[The synergism between Mtx1 from Bacillus sphaericus and Cyt1 Aa from Bacillus thuringiensis to Culex quinquefasciatus].

Mosquitocidal toxin 1 (Mtx1) was synthesized during vegetative phase of Bacillus sphaericus and it had been proved to have higher activity to Aedes spp. larvae and Binary toxin (Bin) resistance Culex larvae. The truncated 97 kDa Mtx1 with a deletion of the signal peptide and the Cyt1 Aa crystal protein, a 27.3 kDa delta-endotoxin from Bacillus thuringiensis subsp. israelensis (Bti), were purified from Escherichia coli and B. thuringiensis recombinant strains respectively. Both purified toxins had high toxicity against Culex quinquefasciatus larvae. Bioassay result revealed the purified Mtx1 toxin had high toxicity against the target mosquito larvae, with LCso of 45.2 ng/mL. However, the mixture of Mtx1 and Cytl Aa exhibited higher toxicity against the mosquito larvae, with a lowest LC50 value of 20.19 ng/mL at the ratio of 1:3. (Mtx1:Cyt1 Aa). The calculated synergistic factor of different mixtures suggested a strong synergistic effect between Cyt1 Aa toxin and Mtx1. Furthermore, the presence of Cyt1Aa in the mixture could induce early larval mortality, enhancing the activity of Mtx1 to the target mosquito larvae. The synergistic effect of Cyt1 Aa on mortality of Mtx1 to mosquito larvae might be caused by the damage of the larval midgut-hemocoel barrier induced by the activated CytlAa toxin, which enhanced the specific pathogenesis of Mtx1 on mosquito larvae. It is suggested that the co-application of Mtx1 and Cyt1 Aa in future will be integrated for mosquito management.