Large-scale, spatially-explicit test of the refuge strategy for delaying insecticide resistance

Abstract

The refuge strategy is used worldwide to delay the evolution of pest resistance to insecticides that are either sprayed or produced by transgenic Bacillus thuringiensis (Bt) crops. This strategy is based on the idea that refuges of host plants where pests are not exposed to an insecticide promote survival of susceptible pests. Despite widespread adoption of this approach, large-scale tests of the refuge strategy have been problematic. Here we tested the refuge strategy with 8 y of data on refuges and resistance to the insecticide pyriproxyfen in 84 populations of the sweetpotato whitefly (Bemisia tabaci) from cotton fields in central Arizona. We found that spatial variation in resistance to pyriproxyfen within each year was not affected by refuges of melons or alfalfa near cotton fields. However, resistance was negatively associated with the area of cotton refuges and positively associated with the area of cotton treated with pyriproxyfen. A statistical model based on the first 4 y of data, incorporating the spatial distribution of cotton treated and not treated with pyriproxyfen, adequately predicted the spatial variation in resistance observed in the last 4 y of the study, confirming that cotton refuges delayed resistance and treated cotton fields accelerated resistance. By providing a systematic assessment of the effectiveness of refuges and the scale of their effects, the spatially explicit approach applied here could be useful for testing and improving the refuge strategy in other crop-pest systems.pesticide resistance | predictive evolutionary models | pest management | resistance management P opulation growth will continue to favor agricultural intensification for decades. Because agricultural intensification is associated with increased pest pressure, pesticides generally help to increase yield (1-3). Although significant progress has been made to reduce reliance on pesticides (4, 5), an increasing number of insects and mites exhibit field-evolved resistance to synthetic pesticides, Bacillus thuringiensis (Bt) sprays, and transgenic Bt crops (6, 7). Negative consequences of resistance include increased pesticide use, disruption of food webs and ecosystem services, increased risk to human health, and loss of profits for farmers and industry (1, 3).One of the main strategies for delaying resistance promotes survival of susceptible pests by providing refuges, which are areas of host plants where pests are not exposed to an insecticide. Theory predicts that refuges will slow the evolution of resistance by reducing the fitness advantage of resistant individuals (7-9). Refuges can also reduce the heritability of resistance when susceptible individuals mate with resistant individuals surviving exposure to an insecticide (7). Empirical support for the refuge strategy was provided by short-term laboratory and greenhouse experiments (10, 11). Although these experiments test the hypothesis that mating between susceptible and resistant individuals delays the evolution of resistance, they do not consider several fact...

Sustained susceptibility of pink bollworm to Bt cotton in the United States

“…[6][7][8]36 A large-scale field test incorporating eight years of data also shows that refuges of unsprayed cotton delayed whitefly resistance to the insecticide pyriproxyfen. 37 We found four factors that probably delayed pink bollworm resistance to Bt cotton in Arizona from 1996 to 2005: abundant refuges of non-Bt cotton, recessive inheritance of resistance, fitness costs associated with resistance and incomplete resistance. 23 Refuges.…”

Contemporary and historical classification of crop types in Arizona

“…This study was driven by an ongoing, spatially explicit study of resistance to insecticides in whitefly populations initiated in 2000. The crop maps produced in this study have been used by entomologists at the University of Arizona to assess the relationship between historical cropping patterns and the development of whitefly resistance to insecticides across the agricultural landscape (Carrière et al 2012). The objectives of this study were therefore to answer the following questions.…”

“…Organizations in the USA, such as the United States Department of Agriculture's (USDA's) National Agricultural Statistics Service (NASS), use remote sensing to create yearly crop maps, but do not currently produce products for the state of Arizona (Johnson 2008). This study focuses on crops present in Pinal County, Arizona, where it has become critically important to correlate historical pest occurrence and resistance to insecticides with crop spatial arrangement to improve management of insects, such as the whitefly (Bemisia tabaci), which adversely affect cotton and other crop production (Palumbo, Horowitz, and Prabhaker 2001;Carrière et al 2006Carrière et al , 2012Crowder et al 2007Crowder et al , 2008.…”

Scientific Opinion on an application from Pioneer Hi‐Bred International and Dow AgroSciences LLC (EFSA‐GMO‐NL‐2005‐23) for placing on the market of genetically modified maize 59122 for food and feed uses, import, processing and cultivation under Regulation (EC) No 1829/2003

“…To improve the development of optimal refuge requirements on a regional scale in the future, resistance monitoring data could be analysed retrospectively in conjunction with data on the spatial and temporal distribution of maize 59122 and refuges (e.g., Carrière et al, 2012).…”