Henneman and Memmott constructed food webs containing Hawaiian plants, butterflies, moths, and parasitic wasps. The webs provided a snapshot of who eats what in the ecosystem and how much the non-native species may have infiltrated the local habitats.
In the swamp, where it can rain more than 32 feet (10 meters) in a year, the researchers collected 2,112 moth caterpillars, then documented the 52 types of plants the insects were feeding on.
Back in the laboratory at the Kauai Agricultural Research Center, Memmott and Henneman reared the caterpillars and watched to see if young wasps emerged from the caterpillars' bodies. About 20 percent of the caterpillars were found to have wasp eggs.
An overwhelming 83 percent of the wasps that had laid the eggs were originally introduced as biocontrol agents. Fourteen percent of the wasp species had been accidentally introduced to the islands over the years. Only 3 percent of the wasps were native to Hawaii.
In an article accompanying the study in Science, Pauline Syrett, a biocontrol expert at Landcare Research, a government-funded institute in Lincoln, New Zealand, said many ecologists and managers of natural areas would be shocked to discover the extent to which non-native species have infiltrated many ecosystems.
Henneman said it's highly likely that biocontrol agents have infiltrated ecosystems all over the world. "Given that we found what we found the first place we looked, odds are it would be found in most places people actually looked," she said. "So few people have looked at so few places at this point, though, that we just can't say much."
While the data clearly show that biocontrol agents can become dominant players in ecosystems far from where the outside species were introduced, Memmott and Henneman said it's important to remember that all of the non-native wasps observed in the study had been introduced before 1945.
Today, Memmott said, scientists and resource managers have better knowledge and are more careful about which insects are introduced as biocontrol agents. Many of those imported into Hawaii in the 1930s and 1940s would not have been introduced there today.
"It is important for people to realize that there is simply not a control method available that is a panacea and that is without environmental effects," said Henneman. "We need to look at each case individually and figure out what makes sense in that case."
SOURCES AND RELATED WEB SITES