Olive Groves May Be Rescued By Helpful Wasp

Agricultural Research Service (ARS) entomologist Victoria Y. Yokoyama and colleagues have imported and studied the beneficial wasp, and have turned it loose—by the thousands—in olive-fruit-fly-infested groves in California, the nation's No. 1 producer of this popular fruit.

Now, the scientists are continuing to carefully evaluate the wasp's effectiveness in thwarting the olive fruit fly, Bactrocera oleae.

First detected in California in 1998, olive fruit flies can now be found in every part of California where olives are grown, according to Yokoyama. She's based at the agency's San Joaquin Valley Agricultural Sciences Center near Parlier, Calif.

The olive fruit fly's young, which are slender, whitish maggots, ruin both the olive and its premium oil by feeding voraciously on the fruit as it ripens. But these destructive maggots are vulnerable to attack by the P. cf. concolor wasp. The attack begins when the wasp lays its eggs inside the maggots. When those eggs hatch, the wasp young kill the olive fly maggots by feeding on them from the inside out.

The wasp is harmless to people, pets and plants. It appears to be more effective in attacking olive fruit fly than some of the fly's other natural enemies, called parasitoids, which were brought to California in the early 2000s.

Yokoyama's ongoing studies, funded by ARS, the Fresno-based California Olive Committee, and other agencies, continue to reveal new details not only about the friendly wasp, but also about the olive fly itself.