Changes in Arthropod Fauna From Weed Management Practices in Genetically Modified Herbicide-Tolerant Maize

Abstract

Genetically modified maize tolerant to broad-spectrum herbicides may greatly alter weed flora composition, abundance and therefore affect organisms of higher trophic levels, including herbivore and detritivore arthropods and their natural enemies. This three-year study measured the effects on arthropods of an intensive use of broad-spectrum herbicides in comparison with one application of conventional pre-emergence herbicide. Numbers of arthropods were measured by three techniques: visual counts on plants, catches in pitfall and yellow sticky traps. Weed density was much higher in conventional treatment in the first year, showed significant difference in the second year, but was no significant difference in the third year. Counts of arthropod taxa were significantly different only in the first year in the two kinds of weed management systems. In visual counts Cicadellidae and Aphididae among herbivores, the two main generalist predators, Orius spp. and Araneae, and the family Coccinellidae were more abundant on plants treated twice with glyphosate. In pitfall there were higher records in glyphosate-treated plots for Myriapoda but the opposite was seen for Carabidae counts. The yellow sticky traps catches were higher in the glyphosate-treated plots for Cicadellidae and Mymaridae, and lower for Thysanoptera. Most of the significant differences found between herbicide regimes disappeared when abundances of weeds (monocotyledons and dicotyledons) were introduced into the analysis as covariates; this finding signals weed abundance as the main cause of arthropod abundance alteration. However, only a drastic alteration of weed abundance causes significant changes in arthropod densities.

Dynamics of canopy‐dwelling arthropods under different weed management options, including glyphosate, in conventional and genetically modified insect‐resistant maize

“…In our case, weeds may have also played this role, as the lowest catches of Cicadellidae occurred in the weediest plots, which were treated twice with glyphosate (Loureiro et al, 2019). With respect to herbicide effects, the contrast between our study results and the observations of Albajes et al (2014) can be explained by the enhanced efficacy of our conventional weed management regime: in addition to a preemergence herbicide application, this regime included a postemergence treatment, the usual practice in the growing area. In a similar study using stacked (Bt and glyphosate-tolerant) maize varieties in Hungary, Pálinkás et al (2012) found a higher abundance of flea beetles and leafhoppers in glyphosate-treated plots than in plots treated with a conventional herbicide.…”

“…All species of this family of Hymenoptera, commonly known as fairyflies, are parasitoids of eggs of other insects, and their most common hosts in maize are leafhoppers (Huber, 1986;Gauld & Bolton, 1988). Similar results have been obtained in other surveys carried out in maize crops in Spain (Albajes et al, 2009(Albajes et al, , 2013(Albajes et al, , 2014Arias-Martín et al, 2018). Moreover, the authors of those studies have proposed Mymaridae as a useful group to evaluate the impact of GM maize on nontarget canopy arthropods, as fairyflies are the most frequent parasitoids of maize phytophages and are very sensitive to possible effects.…”

“…In addition, no significant differences in the abundance of predatory canopy arthropods were found among herbicide treatments. In the abovementioned farm-scale study by Albajes et al (2014), in contrast, Orius spp., Araneae and Coccinellidae predators were more abundant in plots treated twice with glyphosate compared with conventional preemergence treatment, a result probably due to the lower density of weeds and larger populations of canopy phytophages, mainly leafhoppers, in the former. In that study, the differences in the abundance of phytophagous arthropods among herbicide treatments were statistically significant in one of the 3 years of the experiment.…”

“…The overall composition of the maize canopy community in this study was very similar to that obtained in other surveys of maize in Spain (Albajes et al ., 2009, 2014; Arias‐Martín et al ., 2018) and not very different from those described in other parts of Europe (Meissle et al ., 2013). Although some differences related to different sampling methods and years were detected, the most abundant phytophagous groups were leafhoppers (Cicadellidae), aphids (Aphididae) and thrips (Thysanoptera).…”

Weeds and ground-dwelling predators′ response to two different weed management systems in glyphosate-tolerant cotton: A farm-scale study

“…In general, herbivores, pollinators and natural enemies abundance was smaller in GMHT beet and spring oilseed rape but larger in GMHT maize, whereas detritivores increased in abundance under GMHT management across all crops [ 26 , 27 ]. Multiyear field-trials have also been performed for GMHT soybean in Iowa [ 28 ], GMHT beet in Denmark [ 22 ] and GMHT maize in Spain [ 29 , 30 ], Hungary [ 31 ] and Czech Republic [ 11 ]. In general, few negative effects on beneficial insects were found, the effects of GMHT cropping on arthropod populations depending on the timing of herbicide application and the different efficacies of weed-control regimes compared with conventional crops.…”