Dominant fitness costs of resistance to fipronil in Musca domestica Linnaeus (Diptera: Muscidae)

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.

Laboratory-Induced Bifenthrin, Flonicamid, and Thiamethoxam Resistance and Fitness Costs in Rhopalosiphum padi

The bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae) is one of the most economically important pests of wheat crops worldwide. Thiamethoxam, bifenthrin, and flonicamid are extensively used insecticides for controlling this key pest. However, the indiscriminate use of chemical insecticides has led to the development of resistance in insects. In this study, we assessed the development of selection-induced resistance to bifenthrin, flonicamid, and thiamethoxam under controlled laboratory conditions. Additionally, we employed the age-stage, two-sex life table method to examine the fitness of R. padi. After ten generations of selection, bifenthrin-, flonicamid-, and thiamethoxam-resistant strains of R. padi were developed with resistance levels of 34.46, 31.97, and 26.46-fold, respectively. The life table analysis revealed a significant decrease in adult longevity and fecundity in these resistant strains compared to susceptible strain. Furthermore, the key demographic parameters such as net reproductive rate (R0) and reproductive days exhibited a significant reduction in all resistant strains, while the intrinsic rate of increase (r) and finite rate of increase (λ) were decreased only in resistant strains to bifenthrin and thiamethoxam. Taken together, these findings provide a comprehensive understanding of laboratory-induced insecticide resistance evolution and the associated fitness costs in R. padi. This knowledge could help to design resistance management strategies against this particular pest of wheat.

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.

Alpha-Cypermethrin Resistance in Musca domestica: Resistance Instability, Realized Heritability, Risk Assessment, and Insecticide Cross-Resistance

Musca domestica L., the common house fly, is a cosmopolitan carrier of human and livestock disease pathogens. The species exhibits resistance to many insecticides; therefore, effective M. domestica insecticide resistance management programs are required worldwide. In the present study, the development of alpha-cypermethrin resistance, realized heritability (h²), instability of resistance trait (DR), and cross-resistance (CR) was investigated in an alpha-cypermethrin-selected M. domestica strain (Alpha-Sel) across 24 generations (Gs). Compared with an alpha-cypermethrin-unselected strain (Alpha-Unsel), resistance to alpha-cypermethrin increased from 46.4-fold (G₅) to 474.2-fold (G₂₄) in Alpha-Sel females and 41.0-fold (G₅) to 253.2-fold (G₂₄) in Alpha-Sel males. Alpha-cypermethrin resistance declined by between -0.10 (G₅) and -0.05 (G₂₄) in both M. domestica sexes without insecticide exposure for 24 generations. The h² of alpha-cypermethrin resistance was 0.17 and 0.18 for males and females, respectively, in G₁-G₂₄. With selection intensities of 10-90%, the G values required for a tenfold increase in the LC₅₀ of alpha-cypermethrin were 6.3-53.7, 4.1-33.8, and 3.0-24.7, given h² values of 0.17, 0.27, and 0.37, respectively, and a constant slope of 2.1 for males and h² values of 0.18, 0.28, and 0.38, respectively, and a constant slope of 2.0 for females. Compared with Alpha-Unsel, Alpha-Sel M. domestica exhibited moderate CR to bifenthrin (15.5-fold), deltamethrin (28.4-fold), and cyfluthrin (16.8-fold), low CR to two pyrethroids and five organophosphates, and no CR to insect growth regulators. The instability of resistance trait, low h², and absent or low CR associated with alpha-cypermethrin resistance in M. domestica indicate resistance could be managed with rotational use of the insecticide.

Fitness cost of spinosad resistance related to vitellogenin in Frankliniella occidentalis (Pergande)

BACKGROUND

The western flower thrips Frankliniella occidentalis, a worldwide agricultural pest, has developed resistance to an array of insecticides. Spinosad resistance confers an apparent fitness cost in F. occidentalis. In the present study, we compared the reproductive capacities, ovary development, and the expression of the vitellogenin (Vg) gene in spinosad-susceptible (Ivf03) and -resistant (NIL-R) near isogenetic lines of F. occidentalis in order to clarify the reason for the fitness cost in spinosad resistance.

RESULTS

The NIL-R strain exhibited a 17.9% decrease in fecundity (eggs laid per female) as compared to the Ivf03 strain, and the ovariole was significantly shortened by 2.8% in the NIL-R strain relative to the Ivf03 strain. Compared to the Ivf03 strain, the expression levels of Vg mRNA and protein were downregulated by 33.7% and 32.9% in the NIL-R strain, respectively. Moreover, interference with the Vg gene significantly reduced the expression levels of Vg mRNA and protein, and decreased ovariole length, survival rates and the fecundity of both strains.

CONCLUSION

The results indicate that the downregulated expression of Vg may contribute to the reduction of ovariole length and consequently to a fitness cost in spinosad-resistant F. occidentalis. The results not only increase our understanding of the evolution of insecticide resistance, but also could contribute to the formulation of control strategy of F. occidentalis. © 2022 Society of Chemical Industry.

