# Biochemical Responses of Anopheles spp. Larvae to a Novel Brazilian BR101 Bacillus thuringiensis var. israelensis Formulation: Oxidative Stress, Detoxification Enzymes, and Safety for Nontarget Notonectidae and Gerridae Aquatic Insects

## TL;DR

A new Brazilian formulation of Bti effectively kills malaria-carrying mosquito larvae without harming other aquatic insects.

## Contribution

The study introduces a novel Brazilian Bti strain (BR101) with proven larvicidal efficacy and safety for non-target species.

## Key findings

- Bti BR101 caused significant mortality in Anopheles larvae with an LC50 of 3.13 µg/mL.
- Bti BR101 induced oxidative stress and activated detoxification enzymes in larvae.
- Bti BR101 showed no lethal effects on non-target aquatic predators like Notonectidae and Gerridae.

## Abstract

Despite its proven efficacy, Bacillus thuringiensis israelensis (Bti) has not yet been incorporated into Brazilian Ministry of Health programs targeting Anopheles spp., the primary malaria vectors. This study evaluated the larvicidal potential of the Brazilian strain BR101. The strain displayed significant activity, with mortality rates ranging from 11% ± 2% to 91% ± 5% (LC50 = 3.13 µg/mL), accompanied by increased reactive oxygen species (54.67 ± 3 µmol H2O2), lipid peroxidation (57.33 ± 4.5 ηmol), and oxidative protein damage (16.67 ± 2.1 nM reactive carbonyls/mg). Biochemical responses included elevated activities of superoxide dismutase (29.00 ± 3 mU/mg protein), catalase (17.00 ± 1 µmol H2O2), glutathione peroxidase (29.00 ± 3 mmol NADPH/min/mL), mixed‐function oxidases (11.00 ± 3 nmol cytochrome/mg protein), and esterases (α: 20.67 ± 2; β: 25.67 ± 1 µmol/min/mg). Acetylcholinesterase activity was slightly reduced (80.33 ± 7 µmol/min/mg). Ecotoxicological assays revealed no lethal effects on nontarget aquatic predators (Notonectidae, Gerridae), with 100% survival over 30 days, equivalent to controls. These findings demonstrate that Bti BR101 is effective against Anopheles larvae while being safe for nontarget organisms.

Bti BR101 exhibits strong larvicidal activity against Anopheles larvae spp., with dose‐dependent mortality and LC50 of 3.13 µg/mL. Bti increases ROS, lipid and protein oxidation, and activates antioxidant enzymes (SOD, CAT, GPx) and detoxification pathways (MFO and esterases), indicating moderate oxidative stress. Importantly, Bti shows no lethal effects on non‐target aquatic predators, supporting its safety and suitability for vector control.