Development of alpha-cypermethrin resistance and its effect on biological parameters of yellow fever mosquito, Aedes aegypti (L.) (Diptera: Culicidae)

Alpha-cypermethrin interacts with the sodium channel and causes nerve blockage in insects. It is used to manage Aedes aegypti (Linnaeus) (Diptera: Culicidae), a primary vector of dengue worldwide. It not only affects both target and non-target organisms, but overuse of this insecticide increases the chances of resistance development in insect pests. In this study, resistance development, biological parameters, and stability of alpha-cypermethrin resistance were studied in a laboratory-selected strain of Ae. aegypti. The alpha-cypermethrin selected strain (Alpha Sel) developed an 11.86-fold resistance level after 12 rounds of alpha-cypermethrin selection compared to the unselected strain (Unsel). In biological parameters, Alpha Sel and Cross1 (Unsel ♂ and Alpha Sel♀) had shorter larval durations compared to Unsel and Cross2 (Unsel ♀ and Alpha Sel ♂) populations. The pupal duration of Alpha Sel and both crosses was shorter than that in the Unsel strain. The relative fitness of Alpha Sel, Cross1, and Cross2 was significantly less than that of the Unsel strain. These results indicate that alpha-cypermethrin resistance comes with fitness costs. Moreover, the frequency of alpha-cypermethrin resistance decreased when the Alpha Sel population was reared without further selection pressure for four generations. So, resistance was unstable and reversed when insecticide pressure ceased. We concluded that the judicious and rotational use of different insecticides with different modes of action and the adoption of other IPM-recommended practices would suppress resistance development for more extended periods in Ae. aegypti.

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.

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.

Methoxyfenozide tolerance in Chrysoperla carnea: Inheritance, dominance and preliminary detoxification mechanisms

Lacewings exist in insecticide-dominant cropping systems. They are prime biological control agents due to outstanding ability of insecticide resistance development. This study examines occurrence of methoxyfenozide resistance and its subsequent effects on cross-resistance to other insecticides, inheritance and mechanism of resistance in C. carnea. Methoxy-SEL strain of C. carnea selected for 15 generations developed 3531.67-fold resistance to methoxyfenozide. Overlapping fiducial limits of LC₅₀s of F₁ and F_1’ (reciprocal crosses) suggested an autosomal and incompletely dominant mode of inheritance. Resistance to methoxyfenozide was polygenic and its realized heritability value was high (h² = 0.62). Both PBO and DEF significantly changed LC₅₀s indicating cytochrome P450-dependent monooxygenases and esterases detoxifying the resistance in Methoxy-SEL strain. Resistance to all tested insecticide was unstable but decrease rate was very negligible. These results have implications forpreservation of biological control and effective use in insecticide-dominant cropping systems.

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.

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.

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.

Genetics and mechanism of resistance to chlorantraniliprole in Musca domestica L. (Diptera: Muscidae)

The house fly, Musca domestica L. is an important mechanical vector of different pathogens of medical and veterinary importance. It is an organism well-known for its ability to develop insecticide resistance. In the current study, we investigated the genetic basis and mechanism of chlorantraniliprole resistance in a field strain of house fly by selecting it artificially in the laboratory with a commercial formulation of chlorantraniliprole (CTPR-SEL). After seven generations of consecutive selection with chlorantraniliprole, CTPR-SEL strain developed a 644-fold resistance compared with the Susceptible strain and a 3-fold resistance compared with the field strain. Reciprocal crossing between the CTPR-SEL and Susceptible homozygous strains revealed an autosomal and incomplete dominant mode of resistance to chlorantraniliprole. A direct test using a monogenic inheritance model based on chi-square analysis revealed that the resistance was governed by more than one gene. Bioassays with synergists indicated that esterases might be involved in the resistance of house fly to chlorantraniliprole. These findings may be helpful to the development of an improved strategy for chlorantraniliprole resistance management in house fly.

Genetic basis and realized heritability of laboratory selected spirotetramat resistance for insecticide resistance management in Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae)

Dusky cotton bug, Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is become a major pest of cotton. It causes damage to cotton by sucking the cell sap or by staining the cotton seed. Insect pests in Pakistan are mainly managed by use of insecticides, applying this practice leads to resistance development. In this study, O. hyalinipennis was selected with spirotetramat under laboratory conditions to investigate genetic mode of resistance to spirotetramat. Selection with spirotetramat for eleven generations resulted in a 727-fold resistance compared to the susceptible strain. The LC₅₀ values of spirotetramat in both reciprocal crosses were significantly different from each other and degree of dominanace values were 0.25 for cross-1 and 0.01 for cross-2. Monogenic model proved the contribution of more than one gene in controlling the spirotetramat resistance. Moreover, the value for realized heritability of spirotetramat resistance was 0.13. It can be concluded that spirotetramat resistance was sex linked, polygenic and incompletely dominant. These findings could be helpful in management of spirotetramat resistance in O. hyalinipennis as incompletely dominant and polygenic resistance tend to develop slowly and is manageable.