Cross-Resistance and Fitness Costs of the cis-Nitromethylene Neonicotinoid Cycloxaprid Resistance in Melon Aphid, Aphis gossypii (Hemiptera: Aphididae)

The melon aphid, Aphis gossypii Glover, is an important pest on various vegetables around the world and has developed resistance to neonicotinoids in fields. Cycloxaprid is a novel cis-nitromethylene configuration neonicotinoid insecticide that is different from trans-configuration neonicotinoids like imidacloprid and thiamethoxam. Herein, the cross-resistance to the other seven insecticides and fitness costs were investigated in the cycloxaprid-resistant A. gossypii strain (Cpd-R), which has developed 69.5-fold resistance to cycloxaprid. The results showed that the Cpd-R strain had very low levels of cross-resistance to imidacloprid (4.3-fold), acetamiprid (2.9-fold), thiamethoxam (3.7-fold), nitenpyram (6.1-fold), flupyradifurone (2.2-fold), and sulfoxaflor (4.5-fold), while it exhibited a cross-resistance to dinotefuran (10.6-fold). The fitness of the Cpd-R strain by life table analysis was only 0.799 compared to the susceptible strain (Cpd-S). This Cpd-R strain exhibited significantly reduction in fecundity, oviposition days, and developmental time of nymph stage compared to the Cpd-S strain. Moreover, the expression levels of some genes related to the development and reproduction, including EcR, USP, JHAMT, and JHEH were significantly up-regulated, while Vg was down-regulated in the Cpd-R strain. This study indicates that the Cpd-R strain possessed a certain fitness cost. The above research results are useful for rational application of cycloxaprid and implementing the appropriate resistance management strategy for A. gossypii.

Multiple Mechanisms Confer Fipronil Resistance in the German Cockroach: Enhanced Detoxification and Rdl Mutation

Populations of Blattella germanica (L.) (German cockroach) have been documented worldwide to be resistant to a wide variety of insecticides with multiple modes of action. The phenylpyrazole insecticide fipronil has been used extensively to control German cockroach populations, exclusively in baits, yet the highest reported fipronil resistance is 38-fold in a single population. We evaluated five populations of German cockroaches, collected in 2018-2019 in apartments in North Carolina and assayed in 2019, to determine the status of fipronil resistance in the state. Resistance ratios in field-collected strains ranged from 22.4 to 37.2, indicating little change in fipronil resistance over the past 20 yr. In contrast, resistance to pyrethroids continues to escalate. We also assessed the roles of detoxification enzymes in fipronil resistance with four synergists previously shown to diminish metabolic resistance to various insecticides in German cockroaches-piperonyl butoxide, S,S,S-tributyl phosphorotrithioate, diethyl maleate, and triphenyl phosphate. These enzymes appear to play a variable role in fipronil resistance. We also sequenced a fragment of the Rdl (resistant to dieldrin) gene that encodes a subunit of the GABA receptor. Our findings showed that all field-collected strains are homozygous for a mutation that substitutes serine for an alanine (A302S) in Rdl, and confers low resistance to fipronil. Understanding why cockroaches rapidly evolve high levels of resistance to some insecticides and not others, despite intensive selection pressure, will contribute to more efficacious pest management.

Resistance of Sogatella furcifera to triflumezopyrim mediated with the overexpression of CYPSF01 which was regulated by nuclear receptor USP

Sogatella furcifera is one of the main agricultural pests in many Asian countries, bringing about enormous injury. A triflumezopyrim-resistant (Tri) strain of S. furcifera was established through continuous screening in laboratory. The determination of synergist and enzyme activity indicated that P450s, especially for the upregulation expression of CYPSF01, played a key role in the increased resistance, confirmed by RNAi, and the recombinant protein of CYPSF01 and NADPH-P450 reductase was able to degrade triflumezopyrim. CYPSF01 had an obviously co-expression relationship with nuclear receptor ultraspiracle (USP), which were all significantly up-regulated when exposed to triflumezopyrim. Further, a USP-binding motif MA0534.1 was enriched from the upregulated peaks by Assay for Transposase Accessible Chromatin (ATAC-seq) analysis, which exited in the peaks located on the promoter of CYPSF01; the yeast one-hybrid experiments confirmed that USP could bind to the CYPSF01 promoter. And the USP interference significantly down-regulated CYPSF01 expression, and resulted in the significantly increasing sensitivity to triflumezopyrim, its mortality rate increased 28.37%. Therefore, the overexpression of USP could cause to the overexpression of CYPSF01, ultimately resulting in the resistance to triflumezopyrim in S. furcifera.

V101I and R81T mutations in the nicotinic acetylcholine receptor β1 subunit are associated with neonicotinoid resistance in Myzus persicae

BACKGROUND

The peach-potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), is a major pest worldwide. The intensive use of insecticides has led to the development of resistance against neonicotinoid insecticides. The R81T mutation in the nicotinic acetylcholine receptor (nAChR) beta1 subunit is considered a crucial mechanism adaptation to neonicotinoid resistance in M. persicae and Aphis gossypii.

RESULTS

Resistance-related mutations (R81T and V101I) were detected in the imidacloprid-resistant M. persicae AH19 population. The V101I mutation is reported for the first time. The V101I and R81T mutations existed separately, indicating that the two mutations evolved independently. Imidacloprid resistance in the AH19 population was stable without insecticide exposure. Four mutant strains were selected from the population with stable resistance. The resistance of the AH19-T, AH19-I, and AH19-TI strains to imidacloprid, thiamethoxam, and dinotefuran was significantly increased compared with the AH19-W strain. Synergism bioassays showed that the inhibition of three detoxification enzymes did not affect imidacloprid resistance in the AH19-T and AH19-I strains. Expression of nAChR β1 subunits in the AH19-W, AH19-T, and AH19-I strains remained unchanged.

