Intraspecific variation in chemical attraction of rice to insect predators

The olfactory response of predators of the brown planthopper, Nilaparvata lugens Stal, to different genotypes of rice (14 cultivars and breeding lines of Oryza sativa L. and 1 wild species, Oryza nivara Sharma et Shastry) was measured in an airflow olfactometer. Odor from rice plants attracted more females of the mirid predator Cyrtorhinus lividipennis Reuter than plain air (control) on only 6 of the 15 rice genotypes. Orientation of C. lividipennis toward volatiles of certain rice genotypes was apparent even when the plants were free of the brown planthopper. However, the predator distinguished between prey-infested and uninfested plants and preferred plants with eggs over plante with nymphs. The predator did not distinguish different stages of plant growth (vegetative, booting, or flowering). Plants artificially injured to simulate brown planthopper oviposition wounds were not as attractive to the predator as plants on which the planthopper had oviposited. The preassay preconditioning on the cultivar TN1 did not produce a predator bias for this genotype. This suggests that rearing effects or chemically mediated associative learning reported for some natural enemies did not influence C. lividipennis' host response. Results with another predator, the coccinellid Micraspis hirashimai Sasaji, produced less consistent behavior. Planthopper-infested plants attracted more females of M. hirashimai than unifested plants in only 1 of the 12 rice genotypes evaluated. Implications for augmenting predators by rice cultivar selection and modification are discussed.