Risk assessment of cyromazine and methoxyfenozide resistance suggests higher additive genetic but lower environmental variation supporting quick resistance development in non-target Chrysoperla carnea (Stephens).

Insecticides are effective against economic pests, but these pose serious threats to the environment and ecosystem components such as natural enemies. Resistance risk assessment forecasts insecticide resistance development in target pests and non-target biological control agents under special conditions. Field-collected Chrysoperla carnea was selected with two Insect Growth Regulators (IGRs) viz. cyromazine and methoxyfenozide for 15 generations to determine the resistance development potential of this natural enemy. Selection to cyromazine and methoxyfenozide induced 759.08-fold and 3531.67-fold resistance with realized heritability of 0.37 and 0.62 in C. carnea, respectively, suggesting higher additive genetic variations in first half of selection (h2 = 0.46 for cyromazine and h2 = 0.75 for methoxyfenozide) than in second half (h2 = 0.18 and 0.25, respectively). Estimates of projected rate of resistance development indicate C. carnea will take only 6 to 2 generations at h2 = 0.37, 8 to 2 at h2 = 0.27, and 5 to 2 at h2 = 0.27, at constant slope = 1.81 for a tenfold increase in cyromazine resistance. At h2 = 0.37, 3-1, and 10-8 generations would be needed for this increase in LC50 if slope = 0.82 and 2.82, respectively. Similarly, it may take 3 to 1 generations at h2 = 0.62 and 0.72, but 4 to 1 at h2 = 0.52, at constant slope = 1.62, for a tenfold increase in methoxyfenozide resistance. On the same h2 = 0.62, 1-0, and 5-1 generations would be required for increase if slope = 0.62 and 2.62, respectively. Selection and resistance to both insecticides induced an insignificant difference in the sex ratio of C. carnea. These results confirm that this natural enemy has tremendous potential for resistance development under selection pressure.

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 G19. 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.

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.

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.

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.

Characterization of inheritance and preliminary biochemical mechanisms of spirotetramat resistance in Phenacoccus solenopsis Tinsley: An economic pest from Pakistan.

Phenacoccus solenopsis is an economically important insect pest of different agronomic and horticultural field crops. In Pakistan, the cotton crop was severely attacked by P. solenopsis during 2007 and since then a varied group of insecticides are used by farmers to manage this pest. As a result, insecticide resistance has become a barrier in control of P. solenopsis. The current study was designed to explore the basics of genetics, realized heritability and possible genetic mechanisms of resistance against spirotetramat in P. solenopsis. Before selection, the wild population (Wild-Pop) showed 5.97-fold resistance when compared with lab-reared susceptible strain (Susceptible Lab-Pop). The P. solenopsis was selected with spirotetramat to 21 generations, called Spiro-SEL Pop, which showed 463.21-fold resistance as compared with the Susceptible Lab-Pop. The values of LC50 for F1 (Spiro-SEL Pop ♂ × Susceptible Lab-Pop ♀) and F1 (Spiro-SEL Pop ♀ × Susceptible Lab-Pop ♂) populations were statistically similar and values of dominance level were 0.42 and 0.54, respectively. Reciprocal crosses between Susceptible Lab-Pop and Spiro-SEL Pop showed that resistance was of autosomal in nature with incomplete dominant traits. According to the fit test, monogenic model estimation of the number of genes, which are responsible for the development of spirotetramat resistance in a population of P. solenopsis, showed that multiple genes are involved in controlling the resistance levels in tested strains of P. solenopsis. The value of heritability for resistance against spirotetramat was 0.13 in P. solenopsis. Our results suggested the presence of a metabolic-based resistance mechanism associated with the monooxygenases in P. solenopsis, while testing the synergism mechanism. These results will provide the baseline to design an effective control strategy to manage P. solenopsis in the field.

Laboratory selection of chlorpyrifos resistance in an Invasive Pest, Phenacoccus solenopsis (Homoptera: Pseudococcidae): Cross-resistance, stability and fitness cost.

