Acaricidal activities of whole cell suspension,cell-free supernatant,and crude cell extract of Xenorhabdus stokiae against mushroom mite (Luciaphorus sp.)

Xenorhabdus bacterium has been used as a biological control agent against Luciaphorus sp.,a mushroom mite endemic in Thailand.To develop an effective formulation of Xenorhabdus stokiae,treatments using different parts of X.stokiae isolate PB09 culture,including whole cell suspension,cell-free supernatant,and crude cell extract,were performed.The results show that different parts of X.stokiae isolate PB09 culture could induce variable effects on mite mortality and fecundity.Application with cell-free supernatant of X.stokiae culture resulted in both the highest mite mortality rate [(89.00±3.60)%] and the lowest mite fecundity [(41.33±23.69) eggs/gravid female].Whole cell suspen-sion of X.stokiae isolate PB09 culture was found to be slightly less effective than its cell-free supernatant,suggesting that X.stokiae was more likely to release its metabolites with acaricidal activities to the surrounding culture media.Crude cell extract of X.stokiae was not effective against mites.Cell-free supernatant of X.stokiae isolate PB09 was the most effective biological control agent and it could be conveniently used in future formulations instead of live bacteria.