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A new era for biocontrol in the Pacific

The damage Mikania micrantha causes as it smothers crops in its path is nothing short of devastating (Michael Day/Biosecurity Queensland)
The damage Mikania micrantha causes as it smothers crops in its path is nothing short of devastating
Michael Day/Biosecurity Queensland

Invasive species have, over the years, wrought havoc on both natural ecosystems and farming systems of the Pacific islands. Early attempts at biocontrol saw some successes, but these were overshadowed by a few spectacular failures: the Indian mongoose, widely imported to control rats, and the cane toad brought in to control cane beetles in the sugar cane fields of Fiji, have now earned their own places in the World Conservation Union's list of the world's 100 worst invasives. But biocontrol is entering a new era in the Pacific region. A more reliable science of biocontrol, and a renewed commitment to networking across the region to share expertise and best practice, mean that biocontrol can now take its place in helping restore equilibrium within the fragile ecosystems of the islands.

Invasive species are the biggest threat to the biodiversity of the Pacific islands, with many endemic species extinctions to prove it. When generalist predators or highly adaptable weed species arrive on small islands, unique island species that previously faced little or no competition - and have nowhere to retreat to - are often easily overwhelmed. As well as destabilising natural ecosystems, this can have serious economic impacts for livelihoods that are closely linked to them, such as farming and forestry. None of the 22 Pacific island countries and territories have been spared - all face major weed invasions of economic importance. There have been many attempts to tackle the problem, including chemical spraying and hand weeding as well as biocontrol, and there have been some notable successes. But some of the most persistent and widespread weeds remain to be dealt with.

'Mile-a-minute'

The common name of this weed is something of an exaggeration - Mikania micrantha grows at about one metre per month ­- but the damage it causes as it smothers crops in its path is nothing short of devastating. Cocoa trees and banana plants are as vulnerable as low-growing crops like taro. Mile-a-minute currently affects 17 Pacific island countries, and unless checked will continue to spread within and beyond these islands. Biocontrol offers a solution.

After extensive testing, Puccinia spegazzinii has now been released at over 275 sites (Richard Markham/ACIAR)
After extensive testing, Puccinia spegazzinii has now been released at over 275 sites
Richard Markham/ACIAR

The plant originates from South and Central America, and this is where scientists sought - and found, in Ecuador - a natural control agent in the form of a rust fungus, Puccinia spegazzinii. Already in use against mile-a-minute in parts of Asia, the fungus still underwent extensive testing to confirm that it posed no threat to other plant species on the islands of Papua New Guinea (PNG) and Fiji. Beginning in 2008, the fungus has now been released at over 250 sites in PNG and 25 sites in Fiji. "We have successful lab trials, where the rust reduced growth and biomass of Mikania. We're optimistic that, with time, we'll see similar results in the field", says Michael Day, the Queensland-based scientist leading the project.

This work was among regional biocontrol research presented at a workshop in Auckland, New Zealand in November. Biocontrol specialists from Australia, New Zealand, Hawai'i and the UK joined counterparts from the Pacific islands, and pledged their support to help the islands through training and sharing of expertise and best practice, as well as proven biocontrol agents. With limited capacity and resources on most of the islands, such collaboration will be essential to future success.

Conservationists and biocontrol practitioners unite

The failures of the past have, perhaps understandably, put conservationists at odds with biological control practitioners. Now, however, these groups are making common cause, realising that, when carefully done, biological control can be the most ecologically appropriate as well as the most cost-effective approach to dealing with invasives. In Hawai'i and Tahiti, for example, a tree originally brought from South America as an ornamental, Miconia calvescens, is invading both forestry plantations and natural forests with a vengeance and displacing native species.

Leaf-feeding insects from Costa Rica and Brazil are currently being evaluated as biocontrol agents for Miconia (Pablo Allen)
Leaf-feeding insects from Costa Rica and Brazil are currently being evaluated as biocontrol agents for Miconia
Pablo Allen

Hawai'i is currently spending more than US$1 million per year on aerial spraying of herbicides in an attempt to keep it in check. Participants at the Auckland workshop heard how a range of leaf-, stem- and fruit-feeding insects from Costa Rica and Brazil are currently being evaluated as biocontrol agents for Miconia, in the hope of finding a much cheaper and environmentally benign alternative.

In Hawai'i, a committee that includes conservationists as well as agriculturalists and foresters oversees importations of potential biological control agents, ensuring that a consensus is reached on likely risks, costs and benefits before any new species is released. Networking among the Pacific countries, mediated by the Secretariat of the Pacific Community (SPC), will help to promote the adoption of such best practices and should help to see more and more of the aggressive invaders tamed.

Written by: Anne Moorhead

Date published: January 2010

 

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