Three-tier defence against imported insects

Press, 14 August 1982, Page 15

Three-tier defence against imported insects

By

KEN KLITSCHER,

, of the

Forest Research Institute

In February. 1982. the sharp-eved daughter of an Electricity Department worker spotted some un-usual-looking insects while cleaning out a storage shed at the Waiotahi substation near Opotiki. The local farm advisory officer was informed. and he called in entomologists from Rotorua's Forest Research Institute.

They quickly identified the insects, which had entered the country in imported power as subterranean termites, important forest pests in their native Australia. The necessary eradication procedures were set in motion — fumigation of all infected material where it could not be actually removed and destroyed, and soil treatment with persistent insecticides around the site.

The incident highlights the dangers imported insects can create for New Zealand’s forest industry. The 850.000 hectares of exotic forest have a net value of about three billion dollars; the industry employs in excess of 45.000 people, pays salaries of about $4OO million, and generates more than $5OO million a year in export earnings. Possibly even more important are the native forests. which may contribute little revenue to the national purse, but have incalculable value in protecting fragile environments, controlling runoff, and providing recreation.

Both types of forest are at risk. "New Zealand forests have developed in isolation,” says Dr G. P. Hosking, forest entomologist at the Forest Research Institute (F.R.1.), “and they have a relatively incomplete insect fauna. There are gaps, many environmental niches that could be filled by insects from overseas."

To add to . the problem, most imported tree species were brought here without their associated pests; these pests would find a tailormade habitat if they ever do arrive, especially since the New Zealand environment is in many instances more hospitable than their home range. The situation is further complicated by the fact that some, seemingly innocuous imported insects cause unexpected problems in their new environment. Dr Hosking quotes the example of Paropsis. a eucalyptus tortoise beetle that is rare in its native Australia. But here, without its natural predators, it has a severe impact on trees, to the extent that the planting of some species of eucalypts is now considered uneconomic.

To counter the over-all threat, the Forest Service has developed a three-tier defence against invading insects — quarantine, early detection, and control. A successful quarantine is the prime objective, and the Forest Service maintains a force of 44 timber inspectors to ensure that all timber coming into New Zealand is free of bark, insects, and fungi. Bark is specifically singled out because bark beetles, capable of attacking and killing healthy trees, breed in and under it. It is a prohibited import, but bark beetles are among the most commonly intercepted insects at our ports. Mostly, they find refuge in ships’ dunnage. This cheap timber, used to help stack cargo, may have been bought anywhere in the world, is untreated, often bark covered. and frequently

heavily infested. Indeed, insect damage is probably a factor contributing to its cheapness, and it came as no surprise when F.R.I. entomologists once identified seven different species of beetles in a single hold. Packing crates are another problem, together with the skids they often sit on, especially if the bark is facing inwards. One such crate from Russia seemed to be "clean" when inspected at the wharf; on arrival at Rotorua, a major forestry centre, it was found to contain hidden bark in which were sheltering five species of bark and wood boring insects.

Many companies are cooperative, and unpackers often ring the Forest Service or the FIR.I. when they come across insects in imported goods or packaging. Some tourists, however, are less careful, and many potentially dangerous wooden souvenirs arrive undetected: each is an invitation to future problems. New problems have also arisen in recent years with the widespread use of containers. Many of these are not opened on the wharf, and if care is not taken hazardous cargoes may be carried into the heart of major forested areas before being unpacked. Pocuments accompanying containers are supposed to specify any wood content, but such papers are notoriously unreliable. An F.R.I. entomologist, Mr John Bain, reports that in a recent Forest Service survey 50 per cent of containers were incorrectly documented.

Researchers at F.R.I. have over the years simplified the task a little by compiling a list of high-risk ports of

origin and cargoes. Feeler logs from the Pacific Islands, for example, are automatically fumigated, and tropical products like cane furniture are scrutinised very carefully..