Inheritance of polygenic but stable pyriproxyfen resistance in a bio-control agent Chrysoperla carnea (Neuroptera: Chrysopidae): cross-resistance and realized heritability

BACKGROUND

Chrysoperla carnea (Neuroptera: Chrysopidae) is a voracious predator frequently used in biological control programs to suppress pest populations of economic importance. However, it performs its duty in a challenging environment where various stress factors such as non-target effects of insecticides limit expected outcomes. A study providing details of genetics, cross-resistance, realized heritability, and stability of insect growth regulators (IGRs) resistance such as pyriproxyfen in this bio-control agent is essential.

RESULTS

Selection with pyriproxyfen, an IGR, resulted in 3092.10-fold and 39.60-fold resistance when judged against Susceptible and Field Pop, respectively. Very low cross-resistance to buprofezin while no cross-resistance to acetamiprid and spinosad was observed. Incompletely dominant, autosomal and polygenic resistance was also associated with high realized heritability (h² = 0.35). Furthermore, resistance to pyriproxyfen was stable in this bio-control agent.

CONCLUSION

These findings make Chrysoperla carnea an ideal fit in integrated pest management (IPM) programs where biological control approaches are employed in combination with IGRs sprays to control various insect pests especially Whitefly, Bemisia tabaci. Releasing pyriproxyfen-resistant Chrysoperla carnea in a multi-sprayed cropping environment would help to keep pest population below economic threshold level. It would also minimize risk of insecticide resistance development in pests surviving even after several insecticide applications. © 2020 Society of Chemical Industry.

Biochemical mechanism, inheritance and cross-resistance to cyromazine in a non-target Chrysoperla carnea: A potential predator of whiteflies and aphids

Developing an eco-friendly Integrated Pest Management (IPM) approach is only possible by minimizing the use of insecticides and their effects on non-targets such as natural enemies. Chrysoperla carnea is a potential predator of several economic pests including whiteflies and aphids. C. carnea selected with cyromazine for 15 generations indicated a great increase in resistance to this Insect Growth Regulator (IGR). There was no cross-resistance to chlorpyrifos, cypermethrin and nitenpyram in Cyro-SEL population. Inheritance to cyromazine was autosomal, incompletely dominant, and polygenic. A high realized heritability (h₂) value (0.37) confirmed more genetic variability. Synergists piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) showed a significant involvement of P-450 monooxygenase and esterase in cyromazine resistance development. These findings are helpful to design a natural enemy-friendly IPM strategy resulting in increased survival and performance of C. carnea controlling economic pests.

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.

Field evaluation of synthetic and neem-derived alternative insecticides in developing action thresholds against cauliflower pests

Synthetic chemical pesticides can enhance crop yields but also have undesired effects. Alternative 'botanical insecticides' may also have non-target effects on pollinators and biocontrol services. Employing action thresholds (ATs) can reduce pesticide (whether synthetic or botanical) use compared to fixed-interval applications. Here the azadirachtin-based botanical formulation NeemAzal and a neem seed extract (NSE) were evaluated in field spraying trials alongside commonly-used synthetics (Voliam Flexi [chlorentraniliprole plus thiamethoxam] and imidacloprid) in developing ATs for the regular and cosmopolitan cauliflower pests Brevicoryne brassicae, Plutella xylostella and Spodoptera litura. We considered the size of the S. litura larvae infesting the crop in order to derive ATs. ATs per plant were higher for NeemAzal (0.55 larvae for P. xylostella and 3 larvae for large-sized S. litura) than for Voliam Flexi (0.30 larvae for P. xylostella and 0.80 larvae for S. litura) but were similar for B. brassicae (50 individuals). Higher ATs when using azadirachtin were associated with the diverse modes of action of botanicals, for instance NeemAzal and NSE deterred oviposition of S. litura. Although the exact values of ATs are likely to have regional limits, our approach can be applied for determining ATs against common lepidopteran and aphid pests in many other vegetable crop agro-ecosystems.

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.