CONCLUSION

The V101I mutation is associated with neonicotinoid resistance in M. persicae. The resistance of the AH19-T and AH19-I strains to neonicotinoids appears to be mainly due to the R81T and V101I mutations, whereas these mutations, together with changes in the cytochrome P450 monooxygenases and nAChR expression may be responsible for the development of neonicotinoid resistance in the AH19-TI strain. © 2021 Society of Chemical Industry.

Resistance and fitness costs in diamondback moths after selection using broflanilide, a novel meta-diamide insecticide

The diamondback moth (DBM) Plutella xylostella (L.) (Lepidoptera: Plutellidae) is an insect pest found around the world that feeds on cruciferous crops. The DBM has become resistant to most insecticides in current use in the field. Broflanilide is a novel meta-diamide insecticide that binds to a new site on the γ-aminobutyric acid receptor and very efficiently protects against most pests in the order Lepidoptera, including DBM. In this study, the resistance of a laboratory-bred susceptible strain of DBM to broflanilide and the fitness costs posed by broflanilide to the DBM were evaluated. The DBM had no obvious resistance to broflanilide after 10 generations of selection. The realized heritability h² was 0.033, suggesting a low risk of resistance developing in this strain. The F10 generation had no cross-resistance to the insecticides abamectin and endosulfan (which target the γ-aminobutyric acid receptor) and chlorantraniliprole (which targets a non-γ-aminobutyric acid receptor). The specific activities of important detoxification enzymes (cytochrome P450 monooxygenase, esterase, and glutathione S-transferase) were not obviously altered. However, the larval stage was prolonged and the adult stage was shortened significantly in F11 generation than the F0 generation. The total preoviposition period TPOP significantly prolonged 1.90 d in F11 generation. The fitness value R_f (0.93) was lower for the F11 generation than the F0 generation. The results indicated that long-term exposure to broflanilide exerts clear fitness costs in the DBM. This information will be useful in identifying reasonable broflanilide application guidelines for managing broflanilide resistance in the DBM.

Development of fipronil resistance, fitness cost, cross-resistance to other insecticides, stability, and risk assessment in Oxycarenus hyalinipennis (Costa)

Pesticides are extensively used to control pests, diseases, and weeds in order to increase agricultural production. Usage of indiscriminate doses and persistent pesticides has not only caused resistance issues in insect pests but has also had deleterious effects on non-target organisms (beneficial insects, fish, and wildlife) and caused environmental contamination (soil, water, and air) through leaching, overflow, and insecticide spray drift. Exposure from eating food and drinking water contaminated to pesticide residues is also affecting human health. This study was conducted to obtain information to reduce pesticide resistance and environmental pollution. A cotton dusky bug (Oxycarenus hyalinipennis) population was collected from a farmer's field and exposed to fipronil for 18 generations. In comparison to an unselected strain (XYZ-FS) and a field population (Field-Popn), the fipronil-selected strain of O. hyalinipennis (XYZ-FR) developed a 2631.50-fold level of resistance and a 202.42-fold resistance level respectively. Significantly higher fecundity was observed in the XYZ-FS (24.93) compared to that of Hybrid₂ (XYZ-FR ♀ XYZ-FS ♂) (17.60), Hybrid₁ (XYZ-FR ♂ × XYZ-FS ♀) (17.13), and XYZ-FR (12.6). The intrinsic rate of natural increase, relative fitness and biotic potential were highest in XYZ-FS, followed by Hybrid₂, Hybrid₁, and XYZ-FR. The XYZ-FR strain of O. hyalinipennis had very low cross-resistance to profenofos (1.15-2.83-fold), and emamectin benzoate (1.09-2.86-fold) and moderate resistance to bifenthrin (5.49-24.54-fold) when selection progressed from G₄ to G_19. The proper use of this pesticide, along with rotation and a high-dose strategy may helpful to reduce the risk of resistance development and also its negative impacts on the environment and humans.

Sulfoxaflor resistance in Oxycarenus hyalinipennis (Costa) induces negligible cross-resistance to other tested insecticides: stability, risk assessment, and fitness cost

BACKGROUND

Oxycarenus hyalinipennis (Costa) (Hemiptera: Lygaeidae) is a polyphagous insect pest. In Pakistan, O. hyalinipennis is managed by using different insecticides, a major concern for cotton producers, and has developed resistance to many of these. Sulfoxaflor belongs to a newly released sulfoximine family that has high efficacy for controlling sap-feeding insect pests.

