Screening on Synergist of Bacillus thuringiensis Wettable Powder

[Objective] This study aimed to screen the best synergistic material for wettable powder of Bt MB-15 and evaluate their synergistic effect.[Method] The synergism of six different kinds of additives for wettable powder of Bt MB-15 on the 2nd instar larvae of Plutella xylostella was determined by method of leaf dipping in laboratory.[Result] The mixtures of Bt with 0.1% ZnCl2,0.5% ZnCl2,1.0% ZnCl2,1.0% MgCl2,0.5% boric acid,1.0% boric acid,0.5% citric acid and 1.0% citric acid all exhibited synergistic effect,in which synergistic effect of 0.5% boric acid was the highest with 17.2 synergistic ratio,followed by 1.0% ZnCl2 with 15.6 synergistic ratio.Moreover,addition of 0.5% boric acid could shorten the median lethal time of wettable powder of Bt MB-15 by about 10 h.After the mixtures of Bt with 0.5% boracic acid or 1.0% ZnCl2 was stored for 15 d at room temperature,the toxicities of two mixtures did not change significantly.[Conclusion] Boracic acid as the synergist of wettable powder of Bt MB-15,not only could accelerate insecticidal effect of Bt,but also increase its insecticidal rate.So,boracic acid overcomes the disadvantages of wettable powder of Bt MB-15 such as poor insecticidal effect and slow insecticidal speed in a certain degree.