Competitive interactions and the effect of herbivory on Bt-Brassica napus, Brassica rapa and Lolium perenne.
Abstract
The probability of a transgenic crop establishing a feral population outside cultivated areas and possibly outcompeting naturally occurring species needs to be assessed to make an ecological risk assessment of the transgenic crop. The interaction between herbivory and competition is thought to determine the ecological success of insect-resistant plants, and this interaction was investigated in a competition experiment with transgenic insect-resistant Bt-Brassica napus, Brassica rapa, Lolium perenne, and herbivory from the large white butterfly Pieris brassicae. As expected, herbivory had a negative effect on the biomass of B. rapa at high plant densities. The competitive ability of L. perenne, when growing with B. rapa, increased significantly with the level of herbivory on B. rapa. To predict the effect of herbivory in a natural ecosystem, plant competition between the two annual Brassica species was analysed in a population ecological model. It was concluded that it is probable that transgenic Bt-B. napus plants may invade a natural habitat if herbivory is sufficiently high and the habitat is suitable for B. napus. Synthesis and applications. The results indicate that it is important to study the interaction between herbivory and competition when assessing the ecological risk of insect-resistant genetically modified crops. Furthermore, combining ecological data from manipulated experiments with population ecological modelling is a fruitful approach when conducting environmental risk assessments.