Influence of Frequently Used Chemical Insecticides on Mycoflora Carried by Common Housefly, Musca domestica L

The housefly, Musca domestica L. (Diptera: Muscidae), is a major medical and veterinary insect pest. It serves as a vector of many pathogenic microorganisms causing spoilage of food and diseases in human and animals. Use of chemical insecticides is adapted as a principal tool to manage housefly. Insecticides have many unforeseen ecological consequences including effects on non-target organisms. In the present study, we have assessed the effects of 10 different synthetic insecticides on the growth of mycoflora associated with the external body of the housefly by using poison food technique. Our results reveled that all synthetic insecticides enhanced the growth. Surprisingly, in most of the cases, mycelial growth of fungi was significantly increased at high concentration as compared with lower concentration. This study provides useful information about the dangerous effects of synthetic insecticides on environment by increasing the spread of various non-target pathogenic, mycotoxigenic, and food spoiling fungi, carried by houseflies.

Eugenol, a Plant Volatile, Synergizes the Effect of the Thrips Attractant, Ethyl Iso-Nicotinate

The onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a polyphagous pest that causes serious damage to agricultural crops, vegetables, and ornamental plants worldwide. Farmers rely on the extensive usage of synthetic chemical insecticides to control T. tabaci. There is a dire need to develop alternative control strategies to overcome the problems posed by chemical insecticides. Efficient traps would allow sensitive monitoring and possibly mass trapping. A field experiment was conducted to evaluate the potential of three plant compounds with known release rates (ranging from 6-30 mg/d); eugenol (Eug), 1, 8-cineole (eucalyptol), and linalool in all possible combinations with a thrips attractant, ethyl iso-nicotinate (EI). A combination of EI with Eug increased the effect of EI by attracting 100% more thrips (effect size, 1.95) as compared to the control of EI alone. Catches in remaining treatments were lower and or not significantly different from EI alone. The results from our study could be used to develop improved volatile blends to be used for monitoring traps. Our data suggests that these traps could be effective even at very low populations.

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

Due to an unfortunate turn of events, the surname of the last author appeared incorrectly in the original publication as the name should have read Binyameen.

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.

Assessing the combined toxicity of conventional and newer insecticides on the cotton mealybug Phenacoccus solenopsis

Reduced susceptibility to insecticides often results in failure of insect pest control and repetitive use of broad-spectrum insecticides, which could have detrimental effects on beneficial arthropods and surrounding agro-ecosystems. The cotton mealybug, Phenacoccus solenopsis Tinsley is a pest of worldwide importance that can be effectively controlled using a number of insecticides. This insect has developed resistance due to injudicious use and repeated exposure to insecticides throughout the year. The aim of the present study was to investigate the toxicity of the insecticides chlorpyrifos, deltamethrin, spinosad, emamectin benzoate and indoxacarb tested either singly or in combination on laboratory susceptible (Lab-PK) and field population (Field Pop) of P. solenopsis. In the Field Pop, combination of chlorpyrifos with either spinosad or emamectin benzoate or indoxacarb showed a synergistic effect at 1:1, 1:10 and 1:20. The combination of deltamethrin with either emamectin benzoate or indoxacarb at all ratios showed synergistic effect, while the combination of deltamethrin with spinosad at 1:1 and 1:20 ratios showed antagonistic effects and that at 1:10 ratio showed synergistic effect against Field Pop. The results of synergism experiments using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) enzyme inhibitors, when combined with insecticides against the Field Pop, toxicities of all tested insecticides were significantly increased. The present study suggests that insecticide combinations and synergism could help achieve effective control of less susceptible populations of P. solenopsis. This would contribute to suitably managing resistance of this pest to insecticides with reduced negative impacts on the surrounding environment.

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.

Larval Habitat Substrates Could Affect the Biology and Vectorial Capacity of Culex quinquefasciatus (Diptera: Culicidae)

Culex quinquefasciatus Say is an important disease vector throughout much of the world. Experiments were conducted to determine the effects of different larval habitat substrates on the fitness and biting efficiency of Cx. quinquefasciatus adults. Our findings indicate that the development time (egg to adult) of larvae reared in irrigation water was 8.63 d while that of larvae reared in distilled water was 17.10 d (Effect size = 0.95). However, the rate of adult emergence was similar for all the tested treatments. Furthermore, the mean weight of an egg raft varied between larval habitats: distilled water (1.83 mg), rainfall water (1.25 mg), irrigation water (1.52 mg), and sewerage water (2.52 mg) (Effect size = 0.91). But, the fecundity (eggs per female) and hatchability (%) were statistically similar in all the rearing mediums (Effect size = 0.79). Longevity of females in all the tested populations did not differ significantly (Effect size = 0.91). The mean relative growth rates of larvae reared in tap water (0.80) and distilled water (0.86) habitats were lower than growth rates in all other rearing habitats (Effect size = 0.96). The intrinsic rate of natural increase in tap water (0.27) and irrigation water (0.35) was significantly higher than that in distilled water (0.09) and sewerage water (0.16) (Effect size = 0.84). Adults reared in rain water had the highest biting efficiency among all the tested populations. These results provide useful information for the management of Cx. quinquefasciatus.

