Cultivated rice enhances an insect herbivore-parasitoid interaction compared with a wild grass due to its thinner stems

Abstract Crops are more susceptible to insect herbivores than wild plants. It is generally considered that crops combining with farm practices tend to disrupt insect herbivore-enemy interactions. In this study, we compared the parasitism rate of the rice stem borer Chilo suppressalis Walker by its specialized endoparasitoid wasp Cotesia chilonis Matsumura in cultivated rice Oryza sativa L. with that in the wild water-oat Zizania latifolia Griseb. The wild water-oat was never sprayed or fertilized. The parasitism rate was >10-fold higher in cultivated rice than in the wild water-oat. The difference was subsequently confirmed in a common garden experiment which the two host plants were interplanted in the same field. Laboratory assays indicated that female adults of C. chilonis did not discriminate the odors of cultivated rice and the wild water-oat. Larvae of C. chilonis did not develop differently within the haemocoele of the rice feeders and the wild water-oat feeders of the rice stem borer. However, the attack efficiency of C. chilonis significantly negatively correlated the thickness of stems in which the rice stem borers were dwelling. We conclude that cultivated rice has thinner stems than the wild water-oat, which is an important reason why the parasitism rate in cultivated rice is significantly higher than that in the wild water-oat. This finding may be just an exceptional case of the theory of the herbivore-enemy interactions in agroecosystems, but it implies that it is possible to enhance the control efficiencies in agroecosystems by designing appropriate crop phenotypes to promote the search and attack of natural enemies.