House Flies Are Underappreciated Yet Important Reservoirs and Vectors of Microbial Threats to Animal and Human Health

Longevity, feeding behavior, and egg production of adult house flies (Diptera: Muscidae) provided with potential foods on dairy farms

Adult house flies (Musca domestica L.) are often a major pest at livestock facilities, where oviposition occurs on decomposing organic matter, such as manure. Some potential foods that adult house flies might consume on dairy farms were examined. Relative to when they were given water alone, survival of males and females was greater when they were given water along with liquid whole milk, formulated calf feed, or corn silage, or finely milled sorghum or soy, or buckwheat inflorescences. However, survival was significantly lower with these foods than with sucrose, although not significantly so for males with milk. There was little to no survival advantage when flies were given water along with milled hominy, wet spent brewers grain, or manure than with water alone. Both males and females spent significant time with their labellum in contact with corn silage, dandelion inflorescences, and buckwheat inflorescences, but little time with their labellum contacting manure or white clover inflorescences. Egg production was not increased by access to water along with buckwheat inflorescences or corn silage relative to sucrose; but egg production was increased by access to liquid whole milk. Reaching mature vitellogenesis stages was improved by prior exposure to water and sucrose solution along with a mixture of dry sucrose, milk, and yolk, or along with calf manure or formulated calf feed, but not with milled soy, sorghum, or hominy, or with wet spent brewers grain or citrus pellets. The diet including sucrose-milk-yolk resulted in the most females reaching mature vitellogenesis stages.

Flies as vectors of foodborne pathogens through food animal production: Factors affecting pathogen and antimicrobial resistance transmission

Flies play an important role in the transmission of antimicrobial resistant (AMR) and multi-drug-resistant (MDR) foodborne pathogens in animal production systems, posing risks to food safety and public health. Synanthropic fly species, including house flies (Musca domestica), face flies (Musca autumnalis), blow flies (Calliphoridae), and flesh flies (Sarcophagidae), mechanically and/or biologically transmit bacterial pathogens such as Salmonella enterica, Escherichia coli, Listeria monocytogenes, Klebsiella and Campylobacter spp. Their frequent contact with manure, animal waste, and processing environments enables the transfer of AMR pathogens across food production systems. This review synthesizes recent research on the interactions between flies and foodborne pathogens, highlighting the role of fly physiology, behavior, and microbial associations in pathogen transport. Additionally, it introduces the influence of environmental factors on pathogen dissemination and evaluates current Integrated Pest Management (IPM) strategies, including biological, chemical, and physical control methods, for mitigating fly-mediated pathogen transmission. Understanding these systems is essential for developing targeted interventions to reduce the burden of AMR pathogens in food production and enhance public health protection.

Bacterial abundance and antimicrobial resistance prevalence carried by adult house flies (Diptera: Muscidae) at Kansas dairy and beef cattle operations

House flies (Musca domestica L.) are filth-breeding pests of urban and rural environments around the world. Frequenting microbe-rich substrates for nutritional and reproductive needs, house flies pose a risk to human and animal health through their carriage and transmission of pathogenic and antimicrobial resistant bacteria (AMR). Adult house flies were collected from Kansas beef and dairy cattle operations to assess factors influencing bacterial abundance and AMR incidence flies. Aerobic culturable bacteria and suspected coliforms (SC) were enumerated from fly homogenate cultured on nonselective (tryptic soy agar) and selective (violet-red bile agar VRBA) media, respectively. Unique morphotypes of SC isolates were screened for tetracycline resistance and tested for resistance to 4 additional antibiotics to identify multi-drug resistant (MDR) isolates. Female house flies carried greater abundances of both culturable bacteria and SC than male flies. Abiotic factors such as ambient and soil temperatures correlated with culturable bacteria and SC abundances in flies, but farm type correlated only with SC abundance and trends of resistance phenotypes observed in SC isolates. Male and female flies from both farm types carried one or more AMR and MDR SC isolates (73.02% AMR and 31.09% MDR). The majority of AMR and MDR bacteria were Escherichia/Shigella sp., which possessed the widest range of phenotypic resistance variability found in our study. Our results further emphasize the role house flies play in harboring bacteria of risk to human and animal health and identified factors of potential use for the development of strategies to mitigate house fly transmission of bacterial pathogens and AMR within confined cattle operations.

