Western cherry fruit fly Rhagolettis indifferens Curran (Diptera: Tephritidae)

The western cherry fruit fly is a key pest in all cherry growing regions of the western United States. It is native to North America and was reported attacking commercial cherry in the Pacific Northwest in the early 1900s. It was found in the Yakima valley in 1942 and the Wenatchee area in 1950. The fly’s larva develops in ripening cherries. If uncontrolled, the pest can destroy almost all the fruit on a tree. Even poor control can have serious consequences since major markets for Northwest cherries, such as California and many foreign countries, enforce a zero tolerance policy for infestation of packed cherries.

Life cycle

Cherry fruit fly completes only one generation per year. It overwinters as a pupa in the soil. The pupae are affected by soil temperature and do not all develop at the same rate. Adults begin to emerge in May, about five weeks before harvest, and are active until three or four weeks after harvest. Peak emergence often coincides with harvest.

Adult western cherry fruit fly captured on a yellow trap.

Adults live 16 to 35 days, depending on temperatures. They feed on deposits on the leaves, such as honeydew and pollen. Adult females undergo a 7- to 10-day pre-oviposition period before they are sexually mature. After mating, they lay eggs under the skin of the fruit. Females frequently feed on juices exuding from the puncture made during egg laying.

Each female can lay from 50 to 200 eggs in a three-week period. The optimum temperature for egg laying is between 75 and 85°F. The eggs hatch in five to eight days, and the larvae burrow towards the pit of the fruit where they cannot be controlled by most insecticides. When fully developed, 10 to 21 days after hatching, larvae bore out of the cherry and drop to the ground. Within a few hours they burrow into the soil to pupate. The majority of the pupae develop into adults the following season, although a few may remain dormant for two years.

Fruit injury

Maggots, which develop inside the cherries, make the fruit unmarketable.

Adults do no damage to fruit. Maggots, which develop inside the cherries, make the fruit unmarketable. In unsprayed trees a high percentage of fruit is likely to be attacked. The adult cherry fruit fly does not fly long distances so some unsprayed trees may remain uninfested for many years.

Degree-day model

The cherry fruit fly model helps growers know precisely when to apply protective insecticides.

Timing of the first chemical control spray is based on the interval between emergence of the females and the first egg laying, usually 7 to 10 days. The lower developmental threshold for cherry fruit fly is 41°F and no upper threshold is used. A degree-day model predicts first emergence of the western cherry fruit fly, which is very helpful in timing first cover sprays where there is not a reliable site to monitor this event. First fly is expected at 950 degree-days after March 1.

Download degree-day calculator and
phenology look-up

This information was derived from Orchard Pest Management - A Resource Book for the Pacific Northwest. Edited by: Elizabeth H. Beers, Jay F. Brunner, Michael J. Willett and Geraldine M. Warner. Published by Good Fruit Grower, Yakima, WA, 1993.