Insecticidal Properties of Euphorbiaceae: Sebastiania corniculata-derived 8-Hydroxyquinoline and Its Derivatives against Three Planthopper Species (Hemiptera: Delphacidae)

This study examined the insecticidal effects of Sebastiania corniculata materials against Laodelphax striatellus, Nilaparvata lugens, and Sogatella furcifera. Based on the lethal dose∧50 (LD∧50) values, the chloroform fraction of S. corniculata showed the most potential activity against L. striatellus (1.09 ㎍/female), N. lugens (4.46 ㎍/female), and S. furcifera (2.32 ㎍/female). Therefore, we purified the active component of the chloroform fraction, using various chromatographies, and identified it as 8-hydroxyquinoline. To establish the structure-activity relationships, we tested 8-hydroxyquinoline and its derivatives against the 3 planthopper species. Based on 48 h LD∧50 values, isoquinoline and 6-methoxyquinoline were the most effective against the 3 species. 8-Hydroxyquinoline, 4-methylquinoline, 6-methylquinoline, and 8-hydroxy-2-methylquinoline showed high insecticidal effects. These results indicate that changing the nitrogen atom's position in quinoline's pyridine ring plays an important role in the insecticidal effects. We found a high correlation between the introduction of a functional group into the quinoline structure and toxicity against the 3 planthoppers. Our results indicate these insecticidal effects seem to require quinoline derivatives containing hydroxyl (R₄ position), methyl (R₂ and R₃ position), and methoxy (R₃ position) groups and a structural isomer of quinoline and suggest that these derivatives may be useful as new preventative agents against the damage caused by a wide range of pests in rice farming areas.