## 6 Approaches for Improving Resistance Management and for Managing Resistant Populations
Specifically, the use of non-Bt maize with soil-applied insecticide produces a temporal refuge (i.e., a year in which selection for Bt resistance is absent) thereby enabling the survival of Bt-susceptible individuals in addition to relaxing selection for Bt resistance. In situations where maize is grown for several consecutive years, rotating Bt maize with non-Bt maize that has soil-applied insecticide should both preserve yield and delay the evolution of Bt resistance. This concept is supported by the results of a computer simulation study conducted by [PERSON] and [PERSON] [82], which found that use of non-Bt maize with soil-applied insecticide delayed Bt resistance by western corn rootworm. However, it is important to note that the resistance-management benefit of refuges is in delaying resistance [24; 28]. Once resistance evolves and is prevalent within a population, refuges of any type (e.g., structured, integrated, naturally occurring or temporal) will be of minimal value in managing resistance. Rotating fields out of maize production (i.e., crop rotation) may also aid in reducing Bt resistance and the high levels of feeding injury that can be associated with Bt resistance [4; 76; 83]. Because maize is the primary larval host for western corn rootworm, crop rotation will eliminate a western corn rootworm population from a maize field, which should increase the ability of farmers to maintain rootworm population below the economic injury level [9]. Work by [PERSON] and [PERSON] [76] illustrated that high levels of rootworm feeding injury to Bt maize by western corn rootworm, and Bt resistance, were associated with continuous maize cultivation in the local landscape. This study also points to the potential of crop rotation to reduce the occurrence of high levels of feeding injury to Bt maize by Bt-resistant western corn rootworm [76]. [PERSON] et al. [83] found that increased crop rotation was associated with a reduction in high levels of feeding injury to Cry3 Bb1 maize by western corn rootworm. In addition to reducing high levels of feeding injury by Bt-resistant rootworm, [PERSON] and [PERSON] [4] revealed that crop rotation also can delay the evolution of Bt resistance within a field, an effect that likely arises because of the recolonization of a field by rootworm in neighboring fields. However, the benefit crop rotation in delaying resistance will be contingent on the level of Bt resistance in rootworm populations from neighboring fields, because these populations will serve as a source of recolonizing individuals after a field is rotated back to maize. Work by [PERSON] et al. [5] highlights the potential for fields to display a high level of Bt resistance following crop rotation if resistance is prevalent in the surrounding landscape. As such, the use of integrated pest management within the broader agricultural landscape is likely to be an important factor influencing the level of Bt resistance in a field following crop rotation. The success of future transgenic traits may be affected, in part, by resistance to current Bt traits, particularly in cases where current traits will be pyramided with future traits. The use of RNA interference (RNAi), induced by double-stranded RNA (dsRNA), represents a novel approach for managing rootworm, and DvSnf7 will likely be the first RNAi trait used to manage rootworm [84; 85]. However, this RNAi trait will be pyramided with current Bt traits, specifically Cry3 Bb1 and Cry34/35 Ab1 [86]. Consequently, to the extent that resistance to Cry3 Bb1 and Cry34/35 Ab1 is present in the landscape, the IRM benefit of pyramiding will be compromised [30]. Widespread resistance to Cry3 Bb1 in some regions of the Corn Belt, coupled with emerging resistance to Cry34/35 Ab1, may enable the rapid evolution of resistance to RNAi. In a laboratory selection experiment, western corn rootworm was evaluated for resistance to RNAi after seven generations of selection and found to be resistant to multiple insecticidal dsRNA molecules [87].