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

Abstract

This study examined the insecticidal effects of Sebastiania corniculata materials against Laodelphax striatellus, Nilaparvata lugens, and Sogatella furcifera. Based on the lethal dose50 (LD50) values, the chloroform fraction of S. corniculata showed the most potential activity against L. striatellus (1.09 μg/female), N. lugens (4.46 μg/female), and S. furcifera (2.32 μg/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 LD50 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.