(Image: Strawberry guava (Psidium cattleianum) leaves and fruit. Credit: Forest and Kim Starr, USGS.)
A strawberry guava thicket—and they do tend to grow into thickets—is a dense maze of smooth vertical poles, difficult to move through. And very little other vegetation is able to survive in such an infestation.
“Areas of heavy infestation become biological deserts with few native 'ōhi'a or koa and few native birds,” says a press release from the U.S. Forest Service. Tens of thousands of acres on several islands in Hawai'i have been invaded by the plants.
There has been little to do about these pests, short of laboriously poisoning individual plants, and then either hoping native vegetation comes back, or replanting it.
Now conservation scientists believe they may have a partial answer—a scale insect that attacks strawberry guava in its native Brazil.
The Forest Service plans to hold a statewide series of meetings to talk about its proposal to release the scale insect as a biocontrol for strawberry guava.
One problem with this variety of guava is that they're packed with seeds, and those seeds sprout readily in Hawaiian conditions. Sometimes you'll find a place where a fruit has fallen, and see a dozen or more seedlings rising from a space the size of a quarter.
The scale insect is known to science as Tectococcus ovatus, and in its native Brazil, it doesn't kill off all the strawberry guava, but it keeps their numbers low. The insects feed on the young leaves of the guava plants, reducing the amount of vigor needed to aggressively produce fruit and seed.
Research underway for the past 15 years shows that the scale can only survive on strawberry guava and will not move on to other plants in Hawai'i. They don't even kill the plants they're feeding on. They simply reduce reproduction, the Forest Service said.
“Tectococcus would reduce the growth and reproduction of strawberry guava, which would help prevent further destruction of native forests, and allow slower growing native plants like 'ōhi'a and koa a chance to compete,” biocontrol researcher Tracy Johnson of the U.S. Forest Service.
The Forest Service is preparing an environmental assessment for the biocontrol proposal. Details on the proposal, and a series of public meetings starting in September 2008, will be available at www.hawaiiinvasivespecies.org. For more information, reach Johnson at USDA Forest Service, Institute of Pacific Islands Forestry, 60 Nowelo Street, Hilo, Hawaii 96720, phone 808-967-7122.
© 2008 Jan W. TenBruggencate