Investigating the molecular mechanisms of deltamethrin resistance in Musca domestica populations from Saudi Arabia

BACKGROUND

The house fly, Musca domestica L., is a global insect pest that poses serious health risks by carrying pathogens to humans and animals. Pyrethroid (PYR) insecticides have been widely used to control agricultural pests and disease vectors. Multiple reports have documented house fly resistance to PYR insecticides.

METHODS

In this study, we assessed the resistance levels of M. domestica populations collected from slaughterhouses in Riyadh, Jeddah, and Taif, Saudi Arabia, against the PYR insecticide deltamethrin (DM). We also examined the genetic mutations in the voltage-sensitive sodium channel (Vssc) and P450 genes of the collected field flies and analyzed the correlation between these detected genetic mutations and the levels of DM resistance.

RESULTS

The house fly field populations showed very high levels of resistance to DM, with resistance ratio (RR) values of 625-, 256-, and 107-fold for Jeddah, Taif, and Riyadh, respectively. Three VSSC resistance alleles, kdr (T929 + 1014F), kdr-his (T929 + 1014H), and 1B (929I + 1014F), along with the susceptible allele (T929 + L1014) were identified in the Saudi house fly populations. The super-kdr allele (918 T + 1014F) and type N (D600N + M918T + L1014F) were not detected in Saudi house fly populations. Type 1B was the most dominant VSSC resistance allele, followed by kdr and kdr-his, in both field populations and the surviving flies exposed to DM. The resistance CYP6D1v1 allele of P450 was detected in slaughterhouse house fly populations of Riyadh, Jeddah, and Taif, with frequencies of 71%, 58%, and 60%, respectively. The VSSC resistance alleles exhibited a positive correlation with the resistance levels to DM; conversely, the CYP6D1v1 displayed a negative correlation with DM resistance levels.

CONCLUSIONS

In general, the Saudi house fly populations exhibited high genetic diversity, with three VSSC resistance alleles identified in slaughterhouse populations. The Vssc mutations appear to be the principal mechanism of DM resistance in Saudi house fly field populations. This study is the first report on the Vssc and CYP6D1 mutations associated with PYR resistance in M. domestica field populations from Saudi Arabia.

Decreased emergence rates of adult house flies (Musca domestica; Diptera: Muscidae) due to exposure to commercially available insecticidal baits during larval development

House flies, Musca domestica L. (Diptera: Muscidae), are commonplace pests in both urban and agricultural settings. The potential for house flies as vectors of many disease-causing organisms to humans and animals, coupled with their incessant nuisance behaviors toward these hosts has resulted in a desire to manage their populations. Although many house fly management tools are available, insecticide use continues to predominate as the preferred choice. One such option, insecticidal baits, is commercially available in a variety of active ingredients that encompass several modes of action. Though they can be effective, resistance to many of the active ingredients used in bait formulations has been documented. The primary pathway for resistance evolution to bait products likely has been selection at the targeted adult stage. However, exposure at the larval stage may occur when these products are scattered on substrates, contaminating sub-surface developmental areas and ultimately, playing a selective role as well. A study was conducted to assess the potential mortality effects of insecticidal bait products on house fly larval development when applied according to the manufacturer's recommended label rate. Adult house fly emergence was reduced by nearly 40% due to treatment, supporting the implication that bait-driven mortality during larval development may represent a previously unrecognized selection pathway contributing to resistance evolution against these products.

Flies as carriers of antimicrobial resistant (AMR) bacteria in Nigerian hospitals: A workflow for surveillance of AMR bacteria carried by arthropod pests in hospital settings

The dissemination of antimicrobial resistant (AMR) bacteria by flies in hospitals is concerning as nosocomial AMR infections pose a significant threat to public health. This threat is compounded in low- and middle-income countries (LMICs) by several factors, including limited resources for sufficient infection prevention and control (IPC) practices and high numbers of flies in tropical climates. In this pilot study, 1,396 flies were collected between August and September 2022 from eight tertiary care hospitals in six cities (Abuja, Enugu, Kaduna, Kano, Lagos and Sokoto) in Nigeria. Flies were screened via microbiological culture and bacterial isolates were phenotypically and genetically characterised to determine carriage of clinically important antibiotic resistance genes (ARGs). Several clinically relevant ARGs were found in bacteria isolated from flies across all hospitals. blaNDM was detected in 8% of flies and was predominantly carried by Providencia spp. alongside clinically relevant Enterobacter spp, Escherichia coli and Klebsiella pneumoniae isolates, which all exhibited a multidrug resistant phenotype. mecA was detected at a prevalence of 6.4%, mostly in coagulase-negative Staphylococci (CoNS) as well as some Staphylococcus aureus, of which 86.8% were multidrug resistant. 40% of flies carried bacteria with at least one of the two ESBL genes tested (blaOXA-1 and blaCTX-M-15). This multi-site study emphasised that flies in hospital settings carry bacteria that are resistant to multiple classes of antibiotics, including both routinely used and reserve antibiotics. A greater understanding of the global clinical significance and burden of AMR attributable to insect pests is required.