RESULTS

A sulfoxaflor selected-population (Sulfo-Sel-Pop) of O. hyalinipennis showed a 3064.92-fold level of resistance after continuous selection for 18 generations with sulfoxaflor compared to unselected population (UNSel-Pop). The Sulfo-Sel-Pop showed a reduction in resistance (from 3064.92 to 635-fold) without exposure for five generations, indicating unstable resistance to sulfoxaflor. Cross-resistance studies of the Sulfo-Sel-Pop revealed no or very low cross-resistance to triazophos (0.42 to 0.30-fold), deltamethrin (0.85 to 0.18-fold) and acetamiprid (1.16 to 4.86-fold) from G₄ to G₁₉ compared to the field population (Field-Pop). The mean value of realized heritability was 0.15 in the Sulfo-Sel-Pop (G₁₉ ). Significantly reduced relative fitness was determined in the Sulfo-Sel-Pop (Rf = 0.21) followed by Cross₁ [(Sulfo-Sel-Pop ♂ × UNSel-Pop ♀) (Rf = 0.58)]_, and Cross₂ [(Sulfo-Sel-Pop ♀ × UNSel-Pop ♂) (Rf = 0.70)] compared with the UNSel-Pop. The values of intrinsic rate of natural increase (r_m ), biotic potential (Bp) fecundity, egg hatching, and net reproductive rate (R0) were also significantly less in the Sulfo-Sel-Pop compared to UNSel-Pop.

CONCLUSION

A very high fitness cost, unstable resistance and no or very low cross-resistance in the Sulfo-Sel-Pop have great implications in designing effective strategies for managing insecticide resistance to O. hyalinipennis. © 2021 Society of Chemical Industry.

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.

Inheritance, stability, cross-resistance, and life history parameters of a clothianidin-selected strain of house fly, Musca domestica Linnaeus

The house fly, Musca domestica L., is a cosmopolitan insect pest of public and animal health importance that serves as a mechanical vector of pathogens. Aimed at prospective resistance management to reduce environmental pollution, we characterized the inheritance pattern, realized heritability, fitness cost, cross resistance, stability and mechanism of clothianidin resistance in M. domestica that were collected from the poultry farm. By continuous selection with clothianidin for 11 generations, the clothianidin selected M. domestica strain (Clotha-SEL) developed a 3827-fold resistance compared to a susceptible strain. However, resistance to clothianidin was proved to be unstable when selection with clothianidin was removed for five generations (G₇ to G₁₂). Inheritance pattern analysis at G₈ of Clotha-SEL (RR = 897) revealed that resistance to clothianidin was polygenic, autosomal and incompletely dominant. Realized heritability (h²) for resistance value was 0.38 (at G₁₁) in the tested strain. Synergist bioassays showed that microsomal oxidases and esterases might not contribute significantly in resistance evolution. Fitness costs of clothianidin resistance were present, for example, reduction in growth potential of the Clotha-SEL strain in comparison to the untreated counterpart strain (UNSEL) was observed. No cross resistance to bifenthrin and fipronil and a very low cross-resistance to spinosad were observed. These insecticides could be alternated with clothianidin as an insecticide resistance management tool to sustain its efficacy for a longer time period. These results shall be utilized to devise a proactive resistance management strategy for use of clothianidin against M. domestica that will be helpful to alleviate the allied threats to environmental and human health.

Fitness Costs of Chlorantraniliprole Resistance Related to the SeNPF Overexpression in the Spodoptera exigua (Lepidoptera: Noctuidae)

Spodopteraexigua, a multifeeding insect pest, has developed a high level of resistance to chlorantraniliprole, which is a benzoylurea insecticide that targets the ryanodine receptors (RyRs). Herein, the resistant strain (SE-Sel) and sensitive strain (SE-Sus) were obtained by bidirectional screening for six generations. The potential oviposited eggs and oviposition rate of the SE-Sel strain were dramatically lower than those of the SE-Sus strain; on the contrary, the weights of prepupae and preadult were significantly increased. As a post-mating response, the higher number of non-oviposited eggs in the SE-Sel strain was caused by a lower mating rate. In addition, the expression levels of vitellogenin (SeVg) and its receptor (SeVgR) in the SE-Sel strain were consistently lower than those in the SE-Sus strain. An RyR^I4743M mutation, contributing to the resistance to chlorantraniliprole, was located in the S3 transmembrane segments and might have affected the release of calcium ions; it led to the upregulated expression of the neuropeptide SeNPF and its receptor SeNPFR, and the mating and oviposition rate were significantly recovered when the SeNPF was knocked down though RNA interference (RNAi) in the male adult of the SE-Sel strain. Moreover, the expression of the juvenile hormone-binding proteins SeJHBWDS3 and SeJHBAN in the male adult of the SE-Sel strain was significantly decreased, which proved the existence of a fitness cost from another angle. Therefore, these results indicate that the fitness cost accompanied by chlorantraniliprole resistance in S. exigua may be related to the decrease in mating desire due to SeNPF overexpression.

