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BackgroundTransgenic crops expressing Bt toxins have substantial benefits for growers in terms of reduced synthetic insecticide inputs, area-wide pest management and yield. This valuable technology depends upon delaying the evolution of resistance. The ‘high dose/refuge strategy’, in which a refuge of non-Bt plants is planted in close proximity to the Bt crop, is the foundation of most existing resistance management. Most theoretical analyses of the high dose/refuge strategy assume random oviposition across refugia and Bt crops.ResultsIn this study we examined oviposition and survival of Spodoptera frugiperda across conventional and Bt maize and explored the impact of oviposition behavior on the evolution of resistance in simulation models. Over six growing seasons oviposition rates per plant were higher in Bt crops than in refugia. The Cry1F Bt maize variety retained largely undamaged leaves, and oviposition preference was correlated with the level of feeding damage in the refuge. In simulation models, damage-avoiding oviposition accelerated the evolution of resistance and either led to requirements for larger refugia or undermined resistance management altogether. Since larval densities affected oviposition preferences, pest population dynamics affected resistance evolution: larger refugia were weakly beneficial for resistance management if they increased pest population sizes and the concomitant degree of leaf damage.ConclusionsDamaged host plants have reduced attractiveness to many insect pests, and crops expressing Bt toxins are generally less damaged than conventional counterparts. Resistance management strategies should take account of this behavior, as it has the potential to undermine the effectiveness of existing practice, especially in the tropics where many pests are polyvoltinous. Efforts to bring down total pest population sizes and/or increase the attractiveness of damaged conventional plants will have substantial benefits for slowing the evolution of resistance.

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The temporary immersion bioreactor has been found to be an important tool for sugarcane micropropagation, allowing higher shoot formation rates and cost reduction. This research was conducted to demonstrate the agricultural value of temporary immersion bioreactor-derived sugarcane plants. The experiment was carried out for about 2 yr to study the field performance of these plants. Two control treatments were also evaluated representing the conventional forms of micro-and macropropagation. Growth of sugarcane stools, first ratoon and the use of micropropagated plants for macropropagation were recorded. Some botanical and chemical characteristics were evaluated. Differences among propagation systems were only found in the first 6 mo. of field growth, regarding the stem length and diameter. Such differences disappeared with the course of the experiment.

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