Changes in susceptibility to buprofezin following ecdysis in nymphs of brown planthopper, Nilaparvata lugens.

The effect of buprofezin as a molting interferent was investigated in nymphs of Nilaparvata lugens. When susceptibility to buprofezin was examined in 4th-instar nymphs by 6 h splitfeeding with treated rice plants or topical application, susceptibility varied remarkably with 4th-instar nymphal development. The values for LC50 by feeding test and LD50 by topical application in the 0—6 h after 3rd ecdysis were 570 ppm and 21.2 ng/nymph, respectively. The most susceptible period in 4th-instar nymphs is 40—50 h after the 3rd ecdysis when the LC50 and LD50 values are 0.47 ppm and 0.281 ng/nymph, respectively. The susceptibility to buprofezin decreased again after 54 h (approximately 10 h before the next ecdysis). These changes in susceptibility to buprofezin may be linked to physiological changes following development after ecdysis in nymphs. To avoid an unstable LC50 value, continuous contact and/or feeding is recommended for buprofezin laboratory tests.