The cultivation of Bt corn producing Cry1Ac toxins does not adversely affect non-target arthropods

Abstract

Transgenic corn producing Cry1Ac toxins from Bacillus thuringiensis (Bt) provides effective control of Asian corn borer, Ostrinia furnacalis (Guenée), and thus reduces insecticide applications. However, whether Bt corn exerts undesirable effects on non-target arthropods (NTAs) is still controversial. We conducted a 2-yr study in Shangzhuang Agricultural Experiment Station to assess the potential impact of Bt corn on field population density, biodiversity, community composition and structure of NTAs. On each sampling date, the total abundance, Shannon's diversity index, Pielou's evenness index and Simpson's diversity index were not significantly affected by Bt corn as compared to non-Bt corn. The "sampling dates" had a significant effect on these indices, but no clear tendencies related to "Bt corn" or "sampling dates X corn variety" interaction were recorded. Principal response curve analysis of variance indicated that Bt corn did not alter the distribution of NTAs communities. Bray-Curtis dissimilarity and distance analysis showed that Cry1Ac toxin exposure did not increase community dissimilarities between Bt and non-Bt corn plots and that the evolution of non-target arthropod community was similar on the two corn varieties. The cultivation of Bt corn failed to show any detrimental evidence on the density of non-target herbivores, predators and parasitoids. The composition of herbivores, predators and parasitoids was identical in Bt and non-Bt corn plots. Taken together, results from the present work support that Bt corn producing Cry1Ac toxins does not adversely affect NTAs.

Figure 1. Changes in mean ± SE (n = 3) values of descriptors of the NTAs communities in Bt and non-Bt corn.

(a) Total abundance; (b) Shannon's diversity index; (c) Pielou's evenness index; (d) Simpson's diversity index. Empty squares represent Bt corn and empty circles represent non-Bt corn. Statistically significant difference according to one-way ANOVA: *: 0.01<p≤0.05; **: 0.001<p≤0.01; ***: p≤0.001.

Figure 2. Principal response curve (PRC) resulting from the analysis of NTAs abundance dataset for the whole study period.

The vertical axis represents the difference in community structure between Bt (filled squares) and non-Bt (empty circles) corn plots expressed as regression coefficients (Cdt) of the PRC model. The species weight (b_k) can be regarded as the affinity of the taxon to the principal response. Only species with a weight less than -0.5 or greater than 0.5 are shown.

Figure 3. Changes in mean ± SE (n = 6) value of Bray-Curtis dissimilarity between Bt and non-Bt corn plots.

Figure 4. Time-lag analysis of NTAs community dynamics in Bt (a) and non-Bt (b) corn plots.

Figure 5. Changes in mean ± SE (n = 3) density of NTAs in Bt and non-Bt corn plots.

(a) Herbivores; (b) Predators; (c) Parasitoids. Empty squares represent Bt corn and empty circles represent non-Bt corn. Statistically significant difference according to one-way ANOVA: *: 0.01<p≤0.05; **: 0.001<p≤0.01; ***: p≤0.001.

Figure 6. Composition of Bt and non-Bt corn NTAs communities.

(a) NTAs communities; (b) Herbivores; (c) Predators; (d) Parasitoids.