Comparative Analysis of Bioactive Volatiles from Susceptible and Resistant Rice Varieties to the Major Rice Pest Nilaparvata lugens Stål

Infestation by herbivorous pests can change plant volatile profiles leading to increased foraging by natural enemies and reduced attack by the pests. Eight rice bioactive volatiles (semiochemicals) were identified by GC-EAG. The quantitative differences in the production of these volatiles between susceptible and resistant rice varieties to the rice pest Nilaparvata lugens (BPH) were then determined. There was no clear correlation in the production of these volatiles with the rice resistance levels against BPH. The total amount of these volatiles and the expression of genes associated with the biosynthesis of these volatiles were significantly higher in susceptible varieties than in resistant varieties, and as expected further upregulated upon BPH-infestation. In behavioural experiments, the un-infested rice volatiles (UIRVs) were more attractive to BPHs. Interestingly, the attractiveness of UIRVs was significantly reduced by the addition of the blend that mimics the natural composition of these volatiles in the infested rice plants (IRVs). Furthermore, the 1:1 molar mixture of these volatiles identified from IRVs repelled BPHs. These results demonstrate as expected that UIRVs initially serve as attractive signals to rice insect pests. The pest-infestation changes the rice volatile profile to be less attractive, which pushes further colonization to un-infested plants nearby.