INTRASPECIFIC VARIATION IN CHEMICAL ATTRACTION OF RICE TO INSECT PREDATORS

The olfactory response of predators of the brown planthopper, Nilaparv ata lugens Stal, to different genotypes of rice (14 cultivars and bree ding lines of Oryza sativa L. and 1 wild species, Oryza nivara Sharma et Shastry) was measured in an airflow olfactometer. Odor from rice pl ants attracted more females of the mirid predator Cyrtorhinus lividipe nnis Reuter than plain air (control) on only 6 of the 15 rice genotype s. Orientation of C. lividipennis toward volatiles of certain rice gen otypes was apparent even when the plants were free of the brown planth opper. However, the predator distinguished between prey-infested and u ninfested plants and preferred plants with eggs over plants with nymph s. The predator did not distinguish different stages of plant growth ( vegetative, booting, or flowering). Plants artificially injured to sim ulate brown planthopper oviposition wounds were not as attractive to t he predator as plants on which the planthopper had oviposited. The pre assay preconditioning on the cultivar TN1 did not produce a predator b ias for this genotype. This suggests that rearing effects or chemicall y mediated associative learning reported for some natural enemies did not influence C. lividiipennis' host response. Results with another pr edator, the coccinellid Micraspis hirashimai Sasaji, produced less con sistent behavior. Planthopper-infested plants attracted more females o f M. hirashimai than unifested plants in only 1 of the 12 rice genotyp es evaluated. Implications for augmenting predators by rice cultivar s election and modification are discussed. (C) 1996 Academic Press, Inc.