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.

Study of Synergism, Antagonism, and Resistance Mechanisms in Insecticide-Resistant Oxycarenus hyalinipennis (Hemiptera: Lygaeidae)

Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is an economic and key pest of the Malvaceae family widely distributed in the world. Significant field resistance to cypermethrin (26.69-fold), chlorpyrifos (32.60-fold), methomyl (10.87), acetamiprid (20.63-fold), fipronil (5.84-fold), and spirotetramat (116.02-fold) has been reported. Cypermethrin combined with methomyl and spirotetramat, methomyl with spirotetramat, acetamiprid with spirotetramat, and fipronil with spirotetramat had synergistic effects (combination index, (CI) in a laboratory population of O. hyalinipennis named Lab-PK. Methomyl combined with acetamiprid and acetamiprid with fipronil had synergistic effects on O. hyalinipennis in a field in Multan named Field-POP. Cypermethrin combined with methomyl and spirotetramat; chlorpyrifos with methomyl, acetamiprid, and spirotetramat; methomyl with acetamiprid and spirotetramat; and fipronil with spirotetramat also had synergistic effects on O. hyalinipennis in Field-POP. Enzyme inhibitors piperonyl butoxide and S,S,S-tri-n-butyl phosphorotrithioate significantly increased the toxicity of chlorpyrifos, methomyl, acetamiprid, and spirotetramat to O. hyalinipennis in Field-POP, suggesting a monooxygenase- and esterase-based resistance mechanism. However, fipronil did not synergize with PBO and DEF. This study suggests that insecticide mixtures showing synergism must be determined for insecticide resistance management and other strategies such as rotations, mosaics, and cultural control should also be considered for the management of O. hyalinipennis.

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.

Genetics, realized heritability and possible mechanism of chlorfenapyr resistance in Oxycarenus hyalinipennis (Lygaeidae: Hemiptera)

Dusky cotton bug (DCB), Oxycarenus hyalinipennis (Lygaeidae: Hemiptera) is a serious pest of cotton and other malvaceous plants. Chlorfenapyr, a broad spectrum, N-substituted, halogenated pyrrole insecticide is used extensively to control many insect pests in cotton, including DCB. In this study, we investigated a field strain of DCB to assess its potential to develop resistance to chlorfenapyr. After six generations of continuous selection pressure with chlorfenapyr, DCB had a 7.24-fold and 149.06-fold resistance ratio (RR) at G₁ and G_6, respectively. The genetic basis of inheritance of chlorfenapyr resistance was also studied by crossing the chlorfenapyr selected (Chlorfenapyr-SEL) and laboratory population (Lab-PK). Results revealed an autosomal and incompletely dominant mode of inheritance for chlorfenapyr resistance in the Chlorfenapyr-SEL population of DCB. The results of the monogenic model test showed chlorfenapyr resistance was controlled by multiple genes. Estimated realized heritability for chlorfenapyr resistance in the tested DCB strain was 0.123. Synergism bioassays with piperonyl butoxide and S, S, S-butyl phosphorotrithioate revealed chlorfenapyr resistance might be due to esterase activity. These results would be useful for devising an effective resistance management strategy against DCB.

Characterization of Phenacoccus solenopsis (Tinsley) (Homoptera: Pseudococcidae) Resistance to Emamectin Benzoate: Cross-Resistance Patterns and Fitness Cost Analysis

Cotton mealybug Phenacoccus solenopsis (Tinsley) (Homoptera: Pseudococcidae) is a sucking pest of worldwide importance causing huge losses by feeding upon cotton in various parts of the world. Because of the importance of this pest, this research was carried out to select emamectin resistance in P. solenopsis in the laboratory to study cross-resistance, stability, realized heritability, and fitness cost of emamectin resistance. After selection from third generation (G3) to G6, P. solenopsis developed very high emamectin resistance (159.24-fold) when compared to a susceptible unselected population (Unsel pop). Population selected to emamectin benzoate conferred moderate (45.81-fold), low (14.06-fold), and no cross-resistance with abamectin, cypermethrin, and profenofos, respectively compared to the Unsel pop. A significant decline in emamectin resistance was observed in the resistant population when not exposed to emamectin from G7 to G13. The estimated realized heritability (h (2)) for emamectin resistance was 0.84. A high fitness cost was associated with emamectin resistance in P. solenopsis. Results of this study may be helpful in devising insecticide resistance management strategies for P. solenopsis.

