Solanum weeds as hosts for Phthorimaea operculella: Implications for resistance management of genetically modified potatoes (Solanum tuberosum)

Abstract Foliage from Solanum species found within or near potato fields in New Zealand was compared to potato (Solanum tuberosum) foliage for its ability to support growth of larvae of Phthorimaea operculella (potato tuber moth, PTM). Solanum species included S. laciniatum (poroporo), S. physalifolium (hairy nightshade), S. chenopodioides (velvety nightshade), S. nigrum (black nightshade), and S. dulcamara (bittersweet). In detached leaf bioassays larval growth was greater on velvety nightshade and poroporo than on foliage from the potato cultivar, ‘Iwa’, in the first year, but only larval growth on poroporo foliage was greater in the second year (P < 0.05). Larval growth on bittersweet foliage was similar to larvae on ‘Iwa’ foliage. No larvae survived on black nightshade beyond 5 days in both years. From a field survey, no PTM larval mines were found on any foliage of hairy, velvety, or black nightshade plants in or within 100 m of a field trial of transgenic PTM‐resistant potato plants from a survey undertaken in the third summer. Over the entire survey, an average of 0.18 mines/plant were recorded on poroporo plants, all of which were <200 mm 2 , compared to an average of 3.8 mines/ non‐transgenic potato plants (volunteer potato plants >100 m from the field trial and non‐transgenic potato plants of the cultivars ‘Iwa’, ‘Red Rascal’, and breeding line 2390, used as experimental controls within the field trial). This study demonstrated that, under no‐choice conditions, PTM larvae could grow on alternative Solanum species. However, PTM exhibited a clear preference for oviposition and development on potato plants in the field.