population and controlling the gypsy moth’s potential spread.
Long-term options analysed
MAF incursion protocols included establishment of a technical advisory group, stakeholder liaison, development of an economic impact assessment and an environmental impact assessment. During the 2003 winter a number of response options were analysed by MAF based on advice from top New Zealand and international scientists, overseas biosecurity agencies with experience of gypsy moth incursions, and relevant literature.
It was agreed that the trapped moth signalled a high chance of a population existing in the immediate vicinity of the trap, and this needed to be dealt with decisively.
Only one tool suitable for eradication
There are a number of options available to control or manage gypsy moth, but for eradication purposes the only effective tool available is aerial treatment with a bio-pesticide. Given the serious nature of the incursion, MAF accepted a recommendation that to achieve eradication an area of Hamilton would need to be aerial treated using Btk (Foray 48B) during the caterpillar stage of the next generation, i.e. spring/early summer 2003. This is the same product that was used to successfully eradicate the white-spotted tussock moth in Auckland’s eastern suburbs, is currently being used effectively in the painted apple moth response, and has been used in numerous urban situations throughout Europe and North America for a variety of Lepidoptera pests. Cabinet accepted this recommendation and a full-scale response is now in action. Aerial treatment started on 8 October 2003 and was completed after eight treatments on 29 November 2003. Now the focus is on high-density trapping, maintenance of the Controlled Area, ground searching and public reporting. The response will be considered successful if, after two further generations, no gypsy moth activity is found.
Reasons behind response strategy
Much has been made of the fact that only one male moth has been trapped. Analysis has demonstrated that this one moth represents a population, which has a high possibility of establishing. More detailed documentation outlining the reasoning behind the gypsy moth response in Hamilton has been placed on the MAF website.
One of the reports assesses aerial treatment and the alternatives, and gives an insight into the rigorous decision-making process behind MAF’s gypsy moth response.
To access these documents visit:
www.maf.govt.nz/gypsy-moth
Mark Ross, National Adviser, Pest Surveillance and Response, Forest Biosecurity
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