Resistance of Dusky Cotton Bug, Oxycarenus hyalinipennis Costa (Lygaidae: Hemiptera), to Conventional and Novel Chemistry Insecticides

The dusky cotton bug, Oxycarenus hyalinipennis Costa (Lygaidae: Hemiptera), is polyphagous in nature and has become one of the severe sucking pests of cotton in Pakistan. O. hyalinipennis has the potential to develop resistance to a number of insecticides, and as a result, O. hyalinipennis outbreaks occur. There is no previous study from Pakistan regarding O. hyalinipennis resistance to insecticides. Therefore, the aim of this study was to assess the resistance of different field populations of O. hyalinipennis to conventional (bifenthrin, deltamethrin, lambda-cyhalothrin, profenofos, triazophos) and novel chemistry (emamectin benzoate, spinosad, chlorfenapyr, imidacloprid, and nitenpyram) insecticides. Five populations of O. hyalinipennis, collected from Multan, Khanewal, Muzaffargarh, Lodhran, and Bahawalpur, were tested for resistance to selected insecticides by the leaf dip method. For three pyrethroids, the resistance ratios were in the range of 14- to 30-fold for bifenthrin, 2.14- to 8.41-fold for deltamethrin, and 9.12- to 16-fold for lambda-cyhalothrin, compared with the laboratory susceptible strain (Lab-PK). For two organophosphates, the range of resistance ratios was 12- to 14-fold for profenofos and 9.04- to 15-fold for triazophos. For five novel chemistry insecticides, the range of resistance ratios was 4.68- to 9.83-fold for emamectin benzoate, 6.38- to 17-fold for spinosad, 16- to 46-fold for chlorfenapyr, 11- to 22-fold for imidacloprid, and 1.32- to 11-fold for nitenpyram. Regular assessment of resistance to insecticides and integrated management plans like judicious use of insecticides and rotation of insecticides along with different modes of action are required to delay resistance development in O. hyalinipennis.

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.

Stability of Field-Selected Resistance to Conventional and Newer Chemistry Insecticides in the House Fly, Musca domestica L. (Diptera: Muscidae)

The house fly, Musca domestica L. (Diptera: Muscidae), is a pest of livestock and has the ability to develop resistance to different insecticides. We assessed the fluctuations in seasonal stability of house fly resistance to insecticides from poultry facility populations in Pakistan. House fly populations were collected from poultry facilities located at Khanewal, Punjab, Pakistan in three seasons (July, November, and March) to investigate the fluctuations in their resistance to conventional (organophosphate, pyrethroid) and novel chemistry (spinosyn, oxadiazine, neonicotinoid) insecticides. Laboratory bioassays were performed using the feeding method of mixing insecticide concentrations with 20% sugar solutions, and cotton pads dipped in insecticide solutions were provided to tested adult flies. Bioassay results showed that all house fly populations had varying degrees of susceptibility to tested insecticides. Comparisons between populations at different seasons showed a significant fluctuation in susceptibility to organophosphate, pyrethroid, spinosyn, oxadiazine, and neonicotinoid insecticides. Highest resistant levels were found for organophosphate when compared with other tested insecticides. The resistance to conventional insecticides decreased significantly in March compared with July and November, while resistance to oxadiazine and avermectins decreased significantly in November. However, resistance to spinosad and imidacloprid remained stable throughout the seasons. All conventional and novel chemistry insecticides were significantly correlated with each other in all tested seasons except nitenpyram/lambda-cyhalothrin and nitenpyram/imidacloprid. Our data suggests that the variation in house fly resistance among seasons could be due to fitness costs or to the cessation of selection pressure in the off-season. These results have significant implications for the use of insecticides in house fly management.

Inheritance, realized heritability and biochemical mechanism of acetamiprid resistance in the cotton mealybug, Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae)

The cotton mealybug, Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae) is a serious pest in many countries of the world because of its polyphagous nature and has caused huge losses to the cotton crop. The aim of present study was to explore the mode of inheritance and mechanism of acetamiprid resistance in P. solenopsis. After five rounds of selection with acetamiprid, P. solenopsis developed a 315-fold resistance compared with the laboratory susceptible population. The LC50 values of progenies of both reciprocal crosses (F1 and F1') showed no significant difference and degree of dominance values were 0.56 and 0.93 for F1 and F1', respectively. Monogenic model of inheritance and Lande's method revealed that more than one factors were involved in acetamiprid resistance. Realized heritability (h(2)) value was 0.58 for acetamiprid resistance. A synergism study of piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) with acetamiprid also showed the significant presence of P-450 mono-oxygenase and esterase in the acetamiprid resistance. Hence, acetamiprid resistance in the P. solenopsis was autosomal, incompletely dominant and polygenic. These results are a source of basic information to design and plan fruitful management programmes to control P. solenopsis.

