Crops genetically modified to kill herbivorous insects may also have an effect on their natural enemies

Some GM crops are designed to kill predatory insects. Results It’s a dog eat dog world out there in the farmer’s field. Crops can either be lucky and grow in peace until harvest time, or they can be unlucky and succumb to an attack by harmful insects. In turn, the plant’s pests have enemies of their own, such as predators or parasites. This is the tough, but natural course of events.

We humans tend to be on the side of the crops in this eternal battle of survival, because we need the crops for food and feed. We therefore assist the crops in various ways, such as breeding pest-resistant crops, spraying crops with pesticides or more recently, genetically modifying crops.

The advantages are many and well known, but not so well elucidated are the potential effects of GM crops on the natural chain of events. Do crops that are engineered to kill pests affect the predators that normally feed on these pests?

Senior scientist Gabor Lövei from the Faculty of Agricultural Sciences at Aarhus University and his colleagues set out to find some answers using a novel approach. They carried out a literature review using a data-driven, quantitative method to summarize the peer-reviewed literature about the impact of genetically modified plants on arthropod natural enemies in laboratory experiments.

Revealing review

The review revealed surprising results – results that the individual reviewed papers had not revealed or written about.

- First, while many claim that "these aspects have been studied to death", only 55 natural enemy species have ever been studied in the laboratory, and most of them in a single experiment. Beneficial arthropods are numerous; even in Danish fields, there can be 6,000 species or more. Additionally, there is a bias towards a few predator species, especially the green lacewing (Chrysoperla carnea ), which seems to be more sensitive to GM insecticidal plants than predators in general,says Gabor Lövei and continues:

- In contrast to a simple author-vote counting method used by several earlier reviews, this method gave us an objective data-driven summary of existing knowledge about these effects. We found that there are both negative and positive effects of GMO on the natural enemies of the pests, with an overall tendency towards negative effects.

The additional results that the literature review found from studying the reviewed papers from another angle were not all that came to light. The authors of the review article demonstrated – albeit unwittingly – that writing about potential negative side effects of GMO is like poking a stick into a hornet’s nest.

In fact, expressing an opinion on the environmental impacts of GM plants, be it negative or positive, cautious or more partisan, can be so precarious that the prestigious science magazine Nature covered the subject in a recent news feature, in which reactions to Gabor Lövei’s and his co-authors’ article is highlighted as an example.