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Background  Worldwide, mosquito vectors are transmitting several etiological agents of important human diseases, including malaria, causing millions of deaths every year. In Saudi Arabia, as elsewhere, vector-control is based mostly on chemical insecticides which may be toxic and cause environmental deprivation. Here, to support the development of bio-pesticide alternatives, a study was conducted to identify native  Bacillus thuringiensis  ( Bt ) isolates with improved toxicity against the malaria vector,  Anopheles gambiae  ( s.l .).    Methods  Sixty-eight  Bt  isolates were obtained from 300 soil and other samples collected from 16 sites across Saudi Arabia.  Bt  identification was based on morphological characteristics of colonies, shape of parasporal crystals and biochemical profiles. After characterization of their mosquitocidal activity, larvicidal strains were described through 16S ribosomal DNA gene sequencing,  cry ,  cyt  and  chi  genes PCR-amplification profiles, and SDS-PAGE protein analyses.    Results  Spherical  Bt  crystals were predominant amongst the 68 isolates (34%), while irregular, bi-pyramidal and spore-attached crystals were found in 32, 13 and 21% of strains, respectively. LC 50  and LC 90  bioassays showed that 23/68 isolates were larvicidal, with distinct biochemical activity profiles compared to non-larvicidal  Bt  strains. Eight larvicidal strains showed larvicidal activity up to 3.4-fold higher (LC 50  range: 3.90–7.40 μg/ml) than the reference  Bti- H14 strain (LC 50  = 13.33 μg/ml). Of these, 6 strains had  cry  and  cyt  gene profiles similar to  Bti -H14 ( cry4Aa, cry4Ba, cry10, cry11, cyt1Aa, cyt1Ab, cyt2Aa ). The seventh strain ( Bt 63) displaying the highest larvicidal activity (LC 50  = 3.90 μg/ml) missed the  cry 4Aa and  cyt 1Ab genes and had SDS-PAGE protein profiles and spore/crystal sizes distinct from  Bti- H14. The eight strain ( Bt 55) with LC 50  of 4.11μg/ml had  cry  and  cyt  gene profiles similar to  Bti -H14 but gave a  chi  gene PCR product size of 2027bp. No strains harbouring  cry2, cry17 + 27, cry24 + 40, cry25, cry29, cry30,  or  cyt2Ba  were detected.    Conclusion  This study represents the first report of several Saudi indigenous  Bt  strains with significantly higher larvicidal efficacy against  An. gambiae  than the reference  Bti -H14 strain. The very high toxicity of the  Bt 63 strain, combined with distinct  cry  and  cyt  genes and SDS-PAGE-protein profiles makes it a promising candidate for future applications in mosquito bio-control.    Electronic supplementary material  The online version of this article (doi:10.1186/s13071-016-1922-6) contains supplementary material, which is available to authorized users.

parasites and vectors

Isolation and characterization of native Bacillus thuringiensis strains from Saudi Arabia with enhanced larvicidal toxicity against the mosquito vector Anopheles gambiae (s.l.)