Aphid-parasitoid community structure on genetically modified wheat

Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Biology letters (Impact Factor: 3.25). 05/2011; 7(3):387-91. DOI: 10.1098/rsbl.2010.1147
Source: PubMed


Since the introduction of genetically modified (GM) plants, one of the main concerns has been their potential effect on non-target insects. Many studies have looked at GM plant effects on single non-target herbivore species or on simple herbivore-natural enemy food chains. Agro-ecosystems, however, are characterized by numerous insect species which are involved in complex interactions, forming food webs. In this study, we looked at transgenic disease-resistant wheat (Triticum aestivum) and its effect on aphid-parasitoid food webs. We hypothesized that the GM of the wheat lines directly or indirectly affect aphids and that these effects cascade up to change the structure of the associated food webs. Over 2 years, we studied different experimental wheat lines under semi-field conditions. We constructed quantitative food webs to compare their properties on GM lines with the properties on corresponding non-transgenic controls. We found significant effects of the different wheat lines on insect community structure up to the fourth trophic level. However, the observed effects were inconsistent between study years and the variation between wheat varieties was as big as between GM plants and their controls. This suggests that the impact of our powdery mildew-resistant GM wheat plants on food web structure may be negligible and potential ecological effects on non-target insects limited.

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    • "Many field studies have investigated the changes in diversity and abundance of target and non-target taxa using different transgenic crops. Some studies have also presented a number of possible mechanisms through which Bt plants might affect the insect community from the level of food webs, including predator/prey and host/parasitoid systems (Von Burg et al., 2011; Xu et al., 2012). However, most of the studies performed to date have used single farmland or forestland as the subject area, while comparatively less attention has been focused on defining the effects of intercrops and agro-ecosystems on insect populations. "

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    • "In no-choice laboratory population experiments, we measured aphid numbers and individual aphid size on powdery mildew-infected and uninfected plants. Based on the previous findings reported by von Burg et al. [22] and Álvarez-Alfageme et al. [23], we hypothesized that aphid number and body size will be smaller on wheat infected with powdery mildew than on healthy plants. We tested this hypothesis in two experiments. "
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    ABSTRACT: In agricultural ecosystems, arthropod herbivores and fungal pathogens are likely to colonise the same plant and may therefore affect each other directly or indirectly. The fungus that causes powdery mildew (Blumeria graminis tritici) and cereal aphids are important pests of wheat but interactions between them have seldom been investigated. We studied the effects of powdery mildew of wheat on two cereal aphid species, Metopolophium dirhodum and Rhopalosiphum padi. We hypothesized that aphid number and size will be smaller on powdery mildew-infected plants than on non-infected plants. In a first experiment we used six commercially available wheat varieties whereas in the second experiment we used a genetically modified (GM) mildew-resistant wheat line and its non-transgenic sister line. Because the two lines differed only in the presence of the transgene and in powdery mildew resistance, experiment 2 avoided the confounding effect of variety. In both experiments, the number of M. dirhodum but not of R. padi was reduced by powdery mildew infection. Transgenic mildew-resistant lines therefore harboured bigger aphid populations than the non-transgenic lines. For both aphid species individual size was mostly influenced by aphid number. Our results indicate that plants that are protected from a particular pest (powdery mildew) became more favourable for another pest (aphids).
    Full-text · Article · Oct 2012 · PLoS ONE
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    • "For these reasons, effects of powdery mildew infection on aphid densities could only be detected in the semi-field system but not in the field. The convertible glasshouse was also more suitable than the field for analyzing the aphid-parasitoid community structure on the same wheat lines used in our study [42]. This, together with the high financial burden of conducting field experiments with GM plants in Switzerland resulting from government regulatory constraints and public opposition [44], makes the convertible glasshouse a valuable study system for assessing non-target effects of transgenic plants. "
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    ABSTRACT: A concern associated with the growing of genetically modified (GM) crops is that they could adversely affect non-target organisms. We assessed the impact of several transgenic powdery mildew-resistant spring wheat lines on insect herbivores. The GM lines carried either the Pm3b gene from hexaploid wheat, which confers race-specific resistance to powdery mildew, or the less specific anti-fungal barley seed chitinase and β-1,3-glucanase. In addition to the non-transformed control lines, several conventional spring wheat varieties and barley and triticale were included for comparison. During two consecutive growing seasons, powdery mildew infection and the abundance of and damage by naturally occurring herbivores were estimated under semi-field conditions in a convertible glasshouse and in the field. Mildew was reduced on the Pm3b-transgenic lines but not on the chitinase/glucanase-expressing lines. Abundance of aphids was negatively correlated with powdery mildew in the convertible glasshouse, with Pm3b wheat plants hosting significantly more aphids than their mildew-susceptible controls. In contrast, aphid densities did not differ between GM plants and their non-transformed controls in the field, probably because of low mildew and aphid pressure at this location. Likewise, the GM wheat lines did not affect the abundance of or damage by the herbivores Oulema melanopus (L.) and Chlorops pumilionis Bjerk. Although a previous study has revealed that some of the GM wheat lines show pleiotropic effects under field conditions, their effect on herbivorous insects appears to be low.
    Full-text · Article · Jul 2011 · PLoS ONE
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