December 19th, 2011 by

Guava. It’s a juice-bar staple because of its abundant amount of fiber, vitamins A and C, folic acid and other dietary minerals. In the wild, it’s a small tree, only three to 16 feet in height, with colored berries. It’s native to Brazil — and the Hawaiian forests wish it had stayed there.

Brought to the tropical islands in 1825, strawberry guava has become one of the most damaging invasive species in Hawaii. Spreading rapidly across the landscape by shoots and seeds, strawberry guava crowds out native plant species, disrupts animal communities and causes adverse effects on Hawaii’s water. According to a study by the University of Hawaii, forests infested with strawberry guava evapotranspire — or release water into the air — 27 percent more than forests without. This means that 27 percent less water is entering Hawaii’s streams and groundwater, which means that a quarter less water is available for drinking or for feeding agriculture crops. And don’t forget about the oriental fruit flies, which love strawberry guava as much as those juice-bar aficionados, but cost Hawaii millions of dollars each year due to the damage they cause to the state’s agricultural crops.

The Brazilian scale causes strawberry guava to form growths on its leaves, which cause the tree to have less energy to grow and spread. Credit: USDA Forest Service

But hope is on its way — fittingly, from Brazil. For six years, researchers with the Institute of Pacific Islands Forestry have been seeking permission to release Tectococcus ovatus, aka an insect more commonly known as the Brazilian scale, into Hawaii’s forests as a biocontrol to counter the growth and spread of strawberry guava. You see, the scale loves strawberry guava. It loves it so much that it doesn’t eat anything else. And last month, the final step in securing permission to allow the scale to gorge itself on Hawaii’s wild strawberry guava was taken when the final environmental assessment was submitted to the Department of Health’s Office of Environmental Quality Control. Per that filing, insect release will begin this month at a site on the island of Hawaii, pending any last-minute delays spurred by farmers worried that the scale will affect their strawberry guava crops.

Hold on a second: isn’t Hawaii in this mess because of the introduction of a non-native species? True. Then, won’t the introduction of another non-native species as a solution create a bigger problem? Not necessarily.

Scientists studied the Brazilian scale’s potential as a biocontrol for 15 years before proposing its release in Hawaii. During that time, it was determined that it does not and would not pose a threat to other tree and plant species in Hawaiian forests because, as already mentioned, it loves strawberry guava and strawberry guava alone. The very definition of modern biocontrol science revolves around the specification that the biocontrol be host specific — in other words, it only wants to eat the plant or tree which it’s being sought as a biocontrol against. Furthermore, in the case of the Brazilian scale, it also won’t eradicate the strawberry guava from Hawaii entirely. It will just check its growth and spread, allowing native species to have a fighting chance of growing big and strong. So strawberry guava survives, as does Hawaii’s native flora. And the tropical islands are once again a happy place for forests.