Bacillus Thuringiensis Serovariety Israelensis and Bacillus Sphaericus for Mosquito Control

Abstract

Since the discovery of Bacillus thuringiensis (Berliner) serovariety israelensis de Barjac (Bti) and efficacious isolates of Bacillus sphaericus Neide, formulations of these bacteria have become the predominant non-chemical means employed for control of mosquito larvae at several locations in the United States and other countries. An overview of developments in the past 20 years is presented in this chapter regarding the toxins of Bti and B. sphaericus, their modes of action, efficacy and factors that affect larvicidal activity, development of resistance, safety, and their roles in integrated mosquito control. The efficacy of Bti formulations has been demonstrated in a variety of habitats against a multitude of species of mosquitoes. B. sphaericus formulations have been utilized predominantly in organically enriched habitats against Culex species, but they are also active in a variety of habitats having low organic enrichment, against numerous species, and across several genera. Stegomyia spp. are not susceptible to practical doses of B. sphaericus formulations. B. sphaericus has been shown to persist longer than Bti in polluted habitats and, under certain circumstances, can recycle in larval cadavers. A disadvantage of B. sphaericus has been the development of resistance in certain populations of Cx. quinquefasciatus Say and Cx. pipiens Linnaeus. Biotic and abiotic factors that influence the larvicidal activity of Bti and B. sphaericus include species of mosquito and their respective feeding strategies, rate of ingestion, age and density of larvae, habitat factors (temperature, solar radiation, depth of water, turbidity, tannin and organic content, presence of vegetation, etc.), formulation factors (type of formulation, toxin content, how effectively the material reaches the target, and settling rate), storage conditions, production factors, means of application and frequency of treatments. Due to their efficacy and relative specificity, both Bti and B. sphaericus can be ideal control agents in integrated programs especially where other biological control agents, environmental management, personal protection and the judicious use of insecticides are combined.

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

“…Susceptible mosquito larvae have alkaline gut conditions, enzymes and specific receptors for processing and binding of the Bti or Bs toxins (Baumann, Clark, Baumann, & Broadwell, 1991; Bravo, Gill, & Soberón, 2007; Dadd, 1975; Nicolas, Lecroisey, & Charles, 1990; Soberón, Fernández, Pérez, Gill, & Bravo, 2007). 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).…”

Identifying genomic changes associated with insecticide resistance in the dengue mosquito Aedes aegypti by deep targeted sequencing

“…Resistance to pyrethroid insecticides, the primary insecticide family used against adult mosquitoes, is particularly worrying in the context of the re-emergence of dengue and other arboviruses worldwide (Bhatt et al 2013). Although attempts are made to develop new insecticides or alternative mosquito control strategies (Scholte et al 2004;Lacey 2007;Hoffmann et al 2011;Walker et al 2011;Harris et al 2012), their large-scale implementation in tropical regions will require at least a decade. Until this, characterizing molecular mechanisms underlying resistance is crucial for tracking down resistance alleles and improving resistance management strategies .…”

Abbreviations and acronyms

“…israelensis (Bti) is an entomopathogenic bacterium that has demonstrated high efficacy against Ae. aegypti larvae and is commercially available in different formulations that can be utilised in a variety of breeding habitats (Lacey, 2007;Boyce et al, 2013). Its strain AM65-52 in a water-dispersible granulated formulation is recommended by WHOPES (2016).…”