Fitness cost, realized heritability and stability of resistance to spiromesifen in house fly, Musca domestica L. (Diptera: Muscidae)

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.

Fitness costs of resistance to insecticides in insects

The chemical application is considered one of the most crucial methods for controlling insect pests, especially in intensive farming practices. Owing to the chemical application, insect pests are exposed to toxic chemical insecticides along with other stress factors in the environment. Insects require energy and resources for survival and adaptation to cope with these conditions. Also, insects use behavioral, physiological, and genetic mechanisms to combat stressors, like new environments, which may include chemicals insecticides. Sometimes, the continuous selection pressure of insecticides is metabolically costly, which leads to resistance development through constitutive upregulation of detoxification genes and/or target-site mutations. These actions are costly and can potentially affect the biological traits, including development and reproduction parameters and other key variables that ultimately affect the overall fitness of insects. This review synthesizes published in-depth information on fitness costs induced by insecticide resistance in insect pests in the past decade. It thereby highlights the insecticides resistant to insect populations that might help design integrated pest management (IPM) programs for controlling the spread of resistant populations.

Negative Impact of Unstable Spiromesifen Resistance on Fitness of Tetranychus urticae (Acari: Tetranychidae)

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is a phytophagous haplodiploid mite and its control is largely based on the use of pesticides. But, the short life cycle and high reproductive rate allow them to develop resistance to many pesticides. To design a strategy for resistance management, a fitness cost study was conducted on different populations of T. urticae, i.e., spiromesifen selected (SPIRO-SEL), unselected (Unsel), and reciprocal crosses. After twelve rounds of selections, T. urticae developed high spiromesifen resistance (71.7-fold) compared to the Unsel strain. Results showed a fitness cost for SPIRO-SEL, Cross1 (Unsel ♀ × SPIRO-SEL ♂), and Cross2 (SPIRO-SEL ♀ × Unsel ♂) with a relative fitness values of 0.63, 0.86, and 0.70, respectively. There was a significant increase in the incubation period, quiescent larvae, and egg to adult male and female developmental period of the SPIRO-SEL compared with Unsel strain. Moreover, resistance to spiromesifen was unstable with a decline in resistance value of - 0.05. The presence of unstable spiromesifen resistance associated with fitness costs suggests that intermittent withdrawal of its usage could potentially preserve its effectiveness for management of T. urticae.

Unstable fipronil resistance associated with fitness costs in fipronil-selected Aedes aegypti L

Mosquitoes are very serious household and medically important pests transmitting many diseases of humans and animals. Among mosquitoes, Aedes aegypti L., is an active transmitter of dengue and lumpy skin disease virus, horrible and terrifying diseases, causing human and animal death throughout the world. Fipronil is a new chemistry insecticide used to control agriculture and medically important insect pests. It affects the GABA receptors in the nervous system and consequently causes the death of the pests. A laboratory experiment was conducted to investigate the onset of fipronil resistance and associated fitness costs in Ae. Aegypti. Moreover, the stability of fipronil resistance was evaluated after five generations of rearing without selection pressure. The population of Ae. Aegypti was exposed continuously for 12 generations to fipronil under controlled conditions. The fipronil selected population (Fipro-Sel Pop) had a 317 and 115.7-fold level of resistance compared to a susceptible and field population, respectively. Relative fitness for Fipro-Sel Pop was 0.57, with a significant disadvantage in larval duration, developmental time, percent hatchability, intrinsic rate of natural increase (r_m), net reproductive rate (R_o), number of larvae in the next generation, and mean relative growth rate (MRGR) when compared to the Unselected population (Un-Sel Pop). However, the relative fitness value of Cross₁ (Un-Sel Pop ♂ × Fipro-Sel Pop ♀) and Cross₂ (Fipro-Sel Pop ♂ × Un-Sel Pop ♀) was 1.69 and 1.12, respectively. It is evident from the results that fipronil resistance comes with a fitness disadvantage, and it is unstable in the Fipro-Sel Pop of Ae. Aegypti. Therefore, the alternation of fipronil with other chemicals or suspension of fipronil usage for some time could improve its efficacy by delaying resistance development in Ae. Aegypti. Further research should be performed to investigate the field applicability of our findings.

