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

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.

Long-term trends in housefly (Musca domestica L.) insecticide resistance in China

Controlling housefly populations relies on the use of insecticides, which inevitably leads to the development of resistance. A better and more comprehensive understanding of the spatial and temporal distribution of resistance could guide the control of houseflies. However, most studies on housefly resistance in China are scattered and poorly coordinated. We collected resistance data from houseflies in the published literature and from the vector biomonitoring system of the Chinese Center for Disease Control and Prevention. A 5- or 10-year resolution was used to study the temporal dynamics of resistance to five commonly used insecticides: deltamethrin, permethrin, beta-cypermethrin, dichlorvos, and propoxur. ArcGIS was used to visualize their spatial distributions. The correlation between year and resistance coefficient was determined using SPSS 26.0 and RStudio to explore the changes in resistance over the years. A total of 2128 data were included in this study, ranging from 1982 to 2022, based on which we found significant increases in resistance over the past forty years for the five studied insecticides. Among them, pyrethroids had the most strikingly elevated resistance level and were mainly distributed in the northern and southeastern coastal areas. Dichlorvos and propoxur had intermediate increases in resistance, and most of these increases were identified in North China and the Yangtze River. Housefly resistance to commonly used insecticides in China is increasing and spatially heterogeneous. This finding also highlights the necessity of continuous routine surveillance of housefly resistance, which could guide future housefly control operations and slow the development of resistance.

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.

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.

Ecotoxicity effect of aspirin on the larvae of Musca domestica through retinol metabolism

Aspirin is a widely used multi-efficiency pharmaceutical, and its environmental residues are frequently detected. However, limited information is available on its effects on the development of the public health pest and saprophytic insect Musca domestica. In this study, it was demonstrated that aspirin inhibits the larval growth of house flies in a concentration-dependent manner. Microbiome analysis indicated that the composition of larval intestinal bacteria was influenced by aspirin but not greatly. The dominant bacterial genus in the aspirin group was still Klebsiella, as in the control group. Transcriptome sequencing and gene set enrichment analysis showed that retinol metabolism was activated after aspirin treatment. High performance liquid chromatography indicated that the content of retinol in larvae was decreased and that of retinoic acid was increased. The addition of β-carotene, a precursor substance of retinol, in feeding promotes larval development and alleviates the inhibitory effect caused by aspirin. In contrast, retinoic acid delayed the larval development of house flies as well as aspirin. Gene expression analysis after aspirin exposure demonstrated that genes involved in the transformation from retinol to retinoic acid were upregulated. Overall, aspirin exposure impairs larval development by activating retinol metabolism in house flies and can be utilized as an effective pesticide. This work uncovers the mechanism underlying the larval development inhibition induced by aspirin in terms of metabolism and genetics, and provides novel functional exploration of a traditional drug for pest management.

Sex-specific Feeding Behavior of Adult House Flies, Musca domestica L. (Diptera: Muscidae)

House flies, Musca domestica L., (Diptera: Muscidae) mechanically vector diverse disease-causing microorganisms while foraging for food in agricultural and urban habitats. Although flies are diverse feeders, nutrient composition of food is important for both fly longevity and reproduction, especially for anautogenous females who require protein for egg production. We investigated whether fly sex and/or mating status influenced their preference for foods with varying macronutrient composition. Presumably mated or unmated male and female flies were separated by sex and offered four food, each in 10% solution offered on cotton wicks: sugar (carbohydrate-rich), fat-free milk (protein-rich, moderate carbohydrate), egg-yolk (protein and lipid-rich), and water (no macronutrients). Foods were colored with nontoxic dyes, which were rotated between replicates. After 4h exposure, flies were dissected to determine the type of food(s) ingested. The interaction of house fly sex and food type significantly influenced food preference, where females preferred milk (protein and carbohydrate-rich food), and males preferred mainly sugar (carbohydrate-rich). Furthermore, 32.8% of females and 10.6% of males foraged on multiple foods. While interaction of sex and mating status had no effect on food preference, milk preference was significantly higher in presumably mated than unmated females. We also tested whether food color influenced fly feeding preference, and found that color was most significant when flies were offered one food type, but negligible when multiple food types were present. This study suggests that bait-based fly control strategies should consider sex-specific preferences for various food attractants if aiming to target and control both male and female house flies.

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.

Synthetic and Natural Insecticides: Gas, Liquid, Gel and Solid Formulations for Stored-Product and Food-Industry Pest Control

