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

Abstract

The microbial larvicides Bacillus thuringiensis var. israelensis and Bacillus sphaericus have been used extensively for mosquito control and have been found to be effective and safe to non‐target organisms cohabiting with mosquito larvae. Recently developed long lasting microbial larvicides (LLML), although evading the previous challenge of short duration of activity, increase the risk of persistence of toxins in the treated larval habitats. This study monitored the impact of LLML FourStar® and LL3 on non‐target organisms cohabiting with mosquito larvae in an operational study to control malaria vectors in western Kenya highlands. A total of 300 larval habitats were selected in three highland villages. The habitats were first monitored for 5 weeks to collect baseline data on non‐target organisms cohabiting with mosquito larvae and then randomized into two treatment arms (respective FourStar® and LL3) and one control arm. Non‐target organisms were sampled weekly for 5 months after treatment to assess the impact of LLML intervention. Before treatment, the mean density of all non‐target organisms combined in the control, LL3 and FourStar® treated habitats was 1.42, 1.39 and 1.49 individuals per habitat per sampling occasion, respectively. Following treatment, this density remained fairly unchanged for 21 weeks at which time it was 1.82, 2.11, and 2.05 for the respective control, LL3 and FourStar® treated habitats. Statistical analysis revealed that LL3 and FourStar® did not significantly alter abundance, richness or diversity of the 11 taxa studied, when comparing the intervention and control larval habitats. However, both FourStar® and LL3 significantly reduced the density of malaria vectors. In conclusion, one round of label rate application of FourStar® or LL3 in natural larval habitats did not alter richness, abundance or diversity of the monitored aquatic non‐target organisms cohabiting with mosquito larvae to an ecologically significant level.

Mosquito-Borne Diseases Emergence/Resurgence and How to Effectively Control It Biologically

“…Bti formulations are the predominant nonchemical means employed for controlling mosquito larvae [124]. In addition, several studies indicate the highly effective and safe use of individuals or the mixture of Bti and Bs for mosquito control, and they are considered to be safe to non-target organisms cohabiting with mosquito larvae [125].…”

“…Bti formulations are the predominant nonchemical means employed for controlling mosquito larvae [124]. In addition, several studies indicate the highly effective and safe use of individuals or the mixture of Bti and Bs for mosquito control, and they are considered to be safe to non-target organisms cohabiting with mosquito larvae [125]. B. thuringiensis produces three classes of larvicidal proteins: Cry (exert intoxication through toxin activation, receptor binding, and pore formation in a suitable larval gut environment), Cyt (cytolytic for insecticidal activity, metabolites from approximately a thousand microbial isolates were examined [123].…”

“…Bti formulations are the predominant nonchemical means employed for controlling mosquito larvae [124]. In addition, several studies indicate the highly effective and safe use of individuals or the mixture of Bti and Bs for mosquito control, and they are considered to be safe to non-target organisms cohabiting with mosquito larvae [125]. B. thuringiensis produces three classes of larvicidal proteins: Cry (exert intoxication through toxin activation, receptor binding, and pore formation in a suitable larval gut environment), Cyt (cytolytic B. thuringiensis produces three classes of larvicidal proteins: Cry (exert intoxication through toxin activation, receptor binding, and pore formation in a suitable larval gut environment), Cyt (cytolytic toxicity) when sporulating (parasporal crystals), and Vip proteins throughout the vegetative phase (ionic, non-ionic detergents and pore-forming mechanisms of action were suggested), some of which are toxic against a wide range of insect orders, nematodes, and human-cancer cells.…”

“…Over the past 25 years, scientists had much interest and focused on isolating numerous strains because of their potential use as mosquito larvicides [200]. Several formulations used in biocontrol are highly effective against mosquitoes [125]. Recently renamed Lysinibacillus sphaericus (2007) [201], numerous studies have reported various levels of resistance to Bs in laboratory and field populations from different countries [176] (Table 1), mostly on Culex populations.…”

Enterococcus durans with mosquito larvicidal toxicity against Culex quinquefasciatus, elucidated using a Proteomic and Metabolomic approach

“…Microbial larvicides like Bacillus thuringiensis var. israelensis (Bt) and Bacillus sphaericus (Bs) have been found to be effective and used extensively against mosquitoes with being safe to non-target organisms 2 . The mosquito-cidal endotoxins of Bt and Bs have various environmental benefits including safety for humans and other organisms, reduction of pesticides residue in the aquatic environment, increased activity of most other natural enemies and increased biodiversity in aquatic ecosystem.…”