Lethal and sublethal effects of Xenorhabdus nematophila on Plutella xylostella larvae in laboratory

Xenorhabdus nematophila is a broad-spectrum of entomopathogen that lives symbiotically with entomopathogenic nematode.In order to understand the insecticidal activities of X.nematophila,the toxicity and the sublethal effects of X.nematophila ( Xn ) HB310 strain on Plutella xylostella were assayed in laboratory.The bioassay results indicated that Xn HB310 culture broth had high lethal activities against 2nd instar and 3rd instar larvae of P.xylostella, with LC50 values of 3.32×104 CFU/mL and 8.56×104 CFU/mL respectively,at 72 h.The insecticidal ingredient existed in bacterial cells and the free-cell supernatant by 50 kDa ultra-filtration.Furthermore, Xn HB310 also showed obvious antifeedant activity on 2nd instar and 3rd instar larvae of P.xylostella, and the AFC50 values were 4.03×105 CFU/mL and 8.48×105 CFU/mL respectively.When the 2.24×106 CFU/mL Xn HB310 culture broth was directly sprayed on the cabbage seedling,the persistence of the culture broth was up to 3-4 days.After feeding the 2nd instar larvae of P.xylostella with cabbage leaves treated by sublethal concentration of Xn HB310 culture broth,the survival rate and developmental rate of larvae,as well as pupa weight,adult longevity and fecundity decreased significantly as compared to that of control. Xn HB310 showed not only high lethal and antifeedant activities but also obvious sublethal effects on P.xylostella, which illustrated that Xn HB310 has potential to control P.xylostella as insecticidal agent.