Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2008
Publication Date: 6/20/2008
Citation: Hallman, G.J. 2008. Potential increase in fruit fly (Diptera: Tephritidae) interceptions using ionizing irradiation phytosanitary treatments. Journal of Economic Entomology. 101:716-719. Interpretive Summary: Irradiation is a relatively new treatment as far as commercial application, so the regulatory community has not had much opportunity in dealing with it. The biggest difference between irradiation and all other commercial treatments is that irradiation does not kill the pests immediately. Inspectors will find them all essentially alive days after treatment. What irradiation does well is prevent the pests from completing development or reproducing, which satisfies quarantine requirements. Because pests may continue developing, there is a likelihood that inspectors may find a greater pest infestation level with fruit flies in irradiated fruits because very small stages that are usually not found upon inspection (eggs and small larvae) may develop to larger larvae that will be found. This research examined that possibility for Mexican fruit fly in grapefruit and found that, indeed, there is a greater likelihood of finding more larvae in irradiated fruit than if another treatment, such as methyl bromide fumigation, heat or cold, was used. In any case, these findings do not jeopardize the use of irradiation as a quarantine treatment. It is simply to point out to regulators that they may find a greater infestation level when irradiation is used versus any other treatment if eggs and newly hatched larvae are expected to be in the treated fruit. Where infestation levels are very low to begin with, inspectors may notice no difference.
Technical Abstract: Ionizing irradiation is a postharvest phytosanitary treatment that is used increasingly in the world and shows further promise with some advantages compared to other treatments. Its chief disadvantage is that, unlike all other commercially used treatments, it does not provide acute mortality but prevents quarantine pests from completing development or reproducing. The goal of this research was to determine to what extent irradiated egg and early instar tephritids would develop to latter instars that could be found by phytosanitary inspectors. Mexican fruit fly, Anastrepha ludens (Loew), eggs and first instars in grapefruits were irradiated with doses ranging from 70 to 250 Gy and held at about 27 degrees C until third instars completed development. The accepted minimum absorbed phytosanitary dose for this pest is 70 Gy, although significantly higher doses may be applied under commercial conditions. As expected, the more developed a fruit fly was before it was irradiated, a greater proportion survived to the third instar. Also, dose was inversely related to developmental success. For example, a mean of about 65 and 35%, respectively, of late first instars reached the third instar when irradiated with 70 and 250 Gy. Of those, 65.1 and 23.4%, respectively, pupated, although no adults emerged. Therefore, the use of irradiation may result in a greater frequency of live larvae being found upon inspection than would be expected compared with the number of dead larvae found upon inspection of commodities treated with other treatments that provide acute mortality.