Mtx toxins from Lysinibacillus sphaericus enhance mosquitocidal cry-toxin activity and suppress cry-resistance in Culex quinquefasciatus

•Mtx proteins are toxic toward larval Culex quinquefasciatus.•Toxicity was also shown toward Cry-resistant Cx. quinquefasciatus larvae.•Mtx and Cry proteins show greater activity from synergy.•Mtx and Cry synergy suppresses Cry-resistance in mosquito larvae.

The interaction of Mtx toxins from Lysinibacillus sphaericus (formerly Bacillus sphaericus) with Bacillus thuringiensis subsp. israelensis Cry toxins and the influence of such interactions on Cry-resistance were evaluated in susceptible and Cry-resistant Culex quinquefasciatus larvae. Mtx-1 and Mtx-2 were observed to be active against both susceptible and resistant mosquitoes; however varying levels of cross-resistance toward Mtx toxins were observed in the resistant mosquitoes. A 1:1 mixture of either Mtx-1 or Mtx-2 with different Cry toxins generally showed moderate synergism, but some combinations were highly toxic to resistant larvae and suppressed resistance. Toxin synergy has been demonstrated to be a powerful tool for enhancing activity and managing Cry-resistance in mosquitoes, thus Mtx toxins may be useful as components of engineered bacterial larvicides.

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