State agencies have been practicing biocontrol of invasive species for decades, with nary a peep from anyone. So why the uproar over a proposed introduction of a tiny insect to curb the growth of one particular forest pest?

"It’s understandable," said Tracy Johnson, research entomologist for the U.S. Department of Agriculture Forestry Service. "People are used to strawberry guava and they have a certain relationship to it."

The federal service, concerned about the strawberry guava crowding out native plant species, originally proposed the use of an insect to control the fruited weed. But the opposition caused the service to back away, and now the state Department of Agriculture has taken over the project. After public comments are closed (see box), the state Board of Land and Natural Resources will decide whether to go ahead with the biocontrol program.

The plant, otherwise known as Psidium cattleianum, produces a natural snack familiar to and beloved by many hikers here. Its down side is its easy propagation — even stray cuttings can put down roots and spread– which threatens native forests and hosts non-native fruit fly species that cause damage to the state’s agricultural industry.

Johnson knew that people have a history with this plant and understands the reaction, but he was still surprised by the heat of the opposition, which largely stems from fear of the control mechanism. Critics worry about the introduction of a tiny insect known as a scale that selectively feeds on the growing tips of the strawberry guava plant.

As described by state scientists, the insect is expected at best to arrest the further spread of strawberry guava and make targeted removal of plants in key areas a practical possibility. But the opposition insists that this will devastate Psidium throughout the islands, including whatever was purposely planted on private property.

Websites have sprung up (savetheguava.com and biodamage.com among them) shining a light on what opponents believe is a risk. The repercussions of introducing the Brazilian insect Tectococcus ovatus to Hawaii’s environment is uncertain, they argue, also citing the nearly 200-year history of strawberry guava, also known as waiawi, in the islands.

Sydney Ross Singer, a Puna resident and among the most outspoken opponents, posted the two websites. Among his many concerns: The plants grow more densely in Hawaii than in their native Brazil, with the consequence that an infestation could spread more readily. And there are no natural predators for the scale insect in Hawaii, Singer added.

"This is an experiment, and once the genie is out of the bottle, there’s no going back," he added.

Some of the government experts who have studied the issue maintain that the scale insect doesn’t fly, won’t spread easily on the wind and will be released gradually in selected areas where their effect can be watched.

Neil Reimer, chief of the state agriculture Plant Quarantine Branch, acknowledged there have been missteps with introduced species, primarily in the era when few were concerned about the effects on native species. But in more recent decades, since awareness of such threats has been sharpened, the state has successfully used biocontrol in some 50 cases.

"And none have attacked anything that wasn’t meant to be attacked," Reimer added.

The spiraling whiteflies that were such a plague about 30 years ago represent one such success story, he said, because a natural predator was introduced that was specific to them.

Lab tests on the scale — attempts to see if it will feed on anything other than strawberry guava — have included about 100 different species, Johnson said, with about half the tests done in Hawaii. No transference to another species has been found.

If approved as an agent of biocontrol, the scale presents what Johnson describes as "an extremely low risk" of the widespread infestation that some opponents fear. People will continue to find strawberry guava in the wild and in back yards, bug free, he added.

"I wouldn’t be surprised if somebody who has a plant in their yard never ever sees this insect on their tree," Johnson said.