Abstract
We determined whether plant volatiles help explain why Cotesia chilonis (a parasitoid of the target pest Chilo suppressalis) is less abundant in Bt than in non-Bt rice fields. Olfactometer studies revealed that C. chilonis females responded similarly to undamaged Bt and non-Bt rice plants. Parasitoids preferred rice plants damaged by 3rd-instar larvae of C. suppressalis, but did not differentiate between caterpillar-infested Bt and non-Bt plants. According to GC-MS analyses of rice plant volatiles, undamaged Bt and non-Bt rice plants emitted the same number of volatile compounds and there were no significant differences in the quantity of each volatile compound between the treatments. When plants were infested with and damaged by C. suppressalis larvae, both Bt and non-Bt rice plants emitted higher numbers and larger amounts of volatile compounds than undamaged plants, but there were no significant differences between Bt and non-Bt plants. These results demonstrate that the volatile-mediated interactions of rice plants with the parasitoid C. chilonis were not disrupted by the genetic engineering of the plants. We infer that parasitoid numbers are lower in Bt than in non-Bt fields because damage and volatile induction by C. suppressalis larvae are greatly reduced in Bt fields.
Highlights
Will be more heavily damaged by target pests and release greater amounts of plant volatiles or some new volatiles, making them more attractive to the parasitoid wasps
Response of C. chilonis to rice plants damaged by 3rd-instar C. suppressalis larvae
The results from our olfactometer tests showed that female C. chilonis parasitoids, when given a choice between clear air and odor emitted by undamaged rice plants, strongly responded to the undamaged rice plants whether they were Bacillus thuringiensis (Bt) or non-Bt
Summary
Will be more heavily damaged by target pests and release greater amounts of plant volatiles or some new volatiles, making them more attractive to the parasitoid wasps. A few studies have investigated the potential effects of Bt plants on parasitoid behavior as mediated by plant volatiles. Most of these studies have reported that undamaged Bt plants and the corresponding undamaged non-Bt control plants emitted similar types and quantities of volatiles and were attractive to parasitoid species; when infested with and damaged by caterpillars, the non-Bt plants receive more damage than the Bt plants and release qualitatively and quantitatively different volatile profiles, resulting in higher attractiveness to parasitoid wasps[14,15,16,17,18,19]. No data have been reported regarding the potential effect of Bt rice plants on the host-searching behavior of parasitoid wasps. The volatiles from undamaged and damaged plants were characterized in order to determine whether there are qualitative or quantitative differences in the volatile bouquet produced by the Bt and non-Bt plants
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