Efficacy and efficiency of new Bacillus thuringiensis var. israelensis and Bacillus sphaericus formulations against Afrotropical anophelines in Western Kenya

Abstract

SummaryWe evaluated the efficacy of new water-dispersible granular (WDG) formulations of Bacillus thuringienis var. israelensis (Bti; VectoBac Ò ) and B. sphaericus (Bs; VectoLex Ò , Valent BioScience Corp., Illinois, USA) for the control of larval Anopheles gambiae sensu lato Giles mosquitoes in a malaria-endemic area around Lake Victoria, Western Kenya. WDG and powder formulations were compared in laboratory bioassays and followed by efficiency and residual effect assessments of both WDG formulations in open field experiments. LC 50 and LC 95 values for the Bti/Bs strains and their formulations show high susceptibility of A. gambiae sensu stricto under laboratory conditions. The larvae proved more susceptible to Bs than to Bti and the WDG formulations were slightly superior to the powder formulations. High efficiency was also shown in the open field trials, and a minimum dosage of 200 g/ha Bti WDG, representing the LC 95 of the laboratory tests, was sufficient to fully suppress emergence of mosquitoes when applied at weekly intervals. Bti WDG did not show a residual effect, irrespective of the concentration applied. The Bs WDG formulation, however, showed significant larval reductions up to 11 days post-treatment at application doses of either 1 or 5 kg/ha. We conclude that the main malaria vector in our study area is highly susceptible to these microbial control agents. Minimum effective dosages to achieve elimination of the larval population in a given habitat are extremely low and environmental impact is negligible. Microbial products for larval control have therefore great potential within Integrated Vector Management programmes and may augment control efforts against adult vector stages, such as the use of insecticide-treated bednets, in many parts of Africa.

Microbial larvicides for mosquito control: Impact of long lasting formulations ofBacillus thuringiensisvar.israelensisandBacillus sphaericuson non‐target organisms in western Kenya highlands

“…The inherently high level of safety to non‐target organisms makes microbial larvicides not harmful to the environment and ideal for use in IVM operations (Walker & Lynch, 2007). Our findings thus agree with those of previous studies indicating a high level of effectiveness and safety of Bti and Bs when used for mosquito control (Fillinger & Lindsay, 2006; Fillinger et al., 2003; Fillinger, Ndenga, et al., 2009). Comparison of the activity of the two LLML formulations (FourStar ® and LL3) indicated that their efficacy against malaria mosquito vectors and their safety to non‐target organisms were not significantly different.…”

“…Thus, the toxins responsible for the pathogenic effect in mosquito larvae have no effect to vertebrates and some invertebrates, and hence they are suitable for application even in peri‐domestic mosquito breeding habitats (Lacey, 2007; Lacey & Merritt, 2003; Saik, Lacey, & Lacey, 1990). However, the conventional Bti and Bs have low residual activity and require repeated applications, which increase the cost of interventions (Fillinger, Knols, & Becker, 2003; Majambere, Lindsay, Green, Kandeh, & Fillinger, 2007; Majambere et al., 2010). In the recent past, long lasting microbial larvicide formulations that combine both Bti and Bs with potential for sustained release of active ingredients for up to 6 months have become available (Afrane et al., 2016; Zhou et al., 2016).…”

New approaches for integrated and cost-effective malaria vector control

“…Firstly, the short residual effect of Bti under tropical climatic conditions calls for frequent retreatment of breeding sites, roughly every 8 to 10 days 27,28 . Reducing the frequency of treatment intervals would significantly reduce the cost for manpower, transportation, and depending on the used product, the cost of larvicides.…”

Re-Emerging Malaria Vectors in Rural Sahel (Nouna, Burkina Faso): The Paluclim Project

“…The reason for negative findings when compared to results by Fillinger et al, (2003) a certainly due to the fact that the spraying was not only too short but was done too late. Nevertheless it is possible that deciding to treat only 50% of the productive sites was too low, and could not leas to a significant reduction of vectors.…”