Efficacy of entomopathogenic bacteria for control of Musca domestica

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.

ZnO nanoparticles produced in the culture supernatant of Bacillus thuringiensis ser. israelensis affect the demographic parameters of Musca domestica using the age-stage, two-sex life table

BACKGROUND

Indiscriminate use of broad-spectrum insecticides can have deleterious effects on insects and the environment. The use of nanoparticles synthesized from microbes has recently gained importance as a safe alternative to conventional insecticides. Recently, zinc oxide (ZnO) nanoparticles synthesized using Bacillus thuringiensis have shown insecticidal potential; however, in addition to its acute toxicity, it is necessary to determine possible sublethal effects at the organismal level to understand the toxicity of a new insecticide. Bt-derived enzymes such as nitrate reductase and other biomolecules play a vital role in the reduction of metal ions to metal nanoparticles. Here, we assessed the acute toxicity and sublethal effects of ZnO nanoparticles produced in the culture supernatant of B. thuringiensis ser. israelensis (Bti) as a reducing agent on the biological traits of Musca domestica.

RESULTS

Concentration-response larval bioassays using different concentrations of ZnO-Bti-supernatant nanoparticles revealed LC₁₀ , LC₂₀ , LC₅₀ and LC₉₀ values of 4.17, 6.11, 12.73 and 38.90 μg g^-1 of larval diet, respectively. Exposure of M. domestica larvae to two concentrations (LC₁₀ and LC₂₀ ) resulted in a lengthened developmental time (egg to adult) and preoviposition period, and reduced fecundity, survival, longevity and oviposition period. Furthermore, population parameters including net reproductive rate, mean generation time, age-specific survival rate, fecundity, life expectancy and reproductive values, analyzed following age-stage and two-sex life table theory, were significantly decreased after exposure to these concentrations of ZnO-Bti-supernatant nanoparticles compared with the control.

CONCLUSION

ZnO-Bti-supernatant nanoparticles were shown to be toxic to M. domestica. Exposure of M. domestica to low concentrations of ZnO-Bti-supernatant nanoparticles resulted in negative transgenerational effects on progeny production in this fly. © 2022 Society of Chemical Industry.

Lethal and sub-lethal activity of Brevibacillus laterosporus on the mosquito Aedes albopictus and side effects on non-target water-dwelling invertebrates

The biocidal potential of Brevibacillus laterosporus against mosquitoes of major medical importance has been widely documented, but its effects on non-target invertebrates are still poorly known. In this study, we determined the lethal and sub-lethal effects of B. laterosporus strain UNISS 18, an entomopathogenic bacterium known for its effectiveness against synanthropic Diptera, on the larvae of the Asian tiger mosquito Aedes albopictus, a vector of several pathogens to humans. Moreover, we compared the larvicidal activity with the lethal action on the invasive snail Physella acuta and on two non-target water-dwelling species: the mayfly Cloeon dipterum, and the harlequin fly Chironomus riparius. B. laterosporus exhibited significant lethal effects on all the tested species with a concentration-dependent activity. However, the susceptibility varied among species, with a higher susceptibility of Ae. albopictus (LC₅₀ = 0.16 × 10⁷ spores mL^-1) than the other species (LC₅₀ = 0.31, 0.33, and 0.30 × 10⁷ spores mL^-1 for C. dipterum, C. riparius, and P. acuta, respectively). While 1st instar mosquito larvae were very susceptible to the bacterial infection, no effects on preimaginal development stages and adult emergence were observed at sub-lethal spores' concentrations. Even if the efficacy of B. laterosporus against Ae. albopictus and the invasive freshwater snail P. acuta is promising for their control, the susceptibility of non-target beneficial aquatic insects, highlights the need of accurate evaluations before applying B. laterosporus for pest management in water environments.

