Abstract: The insecticidal activities of 9 bacterial symbionts of entomopathogenic nematodes against 4th instar nymph of locust(Locusta migratoria manilensis) were tested by bioassay.It was found that the Xenorhabdus nematophila HB310(Xn HB310)strain showed the highest insecticidal activities against 4th instar nymph of locust.The toxicities of Xn HB310 culture broth against different instars of locust were determined by the method of leaves-tip bioassays.The results showed that the median lethal concentrations(LC50) of Xn HB310 culture broth against 2nd instar nymph,4th instar nymph and adult were 2.97×105,4.90×105 and 6.24×105 CFU/mL at 96 h,respectively.The median lethal times(LT50) of Xn HB310 culture broth against 2nd instar nymph,4th instar nymph and adult were 51.48,52.59 and 64.34 h,respectively.Xn HB310 strain also showed the antifeeding activity to locust.The median antifeedant concentrations(AFC50) of Xn HB310 culture broth against 2nd instar nymph,4th instar nymph and adult were 1.15×105,2.36×105 and 3.16×105 CFU/mL at 48 h,respectively.In order to confirm the antifeeding organs of the locust,the antennae,labial palpi or maxillary palpi of locust were cutting off or were treated by topical application,respectively.The bioassay results showed that the antifeeding rates of locusts for cutting off labial palpi locust,maxillary palpi locust or both labial palpi and maxillary palpi were 37.36%,51.28% and 100%,respectively.Labial palpi and maxillary palpi were sensitive sensory organs to Xn HB310 culture broth.These results explain that Xn HB310 culture broth has fast and high insecticidal activities and has the potential as insecticidal agent of the locust.