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Cañada College Introduces African Wasp to Help Control the Olive Fruit Fly

The campus is the only location in the state where the wasp has returned two consecutive years.

A small African wasp that is the natural enemy of the olive fruit fly appears to be gaining a toehold in the olive trees on the campus of Cañada College in Redwood City.  This could bring good news to California’s olive growers who produce more than 95 percent of the olives grown in the U.S.
Olive Fruit Fly
Diego Nieto, an adjunct biology professor at the college, and students in his Biology 110 class, are part of a statewide effort to find a way to control the olive fruit fly, a serious pest of the olive crop.  Larvae from the fly feed on the fruit of olive trees.
The olive fruit fly was first discovered in California in 1998 and was later found in San Mateo County in 2001. So far, California and Central America are the only areas in the Western Hemisphere where the olive fruit fly has been found.
“The olive fruit fly is one member of a biological family called Tephrididae, which is home to several serious agriculture pests, including the Mediterranean fruit fly, Mexican fruit fly, and oriental fruit fly,” said Nieto. “These flies are capable of laying eggs in ripening fruit, which makes them especially damaging to fruit production. These pests are different than the fruit flies we more commonly encounter, which are in the family Drosophilidae and are only capable of laying eggs in overripe fruit.”
Diego Nieto checks for wasps
The widespread and rapid establishment of the olive fruit fly in California, along with the finding that natural native predators are largely ineffective in controlling the spread of this particular pest, led to a worldwide search for another possible solution.  In particular scientists looked for a parasitoid - an insect (often a wasp) that completes its development within the body of the fruit fly, eventually killing it.  The exploration took researchers to South Africa, Namibia, India, China and other countries. Scientists shipped a number of parasitoids to California and studied them in quarantine before identifying two – Psyttalia lounsburyi and Psyttalia humilis – that have been released throughout the state’s olive growing region. Both species were released at Cañada in 2010-11.
The college is located on 131 acres in the western part of Redwood City in the foothills of the Santa Cruz Mountains. More than 350 olive trees grow on the campus and the school’s symbol is an olive tree. Cañada also hosts the annual Arts & Olive Festival fundraiser for student scholarships every October.
 “These wasps are specialists,” Nieto said. “They have co-evolved with the olive fruit fly and are well-suited to utilize the fruit fly larvae for reproduction.”
P. humilis on an olive
The wasps are very small and look like little ants with wings. They are incapable of stinging people. And while they pose no threat to people or animals, they pose a major threat to olive fruit flies.
Female wasps deposit eggs into a fruit fly maggot inside of an olive. The egg hatches into a smaller larva that feeds internally on the maggot. After this maggot pupates, instead of a fly emerging, a wasp emerges to seek out additional maggots.
Since being released on campus, Nieto and his students have been monitoring the progress of the little African wasp.
“Cañada College is the only site in the state where Psyttalia lounsburyi has been recovered two consecutive years,” Nieto said. “This is encouraging, but several challenges exist and could still derail this project.”
Nieto said the wasp population is dependent on the density of the fruit fly population so, as the fruit fly population shrinks, so do the densities of the wasps.
“The wasps will not completely eliminate the pest,” he said. “Instead, our project strives to reduce the olive fruit fly population in regions outside of commercial production. That includes olive trees that are used for landscaping, located in preserved open space or in residential areas that are not managed and thereby act as a pest reservoir, capable of re-infesting commercial olive groves annually.”
Cañada has partnered with UC Berkeley, UC Riverside, the California Department of Food and Agriculture, and the United States Department of Agriculture, who had initiated this project. A scientific paper describing the work will soon be submitted to the journal Environmental Entomology.
The college also received funding from the San Mateo County Community College District Trustee’s Fund to help integrate the research into the Biology 110 curriculum at Cañada.
“Students collectively generate hypotheses, design experimental protocols, collect olives, rear out insects, graph results, and write a paper describing the project,” Nieto said. “Having hundreds of these trees on campus provides instructors and students wonderful learning opportunities that are literally steps away from the classroom. While I’m still in the process of refining this curriculum, I think it’s a wonderful example of how undergraduate students can participate meaningfully in active research.”





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