Review of Methods to Monitor House Fly (Musca domestica) Abundance and Activity

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.

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.

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.

Terrestrial invertebrate hosts of human pathogens in urban ecosystems

Terrestrial invertebrates in urban ecosystems are extremely species-rich, have many important roles in material flow and energy circulation, and are host to many human pathogens that pose threats to human health. These invertebrates are widely distributed in urban areas, including both out- and in-door environments. Consequently, humans are frequently in contact with them, which provides many opportunities for them to pose human health risks. However, comprehensive knowledge on human pathogen transfer via invertebrates is lacking, with research to date primarily focused on dipterans (e.g., mosquitoes, flies). Here, we take a broad taxonomic approach and review terrestrial invertebrate hosts (incl. mosquitoes, flies, termites, cockroaches, mites, ticks, earthworms, collembola, fleas, snails, and beetles) of human pathogens, with a focus on transmission pathways. We also discuss how urbanization and global warming are likely to influence the communities of invertebrate hosts and have flow-on risks to human health. Finally, we identify current research gaps and provide perspectives on future directions.

A review of Musca sorbens (Diptera: Muscidae) and Musca domestica behavior and responses to chemical and visual cues

Musca flies (Diptera: Muscidae) have been found culpable in the mechanical transmission of several infectious agents, including viruses, bacteria, protozoans, and helminths, particularly in low-income settings in tropical regions. In large numbers, these flies can negatively impact the health of communities and their livestock through the transmission of pathogens. In some parts of the world, Musca sorbens is of particular importance because it has been linked with the transmission of trachoma, a leading cause of preventable and irreversible blindness or visual impairment caused by Chlamydia trachomatis, but the contribution these flies make to trachoma transmission has not been quantified and even less is known for other pathogens. Current tools for control and monitoring of house flies remain fairly rudimentary and have focused on the use of environmental management, insecticides, traps, and sticky papers. Given that the behaviors of flies are triggered by chemical cues from their environment, monitoring approaches may be improved by focusing on those activities that are associated with nuisance behaviors or with potential pathogen transmission, and there are opportunities to improve fly control by exploiting behaviors toward semiochemicals that act as attractants or repellents. We review current knowledge on the odor and visual cues that affect the behavior of M. sorbens and Musca domestica, with the aim of better understanding how these can be exploited to support disease monitoring and guide the development of more effective control strategies.

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.

Simultaneous detection of seven bacterial pathogens transmitted by flies using the reverse line blot hybridization assay

BACKGROUND

Traditional methods for detecting insect-borne bacterial pathogens are time-consuming and require specialized laboratory facilities, limiting their applicability in areas without access to such resources. Consequently, rapid and efficient detection methods for insect-borne bacterial diseases have become a pressing need in disease prevention and control.

METHODS

We aligned the ribosomal 16S rRNA sequences of seven bacterial species (Staphylococcus aureus, Shigella flexneri, Aeromonas caviae, Vibrio vulnificus, Salmonella enterica, Proteus vulgaris, and Yersinia enterocolitica) by DNASTAR Lasergene software. Using DNASTAR Lasergene and Primer Premier software, we designed universal primers RLB-F and RLB-R, two species-specific probes for each pathogen, and a universal probe (catch-all). The PCR products of seven standard strains were hybridized with specific oligonucleotide probes fixed on the membrane for specific experimental procedures. To evaluate the sensitivity of PCR-RLB, genomic DNA was serially diluted from an initial copy number of 1010 to 100 copies/μl in distilled water. These dilutions were utilized as templates for the PCR-RLB sensitivity analysis. Simultaneous detection of seven fly-borne bacterial pathogens from field samples by the established PCR-RLB method was conducted on a total of 1060 houseflies, collected from various environments in Lanzhou, China.

RESULTS

The established PCR-RLB assay is capable of detecting bacterial strains of about 103 copies/μl for S. aureus, 103 copies/μl for S. flexneri, 105 copies/μl for A. caviae, 105 copies/μl for V. vulnificus, 100 copies/μl for S. enterica, 105 copies/μl for P. vulgaris, and 100 copies/μl for Y. enterocolitica. The results demonstrate that the detection rate of the established PCR-RLB method is higher (approximately 100 times) compared to conventional PCR. This method was applied to assess the bacterial carrier status of flies in various environments in Lanzhou, China. Among the seven bacterial pathogens carried by flies, S. enterica (34.57%), S. flexneri (32.1%), and Y. enterocolitica (20.37%) were found to be the predominant species.