Bioactive Potential of Some Bacillus thuringiensis Strains from Macapá, Amazon, Brazil, Against the Housefly Musca domestica (Diptera: Muscidae) Under Laboratory Conditions

The high pathogenic activity of Bacillus thuringiensis (Bt) strains against various insect orders has positioned it as the most effective, environmentally safe, and sustainable approach to integrated insect management. We aimed to identify Bt strains capable of effectively controlling the housefly Musca domestica, a species of significant medical, veterinary, and public health concern. Twelve Bt strains from Macapá, Brazil, were tested against housefly larvae. PCR was employed to detect genes encoding Cry and Cyt proteins and Vips. Six strains exhibited 70 to 100% larval mortality, with five containing cry genes, none harboring cyt genes, and four carrying vip genes. Scanning electron microscopy revealed the production of crystal inclusions with distinct morphologies: spherical (TR4J, SOL5DM, SOL6RN), cuboidal and bipyramidal (TRO1TN and TRO2MQ), and spherical and bipyramidal (UNI2MA). The potential presence of genes from the cry1, cry2, vip1, and vip3 families suggests that these strains also exhibit bioinsecticidal activity against other muscoid flies and insect pests across various orders. This study underscores the bioactive potential of these Brazilian Bt strains for developing new bioinsecticides.

Anise and Fennel Essential Oils and Their Combination as Natural and Safe Housefly Repellents

Essential oils (EOs) are effective repellents and eco-friendly alternatives. We tested single and combination EOs of fennel and anise for repellency and stability against houseflies. All treatments were stored at 27 °C for up to 360 days. Efficacies were compared against α-cypermethrin as a reference. Safety bioassay used on two representative non-target species (guppies and earthworms) confirmed safety. The strongest repellency and stability, 100% repellency and RC50 of 0.4 mL/m3 on day 1, was achieved by a fennel + anise EO combination (1:1). After 360 days, these combinations remained effective (95% repellency), and RC50 = 0.8 mL/m3. The EO combinations were more effective than all single EOs and α-cypermethrin at all times, showing strong synergy with a synergistic repellent index of 2.4 to 3.3. This fennel + anise EO combination was more than 24 times more effective as a repellent than α-cypermethrin. Morphological damage included damaged antennae with twisted flagella and abnormal aristae. All single and combination EOs were not toxic to the non-targets and could be considered safe, whereas α-cypermethrin was highly toxic to them. Thus, the fennel + anise EO combination has great potential to be developed as a safe, natural repellent for managing housefly populations.

Examining imidacloprid behaviorally resistant house flies (Musca domestica L.) (Diptera: Muscidae) for neonicotinoid cross-resistance

The house fly (Musca domestica L.) is a ubiquitous fly species commonly associated with confined animal and urban waste storage facilities. It is known for its pestiferous nature and ability to mechanically vector numerous disease-causing pathogens. Effective control of adult house fly populations has traditionally relied upon insecticidal food baits; however, due to the overuse of insecticides, resistance has proven to yield many insecticidal baits and chemical classes less effective. Imidacloprid, the most widely used neonicotinoid, has been formulated and commonly used in house fly baits for over 2 decades. However, widespread evidence of physiological and behavioral resistance to imidacloprid has been documented. While previous studies have investigated the mechanisms of behavioral resistance to imidacloprid in the house fly, it remains unclear whether behavioral resistance is specific to imidacloprid or if behavioral cross-resistance exists to other compounds within the neonicotinoid class of insecticides. The current study used no-choice and choice-feeding bioassays to examine a lab-selected imidacloprid behaviorally resistant house fly colony for cross-resistance to other insecticides in the neonicotinoid chemical class. All flies exhibited high mortality (97-100%) in no-choice assays, even when exposed to imidacloprid, indicating physiological susceptibility to all tested neonicotinoids. House flies exhibited high mortality (98-100%) in choice assays when exposed to all neonicotinoid insecticides tested besides imidacloprid. These results confirm that imidacloprid behavioral resistance is specific to the compound imidacloprid and that alternative neonicotinoids remain viable options for control. Our study showed no evidence of behavioral cross-resistance to other compounds in the neonicotinoid class.