Toxicity of Bacterial Isolates on Adults of Zaprionus indianus (Diptera: Drosophilidae) and Parasitoids Trichopria anastrephae (Hymenoptera: Diapriidae) and Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae)

Bacillus thuringiensis (Berliner) has demonstrated potential use in insect pest management. We evaluated the toxicity and sublethal effects of formulations of toxic baits composed of bacterial isolates (Bt) B. thuringiensis var. oswaldo cruzi (Bto), B. thuringiensis var. israelensis (Bti), B. thuringiensis var. kurstaki (Btk), and B. circulars (Bc) in combination with three food attractants 50% grape juice, 7% sugar cane molasses, and 7% hydrolyzed protein on adults of Zaprionus indianus (Gupta, 1970), the main pest of fig fruit (Ficus carica) in Brazil. Likewise, we evaluated the toxicity on the parasitoids Trichopria anastrephae Lima, 1940 and Pachycrepoideus vindemmiae (Rondani, 1875) in ingestion bioassays. Adults of Z. indianus showed high susceptibility to Bacterial isolates. However, the Bto isolate (1013 CFU. ml-1) caused adult mortality of 100%, in 72 h after exposure, with LT50 values of ≈20 h. By using the lethal concentrations (LC90) of the Bto isolate, estimated via the concentration-response curves with the food attractants, a significant reduction (40 to 50%) in the total fecundity and in the embryonic viability of eggs from females fed with the toxic baits was observed. The food attractants + Bto (80 × 108 CFU. ml-1) did not cause significant mortality of T. anastrephae and P. vindemmiae adults (mortality < 20%). The bacterial isolates Bti, Btk, Bc, and Bto are considered promising for the formulation of toxic baits, because, besides providing toxic effect on adults of Z. indianus, they showed no toxicity on T. anastrephae and P. vindemmiae adults.

Isolation and characterization of Pseudomonas cedrina infecting Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth, Plutella xylostella, is one of the most destructive pests worldwide and its management relies exclusively on frequent application of chemical insecticides. Resistance to common insecticides is now widespread, and novel classes of insecticides are needed. Entomopathogenic bacteria and their related products play an important role in the management of this pest. In the present work, one bacterial strain was separated from infected pupae of P. xylostella collected from field and its pathogenicity was evaluated. On the basis of the 16S ribosomal RNA sequencing, BLASTN, and phylogenetic analysis, this bacterial isolate was identified as Pseudomonas cedrina. Oral administration of P. cedrina at levels above 10,000 CFU/ml gave significant mortality to P. xylostella larvae. The pathogenicity was also observed by reduced longevity and fecundity in adult females. However, when live bacterial cells were removed, the cultured broth lost any pathogenicity. In response to the bacterial infection, P. xylostella expressed antimicrobial and stress-associated genes. A mixture treatment of P. cedrina and Bacillus thuringiensis showed an additive effect on larval mortality of P. xylostella. These results indicated that P. cedrina is an opportunistic entomopathogen without secretion of toxins. Furthermore, the additive effect of P. cedrina and B. thuringiensis provide a new insight to develop new strategy for controlling P. xylostella.

Larvicidal and adulticidal effects and ultrastructural changes of larvae midgut epithelium of Musca domestica (Diptera: Muscidae) fed with Bacillus thuringiensis var. kyushuensis

INTRODUCTION

Musca domestica is resistant to many insecticides; hence, biological control is a suitable alternative.

METHODS

We evaluated the lethality of strain Btk176 towards the larval and adult M. domestica and the histopathological effects in the larvae midgut.

RESULTS

We observed 99% larval and 78.9% adult mortality within 48 hours of spore ingestion (dosage, 2.4×108 CFU/ml). The histopathological effects were consistent with cytotoxicity. PCR analysis showed the presence of the cry1Ba gene. Transmission electron microscopy revealed a bipyramidal parasporal body. Thurigiensin activity was not detected.

CONCLUSIONS

The serovar, Btk176 might be a potential biocontrol agent for houseflies.

Biological Activity of Bacillus thuringiensis (Bacillales: Bacillaceae) in Anastrepha fraterculus (Diptera: Tephritidae)

Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) is considered to be one of the major pest insects in fruit orchards worldwide. Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) strains are widely used as biological control agents and show high biological activity against different insect species. The objective of this study was to evaluate the biological activity of different strains of B. thuringiensis against A. fraterculus larvae and adults. Bioassays were performed using suspensions of bacterial spores/crystals of B. thuringiensis var. israelensis (Bti), kurstaki (Btk), and oswaldocruzi (Bto) strains at three concentrations [2 × 107, 2 × 108, and 2 × 109 colony-forming units per ml (CFU ml-1)]. At a concentration of 2 × 109 CFU ml-1, a significant larval effect (mortality 60%) was observed when compared with the control treatment. Larvae that ingested spore/crystal suspensions of Bti, Btk, or Bto bacterial strains exhibited significant larval and pupal deformations, leading to a significant decrease (~50%) in the completion of the insects' biological cycle (egg to adult). The B. thuringiensis strains (Bti, Btk, or Bto) at a concentration of 2 × 109 CFU ml-1 in combination with one food attractant (BioAnastrepha 3% or CeraTrap 1.5%) in formulations of toxic baits provided high mortality (mortality > 85%) of A. fraterculus adults 7 d after treatment. However, the Btk strain in combination with CeraTrap 1.5% caused mortality of 40%. On the basis of these results, the native bacterial strains Bti, Btk, and Bto were considered to be promising candidates as biological control agents against A. fraterculus.

