Wasp shows promise in fruit fly fight

University of Hawaii scientists said they have found a tiny wasp that attacks the Mediterranean fruit fly, an insect that causes millions of dollars in crop damage in Hawaii.

"They cause direct economic damage by reducing yield, they increase farm costs (labor and insecticides) and they lead to expensive post-harvest quarantine treatments of produce for export markets," said UH researcher Russell Messing.

The gnat-size wasp, Fopius ceratitivorus, can’t sting human beings, but university scientists have found it lays its eggs in the young of the Mediterranean fruit fly or medfly. The wasp larvae eat the young fly.

The wasp is originally from central Kenya and was collected in highland coffee plantations.

University of Hawaii tropical agriculture scientist Kenneth Grace said the wasp is an additional tool that could be used in the control of Mediterranean fruit flies in Hawaii.

The university has submitted an application to the Hawaii Department of Agriculture Plant Quarantine Branch for a permit to release the wasp into the environment.

A UH environmental assessment says there would be no significant impact if the wasp were released in Hawaii. The findings have been posted for examination on the state Office of Environmental Quality Control website. The deadline for public comments is Oct. 23.

After the comment period, the state plant quarantine program plans to submit a request to the state Board of Agriculture for final approval.

Messing first imported the wasp into quarantine and spent several years testing its safety and efficacy.

Funded in part by the U.S. Department of Agriculture, Messing worked with colleagues from Florida and Texas conducting studies in Kenyan coffee fields.

At least three other fruit flies attack fruits in Hawaii — the oriental fruit fly, the solanaceous fruit fly and the melon fly.

State and federal agricultural researchers have used various strategies in controlling the medfly, or Ceratitis capitata, including pesticide-treated bait sprays and field sanitation, and releasing sterile females to reduce reproduction.

Hawaii farmer Larry Jefts of Sugarland Farms said fruit flies are always a threat to his crops, and he welcomes a biological control that works.

"Anything like natural predators that help reduce the use of pesticides — I’m all for that," said Jefts, who farms thousands of acres on Oahu and Molo­kai. "It would help everyone."

Jefts said fruit flies are not only a threat to fruits, but also to his cucumbers and raise his costs for approved pesticides.

"They’re not inexpensive," he said.

Under the university proposal, the initial release of several hundred to 1,000 Fopius ceratitivorus waspswould be done at the Kauai Agricultural Research Center in the winter.

In Guatemalan coffee plantations, field releases of the wasp resulted in a 50 to 60 percent reduction of the medfly, according to university researchers.

The Mediterranean fruit fly has been in Hawaii since 1907 and became established by 1910.

Some previous attempts to introduce a species as a means to biological control have backfired in Hawaii, while others were quite effective, scientists point out.

In one case, sugar cane plantations in 1883 introduced a species of mongoose to control rats. But the mongooses also preyed on native ground birds and their eggs, as well as the eggs of chickens. Plus, someone also failed to take note that rats are night creatures and mongoose hunt during the day.

State officials now consider the mongoose an invasive species and use poisons and traps to control the population.

In another case, state agriculture officials have succeeded in helping to save many native wili­wili trees beset by the African Erythrina gall wasp, which feeds inside the leaves. Gall wasp infestation has been costly to the islands, with more than $1 million spent to remove dead wili­wili trees.

The biological fix: Officials found female Eurytoma erythrinae wasps that fed on the larvae of Erythrina gall wasps.