Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape

Abstract

Widespread planting of maize throughout the agricultural Midwest may result in detritus entering adjacent stream ecosystems, and 63% of the 2009 US maize crop was genetically modified to express insecticidal Cry proteins derived from Bacillus thuringiensis. Six months after harvest, we conducted a synoptic survey of 217 stream sites in Indiana to determine the extent of maize detritus and presence of Cry1Ab protein in the stream network. We found that 86% of stream sites contained maize leaves, cobs, husks, and/or stalks in the active stream channel. We also detected Cry1Ab protein in stream-channel maize at 13% of sites and in the water column at 23% of sites. We found that 82% of stream sites were adjacent to maize fields, and Geographical Information Systems analyses indicated that 100% of sites containing Cry1Ab-positive detritus in the active stream channel had maize planted within 500 m during the previous crop year. Maize detritus likely enters streams throughout the Corn Belt; using US Department of Agriculture land cover data, we estimate that 91% of the 256,446 km of streams/rivers in Iowa, Illinois, and Indiana are located within 500 m of a maize field. Maize detritus is common in low-gradient stream channels in northwestern Indiana, and Cry1Ab proteins persist in maize leaves and can be measured in the water column even 6 mo after harvest. Hence, maize detritus, and associated Cry1Ab proteins, are widely distributed and persistent in the headwater streams of a Corn Belt landscape.

Fig. 1.

Map of the presence of maize leaves and Cry1Ab-positive maize in streams in a northwestern Indiana county (n = 217). Green shading indicates the planting of soybeans, yellow indicates the planting of maize, and white represents non-row-crop land use in the county.

Fig. 2.

Map of the presence of Cry1Ab-positive stream water in a northwestern Indiana county (n = 215). Green shading indicates the planting of soybeans, yellow indicates the planting of maize, and white represents non-row-crop land use in the county.

Fig. 3.

Conceptual diagram illustrating pathways (and associated literature) of maize and Cry1Ab proteins entering stream ecosystems. The photograph depicts maize accumulation in the riparian zone and active stream channels observed at our study sites. Superscripted numbers cite references listed in the references section (–54).