Efficacy of Lysinibacillus sphaericus against mixed-cultures of field-collected and laboratory larvae of Aedes aegypti and Culex quinquefasciatus

Biotechnological Potential of Microorganisms for Mosquito Population Control and Reduction in Vector Competence

Mosquitoes transmit pathogens that cause human diseases such as malaria, dengue fever, chikungunya, yellow fever, Zika fever, and filariasis. Biotechnological approaches using microorganisms have a significant potential to control mosquito populations and reduce their vector competence, making them alternatives to synthetic insecticides. Ongoing research has identified many microorganisms that can be used effectively to control mosquito populations and disease transmission. However, the successful implementation of these newly proposed approaches requires a thorough understanding of the multipronged microorganism-mosquito-pathogen-environment interactions. Although much has been achieved in discovering new entomopathogenic microorganisms, antipathogen compounds, and their mechanisms of action, only a few have been turned into viable products for mosquito control. There is a discrepancy between the number of microorganisms with the potential for the development of new insecticides and/or antipathogen products and the actual available products, highlighting the need for investments in the intersection of basic research and biotechnology.

Entomopathogen-based biopesticides: insights into unraveling their potential in insect pest management

Global food security is a critical challenge to fulfill the demands of an exponentially growing population. To date, growers rely on chemicals; the broad-spectrum application of synthetic molecules leads to environmental contamination, resistance development, residual toxicity, pest resurgence, and a detrimental effect on human health and cattle. Crop production needs to be improved considering environmental and human health concerns to ensure food security. Furthermore, economically important crops are prone to attack by insect pests, causing considerable yield losses. Microbes are an eco-friendly, versatile alternative, and a potential candidate for combatting destructive pests below the economic injury level and improving the plant's health and productivity. Several microbial pathogens, including parasites, predators, parasitoids, pollinators, and many beneficial microorganisms, possess toxic properties against target organisms but do not cause harm to the non-target organisms. Entomopathogens (ENMs) have great potential for pest suppression due to their remarkable properties. Bacteria are host-specific, but fungi have a broader host range and can be significantly affected by both soil-dwelling and terrestrial insect pests. Virulent pathogens cause mortality in target insect pests known as ENMs and can penetrate through natural openings, ingestions, and integuments to cause a possible effect on target insect pests. The objective of using ENMs is to sustain productivity, improve environmental health, reduce pesticides, and conserve natural resources. Moreover, research is ongoing to discover other possible aspects, especially exploring potential ENMs. Therefore, there is a need for identification, isolation, and bioformulation to overcome the existing issues. This study is mainly focused on the status of bio-formulations, pathogenicity, their mode of action, and the potential application of different types of microbial formulations for sustainable pest management.

Effectiveness of a Buffalo Turbine and A1 Mist Sprayer for the Areawide Deployment of Larvicide for Mosquito Control in an Urban Residential Setting

The control of medically important container-inhabiting mosquitoes is an ongoing challenge for mosquito control operations. Truck-mounted application equipment is a common option for rapid areawide larvicide deployment utilized by mosquito control operations. We tested the effectiveness of two truck-mounted sprayers (A1 Super Duty + Buffalo Turbine CSM3), for the deployment of water-dispersible biopesticides (VectoBac WDG:VectoLex WDG 50:50). Sixty residences within four residential neighborhoods in New Jersey were treated in 2019 and 2020. Three empty bioassay cups were placed in specific locations on each property (front yard/ back yard/ side of house), with an additional cup placed in an adjacent catch basin. This approach was replicated in two untreated control neighborhoods. Following larvicide application, cups were subjected to bioassays wherein larval mortality was tracked through adult eclosion. Overall, average larval mortality rates were 56% higher in treated cups compared against untreated controls. Mortality rates were affected by cup location, with 39% mortality in bioassay cups from back yards, 54% in those from the sides of houses, 73% in front yards, and 76% from cups in catch basins. Mortality did not differ significantly between the four treated neighborhoods, nor by the type of sprayer used. Our research shows that truck-mounted sprayers can be an effective method for larvicide deployment in residential neighborhoods, but effectiveness may depend upon the location of the target treatment area in relation to residences and other geographic obstacles.

Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance

Larvicides based on the bacteria Bacillus thuringiensis svar. israelensis (Bti) and Lysinibacillus sphaericus are effective and environmentally safe compounds for the control of dipteran insects of medical importance. They produce crystals that display specific and potent insecticidal activity against larvae. Bti crystals are composed of multiple protoxins: three from the three-domain Cry type family, which bind to different cell receptors in the midgut, and one cytolytic (Cyt1Aa) protoxin that can insert itself into the cell membrane and act as surrogate receptor of the Cry toxins. Together, those toxins display a complex mode of action that shows a low risk of resistance selection. L. sphaericus crystals contain one major binary toxin that display an outstanding persistence in field conditions, which is superior to Bti. However, the action of the Bin toxin based on its interaction with a single receptor is vulnerable for resistance selection in insects. In this review we present the most recent data on the mode of action and synergism of these toxins, resistance issues, and examples of their use worldwide. Data reported in recent years improved our understanding of the mechanism of action of these toxins, showed that their combined use can enhance their activity and counteract resistance, and reinforced their relevance for mosquito control programs in the future years.