Resistance to insect growth regulators and age-stage, two-sex life table in Musca domestica from different dairy facilities

Among the vectorial insect pests, the domestic house fly (Musca domestica L., Diptera: Muscidae) is a ubiquitous livestock pest with the ability to develop resistance and adapt to diverse climates. Successful management of the house fly in various locations requires information about its resistance development and life table features. The status of insect growth regulators resistance and life table features on the basis of age, stage, and two sexes of the house fly from five different geographical locations of Riyadh, Saudi Arabia: Dirab, Al-Masanie, Al-Washlah, Al-Uraija and Al-Muzahmiya were therefore investigated. The range of resistance levels were 3.77–8.03-fold for methoxyfenozide, 5.50–29.75 for pyriproxyfen, 0.59–2.91-fold for cyromazine, 9.33–28.67-fold for diflubenzuron, and 1.63–8.25-fold for triflumuron in five populations of house fly compared with the susceptible strain. Analysis of life history parameters—such as survival rate, larval duration, pupal duration, pre-female duration, pre-male duration, adult and total pre-oviposition periods, longevity of male, oviposition period, female ratio, and fecundity female^-1—revealed significant variations among the field populations. Additionally, demographic features—including the generation time, the finite and intrinsic rates of increase, doubling time, and net reproductive rate—varied significantly among the field populations. These results will be helpful in planning the management of the house fly in geographically isolated dairies in Saudi Arabia.

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.

Acetamiprid resistance and fitness costs of melon aphid, Aphis gossypii: An age-stage, two-sex life table study

The melon aphid, Aphis gossypii is a globally distributed crop pest with a wide host range. The intensive use of insecticides against this insect over several years has led to develop resistance against many insecticides including acetamiprid. Understanding the relationship between acetamiprid resistance and fitness of A. gossypii is essential to limit the spread of the resistant population in the field. In this study, age-stage, two-sex life table approach was used to investigate these relationships in the lab. Results showed that resistant strain (Ace-R) had a reduced fitness (relative fitness = 0.909) along with significantly decreased adult longevity, fecundity, net reproductive (R₀), mean generation time (T) and gross reproductive rate (GRR). Compared to the susceptible strain (Ace-S), the pre-adult period and total pre-oviposition period (TPOP) were also significantly shorter in Ace-R strain. Moreover, the expression profiles of EcR, JHBP, JHAMT, JHEH, USP and Vg genes supposed to be involved in insect reproduction and development were analyzed using Quantitative Real Time PCR. The EcR, JHBP, JHAMT and USP genes were up-regulated, Vg gene was down-regulated while the mRNA level of JHEH gene was statistically same in the Ace-R strain compared to the Ace-S strain. Collectively, this study provides the occurrence and magnitude of fitness costs of A. gossypii against acetamiprid resistance and could be helpful to manage the resistance evolution in field populations.

Fitness costs in clothianidin-resistant population of the melon aphid, Aphis gossypii

Clothianidin is a second-generation neonicotinoid insecticide, widely used against sap-sucking insect pest including melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae). This pest causes severe economic damage to Cucurbitaceae plants worldwide. In this study, we investigated clothianidin resistance development under continuous selection pressure. Moreover, the age-stage, two-sex life table approach was used to evaluate the impact of clothianidin resistance on the fitness of A. gossypii. A clothianidin resistant strain (CT-R) with a 23.17-fold resistance level was developed from a susceptible strain (CT-S) after continuous selection for 24 generations. Life table results showed a significant reduction in the relative fitness (0.847) of CT-R strain compared to the CT-S strain of A. gossypii. The developmental duration, oviposition days, total pre-oviposition period (TPOP), longevity, and fecundity of CT-R strain were found to be significantly lower when compared to CT-S strain. The demographic parameters, including the intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate (R0), and mean generation time (T) were also significantly decreased in CT-R strain compared to the CT-S strain. Both the reproductive and survival rates were affected by clothianidin resistance in CT-R strain compared with the CT-S strain of A. gossypii. Overall, our results demonstrate that in-depth knowledge about the trade-off at play between resistance degree and fitness cost might be useful to design resistance management strategies against A. gossypii.

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

The house fly, Musca domestica L. (Diptera: Muscidae), is an insect pest of public health and veterinary importance. Spiromesifen is a new chemistry insecticide widely used for the management of sucking insect pests of vegetables and crops. In the present study, assessment of resistance risk and fitness costs associated with spiromesifen resistance in M. domestica was studied. Moreover, stability of resistance to spiromesifen and other tested insecticides (fipronil, spinosad, and bifenthrin) was evaluated in the spiromesifen-selected-strain (SPIRO-SEL-POP). After 7-generations of selection with spiromesifen, SPIRO-SEL-POP developed 108.76-fold resistance compared with the unselected strain (UNSEL-POP). The estimated value of realized heritability was 0.59 for spiromesifen resistance. Due to withdrawal of spiromesifen selection for five generations (F₆-F₁₀) on SPIRO-SEL-POP, a decline in LC₅₀ values against spiromesifen, spinosad and bifenthrin was 0.16, 0.14 and 0.13-folds, respectively. In biological trait experiments, larval weight of Cross₁ (SPIRO-SEL-POP♀ × UNSEL-POP♂) and SPIRO-SEL-POP was significantly lower than that of Cross₂ (SPIRO-SEL-POP♂ × UNSEL-POP♀) and UNSEL-POP. Pupal weight of SPIRO-SEL-POP was higher when compared with Cross₁ while it was similar to that of Cross₂ and UNSEL-POP. Adult emergence rate of UNSEL-POP was higher than Cross₁, but similar to the Cross₂ and SPIRO-SEL-POP. The SPIRO-SEL-POP and Cross₁ showed the lowest relative fitness when compared with USEL-POP and Cross₂. Intrinsic rate of natural increase of SPIRO-SEL-POP was much lower than that of UNSEL-POP and Cross₂ followed by Cross₁. The SPIRO-SEL-POP exhibited lower biotic potential when compared with UNSEL-POP and Cross₂ but similar to Cross₁. Fecundity and hatching rates were lower in SPIRO-SEL-POP compared to UNSEL-POP. It could be concluded that spiromesifen resistance in M. domestica comes with a cost and is instable. Therefore, spiromesifen rotation with other insecticides and withdraw of its usage for some period could help to sustain its efficacy by delaying the development of resistance.

