Managing weeds in herbicide-tolerant GM maize for biological control enhancement

Abstract: Deployment of transgenic herbicide-tolerant maize that allows post-emergencetreatment with broad-spectrum herbicides may lead to changes in the composition and abundanceof weed flora. The consequences of these changes on maize arthropods and particularly on insectpest natural enemies are studied in this work. Weeds, insect herbivores and their natural enemieswere monitored in maize plots treated twice with glyphosate (V4 and V8) in comparison withplots treated once with conventional pre-emergence herbicides. Plots were sampled by visualobservation, pitfall and yellow sticky traps during two consecutive years (2007 and 2008). Inspite of the significant differences recorded in weed abundance between the two herbicidetreatments, there were very few significant differences in the arthropod groups monitored, incontrast with results of a previous study comparing plots with two glyphosate treatments (as inthe present work) and with no herbicide treatment in order to identify the most responsivearthropod to weed abundance alteration. It seems that when maize weed abundance is notdrastically altered, populations of arthropod herbivores and natural enemies are not greatlyaffected. However, more studies are needed to determine the potential impacts of modifyingherbicide use on arthropods and particularly on conservation biological pest control.