Strong oviposition preference for Bt over non-Bt maize in Spodoptera frugiperda and its implications for the evolution of resistance.

Pilar Téllez-Rodríguez,Lianet Rodríguez-Cabrera,Ben Raymond,Denis J Wright,Carlos G Borroto,Camilo Ayra-Pardo,Ivis Morán-Bertot

doi:10.1186/1741-7007-12-48

Pilar Téllez-Rodríguez, Lianet Rodríguez-Cabrera + Show 5 more

Open Access

https://doi.org/10.1186/1741-7007-12-48

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Abstract

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.

Highlights

Transgenic crops expressing Bacillus thuringiensis (Bt) toxins have substantial benefits for growers in terms of reduced synthetic insecticide inputs, area-wide pest management and yield
Oviposition preference for Bt-maize in S. frugiperda correlates with the level of feeding damage in the refuge Damage to the vegetative crop was assessed on a fourpoint visual scale (Figure 1A)
We considered three scenarios: a spray threshold model in which application of synthetic pesticides in refugia was based on the number of egg masses laid per crop plant; a natural predation model with density-dependent mortality of larvae in refugia only; and a predation model in which there was density-dependent mortality occurring throughout the Bt crop and the refuge in addition to the mortality imposed by the plant incorporated Bt toxin

Summary

Introduction

Transgenic 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. By 2012, Bt express Cry toxins at a dose that will impose near completely recessive resistance, that is, be high enough to kill most heterozygous resistant insects In conjunction with these high doses, farmers are required to plant a refuge area of a non-Bt variety of the same crop in close proximity to the Bt crop [7]. This strategy has successfully delayed resistance for Bt crops in many key target species [5,7]

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