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State defends guava biocontrol

By Michael Tsai

POSTED:
LAST UPDATED: 11:56 p.m. HST, Jul 09, 2010


CORRECTION

The estimated cost of the proposed release of Tectococcus ovatus to combat the spread of strawberry guava includes $1.2 million for research, "a few thousand" to breed and release the insect and "a few hundred thousand" to monitor affected areas, said Tracy Johnson, of the U.S. Forest Service. A Page A24 article on Friday, July 9 stated the projected cost was $367 million, which is an estimated cost of controlling the plant through manual and chemical means.

 

State environmentalists have worked hard to educate the public about the potential dangers of introducing nonindigenous species into Hawaii's natural habitats.

In fact, they may have done too good a job of driving home the point, judging by public concern about the state's proposed plan to introduce a Brazilian scale insect to Big Island forests as a means of controlling the spread of non-native strawberry guava.

Christy Martin, spokeswoman for the state Coordinating Group on Alien Pest Species, said the biocontrol measure is necessary to protect native species from the notoriously invasive strawberry guava, which can reduce available water by up to 50 percent in native forests.

While the number of strawberry guava trees in Hawaii has not been quantified, their presence in forest areas around the state is believed to be so pervasive that alternative means of control—including pulling them out by hand—is not feasible, Martin said.

However, during the first weeks of public comment on a recently released environmental assessment of the project, Hawaii residents have voiced concern that introduction of the tiny scale insect could bring with it a whole new set of problems.

Martin said that while such concerns reflect a healthy suspicion of non-native species in the Hawaiian ecosystem, the specific use of Tectococcus ovatus would be effective in slowing the rate of strawberry guava growth without any damage of native forests or wildlife.

The environmental assessment cites several studies (including tests on more than 100 plants) that show the insect feeds exclusively on strawberry guava and is highly unlikely to eat other plants, even those related to strawberry guava.

STRAWBERRY GUAVA QUESTIONS

Why not remove the plants manually? Much of the infestation is on terrain that is dangerous, difficult to access or ecologically sensitive. Even if removal by hand were possible, it would cost hundreds of millions of dollars.

What if the insect attacks other plants? The insect is highly specific and has been rigorously tested on more than 100 plants, including close relatives of the strawberry guava. In its native range it has never attacked agricultural crops.

How can I protect trees on my property? Individual trees and shrubs can be protected by horticultural oil sprays, including natural oils.

So no more strawberry guava at all? The insect will only weaken the trees and keep them from spreading as quickly. There will still be plenty of strawberry guava trees.

Source: Draft Environmental Assessment: Biocontrol of Strawberry Guava by Its Natural Control Agent for Preservation of Native Forests in the Hawaiian Islands

"Biocontrol is a very exact science now," she said. "In nature we know that there are some species that are very mutual; they can't survive without their host partner. There are concerns that (the insect) would evolve here, but in the time line of the cosmic roulette of that ever happening, the chances are so infinitesimally small compared to what would happen if we didn't do anything."

According to the assessment, the insect would weaken but not kill existing strawberry guava plants, thereby limiting their ability to bear fruit and minimizing their spread in native forests. While male insects are able to fly for short distances, females spend their entire lives on the leaves of the plant.

The assessment notes that biocontrol measures have been effective in addressing invasive species like Koster's curse, ivy gourd and banana poka.

Still, many are not convinced that waging yet another battle of alien vs. predator in Hawaii forests is in the public's best interest.

Janet and Jerome Heavenridge of Hawaii Kai planted a strawberry guava tree in their garden 15 years ago. They worry that the release of the scale insect will threaten their "beautiful, small tree."

"To subject our tree to indiscriminate, ugly insect galls on its leaves or tree elimination from a Brazilian insect seems an unwanted, unfair incursion on our property rights," said Janet Heavenridge, 82.

Heavenridge said she might have been willing to support the insect release if it was contained to affected forest areas. However, she said, widespread release could wipe out or damage strawberry guava trees in tourist and residential areas as well, a situation she said "is very unfair and seems wrong."

Heavenridge said she is also not convinced that the insect will not have negative effects on the surrounding environment.

"To argue that this Brazilian insect will not cause any other environmental damage other than to the strawberry guava cannot be proven until after it is introduced, when it will be too late," she said.






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