Agricultural landscape simplification and insecticide use in the Midwestern United States Timothy D. Meehana,1, Ben P. Werlingb, Douglas A. Landisb, and Claudio Grattona aDepartment of Entomology and Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI 53706; and bDepartment of Entomology and Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 Edited by Jonathan Foley, University of Minnesota, St. Paul, MN, and accepted by the Editorial Board June 8, 2011 (received for review January 14, 2011) Agronomic intensification has transformed many agricultural Understanding relationships between landscape simplification, landscapes into expansive monocultures with little natural habi- pest pressure, and insecticide use over a broad range of environ- tat. A pervasive concern is that such landscape simplification mental conditions and crop types is essential if we want science- results in an increase in insect pest pressure, and thus an increased based policy to guide future landscape change (15, 16). Here, we need for insecticides. We tested this hypothesis across a range of explore these relationships, along with their agronomic and eco- cropping systems in the Midwestern United States, using remotely nomic consequences, across 562 counties in seven states of the sensed land cover data, data from a national census of farm Midwestern United States. management practices, and data from a regional crop pest mon- itoring network. We found that, independent of several other Results factors, the proportion of harvested cropland treated with insecti- In this study, landscape simplification was represented by the cides increased with the proportion and patch size of cropland and proportion of land in a county in field crops, vegetable crops, and decreased with the proportion of seminatural habitat in a county. fruit crops (hereafter “proportion cropland”). We chose this We also found a positive relationship between the proportion of measurement because it is easily estimated and interpreted and harvested cropland treated with insecticides and crop pest abun- because it is tightly correlated with several other indicators of dance, and a positive relationship between crop pest abundance landscape simplification, including average crop patch size, crop and the proportion cropland in a county. These results provide patch connectivity, and the proportion of seminatural habitat in SCIENCES broad correlative support for the hypothesized link between a county (Materials and Methods and Fig. S1). We evaluated the ENVIRONMENTAL fi landscape simpli cation, pest pressure, and insecticide use. Using link between landscape simplification and pest pressure using an fi regression coef cients from our analysis, we estimate that, across index of insecticide application (hereafter “insecticide use”), fi the seven-state region in 2007, landscape simpli cation was as- calculated as the proportion of harvested cropland in a county sociated with insecticide application to 1.4 million hectares and an treated with insecticides. A relationship between pest pressure increase in direct costs totaling between $34 and $103 million. and insecticide use is expected, given the standard economic Both the direct and indirect environmental costs of landscape sim- assumption that minimizing cost and maximizing income are key plification should be considered in design of land use policy that objectives of producers, and that these objectives are met using balances multiple ecosystem goods and services. insecticides when pest pressure is observed or expected to cause economic damage (17, 18). The index is positively related to total agriculture | biocontrol | crop pests | land cover change | pesticides mass of insecticide applied per year, indicating that it is not confounded by variation in the number of applications (Materials he last century has brought enormous increases in the extent and Methods and Fig. S2). Tand intensity of agricultural activities (1, 2). During this pe- We used spatial regression (19) to relate insecticide use (Fig. riod, agricultural landscapes across the planet have lost consid- 1A) to proportion cropland (Fig. 1B) after accounting for several erable amounts of natural habitat to crop production, plant other factors that could drive insecticide use and confound our diversity at the patch and landscape scale has declined, and crop evaluation of the impact of landscape simplification. We in- patches have increased in size and connectivity (3, 4). This trend, cluded a covariate describing net farm income per hectare of “ fi ” often termed landscape simpli cation (5, 6), is widely expected harvested cropland (Fig. 1C) to account for the possibility that to increase insect pest pressure on crops, leading to increased use producers in simplified landscapes have larger incomes, in- of insecticides (7, 8). creasing the likelihood that they will use preventative insecticide fi The link between landscape simpli cation, pest pressure, and treatments to manage risk and ensure strong economic returns insecticide use is expected on the basis of two lines of logic. First, (20). We also included the proportion of cropland in corn (Fig. conversion of diverse natural plant assemblages to monocultures, 1D), soybeans and small grains (Fig. 1E), and fruits and vege- at both patch and landscape scales, is known to reduce the tables (Fig. 1F) as covariates, because these crops vary consid- – abundance and diversity of natural enemies of crop pests (9 11), erably in the degree to which they receive insecticides, due to which has been associated with reductions in natural pest-control differences in pest complexes and the sensitivities of crop yield services (9). Second, increases in the size, density, and connec- and crop prices to pest damage (17, 21). These crop-specific tivity of host crop patches are expected to facilitate movement variables also accounted for the possibility that simplified land- and establishment of crop pests (10, 12), leading to higher pest pressure regardless of natural enemy activity. Literature reviews have consistently concluded that the re- Author contributions: T.D.M., B.P.W., D.A.L., and C.G. designed research; T.D.M. per- lationship between landscape simplification and pest pressure, formed research; T.D.M. analyzed data; and T.D.M., B.P.W., D.A.L., and C.G. wrote the although logical, is not well supported by empirical evidence (9, paper. 13, 14). The available studies have been conducted at relatively The authors declare no conflict of interest. small spatial scales, have focused on a narrow assortment of This article is a PNAS Direct Submission. J.F. is a guest editor invited by the Editorial Board. crops and pests, and have yielded mixed results (9, 13). Further, Freely available online through the PNAS open access option. it is not well established that increased pest pressure due to 1To whom correspondence should be addressed. E-mail: [email protected]. fi landscape simpli cation is enough to decrease crop yields to the This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. point where increased insecticide use is necessary (9, 13, 14). 1073/pnas.1100751108/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1100751108 PNAS Early Edition | 1of6 Downloaded by guest on October 1, 2021 Fig. 1. Spatial distribution of model variables. Proportion of harvested cropland in a county that is treated with insecticide (A) compared with the proportion of a county in cropland (B), the net income per hectare of harvested cropland (C), and the proportions of cropland planted in corn (D), soybeans and small grains (E), and fruit and vegetable crops (F). For all maps, each color shade denotes 20% of the observations. Spatial regression of A versus B–F is presented in Table 1. scapes are composed of crops with pests that are intensively culture (USDA), who reported that 25 (10–55), 18 (8–42), and managed with insecticides. Finally, we chose spatial regression 90% (80–99%) of the corn, soybeans and small grains, and fruits over standard multiple regression to account for spatial structure and vegetables, respectively, were treated with insecticides be- in model residuals, possibly due to geographic variation in pest tween 2003 and 2005 in the states in this study (21). As expected, dynamics or farmer behavior. insecticide use was also positively related to net income per fi Of the crop-speci c covariates, insecticide use was most strongly harvested hectare (P = 0.008). The intercept of the spatial re- < related to the proportions of cropland in corn (P 0.001) gression model was not significantly different from zero (P = and fruits and vegetables (P < 0.001, Table 1). There was a 0.83), matching the expectation that counties with no crop- marginally significant relationship between insecticide use and land would receive no insecticides. After accounting for several the proportion of cropland in soybeans and small grains (P = 0.08). The slope coefficients for crop-type terms indicated that, covariates, there was a positive relationship between insecticide fi < for a county composed of 43% cropland and netting $537 per use and landscape simpli cation (P 0.001, Table 1, Fig. 2, and harvested hectare (2007 averages for the study region), having all Table S1). Given the strong economic motive to minimize in- of the cropland planted in corn, soybeans and small grains, or secticide costs, we interpret this positive relationship as correl- fruits and vegetables would lead to 47, 11, or 95% of