Effects of gamma radiation on the survival of four species of thrips (Thysanoptera: Thripidae)

The survival of four species of thrips (Frankliniella occidentalis, Frankliniella schultzei, Thrips tabaci and Thrips imaginis) exposed to gamma irradiation at doses of 0, 200, 300, 400 and 500 Gray was investigated. The aim of the work was to identify a generic dose of gamma radiation capable of killing or sterilising thrips infesting horticultural produce to prevent movement to, and colonisation of host plants in noninfested regions or countries. To simulate naturally occurring thrips populations, mixed life-stages were irradiated, and the effects compared with a nonirradiated control. The eggs of F. occidentalis and T. tabaci were more tolerant to irradiation than those of F. schultzei and Thrips imaginis, but none of the F. occidentalis or T. tabaci eggs developed beyond first stage larvae when irradiated at a target dose of 200 Gy. In mixed life-stage tests, all species had a similar tolerance to gamma irradiation. At a target dose of 200 Gy, all species were sterilised and no further offspring were produced. Based on these results, a minimum generic dose of 200 Gy would be sufficient to control these species of thrips in fresh horticultural produce destined for export to thrips-sensitive regions. A target dose of 250 Gy will provide a further margin of safety, until large-scale confirmatory trials are completed.