The western cherry fruit fly is native to North America, and has been found in the Pacific Northwest since 1940. This pest lives only on cherry, and has been a problem for farmers growing in this region occasionally. Although rarely found in commercial crops, a “zero tolerance” policy with the Department of Agriculture creates problems with exportation of all cherry products. Most infestations of the western cherry fruit fly occur in home orchards, as homeowners often do not have the knowledge to control this pest. Only a single generation of the western cherry fruit fly occurs each year, and coincides with the time of harvest.
The adult western cherry fruit fly is about 1/5 of an inch long, with the female being slightly larger then the male. They have a black body with white bands on the abdomen. The western cherry fruit fly can be distinguished from other species of fruit flies by their wing pattern. Depending on temperature, an adult lives about 35 days.
Western cherry fruit flies over winter under the soil of a host tree as a pupae. For 8 weeks around harvest time, adults emerge from the pupae and stay on the host cherry tree. They feed on cherry fruit wounds, deposits on leaves such as pollen grains and honeydew, and bird feces. Females become sexually mature 7-10 days after emergence. At this time, a female will puncture the skin of a cherry and individually lay between 100-300 eggs under the fruit skin. This process can take up to three weeks, with the female feeding on the juice of the fruit.
The eggs hatch in 5-8 days. The developing western cherry fruit fly then hatches into larvae, where it undergoes three separate growing phase. Each molt reveals larger and more developed larvae. During this process, the larvae burrow themselves toward the center of the fruit. Within 10-21 days after hatching, they will be fully developed and emerge from the fruit to drop to the soil surface.
When the mature larvae drops to the soil surface it immediately burrows itself 1-6 inches underground. Then it undergoes the third stage of its lifecycle and pupates. This hard outer shell allows the western cherry fruit fly to finish its development as it over winters and waits to emerge as an adult in the next growing season.