Turlings, Ted

2002, Hoballah, Maria Elena, Tamo, Cristina, Turlings, Ted

Herbivore-induced plant volatiles can function as indirect defense signals that attract natural enemies of herbivores. Several parasitoids are known to exploit these plant-provided cues to locate their hosts. One such parasitoid is the generalist Cotesia marginiventris, which is, among others, attracted to maize volatiles induced by caterpillar damage. Maize plants can be induced to produce the same blend of attractive volatiles by treating them with regurgitant of Spodoptera species. We collected and analyzed the regurgitant-induced emissions of two plant species (cowpea and maize) and of eight Mexican maize varieties and found significant differences among their volatile emissions, both in terms of total quantity and the quality of the blends. In a Y-tube olfactometer, the odors of the same artificially induced plant species and Mexican varieties were offered in dual choice experiments to naive mated females of C. marginiventris. Wasps preferred cowpea over maize odor and, in 3 of 12 combinations with the maize varieties, they showed a preference for the odors of one of the varieties. A comparison of the odor collection with results from the behavioral assays indicates that not only the quantity of the volatile emissions, but also the quality (composition) of the volatile blends is important for attraction of C. marginiventris. The results are discussed in the context of the possibility of breeding crop varieties that are particularly attractive to parasitoids.

2001, Hoballah, Maria Elena, Turlings, Ted

Herbivore-induced plant volatiles have been suggested to function as indirect defence signals that attract natural enemies of herbivores. Several insect parasitoids are known to exploit such plant-provided cues to locate hosts. It is unclear if individual plants benefit from the action of parasitoids. We investigated this question in maize plants under attack by Spodoptera littoralis larvae and found that parasitization by the endoparasitoids Cotesia marginiventris and Campoletis sonorensis significantly reduced feeding and weight gain in the host larvae. As a result, young maize plants attacked by a single parasitized larva suffered much less feeding damage and, at maturity, produced about 30% more seed than plants that were attacked by an unparasitized larva. Such fitness benefits may have contributed to selection pressures that shaped the evolution of herbivore-induced indirect defence signals in plants.