Resistance to Conventional and New Insecticides in House Flies (Diptera: Muscidae) From Poultry Facilities in Punjab, Pakistan

House flies, Musca domestica L., are pests of poultry facilities and have the ability to develop resistance against different insecticides. This study was conducted to assess the resistance status of house flies to pyrethroid, organophosphate, and novel chemistry insecticides from poultry facilities in Punjab, Pakistan. Five adult house fly populations were studied for their resistance status to selected conventional and novel chemistry insecticides. For four pyrethroids, the range of resistance ratios was 14-55-fold for cypermethrin, 11-45-fold for bifenthrin, 0.84-4.06-fold for deltamethrin, and 4.42-24-fold for lambda-cyhalothrin when compared with a susceptible population. Very low levels of resistance were found to deltamethrin compared with the other pyrethroids. For the three organophosphate insecticides, the range of resistance ratios was 1.70-16-fold for profenofos, 7.50-60-fold for chlorpyrifos, and 4.37-53-fold for triazophos. Very low levels of resistance were found to profenofos compared with the other insecticides. For five novel chemistry insecticides, the range of resistance ratios was 1.20-16.00-fold for fipronil, 3.73-7.16-fold for spinosad, 3.06-23-fold for indoxacarb, 0.96-5.88-fold for abamectin, and 0.56-3.07-fold for emamectin benzoate. Rotation of insecticides with different modes of action showing no or very low resistance may prevent insecticide resistance in house flies. Regular insecticide resistance monitoring and integrated management plans on poultry farms are required to prevent resistance development, field control failures, and environmental pollution.

Genetics and preliminary mechanism of chlorpyrifos resistance in Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae)

Cotton mealybug, Phenacoccus solenopsis Tinsley, is a serious pest of cotton and other crops and infestation by this pest results in yield losses that affect the economy of Pakistan. Various groups of insecticides have been used to control this pest but resistance development is a major factor that inhibits its control in the field. Chlorpyrifos is a common insecticide used against many pests including P. solenopsis. The present experiment was designed to assess the genetics and mechanism of chlorpyrifos resistance and to develop a better resistance management strategy and assess the genetics and mechanism of chlorpyrifos resistance. Before selection, the field strain showed 3.1-fold resistance compared to the susceptible strain (CSS). After 8 rounds of selection with chlorpyrifos, a selected population developed a 191.0-fold resistance compared to the CSS. The LC50 values of F1 (CRR ♀ × CSS ♂) and F1(†) (CRR ♂ × CSS ♀) strains were not significantly different and dominance (DLC) values were 0.42 and 0.55. Reciprocal crosses between chlorpyrifos susceptible and resistant strains indicated that resistance was autosomal and incompletely recessive. The monogenic model of fit test and calculation of number of genes segregating in the chlorpyrifos resistant strain demonstrated that resistance is controlled by multiple genes. A value of 0.59 was calculated for realized heritability for chlorpyrifos resistance. Synergism bioassays with piperonyl butoxide and S, S, S-butyl phosphorotrithioate showed that chlorpyrifos resistance was associated with microsomal oxidases and esterases. It was concluded that chlorpyrifos resistance in P. solenopsis was autosomally inherited, incompletely recessive and polygenic. These findings would be helpful to improve the management of P. solenopsis.

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.

Inheritance mode, cross-resistance and realized heritability of pyriproxyfen resistance in a field strain of Musca domestica L. (Diptera: Muscidae)

Pyriproxyfen is a growth regulator used for the control of different insect pests, including Musca domestica. To assess the risk of resistance and to develop a strategy for resistance management, a field strain of M. domestica was exposed to pyriproxyfen in the laboratory for 30 generations. The inheritance mode, realized heritability of pyriproxyfen resistance and cross-resistance to other insecticides were assessed. Prior to the selection process, the field strain exhibited a resistance ratio (RR) of 25.7, 7.31, 7.67, and 27-fold for pyriproxyfen, methoxyfenozide, cyromazine and lufenuron, respectively, when compared to the pyriproxyfen susceptible strain (Pyri-Sus). After continuous selection with pyriproxyfen, the pyriproxyfen-resistant strain (Pyri-Res) became 206-fold more resistant than the Pyri-Sus strain. The overlapping confidence limits of LC50 values of F1 (Pyri-Res ♂×Pyri-Sus ♀) and F1(†) (Pyri-Res ♀×Pyri-Sus ♂) suggested an autosomal and completely dominant mode of resistance to pyriproxyfen. Monogenic test of inheritance showed that resistance to pyriproxyfen was governed by multiple genes. The Pyri-Res strain showed very low cross resistance to methoxyfenozide, cyromazine, and lufenuron. The estimated realized heritability was 0.02, 0.05, 0.03 and 0.04 for pyriproxyfen, methoxyfenozide, cyromazine, and lufenuron, respectively. It was concluded that pyriproxyfen resistance in M. domestica was autosomally inherited, completely dominant and polygenic. These results would be helpful for the design of an improved control strategy against M. domestica.