The cotton mealybug, Phenacoccus solenopsis is an important polyphagous sucking pest of ornamentals, horticultural and fiber crops worldwide. Some P. solenopsis populations have developed insecticide resistance. This study evaluated cross-resistance, stability of insecticide resistance and life history traits affected by chlorpyrifos resistance in P. solenopsis. After nine generations selected with chlorpyrifos, P. solenopsis exhibited a 539.76-fold resistance level compared to an unselected population (UNSEL Pop). Chlorpyrifos selected population (Chlor-SEL Pop) displayed moderate cross-resistance to profenofos, nitenpyram and high cross-resistance to lambda-cyhalothrin. Biological parameters of P. Solenopsis were affected by chlorpyrifos resistance. The Chlor-SEL Pop had a significant reduction in fitness (relative fitness=0.10), along with significant decreases in pupal weight, fecundity, egg hatching %, intrinsic rate of natural population increase, biotic potential, and mean relative growth rate. It is concluded that selection with chlorpyrifos had marked effect on resistance development in P. solenopsis and upon removal of selection pressure chlorpyrifos resistance declined significantly indicating unstable resistance. Development of resistance led to high fitness costs for the chlorpyrifos-selected strain. These findings should be helpful for better and more successful resistance management of P. solenopsis.

Methoxyfenozide resistance of the housefly, Musca domestica L. (Diptera: Muscidae): cross-resistance patterns, stability and associated fitness costs.

BACKGROUND: The housefly, Musca domestica L. (Diptera: Muscidae), is an insect pest of public health and veterinary importance with the ability to develop resistance to insecticides. Methoxyfenozide, an ecdysone agonist, is a biorational insecticide used for the management of various insect pests, including houseflies. To design an effective resistance management strategy, life history traits based on laboratory observations were established for methoxyfenozide-resistant (MXY-SEL), unselected counterpart (UNSEL) and reciprocal cross-strains of housefly. RESULTS: The MXY-SEL strain developed a resistance ratio of 160.99 after 30 generations of selection with methoxyfenozide by compared with the UNSEL strain. The MXY-SEL strain showed very low cross-resistance to cyromazine, fipronil and chlorpyrifos and no cross-resistance to spinosad and bifenthrin when compared with the Methoxy-Field population. Resistance to methoxyfenozide, cyromazine, fipronil, spinosad, chlorpyrifos and bifenthrin was unstable in the MXY-SEL strain. The MXY-SEL strain had a reduced relative fitness (0.31), with lower hatchability, a lower number of next-generation larvae, a lower intrinsic rate of natural increase and a lower biotic potential compared with the UNSEL strain. CONCLUSIONS: The disadvantageous life history traits of the MXY-SEL strain suggest that development of resistance to methoxyfenozide has considerable fitness costs for this strain. Moreover, the unstable resistance to the tested chemicals provides useful information for preserving the efficacy of these chemicals. © 2016 Society of Chemical Industry.

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

House fly, Musca domestica L., (Diptera: Muscidae) a common pest of poultry, has developed resistance to the commonly used insecticide fipronil. The life history traits were examined in the fipronil-selected (Fipro-SEL), susceptible counterpart (UNSEL), and their hybrid progeny strains in order to design an effective resistant management strategy. Compared to the UNSEL strain, the Fipro-SEL was 181.94-fold resistant to fipronil. This resistance was unstable after five generations without selection. The Fipro-SEL had a significantly longer larval duration, lower pupal weight, lower fecundity, lower hatchability, lower number of next generation larvae, lower intrinsic rate of population increase and lower biotic potential than the UNSEL strain. Most fitness parameters of the hybrid progeny were similar and significantly lower than that in the UNSEL strain, suggesting autosomal and dominant fitness costs. Compared to the UNSEL strain, relative the fitness of the Fipro-SEL, Hybrid1 and Hybrid2 was 0.13, 0.33 and 0.30, respectively. Fipronil resistance resulted in high fitness costs and these fitness costs were dominant and autosomal in the Fipro-SEL strain of M. domestica. Rotation of fipronil with other insecticides having no cross resistance should be useful for delaying the development of resistance in M. domestica.