Cross-resistance and Fitness Cost Analysis of Resistance to Thiamethoxam in Melon and Cotton Aphid (Hemiptera: Aphididae)

The melon/cotton aphid, Aphis gossypii Glover, is a notorious pest in many crops. The neonicotinoid insecticide thiamethoxam is widely used for A. gossypii control. To evaluate thiamethoxam resistance risk, a melon/cotton aphid strain with an extremely high level of resistance to thiamethoxam (>2,325.6-fold) was established after selection with thiamethoxam for 24 generations. Additionally, the cross-resistance pattern to other neonicotinoids and fitness were analyzed. The cross-resistance results showed the thiamethoxam-resistant strain had extremely high levels of cross-resistance against clothianidin (>311.7-fold) and nitenpyram (299.9-fold), high levels of cross-resistance against dinotefuran (142.3-fold) and acetamiprid (76.6-fold), and low cross-resistance against imidacloprid (9.3-fold). Compared with the life table of susceptible strain, the thiamethoxam-resistant strain had a relative fitness of 0.950, with significant decreases in oviposition days and fecundity and prolonged developmental duration. The molecular mechanism for fitness costs was studied by comparing the mRNA expression levels of juvenile hormone acid O-methyltransferase (JHAMT), juvenile hormone-binding protein (JHBP), juvenile hormone epoxide hydrolase (JHEH), ecdysone receptor (EcR), ultraspiracle protein (USP), and Vitellogenin (Vg) in the susceptible and thiamethoxam-resistant strains. Significant overexpression of JHEH and JHBP and downregulation of EcR and Vg expression were found in the thiamethoxam-resistant strain. These results indicate that A. gossypii has the potential to develop extremely high resistance to thiamethoxam after continuous exposure, with a considerable fitness cost and cross-resistance to other neonicotinoids.

Fitness costs associated with thiamethoxam and imidacloprid resistance in three field populations of Diaphorina citri (Hemiptera: Liviidae) from Florida

Insecticide resistance is an increasing problem in citrus production. The Asian citrus psyllid, Diaphornia citri Kuwayama, is recognized as one of the most important citrus pests worldwide and it has developed resistance in areas where insecticides have been overused. The development of insecticide resistance is often associated with fitness costs that only become apparent in the absence of selection pressure. Here, the fitness costs associated with resistance to thiamethoxam and imidacloprid were investigated in three agricultural populations of D. citri as compared with susceptible laboratory colonies. Results showed that all field populations had greater resistance than laboratory susceptible colonies. For both thiamethoxam and imidacloprid, a Candidatus Liberibacter asiaticus-positive (CLas+) colony was more susceptible than the CLas- colony. Resistance ratios ranged from 7.65-16.11 for imidacloprid and 26.79-49.09 for thiamethoxam in field populations as compared with a susceptible, CLas- laboratory strain. Among three resistant field populations, a significantly reduced net reproductive rate and finite rate of population increase were observed in a population from Lake Wales, FL as compared to both susceptible strains. The fecundity of field populations from Lake Wales, FL was statistically lower than both laboratory susceptible populations. Certain changes in morphological characteristics were observed among resistant, as compared, with susceptible strains. Our data suggest fitness disadvantages associated with insecticide resistance in D. citri are related to both development and reproduction. The lower fitness of D. citri populations that exhibit resistance to neonicotinoid insecticides should promote recovery of sensitivity when those populations are no longer exposed to thiamethoxam and/or imidacloprid in the field. The results are congruent with a strategy of insecticide rotation for resistance management.

House fly resistance to chlorantraniliprole: cross resistance patterns, stability and associated fitness costs

BACKGROUND

The house fly, Musca domestica L. (Diptera: Muscidae) is an important public health pest that serves as a carrier for pathogens transmitting various diseases of man and animals. It is well known for rapid resistance development to insecticides applied for its chemical control. Chlorantraniliprole, an anthranilic diamide, a ryanodine receptor agonist, is a promising agent for the integrated pest management of various insect pests. To design a retrospective resistance management strategy, life history traits of the chlorantraniliprole laboratory-selected (CTPR-SEL) and unselected counterpart (UNSEL) sub-populations of a field strain and their reciprocal crosses were studied.

RESULTS

After eight generations of consecutive selection with chlorantraniliprole, a 750-fold resistance level when compared to a susceptible strain and a 124-fold resistance level when compared to the UNSEL strain had developed in CTPR-SEL. Very low cross resistance to bifenthrin but no cross resistance to spinosad and fipronil was observed in the CTPR-SEL strain. Results of the fitness traits suggest that the CTPR-SEL has a lower relative fitness (0.34), reduced fecundity, a decrease in eggs hatchability, lower biotic potential and net reproductive rate as compared to the UNSEL strain. Interestingly, chlorantraniliprole resistance was unstable in the CTPR-SEL.