Lysinibacillus sphaericus III(3)7 and Plasmid Vector pMK4: New Challenges in Cloning Platforms

The acquisition and especially the maintenance of a plasmid usually brings a fitness cost that reduces the reproductive rate of the bacterial host; for strains like Lysinibacillus sphaericus III(3)7, which possesses important environmental properties, this alteration along with morphological changes and reduced sporulation rates may exert a negative effect on metabolic studies using plasmids as cloning platforms. The aim of this study is to approach the metabolic behavior of pMK4-bearing cells of L. sphaericus III(3)7 through the use of bioinformatic and in vitro analyses. An incompatibility model between the pMK4 vector and a predicted megaplasmid, pBsph, inside III(3)7 cells was constructed based on an incA region. Additionally, in vitro long-term plasmid stability was not found in plasmid-bearing cells. Alignments between replicons, mobile genetic elements and RNA-RNA interactions were assessed, pairwise alignment visualization, graphic models and morphological changes were evaluated by SEM. Metabolite analysis was done through HPLC coupled to a Q-TOF 6545, and electrospray ionization was used, finally, Aedes aegypti and Culex quinquefasciatus larvae were used for larvicidal activity assessment. Results found, a decreased growth rate, spore formation reduction and morphological changes, which supported the idea of metabolic cost exerted by pMK4. An incompatibility between pMK4 and pBsph appears to take place inside L. sphaericus III(3)7 cells, however, further in vitro studies are needed to confirm it.

Assessment of the Synergic Effect between Lysinibacillus sphaericus S-Layer Protein and Glyphosate in the Lethality of the Invasive Arboviral Vector Aedes albopictus

Glyphosate and glyphosate-based herbicides are among the most used chemicals in plant pest control. Both glyphosate and its main by-product Aminomethylphosphonic Acid (AMPA) are highly environmentally persistent and, through several processes (including surface runoff and bioaccumulation), affect species beyond their intended targets, especially in aquatic ecosystems. Aedes albopictus is a novel invasive arboviral vector in Colombia and has spread to much of the national territory in recent years. Strains of the bacterium Lysinibacillus sphaericus have shown the ability to degrade glyphosate into environmentally inert compounds, in addition to having great larvicidal efficiency in different mosquito species through the production of several proteins, including the surface layer (S-Layer) protein. The S-Layer is a bacterial structure consisting of glycoprotein monomers, and its functions are thought to include bacterial interactions, protection from the outside medium and biological control. The study assessed the entomopathogenic activity of L. sphaericus S-Layer protein on Ae. albopictus larvae, and the effects that glyphosate and its by-products have in this process. To that end, bioassays were performed to compare the larval mortality between different treatments with and without S-Layer, glyphosate, and glyphosate derivates. Comparisons were made through Analysis of variance (ANOVA) and Tukey's Honestly Significant Difference (HSD) analyses. Significant differences were found in larval mortality in the treatments, and larval mortality was greater when the S-Layer protein was present, though glyphosate field-doses (1.69 g/L) alone had a notable toxicity as well. An apparent synergic effect on the mortality of larval Ae. albopictus when exposed to mixtures containing 1500 ppm of the S-Layer protein, glyphosate, and/or glyphosate derivates was found. Further studies are needed for the in-depth understanding of this mechanism and its consequences on aquatic ecosystems.

Insecticide resistance in Culex quinquefasciatus Say, 1823 in Brazil: a review

Culex quinquefasciatus is a successful invasive species broadly distributed in subtropical regions, including Brazil. It is an extremely annoying mosquito due to its nocturnal biting behavior, in high-density populations and it is a potential bridge between sylvatic arbovirus from birds to man in urban territories. Herein, we present a review concerning the methods of chemical control employed against Cx. quinquefasciatus in Brazil since the 1950’s and insecticide resistance data registered in the literature. As there is no specific national programme for Cx. quinquefasciatus control in Brazil, the selection of insecticide resistance is likely due in part to the well-designed chemical campaigns against Aedes aegypti and the elevated employment of insecticides by households and private companies. There are very few publications about insecticide resistance in Cx. quinquefasciatus from Brazil when compared to Ae. aegypti. Nevertheless, resistance to organophosphates, carbamate, DDT, pyrethroids and biolarvicides has been registered in Cx. quinquefasciatus populations from distinct localities of the country. Concerning physiological mechanisms selected for resistance, distinct patterns of esterases, as well as mutations in the acetylcholinesterase (ace-1) and voltage-gated sodium channel (Na_V) genes, have been identified in natural populations. Given environmental changes and socioeconomical issues in the cities, in recent years we have been experiencing an increase in the number of disease cases caused by arboviruses, which may involve Cx. quinquefasciatus participation as a key vector. It is urgent to better understand the efficiency and susceptibility status to insecticides, as well as the genetic background of known resistant mechanisms already present in Cx. quinquefasciatus populations for an effective and rapid chemical control when eventually required.

The Golden Activity of Lysinibacillus sphaericus: New Insights on Gold Accumulation and Possible Nanoparticles Biosynthesis

Power struggles surrounding the increasing economic development of gold mining give rise to severe environmental and social problems. Two new strains of Lysinibacillus sphaericus were isolated from an area of active alluvial gold mining exploitation at El Bagre, Antioquia. The absorption capacity of these strains and some of the L. sphaericus Microbiological Research Center (CIMIC) collection (CBAM5, OT4b.31, III(3)7) were evaluated by spectrophotometry according to a calibration gold curve of HAuCl₄⁻ with concentrations between 0 µg/mL and 100 µg/mL. Bioassays with living biomass were carried out with an initial gold concentration of 60 µg/mL. Their sorption capacity was evident, reaching percentages of gold removal between 25% and 85% in the first 2 h and 75% to 95% after 48 h. Biosynthesis of possible gold nanoparticles (AuNPs) in assays with living biomass was also observed. Metal sorption was evaluated using scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) analysis. The sorption and fabrication capacity exhibited by the evaluated strains of L. sphaericus converts this microorganism into a potential alternative for biomining processes, especially those related to gold extraction.