Chitosan-based insecticide formulations for insect pest control management: A review of current trends and challenges

Future agricultural practices necessitate green alternatives to replace hazardous insecticides while distinguishing between pests and beneficial insects. Chitosan, as a biological macromolecule derived from chitin, is biodegradable and exhibits low toxicity to non-target organisms, making it a sustainable alternative to synthetic pesticides. This review identifies chitosan-derivatives for insecticidal activity and highlights its efficacy including genotoxicity, defense mechanism, and disruption of insect's exoskeleton at different concentrations against several insect pests. Similarly, synergistic effects of chitosan in combination with natural extracts, essential oils, and plant-derived compounds, enhances insecticidal action against various pests was evaluated. The chitosan-based insecticide formulations (CHIF) in the form of emulsions, microcapsules, and nanoparticles showed efficient insecticide action on the targeted pests with less environmental impact. The current challenges associated with the field-trial application were also recognized, by optimizing potent CHIF-formulation parameters, scaling-up process, and regulatory hurdles addressed alongside potential solutions. These findings will provide insight into achieving the EU mission of reducing chemical pesticides by 50 %.

First molecular evidence of bovine hemoplasmas in houseflies (Musca domestica)

BACKGROUND

Hemoplasma infections in cattle are caused by Mycoplasma wenyonii and Candidatus Mycoplasma haemobos and induce asymptomatic or chronic infections but occasionally lead to life-threatening hemolytic anemia. Despite the global distribution of bovine hemoplasmas, information regarding their transmission vectors and prevalence is still lacking in the Republic of Korea. Therefore, this study aims to investigate the infection rate of bovine hemoplasma in cattle and houseflies and to assess the risk factors associated with hemoplasma infection in cattle.

METHODS

Overall, 376 blood samples were collected from Korean indigenous cattle (male, 10-13 months old), along with 2,690 houseflies (Musca domestica) from the same farm where the cattle were raised. PCR assays targeting the 16S rRNA gene were performed to detect hemoplasmas, and positive samples were sequenced.

RESULTS

The infection rate of bovine hemoplasmas was 50.8% (191/376) in cattle and 7.4% in pooled houseflies. Among cattle, 18.6% (70/376) and 20.0% (75/376) tested positive for M. wenyonii and Candidatus M. haemobos, respectively. Conversely, in houseflies, Candidatus M. haemobos was more frequently detected (5.9%) than M. wenyonii (0.7%). Co-infection was 12.2% (46/376) in cattle and 0.7% in flies. Furthermore, hemoplasma infection was significantly associated with the grazing experience of their dams. Cattle born to cows with grazing experience exhibited a higher risk for M. wenyonii infection (odds ratio [OR] = 1.62; 95% confidence interval [CI]: 1.03-2.55; P = 0.045), whereas these cattle had a lower risk for Candidatus M. haemobos infection (OR = 0.32, 95% CI: 0.19-0.74; P = 0.000) than animals born to cows without grazing experience. The sequences obtained from houseflies were confirmed as Candidatus M. haemobos, which displayed high similarity (98.2-100%) to those from cattle obtained in this study.

CONCLUSIONS

To our knowledge, this study represents the first report of bovine hemoplasmas identified in houseflies. This molecular evidence suggests that houseflies may be possible vectors for Candidatus M. haemobos.

