Herbivore-induced rice semiochemicals and their application in rice insect pest management

It has been well documented that plants in response to herbivory release specific volatiles to attract natural enemies of herbivores and/or repel herbivores. And several field studies have shown that these herbivore-induced volatiles enhance the parasitism or predation of herbivores. Thus, it may decrease the damage of the herbivores by manipulating or applying these volatiles. Using rice plants, rice brown planthopper Nilaparvata lugens (Stål) and its parasitoid Anagrus nilaparvatae Peng et Wang as a model system, induced rice indirect defense and its perspective for application were studied. The results showed that A. nilaparvatae was attracted to volatiles released from rice plants infested by N. lugens or treated by jasmonic acid (JA). JA-treated rice plants also enhanced parasitism of N. lugens eggs in the greenhouse and field. Through chemical analysis, together with behavioral bioassay (tested by using standard chemicals or genetically manipulated plants that lacks one of volatile chemicals), active chemicals, such as linalool, E-2-hexenal and 1-Penten-3-ol, in rice volatiles attractive to the parasitoid were identified and a blend that was active in the field was developed. To screen chemicals (just like JA) that can induce rice plants to release volatiles attractive to the parasitoid, we cloned the promoter of the gene linalool synthase (LIS), which catalyse the production of linalool, a chemical that is attractive to the parasitoid. By using Agrobacterium-based transformation system, we obtained homozygous rice lines with expression of the LIS promoter plus a gene GUS. Based on this genetically manipulated rice lines, we screened one chemical that could induce rice plants to release the volatiles attractive to the parasitoid. The results suggest that the effectiveness of the natural enemies in the field might be enhanced by applying appropriate volatiles or volatiles-eliciting chemicals, which finally reduce the application of the insecticides.