Researchers in California Test New Solutions for Olive Fruit Fly

“Olive fruit fly, in [California’s] North Coast, is the biggest insect pest prob­lem for olive grow­ers,” Cindy Kron, an inte­grated pest man­age­ment advi­sor for the University of California Cooperative Extension, told Olive Oil Times.

Along with her col­league, Bob VanSteenwyk, Kron has con­ducted IR‑4 projects on olives for olive fruit flies in 2020, 2022 and 2023. The IR‑4 Project helps spe­cialty crop grow­ers address pest man­age­ment con­cerns.

The project aims to help grow­ers pro­duce healthy fruits, veg­eta­bles and other crops, such as olives, for a healthy diet. IR‑4 projects cen­ter around two core pro­grams food crops and envi­ron­men­tal hor­ti­cul­ture.

The crop pro­tec­tion indus­try typ­i­cally focuses on major crops, leav­ing spe­cialty crop grow­ers with fewer tools for man­ag­ing pests effec­tively. The IR‑4 Project devel­ops data nec­es­sary for reg­is­ter­ing effec­tive and safe man­age­ment solu­tions, work­ing with the United States Environmental Protection Agency.

”Olive fruit fly is an inva­sive species that lays their eggs in the olive fruit, ​“Kron said. ​“The lar­vae emerge and tun­nel through the fruit as they eat the fruit and deposit frass (poop) along the way.”

The out­come of tun­nel­ing causes the fruit to rot, which results in off char­ac­ter­is­tics in the olive oil pro­duced from infested fruit. This affects the qual­ity and shelf life of the olive oil.

“Olive fruit fly infes­ta­tions in table olives make the fruit unmar­ketable,” Kron said. ​“No one wants rot­ten olives with insects in them. To pre­vent this infes­ta­tion, grow­ers seek alter­na­tives such as insec­ti­cides.”

In areas of the world where the olive fruit fly is estab­lished and not con­trolled, the dam­age is exten­sive. Losses up to 80 per­cent can result from lower quan­tity and lower pro­duce qual­ity. In some vari­eties, the pest can destroy 100 per­cent of the crop.

According to the University of California’s inte­grated pest man­age­ment pro­gram, ​“the expense of treat­ment and the likely crop dam­age have the poten­tial for elim­i­nat­ing olive cul­ture in home orchards or as a viable com­mer­cial indus­try in California.”

To apply a pes­ti­cide on a crop, the prod­uct must be reg­is­tered for that spe­cific crop.

“There are three prod­ucts reg­is­tered on olives,” Kron said. ​“Kaolin clay is a deter­rent and has no insec­ti­ci­dal prop­er­ties mean­ing that although the adults don’t like it, the applied prod­uct will not reduce the insect pop­u­la­tion num­bers. There is one organic and one con­ven­tional pes­ti­cide reg­is­tered on olives.”

One big con­cern about the repeated use of pes­ti­cides is that the insects develop a resis­tance to the prod­uct over time.

“When you apply the same mode of action (how a pes­ti­cide works) over and over again, the prod­uct can become not as effec­tive,” Kron said. ​“Over time, you are select­ing insects that have some kind of nat­ural resis­tance, and the prod­uct will stop hav­ing the same effi­cacy when used.”

Integrative pest man­age­ment (IPM) is a term used to describe pest con­trol meth­ods to man­age pest dam­age safely and eco­nom­i­cally. To pre­vent prod­uct resis­tance from occur­ring, it is rec­om­mended in an IPM pro­gram to rotate modes of action.

Producers and grow­ers are on the look­out for olive fruit flies. Visual inspec­tion is a rig­or­ous activ­ity from pre-har­vest inves­ti­ga­tions and through­out the sum­mer.

The sever­ity of the infes­ta­tion typ­i­cally deter­mines man­age­ment deci­sions for the olive fruit fly. Visually mon­i­tor­ing for mag­gots infest­ing fruit that has fallen from trees in late win­ter and spring can pro­vide some indi­ca­tion of an over­win­ter­ing fly pop­u­la­tion.

Specific traps such as McPhail, Olipe, or yel­low sticky traps can be used to mon­i­tor adult fruit fly num­bers.

“The prob­lem is, we only have three prod­ucts, of which only two have insec­ti­ci­dal prop­er­ties,” Kron said. ​“This is not enough options to truly rotate modes of action, espe­cially if you are an organic grower.”

In response to this prob­lem, she and VanSteenwyk have con­ducted IR‑4 tri­als to test a range of insec­ti­cide prod­ucts for effi­cacy in con­trol­ling olive fruit flies.

“We have a con­trol and an indus­try-stan­dard (con­ven­tional) in each trial so that we can see how the prod­ucts that cur­rently are not reg­is­tered fare in com­par­i­son to what is cur­rently avail­able and what level of dam­age you’d expect from apply­ing noth­ing,” Kron con­cluded.

• University of California Integrated Pest Management