Farm Forestry New Zealand

PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Every moth matters - the eradication of white-spotted tussock moth

Scion is the leading provider of forest-related knowledge in New Zealand
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 72, March 1998.

Some of the most voracious immigrants are insects which are capable of adversely affecting imports and exports, tourism, agriculture and horticulture and the urban, commercial and indigenous forests on which New Zealand is dependent. While strenuous efforts are made at our border control posts to prevent unwanted visitors entering, they do arrive - in used cars, in the baggage of travellers, in packaging for goods and in all of the many ways that global commerce now moves.

One pest which slipped through was the White-Spotted Tussock Moth (a relative of the Asian Gypsy Moth, a serious pest with an international reputation) which turned up in Auckland's eastern suburbs in 1996. By this time it had spread over some 30 square kilometres of residential Auckland. While the white-spotted tussock moth, Orgyia thyellina, is not considered a pest in its home range of Asia and the Russian Far East, its discovery in Auckland was considered by scientists to pose a serious risk. Left alone, they believed the moth could spread throughout the country in 5 to 10 years, causing serious environmental and economic damage as it went.

In response to this risk, the Government decided to take the once-only opportunity to attempt to eradicate the pest. Only two years on, the attempt looks likely to go into the history books as perhaps the most successful insect eradication programme undertaken in an urban area.

The white-tussock moth caterpillars consume large quantities of foliage to the point where repeated defoliation could kill mature trees. Palatability studies commenced on discovery of the insect and, still continuing, confirmed they especially relish five major crop and amenity plant groups - rose/pip fruit (Rosaceae), willow/poplar (Salicaceae), legume (Fabaceae), oak (Fagaceae) and maple (Aceraceae). Also of great concern was their appetite for New Zealand's native black beech (Nothofagus solandri var. solandri), an important indigenous forest species in the lower North Island and northern South Island.

Clearly, if the insect becomes permanently established in New Zealand, it is likely to have serious environmental, economic and social consequences. Most evident would be damage to the amenity plants of New Zealand's urban environment, particularly private gardens, parks and street trees. But perhaps more serious economically and environmentally would be the devastation by white-spotted tussock moth of willow-dominant shelter plantings in horticultural and agricultural areas, damage to pip and stone fruit orchards and the potential damage to beech forests which are an important feature of the central New Zealand mountain lands.

Scientific advice to the New Zealand Government indicated eradication was feasible and had a high chance of success given that the pest appeared to be confined to Auckland's eastern suburbs. In response, the Government agreed to an eradication programme modelled on gypsy moth control programmes in North America. A combination of aerial and ground spraying using the organic Btik spray would be the main line of attack. To carry out the eradication programme, the Ministry of Forestry established Operation Ever Green , a multi-disciplinary project team comprising forest health,  science,  communications,  medical advisers and operational specialists. Extensive consultation and communication with the affected community became a foundation stone of the programme and was integrated with science and operational advice as the base from which all other action was undertaken. Communication included personal contact with local community councils, service organisations, arborists   and   garden   clubs.   Residents newsletters, television, radio, print, the internet and call- free telephone systems were set up to get the key messages through to the households in the area.

The Ministry of Forestry also invested in health advice and monitoring. It commissioned a health risk assessment of the Btk and the spraying programme which was updated twice throughout the  programme.  It  also  contracted  an independent medical adviser to monitor health events and maintain contact with doctors and concerned residents.

The eradication programme began in October 1996 when caterpillars began hatching from their over-wintering eggs. A Canadian firm which specialised in spraying to control pests and which owned eight DC6 aircraft adapted to that purpose, was contracted to carry out the aerial spraying of the 30 square kilometres of infested area plus a surrounding buffer zone involving 80,000 households in all. Based on overseas experience, this was considered the best option for successfully eradicating a pest with such a wide range of host plants and which could climb the tallest trees.

Overseas advice was that the caterpillars would hatch over a two to three week period and just three to five sprays would be all that was required. It is now accepted that this was overly optimistic. In Auckland the first generation of caterpillars hatched over two months and some survived the first round of spraying.

Between October and December 1996, nine early morning aerial sprays were conducted using one DC-6 aircraft. The first flights covered about 30 square kilometres. They later focused on a progressively smaller area. At the same time vegetation on 300 properties at the heart of the infested zone was treated from the ground using mist blowers. A Hughes 500 helicopter was employed to spray areas of dense vegetation in gullies and around Mt Wellington's volcanic cone.

The trapping on Christmas Eve 1996 of moths in the central infested area blew away all hopes that the programme had been successful and between January and April 1997, a twin-engine helicopter carried out 14 more sprays over a smaller 3 kilometre area. About 200 properties were treated from the ground.

Again, it looked as though the operation had been successful and again hopes of success were dashed by the trapping of six moths in April, indicating a small residual population of the pest had probably survived and would over-winter as eggs. One small egg mass was probably all it took to start the original infestation. If just one egg mass remained and no further action was taken, scientists estimated the infestation could grow to its pre-spray size within 12 to 18 months.

Operation Ever Green re-grouped in spring 1997 and with mounting concern from the community about health  issues, the New Zealand Government called for a high density trapping programme to find out if and where tussock moth remained, before any decision on further spraying.

By now the project had a new weapon - a synthetic pheromone developed over the previous 12 months in a collaborative effort by New Zealand and Canadian scientists. In field trials in Japan, conducted over the New Zealand winter, the pheromone proved so successful that male moths were beating on the scientists' car window even before the traps could be baited. Subsequent trials conducted under quarantine conditions in Auckland showed the synthetic pheromone was six times more effective than the live female moths which had been caged and used in monitoring traps in the previous season's trapping programme. Approximately 7000 pheromone-baited  traps  were  placed  in December 1997 on properties in the reduced tussock moth zone in Auckland's eastern suburbs. The traps were checked once a fortnight, with pheromone vials being changed every second check.

With the majority of traps placed on private properties, the cooperation of residents was crucial to the trapping programme's success. Considerable effort went into building up an accurate database of all 2300 households and using this to make personal contact with residents. Supporting staff in the field was a communication programme which included school competitions, postcards dropped into letterboxes at every visit, regular newsletters, and a free-dial 0800 number and web site updated every week. Residents responded with overwhelming support for the trapping programme. Particularly in the first weeks of the programme. Operation Ever Green staff fielded dozens of reports of insects in traps (none of them tussock moth) and requests for more traps.

Now nearing the end of its first season, the trapping programme has failed to snare a single white-spotted tussock moth and hopes are high that the pest was successfully eradicated by the 1996-97 spray programme. The high density trapping programme will continue until June when any remaining tussock moths would begin to over-winter. At the same time preparations are being made for a smaller trapping programme next spring, concentrating on the area where white spotted tussock moth was last trapped in April 1997.

All of the agencies involved in Operation Ever Green are unanimous in their heartfelt thanks to the long suffering residents of Auckland's eastern suburbs for their continuing support, co-operation and encouragement during these trying few years. Inspections of traps on private property, aerial spraying and vegetation removal restrictions were some of many inconveniences that the community bore in the quest to eradicate the White-Spotted Tussock Moth.

(For further information contact Gordon Hosking, Ministry of Agriculture and Forestry, Wellington)

 

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