Bacterial Communities of House Flies from Beef and Dairy Cattle Operations are Diverse and Contain Pathogens of Medical and Veterinary Importance

Adult house flies (Musca domestica L.) are important reservoirs and mechanical vectors of bacteria in livestock operations. House fly bacterial communities are influenced by their local environment, yet a comprehensive understanding of bacterial diversity, pathogen prevalence, and bacterial source is not fully understood. We characterized bacterial communities from adult female house flies and associated manure samples from beef and dairy cattle farms in Kansas, Oklahoma, and Texas over four months (July-October). Bacterial community composition in flies and manure reflected the local environment, and house flies shared the majority (≥ 99%) of bacterial taxa with manure. The variability of bacterial diversity was greater among individual fly (species richness range: 48-1747) samples than manure (species richness range: 345-1162). Temporal variability of fly bacterial diversity was observed within each farm type. Bacterial taxa of veterinary and medical importance such as Corynebacterium, Turicibacter, Staphylococcus, Streptococcus, and Acinetobacter were highly prevalent in flies, constituting core bacterial communities. The prevalence of bacterial taxa associated with bovine keratoconjunctivitis (IBK) and bovine respiratory disease (BRD) was higher in flies than in manure and prevalence varied monthly. This study underscores the crucial role house flies play as carriers of cattle pathogens, contributing to their dissemination among animals and to off-site locations, where they pose a threat to surrounding communities and agricultural operations.

Evaluation of the inheritance and dominance of behavioral resistance to imidacloprid in the house fly (Musca domestica L.) (Diptera: Muscidae)

The house fly, Musca domestica, is a cosmopolitan species known for its pestiferous nature and potential to mechanically vector numerous human and animal pathogens. Control of adult house flies often relies on insecticides formulated into food baits. However, due to the overuse of these baits, insecticide resistance has developed to all insecticide classes currently registered for use in the United States. Field populations of house flies have developed resistance to imidacloprid, the most widely used neonicotinoid insecticide for fly control, through both physiological and behavioral resistance mechanisms. In the current study, we conducted a comprehensive analysis of the inheritance and dominance of behavioral resistance to imidacloprid in a lab-selected behaviorally resistant house fly strain. Additionally, we conducted feeding preference assays to assess the feeding responses of genetic cross progeny to imidacloprid. Our results confirmed that behavioral resistance to imidacloprid is inherited as a polygenic trait, though it is inherited differently between male and female flies. We also demonstrated that feeding preference assays can be instrumental in future genetic inheritance studies as they provide direct insight into the behavior of different strains under controlled conditions that reveal, interactions between the organism and the insecticide. The findings of this study carry significant implications for pest management and underscore the need for integrated pest control approaches that consider genetic and ecological factors contributing to resistance.

Bacterial Communities of House Flies from Dairy Farms Highlight Their Role as Reservoirs, Disseminators, and Sentinels of Microbial Threats to Human and Animal Health

Adult house flies (Musca domestica L.) inhabiting dairy farms not only are nuisance pests but also harbor and disseminate bacteria. We examined the bacterial community composition, diversity, environmental sources, and prevalence in individual adult female house flies and cattle manure samples collected monthly from Florida, North Carolina, and Tennessee dairy farms between May and August 2021. Individual house flies carried diverse bacterial communities, encompassing all bacterial taxa (100%) identified across manure samples, and additional species likely acquired from the animals. Bacterial community assemblage in house flies and manure samples within farms varied by month. Some taxa were differentially associated with either house flies (Corynebacterium, Acinetobacter, and Staphylococcus) or manure samples (Treponema, Succinivibrio, and Clostridia). House fly bacterial communities mostly contained specialist species originating from manure, with several taxa (Escherichia, Corynebacterium, Turicibacter) being potential pathogens of livestock and humans. These findings further support the role of house flies as carriers of cattle-associated bacteria, including pathogens, and their potential for disseminating these microbes among cattle and to neighboring environments. Since their bacterial communities provide a snapshot of their surrounding environment, house flies also serve as effective sentinels in xenosurveillance strategies.

Assessing the toxicity of green Agaricus bisporus-based Cadmium Sulfide nanoparticles on Musca domestica as a biological model

The common housefly, Musca domestica, known for transmitting over 100 infections, was studied using green-synthesized Cadmium Sulfide nanoparticles (CdS NPs) from Agaricus bisporus. These CdS NPs were tested on third-instar larvae under laboratory conditions using dipping and feeding methods with concentrations (75, 100, 125, 150, 175, and 200 µg/mL). The toxicity, measured by LC50, was found to be 138 µg/mL for dipping treatment and 123 µg/mL for feeding treatment. Analysis with an energy-dispersive X-ray microanalyzer confirmed Cd accumulation in the larval midgut, indicating penetration of CdS NPs into the organism, which may potentially increase their toxicity. CdS NPs caused disruptions in Heat Shock Protein 70, cell apoptosis, and various biochemical components. Scanning electron microscopy revealed morphological abnormalities in larvae, pupae, and adults exposed to CdS NPs. Ultrastructural examination showed significant midgut tissue abnormalities in larvae treated with 123 µg/mL of CdS NPs. Our study demonstrated that green-synthesized CdS NPs from A. bisporus can effectively control the development of M. domestica larvae.