Despite the care, some insects do slip through. In the mid-1960s a small ambrosia beetle was detected in a number of locations. F.R.I. entomologists, on checking back, found that telephone cable, had been imported from Europe. The wooden drums on which the cable had been wound were stamped “fumigated," but battens nailed on later to hold the cable on the spools had not been treated; the beetle had arrived in these battens, and had spread to the nearby forest when they were discarded on site.

In such cases of quarantine failure, the second line of defence involves early detection of the pests, and the F.R.I. supports a team of 12 forest health officers stationed about the country, whose job it is to act as observers and continually monitor the forests. Twelve officers may not seem many to cover the country, but they are aided by other Forest Service staff who, in the course of their normal duties, are on the watch for unusual insects. Farm advisory officers attached to the Ministry of Agriculture and Fisheries also monitor farm woodlots and shelterbelts, and the general public can often be very helpful in pointing out anything abnormal. In addition to their normal duties, about twice a year forest health officers and entomologists from the Forest Research Institute “blitz” high-risk areas in search of

new establishments, collecting insects and all vegetation showing signs of insect damage. Such areas would be wharf surrounds, and cityparks and reserves. (Trachymela. a small eucalyptus tortoise beetle related to Paropsis, was discovered by D.S.I.R. scientists in Auckland's Hobson Park in 1976.) Forest health officers are now even taking to the air. As the exotic forests become larger, some compartments may not be visited on the ground for long periods, and insect damage may go undetected. The observers are therefore inspecting all exotic forests from the air, compiling maps to show forest health as it is today, so that future changes can be quickly recognised. They may be aided in the foreseeable future by satellite surveillance, as a new generation of high-resolution techniques becomes available. When insects do become established, the final line of defence must be either eradication or some form of control.

In some cases this may involve insecticides, but such remedies are used with care — if they are non-selective they can be environmentally dangerous, exterminating the desirable species as well as the pest. And they are frequently quite costly for a limited return.

When they are applicable, biological controls are preferable, and some of these have been remarkably effective. For example, the wood wasp, Sirex noctilio, became a major problem in exotic forests in the 1940 s and 19505, when it killed up to one-third of the trees in some stands. The solution was a combination of. introduced parasites which either killed the insects’ larvae or sterilised the adults, together with better forest management to reduce the risk of epidemics. The

wood wasp is not now a serious threat. More recently, entomologists have been working along similar lines in an attempt to control the eucalyptus tortoise beetle. A predator, the ladybird Cleobora mellyi, was introduced and raised in quarantine at the Forest Research Institute. The first liberations have been made in Paropsisinfested areas, but it is too soon yet to assess the success of the experiment. Not all damaging insects have been introduced; some, like the Platypus beetle, are native to New Zealand. This pest is known to kill healthy beech trees and is causing much concern.

April winds destroyed some large areas of beech forest in the Kaimanawas and Ureweras. Unlike the exotic forests, the blown-

down trees will not be salvaged: they-will decay where they lie, creating an ideal insect habitat. With such an abundance of breeding material available, there may be an explosive growth in the Platypus population, with increased risk to the undamaged beech forests. F.R.I. scientists are monitoring the situation carefully. The danger of an insect attack on New Zealand’s forests is always there, and the Forest Service has developed a contingency plan to deal with it. This takes the form of a handbook which would act as a guide to the legal, biological, and management responses that would have to be considered in the event of a serious outbreak. How well have all these measures succeeded in safeguarding the forests? By a recent count. 94

species of forest and timber insects have become established in New Zealand, most of them before the Quarantine Inspection Service was set up in 1948. Against this. 319 different species have been intercepted, some on numerous occasions, so the quarantine and early detection systems seem to be working well. But even the present precautions do not seem able to prevent the establishment of a new. species about once every two years.

So far New Zealand has been lucky in that none of the invading insects now poses a serious threat. Losses due to insects in pine forests are negligible, and no introduced insects have yet seriously affected native tree species. Foresters hope and pray it will stay that way.