Engineered Compost Systems (United States)

Organic yard waste from western Washington, U.S. that may contain puparia of apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), had been moved to central Washington for composting, threatening the $3 billion apple industry concentrated in that region. Heating waste to kill fly puparia before it is transported could be a solution to this problem. Here, we report results of studies in 2016-2021 that sought to identify a minimum heat treatment simulating that obtained using a low-pressure steam generator for maximizing kill of R. pomonella puparia. In two experiments, puparia were exposed to temperatures ramped linearly over 6 h from 21°C to 47.8, 51.1, 55.0, or 60.0°C in an oven. The 47.8, 51.1, and 55°C treatments did not achieve 100% mortality, although only one adult fly from 4,000 puparia was found in the 55°C treatment, while no puparia survived the 60°C treatment. In a third, similar experiment, no puparia out of 2,400 exposed to 55°C survived. In a fourth and final experiment conducted over 3 years, no puparia out of 61,223 exposed to a 6-h ramp from 21°C to 55°C followed by a 1-h hold time at 55°C produced flies. In addition, all puparia in this treatment died. Based on 42.3 to 69.8% control survival, 31,217 puparia were killed by this treatment with no survivors, for a probit 8.7190 level of security. Results suggest that the 55°C and 1-h hold time treatment here is close to the minimum heat regime needed for disinfesting organic waste of R. pomonella puparia.