CONCLUSIONS

Fitness costs associated with chlorantraniliprole resistance suggest that the efficacy of this insecticide could be preserved for a prolonged duration of time by alternating its use with insecticides having dissimilar modes of action and no cross resistance. When cross-resistance is absent, a sequence of two insecticides is expected to be more durable than a mixture unless the population's h² of resistance to the mixture is less than half of the mean of the population's h² of resistance to the two individual components of the mixture. Unstable chlorantraniliprole resistance could also help to sustain its efficacy by being withdrawn from usage for some period of time. © 2019 Society of Chemical Industry.

Fitness costs in chlorfenapyr-resistant populations of the chive maggot, Bradysia odoriphaga

The chive maggot, Bradysia odoriphaga (Yang and Zhang) is an economically important insect pest, affecting many key vegetables, including Chinese chive, especially in northern China. Chlorfenapyr, a halogenated pyrrole insecticide that interferes with mitochondrial oxidative phosphorylation is widely used against B. odoriphaga. In this study, we evaluated selection-induced resistance to chlorfenapyr and fitness costs in B. odoriphaga. The results showed that B. odoriphaga developed 43.32-fold resistance after continuous exposure to chlorfenapyr for over 10 consecutive generations. The life-history traits of chlorfenapyr-resistant and susceptible strains were compared using age-stage, two-sex life table approach. No significant effects were observed on the longevity and pre-adult period. However, reduction in the total pre-oviposition period (TPOP) and fecundity (eggs/female) were observed in the resistant strain. Moreover, the demographic parameters such as intrinsic rate of increase (r), net reproductive rate (R₀) and finite rate of increase (λ) were also decreased significantly in the resistant strain compared to the susceptible strain. These results showed the potential of B. odoriphaga to develop resistance against chlorfenapyr under continuous selection pressure. Furthermore, there was a fitness cost linked with chlorfenapyr resistance in B. odoriphaga. We conclude that a better knowlegde on the trade-off at play between resistance degree and fitness cost could be crucial for developing further management of B. odoriphaga in China.

Fitness costs of sulfoxaflor resistance in the cotton aphid, Aphis gossypii Glover

Aphis gossypii Glover is an economically important pest of numerous crops throughout the world. Some field populations of A.gossypii in China have developed moderate level of resistance to sulfoxaflor, a newly released sulfoximine insecticide for management of sap-feeding pests. To evaluate the effect of sulfoxaflor resistance on the fitness cost of A. gossypii, the life history traits of sulfoxaflor-resistant strain (SulR) and an isogenic susceptible strain (SS) were compared using the age-stage, two-sex life table approach. The results showed that the resistant strain had a reduction in fitness (relative fitness = 0.917), along with significantly decreases in longevity, fecundity, net reproductive (R₀), mean generation time (T) and gross reproductive rate (GRR). Compared to the susceptible strain, SulR strain showing a shorter developmental duration of each nymph instar stage. Moreover, the adult pre-oviposition period (APOP) and total preoviposition period (TPOP) of SulR strain were also significantly shorter than that of the susceptible strain. Investigation of six development and reproduction related genes indicated that EcR, USP and JHBP were overexpressed in the SulR strain, while the mRNA transcript level of Vg was decreased significantly compared to the susceptible strain. These results suggest that there is a fitness cost associated with sulfoxaflor resistance in A. gossypii and the different expression of EcR, USP, JHBP, and Vg may play very important role in this trade-off.

Determination of the Genetic and Synergistic Suppression of a Methoxyfenozide-Resistant Strain of the House Fly Musca domestica L. (Diptera: Muscidae)

Musca domestica Linnaeus (house fly, Diptera: Muscidae) is a major veterinary and medical important pest all over the world. These flies have ability to develop resistance to insecticides. The present trial was performed to discover the inheritance mode (autosomal, dominance, number of genes involved) and preliminary mechanism of methoxyfenozide resistance in order to provide basic information necessary to develop resistance management strategy for this pest. A strain of M. domestica (MXY-SEL) was exposed to methoxyfenozide for 44 generations which developed a 5253.90-fold level of resistance to methoxyfenozide. The overlapping fiducial limits of LC₅₀ values of the reciprocal crosses, F₁ (MXY-SEL ♂ × Susceptible ♀) and F₁^† (MXY-SEL ♀ × Susceptible ♂), suggest that inheritance of methoxyfenozide resistance was an autosomal and likely completely dominant trait (D_LC = 0.93 and 0.94 for F₁ and F₁^†, respectively). Backcrosses of the F₁ with the parental MXY-SEL or Susceptible population predict a polygenic mode of inheritance. Piperonyl butoxide significantly altered the LC₅₀ values, suggesting enhanced detoxification by cytochrome P450-dependent monooxygenases is a major mechanism of resistance to methoxyfenozide in the MXY-SEL strain. The estimated realized heritability was 0.07 for methoxyfenozide. These results would be helpful for the better management of M. domestica.