Cross-resistance, the stability of acetamiprid resistance and its effect on the biological parameters of cotton mealybug, Phenacoccus solenopsis (Homoptera: Pseudococcidae), in Pakistan

BACKGROUND

Acetamiprid is a neonicotinoid insecticide that is effective against both soil and plant insects, including insects of the orders Lepidoptera, Coleoptera, Homoptera and Thysanoptera. In order to estimate the effects associated with insecticide exposure and devise better pest management tactics, a field population of Phenacoccus solenopsis was exposed to acetamiprid in the laboratory. Subsequently, cross-resistance and the effects of acetamiprid on the biological parameters of P. solenopsis were investigated.

RESULTS

Following five rounds of selection with acetamiprid, P. solenopsis developed a 315-fold greater resistance to this chemical compared with an unexposed control population. The selected population also demonstrated very high to moderate cross-resistance to other tested insecticides. Furthermore, acetamiprid resistance remained unstable when the acetamiprid-selected population was not exposed for a further five generations. The acetamiprid-selected population had a relative fitness of 0.22, with significantly lower survival rate, pupal weight, fecundity, percentage hatching, net reproductive rate, intrinsic rate of natural increase, biotic potential and mean relative growth rate, with prolonged male and female nymphal duration, developmental time from egg to female adult and male and female longevity compared with the control population.

CONCLUSION

P. solenopsis biological parameters are greatly affected by acetamiprid, and it is of significant cost for the insects to counter these effects. This study will be a valuable source of information for further understanding of acetamiprid resistance and for assisting the development of resistance management programmes.

Fitness cost and realized heritability of resistance to spinosad in Chrysoperla carnea (Neuroptera: Chrysopidae)

The common green lacewing Chrysoperla carnea is a key biological control agent employed in integrated pest management (IPM) programs for managing various insect pests. Spinosad is used for the management of pests in ornamental plants, fruit trees, vegetable and field crops all over the world, including Pakistan. A field-collected population of C. carnea was selected with spinosad and fitness costs and realized heritability were investigated. After selection for five generations, C. carnea developed 12.65- and 73.37-fold resistance to spinosad compared to the field and UNSEL populations. The resistant population had a relative fitness of 1.47, with substantially higher emergence rate of healthy adults, fecundity and hatchability and shorter larval duration, pupal duration, and development time as compared to a susceptible laboratory population. Mean relative growth rate of larvae, intrinsic rate of natural population increase and biotic potential was higher for the spinosad-selected population compared to the susceptible laboratory population. Chrysoperla species are known to show resistance to insecticides which makes the predator compatible with most IPM systems. The realized heritability (h 2) value of spinosad resistance was 0.37 in spinosad-selected population of C. carnea.

Genetics and realized heritability of resistance to imidacloprid in a poultry population of house fly, Musca domestica L. (Diptera: Muscidae) from Pakistan

Imidacloprid, a post-synaptic, nicotinic insecticide, has been commonly used for the management of different pests including Musca domestica worldwide. Many pests have developed resistance to this insecticide. A 16-fold imidacloprid-resistant population of M. domestica infesting poultry was selected using imidacloprid for 13 continuous generations to study the inheritance and realized heritability of resistance. Toxicological bioassay at G14 showed that the imidacloprid-selected population developed 106-fold resistance when compared to the susceptible population. Reciprocal crosses of susceptible and resistant populations showed an autosomal trait of resistance to imidacloprid in M. domestica. There was incompletely recessive resistance in F1 (Imida-SEL ♂ × Susceptible ♀) and F1(†) (Imida-SEL ♀ × Susceptible ♂) having dominance value 0.53 and 0.31, respectively. Monogenic model of inheritance showed that imidacloprid resistance was controlled by multiple factors. The realized heritability value was 0.09 in the imidacloprid-selected population of M. domestica. It was concluded that imidacloprid resistance in M. domestica was autosomally inherited, incompletely recessive and polygenic. These findings should be helpful for better and more successful management of M. domestica.

