Heat treatments for killing apple maggot fly (Diptera: Tephritidae) puparia for application in disinfesting organic yard waste

Authors: Yee, Wee; O'NIEL, TIM - Engineered Compost Systems; KRUGER, CHAD - Washington State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: In the Pacific Northwest of the USA, apple maggot fly is a quarantine pest of apple. Immature stages of the fly may be moved in organic yard waste transported from fly-infested to fly-free areas in Washington State for composting, affecting the apple industry. One way of reducing the threat of yard waste transport to the apple industry is to heat waste to kill pupae of the fly. Personnel at the USDA laboratory in Wapato, WA, and Engineered Compost Systems in Seattle, WA determined the heat treatment needed to kill 100% of apple maggot puparia in the laboratory. It was found that exposing fly puparia to temperatures of 21ºC to 55ºC over 6 h followed by an additional hour at 55ºC resulted in 100% kill. This result is important because it identifies a heat regime required for treating organic waste so that it can be transported for composting without threatening the apple industry

Technical Abstract: Organic yard waste from western Washington, U.S.A. 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 using an oven 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 over 6 h from 21°C to 47.8, 51.1, 55.0, or 60.0'C momentarily. The 47.8, 51.1, and 55ºC treatments did not cause 100% mortality, although only one 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 21ºC to 55°C followed by an additional hour at 55°C produced adult 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 55ºC and 1-h soak treatment here is close to the minimum heat regime needed for disinfesting organic waste of R. pomonella puparia