Biocontrol potential of Halotolerant bacterial chitinase from high yielding novel Bacillus Pumilus MCB-7 autochthonous to mangrove ecosystem

The multifaceted role of chitinase in medicine, agriculture, environmental remediation and various other industries greatly demands the isolation of high yielding chitinase producing microorganisms with improved properties. The current study aimed to investigate the isolation, characterization and biocontrol prospective of chitinase producing bacterial strains autochthonous to the extreme conditions of mangrove ecosystems. Among the 51 bacterial isolates screened, Bacillus pumilus MCB-7 with highest chitinase production potential was identified and confirmed by 16S rDNA typing. Chitinase enzyme of MCB-7 was purified; the chitin degradation was evaluated by SEM and LC-MS. Unlike previously reported B.pumilus isolates, MCB-7 exhibited highest chitinase activity of 3.36U/mL, active even at high salt concentrations and temperature up to 60°C. The crude as well as purified enzyme showed significant antimycotic activity against agricultural pathogens such as Aspergillus flavus, Aspergillus niger, Aspergillus fumigatus, Ceratorhiza hydrophila and Fusarium oxysporum. The enzyme also exhibited biopesticidal role against larvae of Scirpophaga incertulas (Walker). [Lep.: Pyralidae], a serious agricultural pest of rice. The high chitinolytic and antimycotic potential of MCB-7 increases the prospects of the isolate as an excellent biocontrol agent. To the best of our knowledge, this is the first report of high chitinase yielding Bacillus pumilus strain from mangrove ecosystem with a biocontrol role against phytopathogenic fungi and insect larval pests.

Larvicidal activity and effects on post embrionary development of laboratory reared Musca domestica (Linnaeus, 1758) (Diptera: Muscidae), treated with Brevibacillus laterosporus (Laubach) spore suspensions

The application of a spore suspension of Brevibacillus laterosporus (Laubach) (strain Bon707), at a concentration of 1.94×10(9)CFU/mL in the diet, induced a level of 70% mortality in larvae of Musca domestica. No sublethal effects, upon feeding activity or development were recorded. However, electron microscopic examination of the digestive tract of larvae fed with B. laterosporus, revealed cellular vacuolization and cytoplasmic disorganization.

Molecular detection and antimicrobial resistance of Pseudomonas aeruginosa from houseflies (Musca domestica) in Iran

BACKGROUND

Pseudomonas aeruginosa is a common bacterium that can cause disease in humans and other animals. This study was conducted to screen for molecular detection and antimicrobial-resistant P. aeruginosa in Musca domestica in different locations in the Iranian provinces of Shahrekord and Isfahan.

METHODS

Musca domestica were captured by both manual and sticky trap methods, during the daytime, from household kitchens, cattle farms, animal hospitals, human hospitals, slaughterhouses and chicken farms at random locations in Shahrekord and Isfahan provinces of Iran, and subsequently transported to the laboratory for detection of P. aeruginosa. In the laboratory, flies were identified and killed by refrigeration in a cold chamber at -20 °C, then placed in 5 mL peptone water and left at room temperature for five hours before being processed. Pseudomonas isolates were preliminarily identified to genus level based on colony morphology and gram staining, and their identity was further confirmed by polymerase chain reaction.

RESULTS

Overall blaTEM gene was recovered from 8.8 % (53/600) of the P. aeruginosa isolated from houseflies collected from the two provinces. A slightly higher prevalence (10.7 %; 32/300) was recorded in Shahrekord province than Isfahan province (7.0 %; 21/300). The locations did not differ statistically (p < 0.05) in bacterial prevalence in flies. Seasonal prevalence showed a significantly lower infection frequency during autumn.

CONCLUSIONS

Houseflies are important in the epidemiology of P. aeruginosa infections.