Assessment of resistance risk to fipronil and cross resistance to other insecticides in the Musca domestica L. (Diptera: Muscidae).

Fipronil, a phenyl-pyrazole insecticide has been used frequently for the control of disease vector house flies, Musca domestica L., (Diptera: Muscidae) worldwide including Pakistan. This experiment was performed to determine the selection and assessment of fipronil resistance evolution along with cross resistance to other three insecticides. After 26 generations of selection, the house fly strain developed 430-fold resistance to fipronil compared to a susceptible strain. Realized heritability (h(2)) of resistance to fipronil was 0.05. The projected rate of resistance development revealed that if 30-90% house flies were selected then a tenfold increase in lethal concentration 50 happened after 95.51-26.59 generations for fipronil (h(2)=0.05, Slope=2.34). At similar slope, if h(2)=0.15, then 31.84-8.86 generations are required for tenfold increase in LC50 at 30-90% selection intensity, respectively. Likewise, if h(2)=0.25, then similar would occur in 19.10-5.32 generations. Differences in any of the variable would affect the rate of resistance development. Selection with fipronil did not increase the level of resistance to lambda-cyhalothrin, profenofos and indoxacarb, suggesting no cross resistance to these insecticides. The results of our study concluded that house flies have the potential to develop resistances following continued selection pressure with fipronil.

Assessment of resistance risk in Musca domestica L. (Diptera: Muscidae) to methoxyfenozide.

Methoxyfenozide, an ecdysone receptor agonist is an effective larvicide against many pests of public health and veterinary importance including house fly, Musca domestica L. (Diptera: Muscidae). Methoxyfenozide is a bio-rational insecticide having many environmentally friendly attributes that make it compatible with integrated pest management programs. This experiment was performed for the assessment of resistance evolution in M. domestica to methoxyfenozide. A field population of M. domestica, after 24 rounds of selection with methoxyfenozide, resulted in 64 fold and 915-fold increase in lethal concentration 50 (LC50) compared to field and susceptible strain, respectively. Realized heritability (h(2)) of resistance to methoxyfenozide was 0.17 in methoxyfenozide-selected strain of M. domestica. The projected rate of resistance development indicated that, if slope=1.71 and h(2)=0.17, then 13-5 generations are required for tenfold increase in LC50 at 50-95% selection intensity. These findings suggest that a risk for resistance development to methoxyfenozide occurred in M. domestica under continuous selection pressure.

Assessment of resistance risk to lambda-cyhalothrin and cross-resistance to four other insecticides in the house fly, Musca domestica L. (Diptera: Muscidae).

Lambda-cyhalothrin, a sodium channel modulator insecticide, has been used frequently for the control of house flies, Musca domestica L. (Diptera: Muscidae) worldwide, including Pakistan. This experiment was performed to determine the selection and assessment of lambda-cyhalothrin resistance evolution along with four other insecticides. After 26 generations of selection, the lambda-cyhalothrin-selected population developed 445-fold resistance to lambda-cyhalothrin compared to the susceptible population. There was low cross-resistance to bifenthrin and very low cross-resistance to methomyl, imidacloprid, and fipronil in the lambda-cyhalothrin-selected population compared to the field population (G1). Realized heritability (h (2)) of resistance to lambda-cyhalothrin, bifenthrin, methomyl, imidacloprid, and fipronil was 0.07, 0.05, 0.01, 0.08, and 0.08, respectively. The projected rate of resistance development revealed that if 90 % house flies were selected, then a tenfold increase in lethal concentration 50 occurred after 17, 20, 159, 13, and 14 generations for lambda-cyhalothrin (h (2) = 0.07, slope = 2.09), bifenthrin (h (2) = 0.05, slope = 1.73), methomyl (h (2) = 0.01, slope = 2.52), imidacloprid (h (2) = 0.08, slope = 1.89), and fipronil (h (2) = 0.08, slope = 2.03), respectively. The results of our study concluded that the house fly has the potential to develop multiple insecticide resistances following continued selection pressure with lambda-cyhalothrin. This study will be helpful for assisting the development of resistance management strategies.

