Invertebrate communities improve the efficiency of the biological pesticide Bacillus thuringiensis var. israelensis (Bti) in mosquito control: A case study in Cameroon, Central Africa

Abstract

We investigated the influence of different combinations of natural aquatic invertebrate communities and the biological insecticide Bacillus thuringiensis var israelensis (Bti) on the establishment of larval populations of mosquitoes in temporary ponds in the field. The study involved two experiments so called “Bti and community” and “community density” experiments respectively. In the “Bti and community” part, three treatments were tested: added aquatic invertebrate community alone (“com”), Bti alone (“Bti”), and a combination of added invertebrate community and Bti (“comBti”). The “community density” experiment included three setups, all treated with Bti but having different densities of aquatic invertebrate communities (that is, “low”, “medium” and “high”). The two species of mosquitoes that established in the ponds were Anopheles spp. and Culex spp. In both experiments and after 24 h following the application of Bti, larval abundance of these mosquitoes decreased by about 78 to 99% in the setups where the biological pesticide was used. However, the recovery of mosquito larvae in these ponds was fast, and the most important in low community density conditions (“Bti” and “low”), moderate in medium community density (“medium”) and did not occur in high community density (“high” and “comBti”). By contrast with the combined treatment of invertebrate community and Bti (“comBti”), the abundance of mosquito larvae in the setup treated with invertebrate community alone (“com”) showed an increase during some days and then a progressive decrease until the end of the experiment. These results suggest that the treatment with Bti alone was efficient but only for a short time as recovery occurred; the addition of community alone was efficient in a longer term whereas the combination of Bti and added community was efficient in both the short and longer terms. This implies that the efficacy of larval control of mosquitoes by Bti was improved with high community density.

Keywords: Mosquito control, biological pesticide, Anopheles spp., Culex spp., community, temporary ponds.