Botanical and arthropod diversity in GM HT maize treated with glyphosateor conventional herbicides

Abstract: Weed management in genetically modified herbicide tolerant (GMHT) crops maychange the weed composition and arthropod (specifically non-target arthropod) species spectrum,densities and impact higher trophic layers as well. Integrated Pest Management aims atmaintaining biological diversity, and ecological functions (e.g. natural control mechanisms) inagro-ecosystems. Changes however do not necessarily result in adverse effects. Therefore themagnitude and direction of changes outlined above needs to be understood and studied. HTmaize hybrids (including stacked events of lepidopteran and coleopteran resistance), weresurveyed for botanical and arthropod diversities in maize hybrid treated with glyphosate or withconventional herbicides. Our null hypothesis was that there is difference between the effects ofglyphosate and non-glyphosate treatment on above diversities. HT maize plots were treated twicewith glyphosate or once with non-glyphosate herbicides in 2007 and 2008. These plots wereestablished and arranged in a randomized complete block design with four replications. Weedspecies and their area coverage were estimated on 3×1 m on each plot in the same growth maizestages in both years. Arthropods were sampled at four dates by visual observation, pitfall, andyellow sticky traps. Total weed coverage was significantly lower in glyphosate treated plotscompared to plots with conventional herbicide treatment. Weed composition was also altered byherbicide treatments. The Rényi diversity profile showed higher weed diversity in glyphosatetreated plots in most cases. Indirect effects of altered weed composition and coverage did notresult in significant changes of abundance of most invertebrate groups.