Selection, Reversion, and Characterization of House Fly (Diptera: Muscidae) Behavioral Resistance to the Insecticide Imidacloprid

Ultrastructural changes in epithelial cells on different stages of sinantropic muscoid dipterans fed with spores of Brevibacillus laterosporus

Brevibacillus laterosporus is a sporulating bacteria, with typical canoe-shaped parasporal bodies attached to the spores. It has shown great biotechnological potential, including its broad pathogenic spectrum against different orders of insects and other invertebrates with medical-veterinary-sanitary importance. The high degree of synanthropy of muscoid dipterans and the damage they cause being a source of myiasis and carriers of pathogens encourage research into their population control. The objective of the study was to evaluate the histopathological effects caused by B. laterosporus NRS 590 on larvae and adults of M. domestica and C. megacephala. The flies were collected in garbage dumpsters, identified and the respective colonies were adapted to laboratory conditions (air-conditioned chamber with regulated humidity and temperature). Different concentrations of bacterial spore suspensions were offered to neo larvae and adults. Larvae and adults were dissected and intestinal epithelial cells of the flies, in temporal kinetics, were demonstrated using transmission electron microscopy (TEM) techniques. Irregular microvilli were observed in the intestines of both adult and larvae tested after 6 h of treatment. At 12 h and 24 h, intense cellular disorganization was observed and at 24 h and 48 h there was discontinuity of microvilli, cell extrusion and nuclear damage in some cells, as well. Spores of B. laterosporus NRS590 produce histopathological effects on both larvae and adults of synanthropic flies, being an alternative active principle in eco-friendly insecticides.

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.

Behavioral response of house flies (Diptera: Muscidae) to 3 bittering agents

House flies, Musca domestica L., are pests at livestock facilities. House fly numbers are controlled mainly by manure management and chemical controls, like use of toxic baits. Some toxic baits contain denatonium benzoate as a bittering agent, to avoid poisoning of children. House fly behavioral response to denatonium benzoate was examined, using 2 different diluents, sucrose solution or orange juice. Response of flies to quinine and sucrose octaacetate, 2 other bittering agents, was also examined in sucrose. Sucrose is the sweetener in commercially available toxic house fly baits. The proboscis extension response of both male and female flies was significantly reduced by addition of 1,000 ppm of denatonium benzoate to sucrose. Response in males was also reduced at 100 ppm. Consumption of sucrose by both male and female flies was reduced by addition of 100, 500, and 1,000 ppm of denatonium benzoate, but consumption by males was also reduced at 10 ppm. Addition of sucrose octaacetate had no detectable effect on consumption of sucrose at 100, 500, or 1,000 ppm. In contrast, addition of quinine reduced consumption by both male and female flies in all tested concentrations. In orange juice, 10 ppm of denatonium benzoate is often avoided by children. With orange juice, fly proboscis extension response patterns were the same for both sexes, with a reduction at 1,000 ppm of denatonium benzoate. Orange juice consumption by flies was reduced significantly at 1,000 ppm of denatonium benzoate for females but not at any of the concentrations tested for males.

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.

Behavioral resistance to insecticides: current understanding, challenges, and future directions

Identifying and understanding behavioral resistance to insecticides is vital for maintaining global food security, public health, and ecological balance. Behavioral resistance has been documented to occur in a multitude of insect taxa dating back to the 1940s, but has not received significant research attention due primarily to the complexities of studying insect behavior and a lack of any clear definition of behavioral resistance. In recent years, a systematic effort to investigate the mechanism(s) of behavioral resistance in pest taxa (e.g. the German cockroach and the house fly) has been undertaken. Here, we practically define behavioral resistance, describe the efforts taken by research groups to elucidate resistance mechanisms, and provide insight on designing appropriate bioassays for investigating behavioral resistance mechanisms in the future.

The exposure risk of heavy metals to insect pests and their impact on pests occurrence and cross-tolerance to insecticides: A review

Heavy metal (HM) pollution is a severe global environmental issue. HMs in the environment can transfer along the food chain, which aggravates their ecotoxicological effect and exposes the insects to heavy metal stress. In addition to their growth-toxic effects, HMs have been reported as abiotic environmental factors that influence the implementation of integrated pest management strategies, including microbial control, enemy insect control, and chemical control. This will bring new challenges to pest control and further highlight the ecotoxicological impact of HM pollution. In this review, the relationship between HM pollution and insecticide tolerance in pests was analyzed. Our focus is on the risks of HM exposure to pests, pests tolerance to insecticides under HM exposure, and the mechanisms underlying the effect of HM exposure on pests tolerance to insecticides. We infer that HM exposure, as an initial stressor, induces cross-tolerance in pests to subsequent insecticide stress. Additionally, the priming effect of HM exposure on enzymes associated with insecticide metabolism underlies cross-tolerance formation. This is a new interdisciplinary field between pollution ecology and pest control, with an important guidance value for optimizing pest control strategies in HM polluted areas.

