Marking potato tuberworm (Lepidoptera: Gelecheiidae) with rubidium for dispersal studies

The potato tuberworm, Phthorimaea operculella (Zeller), is a major pest of potatoes worldwide. In Israel, this oligophagous pest also damages processing tomatoes. Correlative data suggest that the pest moves from harvested potatoes to nearby tomato fields. To measure directly the movement of moths between fields, adults need to be marked in release-recapture experiments. In the current study, we tested whether adult tuberworms could be marked with rubidium (Rb) by applying Rb chloride to the foliage of their larval food-plant. We tested for adverse effects of Rb on several fitness components of the pest in the laboratory, and then demonstrated the applicability of the technique in a mark-release-recapture experiment in the field. A single application of Rb chloride to potato was sufficiently in marking tuberworn adults, both in the laboratory and in the field. At a low application rate (3 g RbCl/liter), no adverse effect of Rb on the tuberworn was detected. However, higher application rates increased larval mortality and development time, and decreased adult size (dry weight) and longevity. Although recapture rates of both Rb- and dye-marked moths were low in a preliminary experiment, results agree with previous reports and suggest a low dispersal rate of the potato tuberworn in the field.