The selective application of insecticides is one of the cornerstones of integrated pest management (IPM) and management strategies for pest resistance to insecticides. The present work provides a comprehensive overview of the traditional and new methods for the application of gas, liquid, gel, and solid physical insecticide formulations to control stored-product and food industry urban pests from the taxa Acarina, Blattodea, Coleoptera, Diptera, Hymenoptera, Lepidoptera, Psocoptera, and Zygentoma. Various definitions and concepts historically and currently used for various pesticide application formulations and methods are also described. This review demonstrates that new technological advances have sparked renewed research interest in the optimization of conventional methods such as insecticide aerosols, sprays, fumigants, and inert gases. Insect growth regulators/disruptors (IGRs/IGDs) are increasingly employed in baits, aerosols, residual treatments, and as spray-residual protectants for long-term stored-grain protection. Insecticide-impregnated hypoxic multilayer bags have been proven to be one of the most promising low-cost and safe methods for hermetic grain storage in developing countries. Insecticide-impregnated netting and food baits were originally developed for the control of urban/medical pests and have been recognized as an innovative technology for the protection of stored commodities. New biodegradable acaricide gel coatings and nets have been suggested for the protection of ham meat. Tablets and satchels represent a new approach for the application of botanicals. Many emerging technologies can be found in the form of impregnated protective packaging (insect growth regulators/disruptors (IGRs/IGDs), natural repellents), pheromone-based attracticides, electrostatic dust or sprays, nanoparticles, edible artificial sweeteners, hydrogels, inert baits with synthetic attractants, biodegradable encapsulations of active ingredients, and cyanogenic protective grain coatings. Smart pest control technologies based on RNA-based gene silencing compounds incorporated into food baits stand at the forefront of current strategic research. Inert gases and dust (diatomaceous earth) are positive examples of alternatives to synthetic pesticide products, for which methods of application and their integration with other methods have been proposed and implemented in practice. Although many promising laboratory studies have been conducted on the biological activity of natural botanical insecticides, published studies demonstrating their effective industrial field usage in grain stores and food production facilities are scarce. This review shows that the current problems associated with the application of some natural botanical insecticides (e.g., sorption, stability, field efficacy, and smell) to some extent echo problems that were frequently encountered and addressed almost 100 years ago during the transition from ancient to modern classical chemical pest control methods.

Toxicity, behavioural and biochemical effect of Piper betle L. essential oil and its constituents against housefly, Musca domestica L

Housefly, Musca domestica L. is a pest of public health importance and is responsible for spreading diseases like typhoid, diarrhoea, plague etc. Indiscriminate reliance on synthetic insecticides has led to development of insecticide resistance and ill effect to humans and nontarget animals. This demands an alternative and safer pest control option. This study evaluates the biological effect of Piper betle L essential oil and its constituent eugenol, eugenol acetate, and β - caryophyllene on the housefly. The major components present in P. betel EO were safrole (44.25%), eugenol (5.16%), β -caryophyllene (5.98%), β -selinene (5.93%), α-selinene (5.27%) and eugenol acetate (9.77%). Eugenol caused 4.5fold higher ovicidal activity (EC₅₀ 86.99 μg/ml) than P. betle EO (EC₅₀ 390.37 μg/ml). Eugenol caused fumigant toxicity to adults (LC₅₀ 88.38 mg/dm³). On contact toxicity by topical application, eugenol acetate, eugenol and β-caryophyllene caused higher mortality to larval and adult stages than EO. FESEM (Field Emission Scanning Electron Microscope) images reveal that exposure to P. betle EO causes the shrinkage of the larval cuticle. Both EO and eugenol induced the detoxifying enzymes Carboxyl esterase (Car E) and Glutathione S - transferases (GST) in larvae and adults. EO and eugenol at 0.2% caused effective repellence and oviposition deterrence to M. domestica adults and this merits their use as alternative strategy to manage M. domestica.

Salivary Digestion Extends the Range of Sugar-Aversions in the German Cockroach

Simple Summary

The gustatory sense of animals discriminates nutrients from noxious substances. However, enzymes in saliva can digest food components, potentially transforming the quality and taste of foods, and consequently altering feeding behavior. In the omnivorous German cockroach, Blattella germanica, feeding is highly stimulated by sugars, which are ubiquitous in its indoor environment. Glucose-averse cockroaches accept complex sugars, but they perceive glucose as a noxious tastant and reject it. We demonstrated that during feeding, saliva digests complex sugars, releasing glucose, and as a result, glucose-averse cockroaches interrupt their feeding on complex sugars. Moreover, we discovered that salivary alpha-glucosidases contributed to the breakdown of complex sugars to glucose. Therefore, the evolutionary adaptation of glucose-aversion, which protects cockroaches from insecticide-containing baits by changing the taste of glucose from sweet to bitter, also dramatically limits the suitability of complex sugars to glucose-averse cockroaches. We highlight the importance of pre-oral and oral saliva-mediated digestion in insect feeding behavior and the importance of considering the effects of saliva in design of sugar-containing insecticide baits.

Abstract

Saliva has diverse functions in feeding behavior of animals. However, the impact of salivary digestion of food on insect gustatory information processing is poorly documented. Glucose-aversion (GA) in the German cockroach, Blattella germanica, is a highly adaptive heritable behavioral resistance trait that protects the cockroach from ingesting glucose-containing-insecticide-baits. In this study, we confirmed that GA cockroaches rejected glucose, but they accepted oligosaccharides. However, whereas wild-type cockroaches that accepted glucose also satiated on oligosaccharides, GA cockroaches ceased ingesting the oligosaccharides within seconds, resulting in significantly lower consumption. We hypothesized that saliva might hydrolyze oligosaccharides, releasing glucose and terminating feeding. By mixing artificially collected cockroach saliva with various oligosaccharides, we demonstrated oligosaccharide-aversion in GA cockroaches. Acarbose, an alpha-glucosidase inhibitor, prevented the accumulation of glucose and rescued the phagostimulatory response and ingestion of oligosaccharides. Our results indicate that pre-oral and oral hydrolysis of oligosaccharides by salivary alpha-glucosidases released glucose, which was then processed by the gustatory system of GA cockroaches as a deterrent and caused the rejection of food. We suggest that the genetic mechanism of glucose-aversion support an extended aversion phenotype that includes glucose-containing oligosaccharides. Salivary digestion protects the cockroach from ingesting toxic chemicals and thus could support the rapid evolution of behavioral and physiological resistance in cockroach populations.