Expression of defensin genes across house fly (Musca domestica) life history gives insight into immune system subfunctionalization

Animals encounter diverse microbial communities throughout their lifetime, which exert varying selection pressures. Antimicrobial peptides (AMPs), which lyse or inhibit microbial growth, are a first line of defense against some of these microbes. Here we examine how developmental variation in microbial exposure has affected the evolution of expression and amino acid sequences of Defensins (an ancient class of AMPs) in the house fly (Musca domestica). The house fly is a well-suited model for this work because it trophically associates with varying microbial communities throughout its life history and its genome contains expanded families of AMPs, including Defensins. We identified two subsets of house fly Defensins: one expressed in larvae or pupae, and the other expressed in adults. The amino acid sequences of these two Defensin subsets form distinct monophyletic clades, and they are located in separate gene clusters in the genome. The adult-expressed Defensins evolve faster than larval/pupal Defensins, consistent with different selection pressures across developmental stages. Our results therefore suggest that varied microbial communities encountered across life history can shape the evolutionary trajectories of immune genes.

The Carotenoid Composition of Larvae Feed Is Reflected in Adult House Fly (Musca domestica) Body

Carotenoids are common and diverse organic compounds with various functional roles in animals. Except for certain aphids, mites, and gall midges, all animals only acquire necessary carotenoids through their diet. The house fly (Musca domestica) is a cosmopolitan pest insect that populates diverse habitats. Its larvae feed on organic substrates that may vary in carotenoid composition according to their specific content. We hypothesized that the carotenoid composition in the adult house fly's body would reflect the carotenoid composition in the larval feed. House fly larvae were reared on diets that differed in carotenoid composition. HPLC analysis of the emerging adult flies indicate that the carotenoid composition of adult house flies is related, but not identical, to the carotenoid composition in its natal substrate. These findings may be developed to help identify potential sources of house fly infestations. Also, it is recommended that rearing substrates of house fly larvae, used for animal feed, should be carefully considered.

Increased Dissemination of Aflatoxin- and Zearalenone-Producing Aspergillus spp. and Fusarium spp. during Wet Season via Houseflies on Dairy Farms in Aguascalientes, Mexico

Crops contamination with aflatoxins (AFs) and zearalenone (ZEA) threaten human and animal health; these mycotoxins are produced by several species of Aspergillus and Fusarium. The objective was to evaluate under field conditions the influence of the wet season on the dissemination of AF- and ZEA-producing fungi via houseflies collected from dairy farms. Ten dairy farms distributed in the semi-arid Central Mexican Plateau were selected. Flies were collected in wet and dry seasons at seven points on each farm using entomological traps. Fungi were isolated from fly carcasses via direct seeding with serial dilutions and wet chamber methods. The production of AFs and ZEA from pure isolates was quantified using indirect competitive ELISA. A total of 693 Aspergillus spp. and 1274 Fusarium spp. isolates were obtained, of which 58.6% produced AFs and 50.0% produced ZEA (491 ± 122; 2521 ± 1295 µg/kg). Houseflies and both fungal genera were invariably present, but compared to the dry season, there was a higher abundance of flies as well as AF- and ZEA-producing fungi in the wet season (p < 0.001; 45.3/231 flies/trap; 8.6/29.6% contaminated flies). These results suggest that rainy-weather conditions on dairy farms increase the spread of AF- and ZEA-producing Aspergillus spp. and Fusarium spp. through houseflies and the incorporation of their mycotoxins into the food chain.

