Effect of steam distillate extract of resistant wild riceOryza officinalis on behavior of brown planthopperNilaparvata lugens (Stal) (Homoptera: Delphacidae)

Rice plant volatiles extracted as steam distillates significantly affected the behavior of the brown planthopperNilaparvata lugens (Stal). In a choice test, significantly more females settled and fed on tillers of a susceptible rice variety, Taichung Native 1 (TN 1), sprayed with acetone or untreated TN 1 plants than on TN 1 tillers sprayed with the extracts of resistant wild riceOryza officinalis. O. officinalis steam distillate was highly toxic to first-instar nymphs ofN. lugens. Ingestion and assimilation of food by females was significantly reduced on TN 1 plants sprayed withO. officinalis distillate compared to TN 1 plants sprayed with acetone. Application of0. officinalis distillate on TN 1 plants adversely affected hatchability of eggs ofN. lugens.     

Isolation ofC-glycosylflavones as probing stimulant of planthoppers in rice plant

Three species of planthopper,Nilaparvata lugens,Sogatella furcifera, andLaodelphax striatellus, showed characteristic behavior of stylet probing in parenchymal tissues of plants. Feeding experiments of planthoppers on aqueous sucrose solution containing the extract of rice plants or barnyard grass revealed the presence of the stimulant for the probing behavior in the plant tissues. EightC-glycosylflavones which stimulated stylet probing were isolated from rice plants. Four of them were identified to be schaftoside, neoschaftoside, carlinoside, and neocarlinoside, the last one being a new compound isolated from the plant. The isolatedC-glycosylflavones showed the same level of the activity for the probing ofN. lugens as the rice plant extract only when all of them were combined.     

Role of plant volatiles in resistance of selected rice varieties to brown planthopper,Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

Rice plant volatiles extracted as steam distillates significantly affected the behavior and biology of the brown planthopper,Nilaparvata lugens (Stål). In a multichoice test, more females settled and fed on tillers of a susceptible rice variety Taichung Native 1 (TN1), sprayed with its own extract or acetone than on TN1 tillers sprayed with the extract of the resistant variety ARC6650 or Ptb33. In another test,N. lugens females ingested significantly more of a 10% sucrose solution mixed with TN1 steam distillate extract than of plain sucrose solution or that mixed with extracts of resistant varieties. Topical application of the extracts of resistant varieties Mudgo, ASD7, Rathu Heenati, Babawee, Ptb33, and ARC6650 caused significantly higher mortality of females than did the TN1 extract. Likewise, significantly more first-instar nymphs died when they were caged on susceptible TN1 plants sprayed with the extracts of resistant varieties than on plants sprayed with TN1 extract. The extract of 60-day-old resistant plants was more toxic than the extract of 30-, 45-, or 100-day-old plants. However, toxicity of the extract from susceptible TN1 remained low at all plant growth stages.Principal Research Scientist (ICIPE), based at International Rice Research Institute (IRRI), P.O. Box 933, Manila, Philippines.