title: A strain of Bacillus sphaericus causes slower development of resistance in Culex quinquefasciatus.
abstract: Two field-collected Culex quinquefasciatus colonies were subjected to selection pressure by three strains of Bacillus sphaericus, C3-41, 2362, and IAB59, under laboratory conditions. After 13 and 18 generations of exposure to high concentrations of C3-41 and IAB59, a field-collected low-level-resistant colony developed >144,000- and 46.3-fold resistance to strains C3-41 and IAB59, respectively. A field-collected susceptible colony was selected with 2362 and IAB59 for 46 and 12 generations and attained >162,000- and 5.7-fold resistance to the two agents, respectively. The pattern of resistance evolution in mosquitoes depended on continuous selection pressure, and the stronger the selection pressure, the more quickly resistance developed. The resistant colonies obtained after selection with B. sphaericus C3-41 and 2362 showed very high levels of cross-resistance to B. sphaericus 2362 and C3-41, respectively, but they displayed only low-level cross-resistance to IAB59. On the other hand, the IAB59-selected colonies had high cross-resistance to both strains C3-41 and 2362. Additionally, the slower evolution of resistance against strain IAB59 may be explained by the presence of another larvicidal factor. This is in agreement with the nontoxicity of the cloned and purified binary toxin (Bin1) of IAB59 for 2362-resistant larvae. We also verified that all the B. sphaericus-selected colonies showed no cross-resistance to Bacillus thuringiensis subsp. israelensis, suggesting that it would be a promising alternative in managing resistance to B. sphaericus in C. quinquefasciatus larvae.
authors.affiliation: Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, China.
authors.forename: Guofeng
authors.initials: G
authors.lastname: Pei
authors.forename: Cláudia M F
authors.initials: CM
authors.lastname: Oliveira
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Yuan
authors.forename: Christina
authors.initials: C
authors.lastname: Nielsen-LeRoux
authors.forename: Maria Helena
authors.initials: MH
authors.lastname: Silva-Filha
authors.forename: Jianpin
authors.initials: J
authors.lastname: Yan
authors.forename: Lêda
authors.initials: L
authors.lastname: Regis
mesh_terms: D000818:Animals; D001407:Bacillus / Q000502:physiology*; D005075:Biological Evolution; D003465:Culex / Q000502:physiology*; D004351:Drug Resistance / Q000502:physiology*