Insecticidal activity of Stemona collinsiae root extract against Parasarcophaga ruficornis (Diptera: Sarcophagidae)

In Thai indigenous knowledge, Stemona plant has traditionally been used as insecticide on plantations. Recently, S. collinsiae extract was showed to be an anti-feedant and growth inhibitor and to exert strong insecticidal activity. Here, the insecticidal activity of S. collinsiae root extract against Parasarcophaga ruficornis is studied. The larvicidal and pupicidal activities of the ethanolic root extract of S. collinsiae were tested using contact toxicity tests, and adulticidal activity was tested using the topical contact toxicity and sugar bait methods The ethanolic extract at concentration ranging of 0.3-320mg/larva for the direct contact toxicity test and from 0.3 to 3.2mg/cm²/larva for the secondary contact toxicity test showed 3.0-51.0 and 1.0-94.0% corrected mortality, respectively. Against third-instar larvae, the LD₅₀ concentrations of the ethanolic extract were 31.7±0.0mg/larva and 1.4±0.0mg/cm²/larva for direct and secondary contact toxicity tests, respectively. Pupae were not eliminated at all concentrations of the ethanolic extract. Against adult flies, which were killed via oral administration, the LD₅₀ concentration of the ethanolic extract was 0.145±0.070g extract/g glucose. Thus, the ethanolic extract of S. collinsiae was capable of eliminating P. ruficornis in larval and adult stages via topical and ingestion administration, respectively.

Selection, Realized Heritability, and Fitness Cost Associated With Dimethoate Resistance in a Field Population of Culex quinquefasciatus (Diptera: Culicidae)

Mosquitoes are known to be vectors of numerous diseases leading to human morbidity and mortality at large scale in the world. Insecticide resistance has become a serious concern in controlling the insect vectors of public health importance. Dimethoate is an organophosphate insecticide used to control different insect pests including mosquitoes. Biological parameters of susceptible, unselected, and dimethoate-selected strains of Culex quinquefasciatus Say were studied in the laboratory to recognize resistance development potential and associated fitness cost. The dimethoate-selected strain showed 66.48-fold resistance to dimethoate compared with the susceptible strain after three continuous selections of generations. Realized heritability estimates of dimethoate resistance in Cx. quinquefasciatus yielded a value of 0.19. In dimethoate-selected strain, the biological traits including larval weight, survival from first instar to pupae, fecundity, number of next-generation larvae, relative fitness, net reproductive rate, intrinsic rate of natural increase, and biotic potential were significantly reduced as compared with the unselected strain. However, adult longevity, mean relative growth rate, weight of egg raft, female ratio, pupal duration, and emergence rate of the dimethoate-selected strain did not differ significantly compared with that of the unselected strain. This study provides useful information to devise retrospective management strategy for dimethoate resistance in Cx. quinquefasciatus.

Spirotetramat Resistance Selected in the Phenacoccus solenopsis (Homoptera: Pseudococcidae): Cross-Resistance Patterns, Stability, and Fitness Costs Analysis

The Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae) is a major agricultural and horticultural pest of crops throughout the world. To develop a better resistance management strategy for P. solenopsis, we conducted a study on life history parameters of different populations of this pest, one selected with spirotetramat (Spiro-SEL), an unselected (UNSEL) population, and their reciprocal crosses. We also studied the cross-resistance and the stability of spirotetramat resistance. The Spiro-SEL of P. solenopsis exhibited a 328.69-fold resistance compared to the susceptible population (Lab-PK). The Spiro-SEL population also displayed a moderate level of cross-resistance to profenofos and bifenthrin and a high level of cross-resistance to abamectin. Resistance to spirotetramat in Spiro-SEL was unstable in the absence of selection. The study of life history parameters showed that there was a significant reduction in fitness parameters of Spiro-SEL population with a relative fitness value of 0.14. There was a significant decrease in survival rate, pupal weight, fecundity, egg hatching percentage, male and female generation time, intrinsic rate of population increase of males and females, biotic potential, and mean relative growth rate. It is concluded that selection with spirotetramat had marked effect on resistance development in P. solenopsis and upon removal of selection pressure spirotetramat resistance declined significantly, indicating unstable resistance. Development of resistance led to high fitness costs for the spirotetramat-selected population. Our study may provide the basic information on spirotetramat resistance and its mechanism to help develop the resistance management strategies.

Persistence of a sugar-rejecting cockroach genotype under various dietary regimes

Glucose-aversion is a heritable trait that evolved in a number of German cockroach (Blattella germanica L.) populations in response to strong selection with glucose-containing insecticide baits. However, in the absence of glucose-containing bait, glucose-averse (GA) cockroaches have lower performance than wild-type (WT) cockroaches in several fitness-determining traits. We allocated 48 caged populations initiated with homozygous GA and WT adults to four dietary treatments consisting of either pure rodent chow, rodent chow mixed to yield a content of either 20% glucose or 20% fructose, or a treatment consisting of choice between the 20% glucose- and the 20% fructose-containing food. After 6 months we found significantly higher frequency of WT individuals in populations restricted to the 20% glucose food, and after 12 months all dietary treatments contained significantly more WT individuals than expected. In accompanying experiments, we found lower survival and longer development time of GA nymphs restricted to glucose-containing food. We furthermore found evidence for assortative mating of females with males from their own genotype, with significant differences within WT cockroaches. Our study shows experimental evidence that within heterogeneous populations, WT German cockroaches will over time prevail in abundance over GA individuals, even when glucose is not a dietary component.