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L. D. Dwinell There is interest in irradiation as an alternative to fumigation for the disinfestation of plants, plant products, and other materials for pests and pathogens. There is a paucity of information, however, on the use of ionizing irradiation for the control of pests associated chips, logs, and sawn wood. Although there is little known about the sensitivity of wood-inhabiting insects to irradiation, there is a wealth of information on the radiosensitivity of stored-products insects from which to draw. In stored products insect tolerance to irradiation increases progressively from egg to larval to adult insect stages. The dosages required for death after several weeks and for sterilization are typically between 0.2 and 0.5 kGy for coleopterous and mite pests but more than 1.0 kGy for moths. The time to complete mortality after a given dosage varies widely among species. High radiation doses (3 to 5 kGy) can cause significant commodity damage. Irradiation to eradicate the pine wood nematode (Bursaphelenchus xylophilus) in pine chips has been investigated. Pine wood nematode-infested wood chips were exposed (for periods from 1 h to 2 weeks), to gamma ray doses up to 12 kGy. Lethal doses lay in the range above 6 to 9 kGy, which was considered too high to make irradiation an economically attractive means of decontaminating commercial wood chips. Forintek Canada Corp. researchers reported that a similar dosage of 7 kGy was required to kill pine wood nematodes in aqueous solution, which supports the contention that a higher dosage is necessary to eliminate the pine wood nematode in vivo than in vitro. Recent studies on irradiation effects on nematodes confirmed the relative high dosages required to cause mortality (i.e., a dose of 7.5 kGy was required to kill all J2 larvae of Meloidogyne javanica). The use of irradiation for decontaminating chips, logs, or sawn wood does not appear to be economically feasible. Irradiation may, however, be useful in managing pests on high-value forest products that cannot normally be heat-treated or fumigated. References Eichholz, G.G., Bogdanov, A.A., and Dwinell, L.D. 1991. Radiation sensitivity of pinewood nematodes in woodchips. Appl. Radiat. Isot. 42:177-179. Smith, R.S., ed. 1991. The use of heat treatment in the eradication of the pinewood nematode and its insect vectors in softwood lumber. Report of the Task Force on Pasteurization of Softwood Lumber, Forintek Canada Corp., Vancouver, B.C., Canada.
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