LAUSR

Abstract Culex quinquefasciatus resistance to the Binary protoxin from Lysinibacillus sphaericus biolarvicides can rely on mutations in the cqm1 gene, which encodes its Cqm1 receptor. Bacillus thuringiensis svar. israelensis (Bti) biolarvicides can be used to manage L. sphaericus resistance since their protoxins act through distinct receptors from Cqm1. This study aimed to evaluate the effect of a L. sphaericus/Bti combined biolarvicide treatment on the frequency of three cqm1 resistance alleles in Cx. quinquefasciatus larvae from one subarea (SA2) compared to another (SA1) where only L. sphaericus was kept. Larvae collected before and during a two-year trial were subjected to bioassays and PCR assays. Susceptibility to L. sphaericus showed oscillations in both areas, but no significant alterations of the lethal concentrations were detected. The pre-trial frequency of the resistance alleles was 0.057, while during the trial, the mean frequency was significantly lower in SA2 (0.068) than in SA1 (0.088). All three alleles investigated were detected in the study subareas and the cqm1REC-D19 was the most frequent allele found, regardless the treatment employed. This study showed that the use of the L. sphaericus/Bti biolarvicide was associated with a lower frequency of the resistance alleles and can be a useful tool to prevent the onset of L. sphaericus resistance.