Hospital Wastes as Potential Sources for Multi-Drug-Resistant ESBL-Producing Bacteria at a Tertiary Hospital in Ethiopia

The hospital environment is increasingly becoming an important reservoir for multi-drug-resistant (MDR) Gram-negative bacteria, posing serious challenges to efforts to combat antimicrobial resistance (AMR). This study aimed to investigate the role of hospital waste as a potential source of MDR ESBL-producing bacteria. Samples were collected from multiple sources within a hospital and its vicinity, including surface swabs, houseflies, and sewage samples. The samples were subsequently processed in a microbiology laboratory to identify potential pathogenic bacteria and confirmed using MALDI-TOF MS. Bacteria were isolated from 87% of samples, with the predominant isolates being E. coli (30.5%), Klebsiella spp. (12.4%), Providencia spp. (12.4%), and Proteus spp. (11.9%). According to the double disc synergy test (DDST) analysis, nearly half (49.2%) of the bacteria were identified as ESBL producers. However, despite exhibiting complete resistance to beta-lactam antibiotics, 11.8% of them did not test positive for ESBL production. The characterization of E. coli revealed that 30.6% and 5.6% of them carried blaCTX-M group 1 type-15 and blaNDM genes, respectively. This finding emphasizes the importance of proper hospital sanitation and waste management practices to mitigate the spread of AMR within the healthcare setting and safeguard the health of both patients and the wider community.

Evaluation of the stability of physiological and behavioral resistance to imidacloprid in the house fly (Musca domestica L.) (Diptera: Muscidae)

BACKGROUND

The house fly (Musca domestica L.) is a synanthropic fly species commonly associated with confined animal facilities. House fly control relies heavily on insecticide use. Neonicotinoids are currently the most widely used class of insecticide and have been formulated into granular fly baits since 2002. Physiological resistance to imidacloprid in house flies has been observed to be unstable and decline over time without continual selection pressure, indicating that resistance has a fitness cost to individuals in the absence of exposure to insecticides. The stability of behavioral resistance to imidacloprid in the house fly has not been evaluated. In the current study, we assess the stability of physiological and behavioral resistance in house flies to imidacloprid over time.

RESULTS

Physiological susceptibility to imidacloprid varied significantly among three house fly strains examined, with WT-15 exhibiting the greatest susceptibility to imidacloprid with an LC50 and LC95 of 109.29 (95.96-124.49) μg g-1 and 1486.95 (1097.15-2015.23) μg g-1 , respectively. No significant differences in survival were observed across 30 generations of a house fly strain (BRS-1) previously selected for behavioral resistance to imidacloprid with percentage survival ranging from 93.20% at F0 in 2020 to 96.20% survival at F30 in 2022.

CONCLUSION

These results have significant implications for the management of house flies exhibiting behavioral resistance in field settings. It appears that standard resistance management tactics deployed to reduce the prevalence of physiological resistance, such as rotating or temporarily discontinuing the use of specific insecticides, may not lead to reduced behavioral resistance to imidacloprid. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Biological Fitness Cost, Demographic Growth Characteristics, and Resistance Mechanism in Alpha-Cypermethrin-Resistant Musca domestica (Diptera: Muscidae)

Musca domestica L., a pest of animals and humans, has developed resistance to alpha-cypermethrin, a pyrethroid insecticide commonly used to control medically important pests in many countries, including Saudi Arabia. We investigated the mechanism underlying the development of alpha-cypermethrin resistance and life history characteristics of alpha-cypermethrin-susceptible (Alpha-SS) and alpha-cypermethrin-resistant (Alpha-RS) M. domestica using the age-stage, two-sex life table theory, which is crucial for developing a future rational management strategy and minimizing the negative effects of alpha-cypermethrin on the environment. Our results showed that Alpha-RS M. domestica had a 405.93-fold increase in resistance to alpha-cypermethrin relative to Alpha-SS M. domestica. This increase in the resistance toward insecticide was attributed to metabolic enzymes, such as glutathione S-transferases, specific esterases, and cytochrome P450 monooxygenases. Furthermore, Alpha-RS M. domestica exhibited lower relative fitness (0.50), longevity, survival rate, life expectancy, reproductive values, intrinsic rate of increase, net reproductive rate, fecundity, maternity, and finite rate of increase, along with shorter larval, female preadult, and adult durations than Alpha-SS M. domestica, indicating fitness costs associated with most parameters. However, no significant differences were found between the strains in the following parameters: egg, pupa, and male preadult durations; adult preoviposition, total preoviposition, and oviposition periods; female ratio; and total generation time. Additionally, Alpha-RS M. domestica had a markedly lower intrinsic rate of increase, net reproductive rate, and finite rate of increase than Alpha-SS M. domestica. The results of this study suggest that alpha-cypermethrin resistance may lead to dominant fitness costs in M. domestica. Overall, these findings will aid in the development of rational control strategies for M. domestica as well as help to reduce pesticide pollution.