for National Geographic News
Bugs don't pay much attention to human-drawn battle lines.
That's the lesson scientists learned when they went to Hawaii to look at what happens when farmers import specialized insects to combat invasive weeds and pests—a practice known as biocontrol.
Over time, they found, the non-native insect may go AWOL (absent without leave), leaving the farm and settling into local ecosystems far afield.
More than a century ago Hawaiian farmers imported parasitic wasps from China and Texas to prey on moths and butterflies that were devouring fields of sugarcane. Those wasps, the study revealed, infiltrated a pristine boggy forest on Kauai, many miles from where they had been deployed to do battle, and are now a dominant species in the forest's habitats.
The results shows that land managers need to carefully consider the possible implications of introducing non-native species as biocontrol agents, said Jane Memmott, an ecologist at the University of Bristol in England and co-author of the study, which was reported in the August 17 issue of the journal Science.
"We need to be aware there are risks, and we need to weigh them up," she said. "Very few things in life are 100 percent safe."
Controversial Practice
To control weeds, bugs, and even diseases, some agricultural experts, foresters, and conservationists see the introduction of non-native species as environmentally friendlier than the use of chemicals such as insecticides and pesticides.
Parasitic wasps, for example, are commonly deployed to kill moths and butterflies. The wasps lay eggs inside moth and butterfly caterpillars, causing the victims to die before they metamorphose into winged insects.
The use of biological controls, however, is controversial. Some scientists argue that species introduced as biocontrols can run amok in the ecosystem and do more damage than the pest or weed they were enlisted to destroy.
"At least chemicals are not a permanent addition to the environment, as biological organisms are," said Laurie Henneman, a co-author of the paper and a colleague of Memmott's at the University of Bristol.
The researchers went to Kauai's Alakai Swamp to see if they could find any of the more than 122 species that have been introduced as biological controls in Hawaii over the last century. The swamp is higher, wetter, and cooler than the lowland agricultural fields, making it a distinct ecosystem.
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