Impact of Insecticides at Sublethal Concentrations on the Enzyme Activities in Adult Musca domestica L

Nowadays, the use of pesticides is, as before, the most common way to control arthropod plant pests and the ectoparasites of animals. The sublethal effects of pesticides on insects can appear at different levels, from genetics to populations, and the study of these effects is important for a better understanding of the environmental and evolutionary patterns of pesticidal resistance. The current study aimed to assess the sublethal effects of chlorfenapyr and fipronil on the activities of detoxifying enzymes (carboxylesterase-CarE, acetylcholinesterase-AChE, glutathione-S-transferase-GST, and cytochrome P450 monooxygenase-P450) in adults Musca domestica L. The insects were exposure to insecticides by a no-choice feeding test and the enzyme activities and the AChE kinetic parameters were examined in female and male specimens at 24 h after their exposure. According to Tukey's test, the CarE activity was statistically significantly decreased by 29.63% in the females of M. domestica after an exposure to chlorfenapyr at a concentration of 0.015% when compared to the controls (p ≤ 0.05). An exposure to the sublethal concentration of fipronil (0.001%) was followed by a slightly decrease in the specific activity (33.20%, p ≤ 0.05) and the main kinetic parameters (Vmax, Km) of AChE in females in comparison with the control values. The GST and P450 activities had not significantly changed in M. domestica males and females 24 h after their exposure to chlorfenapyr and fipronil at sublethal concentrations. The results suggest that the males and females of M. domestica displayed biochemically different responses to fipronil, that is a neurotoxin, and chlorfenapyr, that is a decoupler of oxidative phosphorylation. Further research needs to be addressed to the molecular mechanisms underlying the peculiarities of the insect enzyme responses to different insecticides.

Toxicities and Cross-Resistance of Imidacloprid, Acetamiprid, Emamectin Benzoate, Spirotetramat, and Indoxacarb in Field Populations of Culex quinquefasciatus (Diptera: Culicidae)

Culex quinquefasciatus is a major vector of several pathogens and is capable of breeding in various aquatic habitats. The extensive and injudicious use of synthetic chemicals against the mosquito species has led to the problem of insecticide resistance. To explore this resistance in detail, toxicity bioassays of imidacloprid, acetamiprid, emamectin benzoate, spirotetramat, and indoxacarb were performed on five Cx. quinquefasciatus field populations from Pakistan in addition to a laboratory susceptible strain. Compared with the susceptible strain, results for the five Cx. quinquefasciatus field populations were as follows: susceptibility to high resistance against imidacloprid (resistance ratio (RR): 0.09-11.18), susceptibility to moderate resistance against acetamiprid (RR: 0.39-8.00), susceptibility to emamectin benzoate (RR: 0.002-0.020), susceptibility to spirotetramat (RR: 0.01-0.07), and low to high resistance against indoxacarb (RR: 3.00-118.00). Correlation analyses revealed a significant positive correlation between imidacloprid, acetamiprid, and spirotetramat median lethal concentration (LC₅₀) values, indicating the possibility of cross-resistance. In contrast, there were no significant correlations between the LC₅₀ values of other tested insecticides, indicating the possible absence of cross-resistance. These results can assist public health authorities, medical entomologists, and pest managers to manage the insecticide resistance of Cx. quinquefasciatus as well as the associated pollution and human health issues.

Risk assessment of resistance to diflubenzuron in Musca domestica: Realized heritability and cross-resistance to fourteen insecticides from different classes

