Effect of Herbicide-tolerant Corn on the Abundance of Field Bugs in Spain

Use of GM herbicide tolerant crops may affect the abundance and composition of weeds in the field, and thus impact the pests and their natural enemies. Orius species, known as minute pirate bugs, are the most abundant on-plant predators in Spain. Thus, Ramon Albajes and other scientists at the Universitat de Lleida chose Orius to study the impact of glyphosate use on predators. They also used damsel bugs (Nabis sp.) in the four-year impact study because it is commonly observed in the study area. Three different herbicide regimes were compared: two glyphosate (a broad-spectrum herbicide) treatments per season, no herbicide treatment, and one pre-emergence conventional treatment with selective herbicides against broadleaf and grassy weeds.

Densities of the predators (arthropods and heteropterans) in plants were recorded. The annual density of Orius spp. per plot was significantly correlated with annual density of leafhoppers and aphids. On the other hand, densities of Nabis sp. are similar in glyphosate-treated and conventionally treated plots.

The scientists concluded that "no significant changes in heteropteran predator densities may be expected from moderate alterations in weeds arising from the deployment of herbicide tolerant corn varieties and that leafhoppers are probably the herbivore prey that most influences Orius spp. densities in corn in the study area."

Read the abstract at http://dx.doi.org/10.1016/j.biocontrol.2011.03.008.