Effects of Bacillus thuringiensis var. israelensis on nonstandard microcrustacean species isolated from field zooplankton communities

Larval mosquito management and risk to aquatic ecosystems: A comparative approach including current tactics and gene-drive Anopheles techniques

Genetic engineering of mosquitoes represents a promising tactic for reducing human suffering from malaria. Gene-drive techniques being developed that suppress or modify populations of Anopheles gambiae have the potential to be used with, or even possibly obviate, microbial and synthetic insecticides. However, these techniques are new and therefore there is attendant concern and uncertainty from regulators, policymakers, and the public about their environmental risks. Therefore, there is a need to assist decision-makers and public health stewards by assessing the risks associated with these newer mosquito management tactics so the risks can be compared as a basis for informed decision making. Previously, the effect of gene-drive mosquitoes on water quality in Africa was identified as a concern by stakeholders. Here, we use a comparative risk assessment approach for the effect of gene-drive mosquitoes on water quality in Africa. We compare the use of existing larvicides and the proposed genetic techniques in aquatic environments. Based on our analysis, we conclude that the tactic of gene-drive Anopheles for malaria management is unlikely to result in risks to aquatic environments that exceed current tactics for larval mosquitoes. As such, these new techniques would likely comply with currently recommended safety standards.

Responses of benthic macroinvertebrate communities to a Bti-based insecticide in artificial microcosm streams

Bioinsecticides based on the bacterium Bacillus thuringiensis subsp. israelensis (Bti) are increasingly being applied directly into aquatic compartments to control nuisance mosquitoes and blackflies and are generally considered environmentally friendly alternatives to synthetic insecticides. Bti-based insecticides are considered highly selective, being Diptera-specific, and supposedly decompose rapidly in the environment. Nevertheless, their safety to non-target species and freshwater ecosystems has been questioned by recent studies, which in fact document possible indirect effects in aquatic food webs such as the decrease of prey availability to predators. This work aimed to evaluate the potential effects of a Bti-based insecticide (VectoBac® 12AS) on a freshwater macroinvertebrate community and on stream ecological functions by using artificial microcosm streams. Artificial microcosm streams were colonized with a macroinvertebrate community plus periphyton collected in a stream together with Alnus glutinosa leaf packs. They were exposed for 7 days to different Bti treatments (0, 12, 120, 1200 μg/L), which are within the recommended concentrations of application in aquatic compartments for blackfly and mosquito control. Besides invertebrate community structure and abundance, effects were evaluated regarding leaf decomposition and primary production as measures of ecosystem functioning. Community structure was significantly altered in all Bti treatments after 7 days of exposure, mostly due to a decline in chironomids, followed by oligochaetes, which both belong to the deposit-feeders' functional group. Direct effects on oligochaetes are surprising and require further research. Also, reductions of leaf decomposition due to Bti-induced sublethal effects on shredders (reduced feeding) or mortality of chironomids (that can also feed on coarse organic matter) observed in our study, represent potential indirect effects of Bti in aquatic ecosystems. Our short-exposure experiment evidenced some negative effects on stream benthic invertebrate communities and on ecosystem functioning that must be considered whenever Bti is used in water bodies for blackfly or mosquito control programs.

Dissecting the Environmental Consequences of Bacillus thuringiensis Application for Natural Ecosystems

Bacillus thuringiensis (Bt), a natural pathogen of different invertebrates, primarily insects, is widely used as a biological control agent. While Bt-based preparations are claimed to be safe for non-target organisms due to the immense host specificity of the bacterium, the growing evidence witnesses the distant consequences of their application for natural communities. For instance, upon introduction to soil habitats, Bt strains can affect indigenous microorganisms, such as bacteria and fungi, and further establish complex relationships with local plants, ranging from a mostly beneficial demeanor, to pathogenesis-like plant colonization. By exerting a direct effect on target insects, Bt can indirectly affect other organisms in the food chain. Furthermore, they can also exert an off-target activity on various soil and terrestrial invertebrates, and the frequent acquisition of virulence factors unrelated to major insecticidal toxins can extend the Bt host range to vertebrates, including humans. Even in the absence of direct detrimental effects, the exposure to Bt treatment may affect non-target organisms by reducing prey base and its nutritional value, resulting in delayed alleviation of their viability. The immense phenotypic plasticity of Bt strains, coupled with the complexity of ecological relationships they can engage in, indicates that further assessment of future Bt-based pesticides' safety should consider multiple levels of ecosystem organization and extend to a wide variety of their inhabitants.

Bacillus spp. metabolites are effective in eradicating Aedes aegypti (Diptera: Culicidae) larvae with low toxicity to non-target species