The Musca domestica L. is a well-known vector for a number of livestock and human diseases. One major challenge for maintaining effective control of this pest is its propensity to develop resistance to insecticides. This study utilized laboratory selection and realized heritability methods to examine the risk of resistance development to diflubenzuron in Musca domestica L. Cross-resistance (CR) to fourteen other insecticides was measured in diflubenzuron-selected (Diflu-SEL) strain which was selected for 20 generations. The resistance ratio (RR) of Diflu-SEL larvae to diflubenzuron increased from 30.33 in generation five (G₅) to 182.33 in G₂₄ compared with the susceptible strain, while realized heritability (h²) was 0.08. The number of needed generations (G) for a tenfold increase in the median lethal concentration (LC₅₀) for diflubenzuron ranged from 4 to 45 at h² values of 0.08, 0.18, and 0.28, at a slope of 1.51. At h² = 0.08 and slopes of 1.51, 2.51, and 3.51, the number of needed G for a tenfold increase in the LC₅₀ ranged from 9 to 104. The level of CR shown by the Diflu-SEL strain to all other fourteen tested insecticides (insect growth regulators, organophosphates, and pyrethroids) was either absent or very low compared to the field population. The value of h² and the absent or low CR indicate potential successful management of resistance to diflubenzuron and recommend the use of the tested insecticides in rotation with diflubenzuron to control M. domestica.

Cross resistance, inheritance and fitness advantage of cyetpyrafen resistance in two-spotted spider mite, Tetranychus urticae

Cyetpyrafen belonging to mitochondrial electron transport inhibitors of complex II (METI II) has been widely applied to manage pest mites in China. To investigate the adaption of Tetranychus urticae in the evolution of cyetpyrafen resistance, a study of cross resistance, mode of inheritance and fitness comparison of resistance using indoor cyetpyrafen resistant strain (resistance ratio, RR > 2, 000-fold) was executed. Cyet-R showed serious cross resistance to cyenopyrafen (>2500-fold) and cyflumetofen (~190-fold). The number of resistant genes was evaluated via chi-square (χ²) test and the concentration-response curve regarding goodness-of-fit between observed and the expected mortality. The LC₅₀s of F_1RS (Cyet-R^♀ × Tu-YN^♂) and F_1SR (Tu-YN^♀ × Cyet-R^♂) were 3126.30 mg/L and 2743.97 mg/L, respectively, without significance, suggesting autosomal inheritance. The degree of dominance (D) values of F_1RS and F_1SR ranged between 0 and 1, revealing an incompletely dominant inheritance in the tested population of Tetranychus urticae. Plots of concentration-response data for the orthogonal backcross and reverse backcross progenies showed a significant deviation from the expected lines, pointing out a polygenic inheritance. Besides, lifetable analysis showed a fitness advantage of Cyet-R with a significantly decreased adult preadult period and significantly increased total fecundity. This study suggested that cyetpyrafen resistance against T. urticae was inherited as autosomal, incompletely dominant and multigenetic and characterized with serious cross resistance and fitness advantage. Therefore, rational application and preventive strategy should be considered to sustain the efficacy of cyetpyrafen against T. urticae.

Stability and fitness cost associated with spirotetramat resistance in Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae)

BACKGROUND

Dusky cotton bug, Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is an important pest of cotton and causing economic losses to this crop. It also remains active round the year, infesting a number of host plants. Spirotetramat is a systemic insecticide and is effective against many sucking insect pests. A field collected population of O. hyalinipennis was reared in the laboratory under continuous spirotetramat selection pressure for 21 generations for the development of resistance to spirotetramat. The Spiro-Sel population was further reared for seven generations without insecticide exposure to assess the stability of spirotetramat resistance. Leaf dip method was used for the bioassays and selection. In this study, the impact of spirotetramat resistance on its stability and life history traits of Spiro-Sel, C₁ (15 Spiro-Sel♀ × 15 UNSEL ♂) and C₂ (15 Spiro-Sel♂ × 15 UNSEL ♀) O. hyalinipennis was assessed.

RESULTS

Spiro-Sel (G₂₁ ) population developed 2333-fold and 20.83-fold resistance compared with the susceptible and unselected (UNSEL) populations, respectively. Resistance to spirotetramat was unstable after seven generations (G₂₈ ) when reared without exposure to any insecticide. A significant reduction in overall nymphal survival, fecundity, egg hatching and net reproductive rate of Spiro-Sel population was observed when compared with UNSEL population. Intrinsic rate of natural increase, biotic potential and mean relative growth rate were also lower in Spiro-Sel population compared to UNSEL population. The Spiro-Sel, C₁ and C₂ population had a relative fitness of 0.44, 0.51 and 0.44, respectively.

