Fluidized Bed Heat Treatment for Controlling the Lesser Grain Borer (Rhyzopertha dominica) and Sawtoothed Grain Beetle (Oryzaephilus surinamensis) on Paddy cv. Khao Dawk Mali 105

Abstract

The efficacy of fluidized bed (FDB) heating was studied for controlling stored product insects on rough rice using laboratorial heat-fluidized bed equipment, and the milling quality of rice was later examined. Rough rice cv. Khao Dawk Mali 105 (13% wb) infested with insects was treated with FDB. The lesser grain borer (Rhyzopertha dominica, Fabricius) (internal feeders) had a higher tolerance for heat than the sawtoothed grain beetle (Oryzaephilus surinamensis Linnaeus, external feeders). At a hot air velocity of 3.7 m/s at 55°C for 90 s, the mortality of the lesser grain borer treated by FDB significantly differed (P <0.05) between all stages and from the untreated control. The pulpal stage, as an FDB-tolerant stage of the lesser grain borer, was treated with 55–65 °C for 60–150 s. FDB heat treatment at 55°C for 150 s, 60°C for 90 s, and 65°C for 60 s caused 100% mortality. At a hot air velocity of 3.7 m/s at 40°C for 120 s, the mortality of the sawtoothed grain beetle significantly differed (P <0.05) between all stages and the untreated control. The egg stage, as the FDB-tolerant stage, was treated at 40–50 °C for 60–150 s. FDB heat treatment at 45°C for 150 s and 50°C for 60 s caused 100% mortality. Some of the adults that survived FDB exposure were able to reproduce, but there were significantly less progeny than in the untreated control. Heat FDB slightly affected rice quality in terms of physical and chemical properties. Keywords: Heat, Fluidized bed heat, Paddy, Stored insect pests