The growing spread of dengue, chikungunya and Zika viruses demand the development of new and environmentally safe control methods for their vector, the mosquito Aedes aegypti. This study aims to find novel larvicidal agents from mutualistic (endophytic and rhizospheric) or edaphic bacteria that have no action against non-target organisms. Eleven out of the 254 bacterial strains tested were able to kill Ae. aegypti larvae. Larvicidal activity did not depend on presence of cells, since culture supernatants or crude lipopeptide extracts (CLEs) killed the larvae. Bacillus safensis BacI67 and Bacillus paranthracis C21 supernatants were the best performing supernatants, displaying the lowest lethal concentrations (LC50 = 31.11 µL/mL and 45.84 µL/mL, respectively). Bacillus velezensis B64a and Bacillus velezensis B15 produced the best performing CLEs (LC50 = 0.11 mg/mL and 0.12 mg/mL, respectively). Mass spectrometry analysis of CLEs detected a mixture of surfactins, iturins, and fengycins. The samples tested were weakly- or non-toxic to mammalian cells (RAW 264.7 macrophages and VERO cells) and non-target organisms (Caenorhabditis elegans, Galleria mellonella, Scenedesmus obliquus, and Tetrahymena pyriformis) - especially B. velezensis B15 CLE. The biosynthetic gene clusters related to secondary metabolism identified by whole genome sequencing of the four best performing bacteria strains revealed clusters for bacteriocin, beta-lactone, lanthipeptide, non-ribosomal peptide synthetases, polyketide synthases (PKS), siderophores, T3PKS, type 1 PKS-like, terpenes, thiopeptides, and trans-AT-PKS. Purification of lipopeptides may clarify the mechanisms by which these extracts kill Ae. aegypti larvae.

Environmental and socioeconomic effects of mosquito control in Europe using the biocide Bacillus thuringiensis subsp. israelensis (Bti)

Bacillus thuringiensis subsp. israelensis (Bti) has been used in mosquito control programs to reduce nuisance in Europe for decades and is generally considered an environmentally-safe, effective and target-specific biocide. However, the use of Bti is not uncontroversial. Target mosquitoes and affected midges represent an important food source for many aquatic and terrestrial predators and reduction of their populations is likely to result in food-web effects at higher trophic levels. In the context of global biodiversity loss, this appears particularly critical since treated wetlands are often representing conservation areas. In this review, we address the current large-scale use of Bti for mosquito nuisance control in Europe, provide a description of its regulation followed by an overview of the available evidence on the parameters that are essential to evaluate Bti use in mosquito control. Bti accumulation and toxin persistence could result in a chronic expose of mosquito populations ultimately affecting their susceptibility, although observed increase in resistance to Bti in mosquito populations is low due to the four toxins involved. A careful independent monitoring of mosquito susceptibility, using sensitive bioassays, is mandatory to detect resistance development timely. Direct Bti effects were documented for non-target chironomids and other invertebrate groups and are discussed for amphibians. Field studies revealed contrasting results on possible impacts on chironomid abundances. Indirect, food-web effects were rarely studied in the environment. Depending on study design and duration, Bti effects on higher trophic levels were demonstrated or not. Further long-term field studies are needed, especially with observations of bird declines in Bti-treated wetland areas. Socio-economic relevance of mosquito control requires considering nuisance, vector-borne diseases and environmental effects jointly. Existing studies indicate that a majority of the population is concerned regarding potential environmental effects of Bti mosquito control and that they are willing to pay for alternative, more environment-friendly techniques.

A Bacillus thuringiensis kurstaki Biopesticide Does Not Reduce Hatching Success or Tadpole Survival at Environmentally Relevant Concentrations in Southern Leopard Frogs (Lithobates sphenocephalus)

Amphibians are in global decline, and anthropogenic activities are known leading causes of their demise. Thus the interaction between agriculture and amphibian health has been examined for decades. Many facets of amphibian physiology and ecology place them at high risk among the nontarget organisms affected by agricultural byproducts. Research has shown that many chemicals and fertilizers affect amphibian growth, reproduction, and survival. The impacts differ based on the type of agricultural byproduct (e.g., chemical pesticide or nutrient-heavy fertilizer) and amphibian species, but the effects are usually negative. However, minimal research exists on how organic biopesticides interact with amphibian populations. Biopesticides utilize insecticidal bacteria as the active ingredient in lieu of synthetic chemicals. The inert ingredients present in biopesticide commercial products are considered safe to nontarget organisms. The present study tested the impacts of a commercial biopesticide on the survival of amphibian embryos and larvae. We found that expected environmental concentrations of the microbial biopesticide Monterrey B.t. did not significantly reduce survival in embryos or larvae. However, the higher doses used to assess threshold toxicity levels caused significant mortality. Our data suggest that biopesticides are not directly harmful to amphibian embryos or larvae in concentrations regularly applied for pest control. Environ Toxicol Chem 2019;39:155-161. © 2019 SETAC.

Safety of Bacillus thuringiensis Cry1C protein for Daphnia magna based on different functional traits

Cry1C is a Bacillus thuringiensis (Bt) insecticidal protein and it can be produced by transgenic rice lines developed in China. Cladocera species are common aquatic arthropods that may be exposed to insecticidal proteins produced in Bt-transgenic plants through ingestion of pollen or crop residues in water. As the cladoceran Daphnia magna plays an important role in the aquatic food chain, it is important to assess the possible effects of Bt crops to this species. To evaluate the safety of the Cry1C protein for D. magna, individuals were exposed to different concentrations of purified Cry1C protein in M4 medium for 21 days. Potassium dichromate (K₂Cr₂O₇), a known toxicant to D. magna, was added to M4 medium as a positive control treatment, and pure M4 medium was used as a negative control. Our results show that developmental, reproductive, and biochemical parameters of D. magna were not significantly different between Cry1C and negative control treatments but were significantly inhibited by the positive control. We thus conclude that D. magna is insensitive to Cry1C.