CONCLUSION

Results of our study suggested that fitness cost is involved in the development of spirotetramat resistance. Unstable resistance and high fitness cost may provide great benefits to limit the evolution of resistance to spirotetramat in O. hyalinipennis. © 2021 Society of Chemical Industry.

SlGSTE9 participates in the stability of chlorpyrifos resistance in Spodoptera litura

BACKGROUND

Spodoptera litura is an important agricultural pest and has developed serious resistance to multiple insecticides. The resistance level to several insecticides is reported to be unstable, but the mechanism is less reported.

RESULTS

Chlorpyrifos and phoxim resistance level in a field-collected population of S. litura declined continuously from the first to the tenth generation and remained stable at the 11th and 12th generations without insecticide exposure. Synergist experiment showed that diethyl maleate and piperonyl butoxide significantly increased mortality to chlorpyrifos and phoxim in the first and sixth generations, but not in the 12th generation. The expression of 31 identified glutathione S-transferase (GST) genes in the third-instar larvae of S. litura in the first, sixth and 12th generations was determined, and eight genes were seen to decrease significantly in the sixth and 12th generations compared with the first generation. SlGSTe9 was selected for further functional study as it had higher abundance and significantly higher expression in the chlorpyrifos-resistant population than in the susceptible population. The recombinant protein of SlGSTE9 showed metabolism activity to chlorpyrifos in vitro and in Escherichia coli, but not to phoxim. Silencing of SlGSTe9 increased the cumulative mortality to chlorpyrifos significantly. SlGSTE9 also showed antioxidant activity to cumene hydroperoxide.

CONCLUSION

Our results suggest that SlGSTe9 is directly involved in chlorpyrifos resistance stability, but not in phoxim. SlGSTE9 may also participate in insecticides resistance by relieving the oxidase stress induced by insecticides. © 2021 Society of Chemical Industry.

Electrophysiological, behavioural and biochemical effect of Ocimum basilicum oil and its constituents methyl chavicol and linalool on Musca domestica L

Ocimum basilicum essential oil (EO) was evaluated for its biological effects on M. domestica. Characterization of O. basilicum EO revealed the presence of methyl chavicol (70.93%), linalool (9.34%), epi-α-cadinol (3.69 %), methyl eugenol (2.48%), γ-cadinene (1.67%), 1,8-cineole (1.30%) and (E)-β-ocimene (1.11%). The basil EO and its constituents methyl chavicol and linalool elicited a neuronal response in female adults of M. domestica. Adult female flies showed reduced preference to food source laced with basil EO and methyl chavicol. Substrates treated with EO and methyl chavicol at 0.25% resulted in an oviposition deterrence of over 80%. A large ovicidal effect was found for O. basilicum EO (EC₅₀ 9.74 mg/dm³) followed by methyl chavicol (EC₅₀ 10.67 mg/dm³) and linalool (EC₅₀ 13.57 mg/dm³). Adults exposed to EO (LD₅₀ 10.01 μg/adult) were more susceptible to contact toxicity than to methyl chavicol and linalool (LD₅₀ 13.62 μg/adult and LD₅₀ 43.12 μg/adult respectively). EO and its constituents methyl chavicol and linalool also induced the detoxifying enzymes Carboxyl esterase (Car E) and Glutathione S - transferases (GST).

Risk Assessment of Flonicamid Resistance in Musca domestica (Diptera: Muscidae): Resistance Monitoring, Inheritance, and Cross-Resistance Potential

