Given a safe and sustainable environment in which to thrive, human potential is truly extraordinary. In a perfect world, our achievements would be bound only by our imagination and our ambition.
But the world we live in is far from perfect. Beyond the threats posed by war, famine, and irresponsible use of our environment, disease spread by insects continues to pose a significant challenge to many people around the globe.
Fortunately, dedicated abatement professionals everywhere champion the vision of a world where people can live their lives without fear of insect-borne illnesses. Valent BioSciences is helping make this vision a reality by developing and manufacturing sustainable solutions for mosquito control programs around the world . Through science and technology, we help protect and grow global potential by working with the world’s most respected public health professionals.
Bacillus thuringiensis subsp. israelensis strains, AM 65-52 and SA3A
Bacillus thuringiensis israelensis (Bti) serotype H14 was first isolated from mosquito larvae in an isolated stagnant pond in the Negev Desert of Israel (Goldberg and Margalit 1977). Bti is ubiquitous in insects, soils, and aquatic habitats. The action of Bacillus thuringiensis subsp. israelensis is highly specific against certain families of Diptera in the suborder Nematocera, including mosquitoes (Culicidae: Lacey 2007); black flies (Simuliidae: Molloy 1982; Lacey and Undeen 1987; Guillet et al. 1990; Adler et al. 2004); chironomid midges (Chironomidae: Ali 1981; Mulla et al. 1990; Rodcharoen et al. 1991; Hughes et al. 2005); fungus gnats (Sciaridae: Cantwell and Cantelo 1984; Grewal 2000); crane flies (Tipulidae: Waalwijk et al. 1992); filter flies (Pyschodida: Houston et al. 1989); and certain species in other families of Nematocera (Boisvert and Boisvert 2000; Lacey and Merritt 2003). During almost 30 years of field use in a variety of settings around the globe, Bti has been shown to provide effective, reliable, and environmentally compatible control of mosquito larvae. In addition to Bti’s effectiveness, it has an excellent safety record and very low mammalian toxicity: LD50 values for both oral and dermal toxicity are more than 30,000 mg/kg. The mosquitocidal crystal proteins, spores, and vegetative cells of Bti administered by different routes have been found to be nonpathogenic and nontoxic to various animal species in maximum challenge tests (Siegel and Shadduck 1990). Bti is safe for use in aquatic environments, including drinking water reservoirs, for the control of mosquito, black fly, and nuisance-insect larvae (WHO 2004).
The specificity of Bti is a function of its mode of action. Bti produces crystal proteins known as protoxins during sporulation. When these proteins are applied to larval habitats of mosquitoes, the mosquito larvae ingest them by filter feeding. The crystal proteins are solubilized by the alkaline juices in the larval midgut and are cleaved by the midgut proteases, yielding active peptide toxins called delta-endotoxins. The delta-endotoxins cause the formation of holes in the midgut cell wall, leading to immediate lysis of cells and larvae death within 2–24 hours. The experience that Bti strains AM 65-52 (VectoBac, VectoMax, and Bactimos brands) and SA3A (Teknar brand) present little or no risk for non-target organisms, human health, and the environment has been confirmed by numerous studies and numerous years of field experience.
|Species:||Bacillus thuringiensis subspecies israelensis|
|Strains:||de Barjac 1978|
|First Description:||AM 65-52 (VectoBac, Bactimos) and SA3A (Teknar)|
Bacillus sphaericus 2362, strain ABTS-1743
Bacillus sphaericus is a gram-positive, spore-forming aerobic bacterium found in a multitude of soil and aquatic habitats around the world (Lacey 2007).
The moiety responsible for mosquito larvicidal activity in serotype 5a5b isolates of Bs is a binary toxin (Charles et al. 1996). As with Bti, when Bs proteins are applied to larval habitats of mosquitoes, the mosquito larvae ingest them by filter feeding. The crystal proteins are solubilized by the alkaline juices in the larval midgut and are cleaved by the midgut proteases. This yields the two component proteins of the toxin: BinA (42 kDa) and BinB (51 kDa) (Lacey 2007). These active moieties cause the formation of holes in the midgut cell wall, leading to lysis of cells and larvae death. The Bs binary toxin is more specific than Bti toxins, being principally active against mosquitoes. The range of mosquito species that are affected by Bs is also narrower than that of Bti. Excellent control of larvae of certain mosquito species is observed with Bs, especially in the genera Culex and Psorophora and, to a lesser extent, Anopheles, Aedes, Ochlerotatus, and Mansonia species; Stegomyia (Aedes) species such as Aedes aegypti are largely unaffected (Lacey 2007).
Commercial preparations of Bs persist longer under natural conditions than Bti (Hertlein et al. 1979; Mulligan et al. 1980), particularly in organically enriched habitats.
Laboratory and field tests against several invertebrate/non-target species confirm the specificity of Bs for mosquitoes and safety for the vast majority of non-targets, including a variety of mosquito predators, chironomids, and other species of Nematocera (Mulla et al. 1984; Aly and Mulla 1987; Karch et al. 1990; Lacey and Mulla 1990; Rodcharoen et al. 1991; Walton and Mulla 1991; Yousten et al. 1991, 1992; Lacey and Siegel 2000; Lacey and Merritt 2003; Brown et al. 2004). The specificity of Bs for mosquito larvae also eliminates its direct risk to vertebrates including fish, birds, and mammals (Shadduck et al. 1980; Saik et al. 1990; Siegel and Shadduck 1990b, 1990c; Lacey and Siegel 2000; Lacey and Merritt 2003). Few long-term effects of repeated applications of Bs on aquatic-community structure and diversity have been reported (Lacey 2007). Mulla et al. (1984) and Lacey and Mulla (1990) reported no noticeable adverse effects on invertebrate fauna after season-long control of Culex spp. With Bs, Merritt et al. (2005) conducted a 3-year study in southeastern Wisconsin to assess the effects of Bs applied for mosquito control on non-target wetland invertebrates. The authors used 5 bioassessment measures: mean taxa richness; mean diversity; Diptera richness (minus mosquitoes); Diptera abundance (minus mosquitoes); and functional group changes in the percentage of collector-gatherers, collector-filterers, scrapers, shredders, and predators. No detrimental effects to non-target organisms could be attributed to routine application of Bs (Lacey 2007).
Since 1995, Bs has demonstrated the ability to provide residual control of mosquito larvae in a great variety of aquatic habitats around the world. This biological larvicide is capable of providing residual control in highly organic environments, including catch basins, sewage effluent, sewage lagoons, oxidation ponds, animal waste lagoons, septic ditches, etc.
|Species:||Bacillus sphaericus 2362|
|First Description:||Kellen and Meyers 1964|