Raintree Nursery: Organic Control of Some Orchard Insect Pests

A second fruit fly monitoring season in my work in the orchards at Raintree has come to a close. Certain flies can be significant pests of orchard fruit, but they can also be monitored and controlled to minimize damage to fruit. As someone who went to graduate school to study insects (among other ecological, forestry, and agricultural topics), the scientist in me is super happy to be studying these and other insects at Raintree. The most wanted flies for us, in terms of significance in being a threat to fruit production, are apple maggots and Suzuki fruit flies.

Key to any success in controlling a pest is understanding its biology and natural history. Apple maggots (Rhagoletis pomonella) and Suzuki fruit flies (also known as spotted wing drosophila, Drosophila suzukii) are non-native to the Pacific Northwest. In the case of the apple maggot, some flies evolved to switch hosts from native hawthorn in northeastern North America to apples introduced by Europeans. This is a fascinating story of sympatric speciation, occurring in the last 200 years, that I would recommend the curious reader look into further.

Apple maggots are such important pests that the state of Washington has a quarantine law to protect the valuable apple orchards of eastern Washington from them. The apple maggot has figured out how to hide its larvae (maggots) away from predators in a large, protective food source. Flies emerge in the late spring as the ground warms from overwintering puparia (protective coverings of the middle life stage), mate, and then females lay their eggs into apples. Large, red apples seem to especially attract them on warm afternoons. The larvae develop in apples, which, being larger than hawthorn fruits, offer better protection from parasitoid predators like wasps. Adult apple maggot emergence is staggered through the summer and fall, meaning that flies emerge throughout the apple ripening season. The maggots mature in the fruit and then crawl out from ruined and rotting fruit that has fallen to the ground, going underground to pupate overwinter. This life cycle provides clues as to how to control apple maggot. It’s not by targeting the feeding larvae hiding in your apples! Perhaps the emerging adults could somehow be distracted or trapped? What of the ground fruit that may contain maggots about to crawl underground?