Putting the brakes on a cycle: bottom-up effects damp cycle amplitude.

Pest population density oscillations have a profound effect on agroecosystem functioning, particularly when pests cycle with epidemic persistence. Here, we ask whether landscape-level manipulations can be used to restrict the cycle amplitude of the European corn borer moth [Ostrinia nubilalis (Hübner)], an economically important maize pest. We analysed time series from Minnesota (1963-2009) and Wisconsin (1964-2009) to quantify the extent of regime change in the US Corn Belt where rates of transgenic Bt maize adoption varied. The introduction of Bt maize explained cycle damping when the adoption of the crop was high (Minnesota); oscillations were damped but continued to persist when Bt maize was used less intensely (Wisconsin). We conclude that host plant quality is key to understanding both epidemic persistence and the success of intervention strategies. In particular, the dichotomy in maize management between states is thought to limit the spatial autocorrelation of O. nubilalis.