May 23, 2011

Research Projects

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Impacts of transgenic wheat on herbivorous insects and their antagonists

(2007 – 2011) Agroscope Reckenholz-Tänikon Research Station, Zürich

Topic

Genetically modified wheat, into which a gene has been inserted that confers resistance to powdery mildew could potentially have undesirable effects on non-target organisms. Important non-target organisms include plant-eating insects (herbivores). In turn, herbivorous insects have antagonists that include predatory insects and parasitic wasps (parasitoids), which lay their eggs inside the insect larva, leading to the death of the host insect. Plants, herbivores and their antagonists therefore exist in an interrelated food web.

This project studied selected insect species (aphids) and their antagonists (parasitic wasps) to investigate whether transgenic wheat has an impact on the existing food web.

Experiment description

Test organisms: Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae, three aphid species commonly found on wheat in Europe, were used as test organisms. They are targeted by parasitic wasps, known as primary parasitoids, that lay their eggs inside the aphids. The eggs develop into larvae, which feed on the living aphids. In the final larval stage, shortly before pupation, the larvae feed on their hosts’ vital organs, causing them to die. The aphid shell hardens into a mummy, in which the larva pupates and from which the adult parasitic wasp emerges. The primary parasitoids are in turn targeted by secondary parasitoids.

Trial plants: In 2008 and 2009, two genetically modified lines were planted, along with their isogenic parent varieties (Bobwhite SH 98 26 and Frisal) and one conventional variety (Rubli). Bobwhite was transformed with an allele of a resistance gene taken from wheat (Pm3b). This allele confers a specific resistance to powdery mildew. The Frisal variety was transformed with two enzyme-producing genes taken from barley. These enzymes, chitinase and glucanase, are intended to confer an unspecific fungal resistance on the wheat plants by dissolving fungal hyphal walls.

Experimental procedure: Cultivation took place outdoors on the trial fields of the Agroscope Reckenholz Tänikon (ART) research station in Switzerland and in a semi-open greenhouse. The roof and side walls of the greenhouse open automatically in fine weather and close during windy and wet weather and at night. In the greenhouse the trial plants were grown on 40 plots (80 x 60 x 80 cm) arranged in two rows. A cylinder with a diameter of 26 cm containing ten plants of one of the wheat lines used in the experiment was placed in each plot. The associated non-transgenic parent variety or the conventional variety was grown as a buffer around the cylinder. (For a detailed description of the greenhouse see Romeis et al. (2007)).

Aphids were counted from mid-May to the autumn – every week in the greenhouse and every two weeks in the field – and aphid mummies were collected. The mummies were stored at room temperature until the wasps emerged so that they could be identified.

Results

Semi-open greenhouse

The number of aphids and their antagonists varied both within the various wheat lines and from year to year. The composition of the insect communities was not consistent. Nevertheless, the effects between the GM and non-GM wheat were smaller than the effects within the varieties and between the years and can therefore probably be regarded as insignificant from an ecological perspective.

Field

The numbers of aphids and aphid mummies were so small that it was not possible to conduct a statistical analysis. However, the same three aphid species and the same parasitoid species were found both in the field and in the greenhouse. It is therefore to be assumed that the data from the open greenhouse can be transferred to the field.