Performance ofSesamia nonagrioideson cultivated and wild host plants: Implications for Bt maize resistance management

BACKGROUND Sesamia nonagrioidesis an important maize pest in the Mediterranean basin that is effectively controlled by Cry1Ab-expressing maize (Bt maize). The continued cultivation of Bt maize in Spain exerts high selection pressure on the target pests, which could lead to the development of resistance. Provision of refuges of non-Bt plants is an essential component in the high-dose/refuge (HDR) strategy to delay resistance evolution. Here we analyze the suitability of cultivated (rice and sorghum) and wild (Johnsongrass, cattail, common reed and giant reed) plants, reported as hosts ofS. nonagrioides, for larval development and oviposition of this pest compared to maize, and we evaluate their potential role in delaying resistance development to Bt maize. RESULTS Bioassays conducted with plant pieces or whole plants showed that the larval cycle could only be completed in the three cultivated plants and in Johnsongrass. Females showed a strong preference for ovipositing on maize in comparison with sorghum or rice. Although young larvae consumed more sorghum than maize in two-choice bioassays, both larvae and adults had a better performance (shorter larval period and higher pupal weight, fecundity and fertility) when larvae fed on maize throughout their larval stage than when they fed on sorghum or rice. CONCLUSION None of the alternative hosts ofS. nonagrioidestested here should be considered as natural unstructured refuges within the HDR strategy for Bt maize and this pest in Spain, as some of the necessary requirements to fulfill this strategy would not be met.