World Underfoot

Forest and Bird, Issue 307, 1 February 2003, Page 33

World Underfoot

is Forest and Bird’s biosecurity

specialist.

GEOFF KEEY

over 500 finds. Invertebrates feature prominently in the list of discoveries. Trade and transport has enabled these cosmopolitan species to traverse the globe. A biological globalisation is following economic globalisation. The isolation that has protected New Zealand's fauna and enabled it to diversify into weird and wonderful forms has gone and with it our precious native fauna is going too. Other forces are also working in concert to change New Zealand’s invertebrate fauna. Land clearance, wetland drainage and urbanisation have wiped out many important habitats. As forests have been cleared and wetlands drained, the invertebrates that depend on them have gone. These changes have also created the conditions that favour more robust species introduced from around the world. We humans are accompanied by a whole assemblage of invertebrates that are adapted to live with us. Cosmopolitan invertebrates such as ants and cockroaches readily survive the disturbed environments we create. Some species of ant are so effective at coping with the frequent disturbance of human activity that they have been nicknamed ‘hitchhikers’ — because of their ability to move around the world on cargo. ntomologist Brian Patrick of Otago says that New Zealand’s invertebrate fauna is more special than we think. ‘If you look at the insect fauna of the UK, it is shared with the rest of Europe. In contrast, our insect fauna is largely peculiar to New Zealand. ‘We have a responsibility to look after an invertebrate fauna that occurs nowhere else, he says. ‘Introduced invertebrates

"pollute and dilute" the native fauna much like weeds do in a forest. Brian Patrick warns, ‘every time we modify an ecosystem, the new animals we have introduced are sitting there waiting — cockroaches, slaters, spiders and earwigs — and they take the opportunity to quickly invade the modified ecosystem we have created.’ A major concern for Brian Patrick is the change caused by the deliberate release of biological control agents. These animals, often insects, have been introduced to control weeds and animal pests as a ‘clean, green alternative to spraying and other more conventional pest control methods. On a recent trip to Mount Hutt skifield, Brian Patrick found one biological control agent — gorse pod moth — at around 1100 metres above sea level on the mountain. He has found this moth in many habits from Dunedin to Marlborough, from the coast to the mountains. He is concerned it is becoming an insect ‘weed’. ‘The idea of biological control is a neat concept, but we need to be very careful. Caterpillars may eat the leaves, but the adults may pollinate the unwanted plant. Nature is often more complicated than we realise.’ Brian Patrick notes that biological control agents are often parasites or browsers of hosts and have evolved with their hosts. ‘They don't bite the hand that feeds them. If a biological control agent was really effective it would become extinct because it would eliminate its host. But in fact, nature is more sophisticated and the biological control agent survives along with its host. Brian Patrick’s caution about biological control seems well founded. Both the native red and yellow admiral butterflies are being attacked by a parasitoid wasp, introduced

into New Zealand in 1932 to control the white cabbage butterfly. The admiral butterflies are attracted to gardens because of the presence of a common introduced nettle. This brings them into contact with the wasp Pteromalus puparum which lays its eggs in the butterflies’ pupae. Around 20-40 wasps emerge from the pupa, killing it. Another butterfly that appears to be under attack from introduced wasps is the beautiful forest ringlet butterfly. A Victoria University entomologist, Dr George Gibbs, is concerned at the decline which seems to be primarily from areas with human influences. The most likely reason appears to be predation from the introduced common wasp. Auckland-based entomologist Dr Peter Maddison makes regular forays into the Waitakere Ranges to look for invertebrates. On a recent trip, he found five undescribed species of moth. Unfortunately, in his regular forays into the Waitakere Ranges, Peter Maddison no

longer finds the forest ringlet butterfly; he believes it has probably become extinct in the Waitakere Ranges. He too warns of the threat posed by introduced predatory insects. In his view introduced ants and wasps are the rats and stoats of the insect world, rapacious predators that threaten native invertebrates. ew Zealand was slow to realise the | \ | threat posed by hitch-hiking ants. In 1990, the Argentine ant entered New Zealand during the course of the Commonwealth Games. At the time, nothing was done about them. A decade later, people woke up to the threat and now

there are efforts to eradicate them. Peter Maddison likens our approach towards insect pests as being a bit like New Zealand’s historic approach towards deer. ‘New Zealanders did not worry about deer at first, until they became an obvious problem. We need to make sure we don’t repeat those mistakes.’ Wasps are usually thought of as a South Island beech-forest problem. Tiny scaleinsects drink the sap of beech trees and exude the excess water and sugar in the form of a sweet liquid called honeydew. This provides a vast renewable energy source for wasps and they thrive, creating an annual cycle of large populations in the

summer and dying off again in the winter. In summer honey-dew laden beech forest literally hums loudly with the activity of wasps. Peter Maddison warns that wasps are also a threat in northern regions, however. ‘The warmer winters do not knock back the wasp populations like the cold winters further south and this creates the ideal conditions for wasps to hunt native invertebrates all year round. We don’t realise the damage that is being done’ Peter Maddison has been noticing a decline in stick insects. He believes that wasps are at least partly to blame. ‘I have personally seen three attacks on stick insects by wasps, he says. ate last year, the Ministry of and Forestry released a report on ‘biosecurity surveillance’. Biosecurity is a new word minted by scientists to describe keeping New Zealand free from new pests and weeds. Surveillance is the word used to describe the different systems for locating new pests so that they can be eradicated before becoming a problem. The report made over 90 recommendations for improving biosecurity surveillance. Key findings were that efforts to protect New Zealand from pests and diseases were being hampered by a lack of people to identify new pests, over-stretched

agencies, poor coordination between government agencies and an insufficient emphasis on threats to New Zealand’s native ecosystems. To date, the various reviews of biosecurity, including the report by the Parliamentary Commissioner for the Environment in 2001 and the recent report by the Office of the Auditor General, make over 200 recommendations of ways to improve New Zealand’s biosecurity system. The Government has now released a draft Biosecurity Strategy for discussion. It has the working title of ‘Guarding Pacific’s Triple Star’, an allusion to the New Zealand national anthem. This strategy sets out the approach the government intends to take to protect New Zealand from pests and diseases. It readily acknowledges the pressure New Zealand can come under from trading partners who may object to a robust biosecurity system. In its report, the Office of the Auditor General stated that New Zealand has one of the best biosecurity systems in the world, but the Office does not believe the system is

good enough. This is a reflection of the critical importance of biosecurity to New Zealand, with our economic dependence on plants and animals, and our responsibility to look after our unique biodiversity.

The success of the Biosecurity Strategy will be critical to New Zealand’s future, and the continued existence of the remarkable but threatened world beneath our feet.