CONCLUSIONS

Overall, this research shows that the rapid and efficient PCR-RLB detection technology could be a useful for surveillance and therefore effective prevention and control the spread of insect-borne diseases. Meanwhile, the experimental results indicate that urban sanitation and vector transmission sources are important influencing factors for pathogen transmission.

Lack of fitness costs associated with resistance to permethrin in Musca domestica

Resistance to permethrin has been reported in Pakistani strains of Musca domestica. The present study explored the performance of biological traits and analyzed life tables to determine whether there is any detrimental effect of permethrin resistance on the fitness of permethrin-resistant strains [an isogenic resistant strain (Perm-R) and a field strain (Perm-F)] compared to a susceptible strain (Perm-S). Perm-R and Perm-F exhibited 233.93- and 6.87-fold resistance to permethrin, respectively. Life table analyses revealed that the Perm-R strain had a significantly shorter preadult duration, longer longevity, shorter preoviposition period, higher fecundity, finite rate of increase, intrinsic rate of increase, net reproductive rate and a shorter mean generation time, followed by the Perm-F strain when compared to the Perm-S strain. Data of the performance of biological traits reveled that permethrin resistance strains had a better fit than that of the Perm-S strain. The enhanced fitness of resistant strains of M. domestica may accelerate resistance development to permethrin and other pyrethroids in Pakistan. Some possible measures to manage M. domestica and permethrin resistance in situations of fitness advantage are discussed.

Genetic evaluation and characterization of behavioral resistance to imidacloprid in the house fly

Insecticide resistance in pest populations is an increasing problem in both urban and rural settings due to over-application of insecticides and lack of rotation among insecticidal chemical classes. The house fly (Musca domestica L.) is a cosmopolitan pest fly species implicated in the transmission of numerous pathogens. The evolution of insecticide resistance long has been documented in house flies, with resistance reported to all major insecticide classes. House fly resistance to imidacloprid, the most widely used neonicotinoid insecticide available for fly control, has evolved in field populations through both physiological and behavioral mechanisms. Previous studies have characterized and mapped the genetic changes that confer physiological resistance to imidacloprid, but no study have examined the genetics involved in behavioral resistance to imidacloprid to date. In the current study, several approaches were utilized to characterize the genetics and inheritance of behavioral resistance to imidacloprid in the house fly. These include behavioral observation analyses, preference assays, and the use of genetic techniques for the identification of house fly chromosome(s) carrying factors. Behavioral resistance was mapped to autosomes 1 and 4. Inheritance of resistance was shown to be neither fully dominant nor recessive. Factors on autosomes 1 and 4 independently conferred contact-dependent avoidance of imidacloprid and a feeding preference for sugar alone or for sugar with dinotefuran, another neonicotinoid insecticide, over imidacloprid. This study serves as the first linkage analysis of a behavioral trait in the house fly, and provides new avenues for research regarding inherited behavior in the house fly and other animals.

Monitoring House Fly (Diptera: Muscidae) Activity on Animal Facilities

Monitoring house fly (Diptera: Muscidae) activity on animal facilities is a necessary component of an integrated pest management (IPM) program to reduce the negative impacts of these flies. This article describes monitoring methods appropriate for use on animal facilities with discussion of monitoring device use and placement. Action thresholds are presented where these have been suggested by researchers. Sampling precision is an important aspect of a monitoring program, and the number of monitoring devices needed to detect a doubling of fly activity is presented for monitoring methods where this information is available. It should be noted that both action thresholds and numbers of monitoring devices will be different for every animal facility. Suggested action thresholds and numbers of monitoring devices are presented only to provide guidance when initiating a fly monitoring program. Facility managers can adjust these values based upon the fly activity data recorded at their facility. Spot cards are generally recommended as an easy-to-use method for monitoring fly activity for most animal facilities. Fly ribbons or similar sticky devices are recommended where several pest fly species may be abundant and identifying the activity of each species is important, but a sampling period of <7 d may be needed in dusty conditions or when fly density is high. Fly ribbons are not recommended for outdoor use. Insecticide-baited traps may be used in outdoor locations where environmental conditions limit the use of spot cards, fly ribbons, and sticky traps.