Mechanism, stability and fitness cost of resistance to pyriproxyfen in the house fly, Musca domestica L. (Diptera: Muscidae).

Pyriproxyfen, a bio-rational insecticide, used worldwide for the management of many insect pests including the house fly, Musca domestica. To devise a retrospective resistance management strategy, biological parameters of pyriproxyfen resistant (Pyri-SEL), unselected (UNSEL), Cross1 and Cross2M. domestica strains were studied in the laboratory. Additionally, the stability and mechanism of resistance was also investigated. After 30 generations of pyriproxyfen selection, a field-collected strain developed 206-fold resistance compared with susceptible strain. Synergists such as piperonyl butoxide and S,S,S-tributylphosphorotrithioate did not alter the LC50 values, suggesting another cause of target site resistance to pyriproxyfen in the Pyri-SEL strain. The resistance to all tested insecticides was unstable in Pyri-SEL strain. The relative fitness of 0.51 with lower fecundity, hatchability, lower number of next generation larvae, reduced mean population growth rate and net reproductive rate were observed in the Pyri-SEL strain compared with the UNSEL strain. The cost of fitness associated with pyriproxyfen resistance was evident in Pyri-SEL strain. The present study provides useful information for making pro-active resistance management strategies to delay resistance development.

Cross-resistance, stability, and fitness cost of resistance to imidacloprid in Musca domestica L., (Diptera: Muscidae).

Imidacloprid, a neonicotinoid insecticide, has been used frequently for the management of Musca domestica L., (Diptera: Muscidae) worldwide. To design the strategy for resistance management, life history traits were established for imidacloprid-resistant, susceptible counterpart, and reciprocal crosses M. domestica strains based on laboratory observations. Bioassay results showed that the imidacloprid-selected strain developed a resistance ratio of 106-fold to imidacloprid, 19-fold to nitenpyram, 29-fold to chlorpyrifos, and 3.8-fold to cypermethrin compared to that of the susceptible counterpart strain. The imidacloprid-selected strain showed very low cross-resistance against nitenpyram and cypermethrin and a lack of cross-resistance to chlorpyrifos. Resistance to imidacloprid, nitenpyram, and chlorpyrifos was unstable, while resistance to cypermethrin was stable in Imida-SEL strain of M. domestica. The imidacloprid-selected strain had a relative fitness of 0.61 and lower fecundity, hatchability, number of next-generation larvae, and net reproductive rate compared with the susceptible counterpart strain. Mean population growth rates, such as intrinsic rate of population increase and biotic potential, were lower for the imidacloprid-selected strain compared with the susceptible counterpart strain. Development of resistance can cost considerable fitness for the imidacloprid-selected strain. The present study provided useful information for making potential management strategies to overcome development of resistance.

Selection, resistance risk assessment, and reversion toward susceptibility of pyriproxyfen in Musca domestica L.

Pyriproxyfen, a juvenile hormone mimic, is an effective larvicide against many pests of veterinary and public health importance. Pyriproxyfen is a biorational insecticide having many environmentally friendly attributes that make it compatible with integrated pest management programs. This experiment was performed for the assessment of resistance evolution and reversion toward susceptibility of Musca domestica to pyriproxyfen. Repeated selection at successive generations resulted in 5.09- and 130-fold increase in lethal concentration 50 (LC50) compared to field and susceptible strain, respectively. A significant decline after 22 generations without selection suggesting resistance to pyriproxyfen was unstable in M. domestica. Realized heritability (h (2)) of resistance to pyriproxyfen was 0.035 in pyriproxyfen-selected strain of M. domestica. The projected rate of resistance development indicated that, if slope = 1.28 and h (2) = 0.035, then 46-21 generations are required for 10-fold increase in LC50 at 50-90 % selection intensity. These findings suggest that a risk for resistance development to pyriproxyfen occurred in M. domestica under continuous selection pressure. Pyriproxyfen susceptibility reversed when its application is ceased for a specified duration.