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.

Concentration Dependent Feeding on Imidacloprid by Behaviorally Resistant House Flies, Musca domestica L. (Diptera: Muscidae)

The house fly (Musca domestica L.) is a cosmopolitan and synanthropic pest fly commonly associated with confined animal facilities, known to mechanically vector numerous disease-causing pathogens. Control of adult house flies often relies on insecticides formulated into insecticidal baits, though many baits have failed due to insecticide resistance. House fly resistance to imidacloprid, the most widely used neonicotinoid insecticide available for fly control, has evolved through physiological and behavioral mechanisms in field populations. Behavioral resistance to imidacloprid was documented in field populations of flies from southern California dairies. Lab colonies of these flies were established and behavioral resistance to imidacloprid was selected over several generations. The current study examined the ability of these lab-selected flies to feed on varying concentrations of imidacloprid formulated in sucrose, and if these flies would demonstrate a feeding preference for different concentrations of imidacloprid when exposed in bioassays. Behaviorally resistant flies preferred to feed on untreated sucrose as opposed to treated sucrose at concentrations greater than 25 µg/g imidacloprid when provided sucrose treated with and without imidacloprid. When provisioned with only sucrose treated with a low and high imidacloprid concentration, flies fed on the low concentrations (≤100 µg/g) imidacloprid but reduced feeding on either treatment when concentrations were >100 µg/g imidacloprid. The current study extends the body of knowledge on house fly behavioral resistance to imidacloprid, which could provide insights into future failures of granular fly baits.

Multiple Genetic Mutations Related to Insecticide Resistance are Detected in Field Kazakhstani House Flies (Muscidae: Diptera)

The house fly (Musca domestica Linnaeus) is an important disease vector. Insecticide resistance is an obstacle to effective house fly control. Previous studies have demonstrated that point mutations in acetylcholinesterase (Ace), carboxylesterase (MdαE7) and voltage-sensitive sodium channel (Vssc), and over-expression of CYP6D1v1 confer insecticide resistance in the house fly. However, information about the status and underlying mechanisms of insecticide resistance in Kazakhstani house flies is lacking. In this study, we investigated the occurrence of genetic mutations associated with insecticide resistance in field house flies collected at six different locations in southern Kazakhstan. Four mutations (V260L, G342A/V, and F407Y) in Ace and three mutations (G137D and W251L/S) in MdαE7 were detected with appreciable frequencies. Notably, haplotypes carrying triple-loci mutations in Ace and double mutations in MdαE7 were found in Kazakhstan. The L1014H and L1014F mutations in Vssc, and CYP6D1v1 resistance allele were detected at a low frequency in some of the six investigated house fly populations. Phylogenetic analyses of haplotypes supported multiple origins of resistance mutations in Ace and MdαE7. These observations suggest that house flies in southern Kazakhstan may exhibit significant resistance to organophosphates and carbamates. Regular monitoring of insecticide resistance is recommended to achieve effective house fly control by chemical agents in southern Kazakhstan.

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.

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

The house fly is a ubiquitous pest commonly associated with animal facilities and urban waste. When present in large numbers, house flies can negatively impact humans and animals through nuisance and the transmission of pathogens. Since the development of fly traps and sticky papers to capture flies in the late 1800s, these and other methods have been used as a means to monitor change in house fly density or fly activity over time. Methods include substrate sampling to record density of immature flies, visual observations of adult fly activity, instantaneous counts of landing or resting flies, accumulation of adult flies on/in traps, or accumulation of fly fecal and regurgitation spots deposited by flies onto white cards. These methods do not estimate true house fly density, but rather provide an index of house fly activity that is related to both fly density and the frequency of individual fly behavior (e.g., frequency of flight, landing events) and which is likely more predictive of negative impacts such as nuisance and pathogen transmission. Routine monitoring of house fly activity is a critical component of a house fly management program. Fly activity should be held to a level below a predetermined activity threshold ('action threshold') above which negative impacts are anticipated to occur. This article is a review of methods utilized for monitoring house fly (Diptera: Muscidae) activity.

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.