Agricultural landscape simplification and insecticide use in the Midwestern United States

Abstract

Agronomic intensification has transformed many agricultural landscapes into expansive monocultures with little natural habitat. A pervasive concern is that such landscape simplification results in an increase in insect pest pressure, and thus an increased need for insecticides. We tested this hypothesis across a range of cropping systems in the Midwestern United States, using remotely sensed land cover data, data from a national census of farm management practices, and data from a regional crop pest monitoring network. We found that, independent of several other factors, the proportion of harvested cropland treated with insecticides increased with the proportion and patch size of cropland and decreased with the proportion of seminatural habitat in a county. We also found a positive relationship between the proportion of harvested cropland treated with insecticides and crop pest abundance, and a positive relationship between crop pest abundance and the proportion cropland in a county. These results provide broad correlative support for the hypothesized link between landscape simplification, pest pressure, and insecticide use. Using regression coefficients from our analysis, we estimate that, across the seven-state region in 2007, landscape simplification was associated with insecticide application to 1.4 million hectares and an increase in direct costs totaling between $34 and $103 million. Both the direct and indirect environmental costs of landscape simplification should be considered in design of land use policy that balances multiple ecosystem goods and services.

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.

Fig. 2.

The partial effects of proportion cropland and proportion seminatural land on insecticide use. In these partial residual plots, y values are calculated by adding the residual from the full model to the product of proportion cropland and the slope estimate for proportion cropland (A, Table 1) or the product of proportion seminatural land and the slope estimate for proportion seminatural land (B, Table S1).

Fig. 3.

Spatial correspondence (A) and bivariate relationship (B) between the proportion of cropland treated with insecticide in a 48-km radius buffer and the natural log of crop pest abundance, as represented by the number of corn leaf aphids (Rhopalosiphum maidis), soybean aphids (Aphis glycines), and bird cherry-oat aphids (Rhopalosiphum padi, a small grains pest) captured in suction traps throughout the Midwestern United States. (C) Relationship between the proportion cropland in a 48-km radius buffer and the natural log of crop pest abundance. Suction trap data are from the North Central Soybean Aphid Suction Trap Network (Results).