[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 inatar larvae of Plulella xylostel-la 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 synergis-tic effect of 0.5% boric acid was the highest with 17. 2 synergistic ratio, followed by 1.0% ZnCl2 with 15.6 synergislic ratio. Moreover, addition of 0.5% boric acid could shorten the median lethal time of wettabie powder of Bt MB-15 by about 10 h. After the mixtures of Bt with 0.5% horacic 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 insec-ticidal speed in a certain degree.%[目的]筛选对苏云金芽胞杆菌(Bacillus thuringiemis,简称Bt)MB-15可湿性粉剂具有最佳增效作用的物质,并对增效作用显著的混配组合进行了增效作用的评定.[方法]以小菜蛾为生物测定昆虫,采用浸叶法测定了6种添加物对苏云金杆菌MB-15可湿性粉剂的毒杀增效作用.[结果]研究发现0.1％ ZnCl2、0.5％ ZnCl2、1.0％ZnCl2、1.0％MgCl2、0.5％硼酸、1.0％硼酸、0.5％柠檬酸和1.0％柠檬酸对Bt MB-15可湿性粉剂表现出增效作用,其中0.5％硼酸对Bt MB-15可湿性粉剂的增效作用最强,增效比为17.2,1.0％ ZnCl2次之,增效比为15.6.同时,杀虫速度的测定结果显示,0.5％硼酸的加入使Bt MB-15可湿性粉剂的致死中时缩短了约10h,加快了Bt的杀虫速度.此外,当将1.0％ ZnCl2和0.5％硼酸分别与Bt MB-15 或可湿性粉剂溶液室温下混合放置15 d后,两种混合物的毒力均没有明显的变化.[结论]硼酸作为Bt MB-15可湿性粉剂的增效因子,不但有利于增强Bt制剂的杀虫效果而且还可以提高其杀虫速度,从而在一定程度上克服了Bt制剂杀虫效果差和杀虫速度慢等实际问题.
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