Flonicamid is a chordotonal modulator and novel systemic insecticide that has been used frequently for controlling a broad range of insect pests. The risk of flonicamid resistance was assessed through laboratory selection and determining inheritance pattern and cross-resistance potential to five insecticides in house fly, Musca domestica L. Very low to high flonicamid resistance in M. domestica populations was found compared with the susceptible strain (SS). A flonicamid-selected (Flonica-RS) M. domestica strain developed 57.73-fold resistance to flonicamid screened for 20 generations compared with the SS. Overlapping 95% fiducial limits of LC50 of the F1 and F1ǂ, and dominance values (0.87 for F1 and 0.92 for F1ǂ) revealed an autosomal and incomplete dominant flonicamid resistance. The monogenic model of resistance inheritance suggested a polygenic flonicamid resistance. The Flonica-RS strain displayed negative cross-resistance between flonicamid and sulfoxaflor (0.10-fold) or clothianidin (0.50-fold), and very low cross-resistance between flonicamid and flubendiamide (4.71-fold), spinetoram (4.68-fold), or thiamethoxam (2.02-fold) in comparison with the field population. The estimated realized heritability (h2) value of flonicamid resistance was 0.02. With selection mortality 40-90%, the generations required for a 10-fold increase in LC50 of flonicamid were 94-258 at h2 (0.02) and slope (3.29). Flonicamid resistance was inherited as autosomal, incomplete dominant, and polygenic in the Flonica-RS. Negative or very low cross-resistance between flonicamid and sulfoxaflor, clothianidin, flubendiamide, spinetoram, and thiamethoxam means that these insecticides can be used as alternatives for controlling M. domestica. These data can be useful in devising the management for M. domestica.

Laboratory induced selection of pyriproxyfen resistance in Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae): Cross-resistance potential, realized heritability, and fitness costs determination using age-stage, two-sex life table

Pyriproxyfen is a biorational insecticide from IGR family, used worldwide against several economic pests. To evaluate the risk of pyriproxyfen resistance in dusky cotton bug, Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae), a major concern for cotton producers, and to formulate strategies effective to tackle resistance, a field collected population was selected with pyriproxyfen under laboratory conditions using seed-dip method. A resistant strain designated as Pyr-SEL (G₁₈) was developed after repeatedly selecting O. hyalinipennis with pyriproxyfen over eighteen generations. Thereafter, fitness costs, realized heritability (h²) and cross-resistance were investigated. As a result of selection, Pyr-SEL (G₁₈) developed a very high level of resistance (resistance ratio = 464.23-fold) compared with the susceptible strain unselected over twenty generations Un-SEL (G₂₀). The Pyr-SEL (G₁₈) conferred strong cross-resistance to bifenthrin (146.59-fold), lambda-cyhalothrin (132.96-fold) and fenoxycarb (91.06-fold), whereas showed moderate cross-resistance to diafenthiuron (28.86-fold) and fipronil (22.73-fold). The h² estimate was 0.16 in Pyr-SEL (G₁₈). The developmental duration of O. hyalinipennis pre-adult prolonged, but traits of λ, r and R₀ reduced in Pyr-SEL (G₁₈) compared with the Un-SEL (G₂₀). Also, the population projection obtained lower population size for Pyr-SEL (G₁₈) than Un-SEL (G₂₀). Fitness studies revealed that high resistance development to pyriproxyfen lowered the relative fitness of Pyr-SEL (G₁₈) (R_f = 0.38) compared with the Un-SEL (G₂₀). These findings may be practically valuable in tackling O. hyalinipennis resistance for better pest management.

Fitness cost of imidacloprid resistance in the cotton-staining bug, Dysdercus koenigii

Dysdercus koenigii, a serious cotton-staining insect pest in many countries, has shown high resistance to imidacloprid, a systemic neonicotinoid insecticide used to control sap-sucking pests. With the aim of creating an effective management strategy, the biological traits of susceptible (SS) and imidacloprid-resistant (Imida-RS) D. koenigii, as well as their reciprocal crosses (CR1 and CR2), were investigated here using a life table established on age, stage, and two-sex patterns. Compared with SS D. koenigii, Imida-RS and CR1 strains had lower relative fitness (0.80 and 0.47, respectively) and fecundity (eggs per female); prolonged egg duration and a prolonged adult preoviposition period; shorter nymphal duration, male/female total longevity, and oviposition days, and a shorter total preoviposition period. However, there were no differences among strains in nymphal survival rates and female ratio. The CR2 D. koenigii had similar relative fitness value (1.09), suggested no fitness cost in most of the parameters. Demographic parameters, including net reproductive rate, were lower in the Imida-RS strain than in SS and CR2 D. koenigii. Similarly, the Imida-RS and CR1 strains had shorter generation time and doubling time, lower reproductive value and life expectancy relative to the SS and CR2 D. koenigii. In addition, age-specific fecundity was negatively affected in the CR1 strain compared with the other strains. These findings could help facilitate the development of rational D. koenigii control strategies.