Resistance of the house fly Musca domestica (Diptera: Muscidae) to lambda-cyhalothrin: mode of inheritance, realized heritability, and cross-resistance to other insecticides

Lambda-cyhalothrin, a pyrethroid insecticide, has been used frequently for the control of house flies, Musca domestica L., worldwide including Pakistan. To assess the resistance risk and design a resistance management strategy, a house fly population was exposed to lambda-cyhalothrin in the laboratory to assess inheritance and heritability, and cross-resistance to other insecticides, including different chemical classes. After 11 generations of selection, the population developed 113.57-fold resistance to lambda-cyhalothrin compared to the susceptible population. There was no cross-resistance to bifenthrin and methomyl, but very low cross-resistance to abamectin and indoxacarb in the lambda-cyhalothrin selected population compared to the field population. Synergism bioassay with piperonyl butoxide and S,S,S-tributylphosphorotrithioate indicated that lambda-cyhalothrin resistance was associated with microsomal oxidases and esterases. The LC50 values of F1 (Lambda-SEL ♀ × Susceptible ♂) and F'1 (Lambda-SEL ♂ × Susceptible ♀) populations were not significantly different and dominance (DLC) values were 0.68 and 0.62. The resistance to lambda-cyhalothrin was completely recessive (DML = 0.00) at highest dose and completely dominant at lowest dose (DML = 0.95). The monogenic model of inheritance showed that lambda-cyhalothrin resistance was controlled by multiple factors. The heritability values were 0.20, 0.04, 0.003, 0.07 and 0.08 for lambda-cyhalothrin, bifenthrin, methomyl, indoxacarb and abamectin resistance, respectively. It was concluded that lambda-cyhalothrin resistance in house flies was autosomally inherited, incompletely dominant and controlled by multiple factors. These findings would be helpful to improve the management of house flies.

Genetics, cross-resistance and mechanism of resistance to spinosad in a field strain of Musca domestica L. (Diptera: Muscidae)

The house fly, Musca domestica L., is a cosmopolitan insect with the ability to develop resistance to insecticides used for their management. In the present study, we investigated the genetics of spinosad resistance, and cross-resistance potential to other insecticides by selecting a field strain with a commercial spinosad formulation. Bioassays with the field strain, before selection with spinosad, gave resistance ratios (RRs) of 4, 5, 66, 21 and 5 fold for spinosad, indoxacarb, abamectin, imidacloprid and deltamethrin, respectively, in comparison to a laboratory susceptible (Lab-susceptible) strain. After continuous selection of the field strain (Spin-SEL) with spinosad, the RR was increased up to 155 fold; however, the resistance was unstable (RR decreased 1.43 fold) when this strain was not exposed to spinosad for five generations. The Spin-SEL strain did not show cross-resistance to abamectin, indoxacarb or deltamethrin, but showed negative cross-resistance to imidacloprid. Crosses between the Spin-SEL and Lab-susceptible strains revealed an autosomal and incomplete dominant mode of resistance to spinosad. A direct test using a monogenic inheritance model based on Chi-square analysis revealed that the resistance was governed by more than one gene. Moreover, the resistance was neither overcome with the insecticide synergist piperonyl butoxide nor with S,S,S-tributylphosphorotrithioate. Lack of cross-resistance and instability of resistance suggest that rotation with spinosad could be an effective resistance management strategy.

Cross-resistance, genetics, and realized heritability of resistance to fipronil in the house fly, Musca domestica (Diptera: Muscidae): a potential vector for disease transmission

Houseflies, Musca domestica (L.), are ubiquitous pests that have the potential to spread a variety of pathogens to humans, poultries, and dairies. Pesticides are commonly used for the management of this pest. Fipronil is a GABA-gated chloride channel-inhibiting insecticide that has been commonly used for the management of different pests including M. domestica throughout the world. Many pests have developed resistance to this insecticide. A field-collected strain of M. domestica was selected with fipronil for continuous 11 generations to assess the cross-resistance, genetics, and realized heritability for designing a resistance management strategy. Laboratory bioassays were performed using the feeding method of mixing insecticide concentrations with 20% sugar solutions and cotton soaks dipped in insecticide solutions were provided to tested adult flies. Bioassay results at G12 showed that the fipronil-selected strain developed a resistance ratio of 140-fold compared to the susceptible strain. Synergism bioassay with piperonyl butoxide (PBO) and S,S,S,-tributyl phosphorotrithioate (DEF) indicated that fipronil resistance was associated with microsomal oxidase and also esterase. Reciprocal crosses between resistant and susceptible strains showed an autosomal and incompletely dominant resistance to fipronil. The LC50 values of F1 and F'1 strains were not significantly different and dominance values were 0.74 and 0.64, respectively. The resistance to fipronil was completely recessive (D(ML) = 0.00) at the highest dose and incompletely dominant at the lowest dose (D(ML) = 0.87). The monogenic resistance based on chi-square goodness of fit test and calculation of the minimum number of segregating genes showed that resistance to fipronil is controlled by multiple genes. The fipronil resistance strain confirmed very low cross-resistance to emamectin benzoate and spinosad while no cross-resistance to chlorpyrifos and acetamiprid when compared to that of the field population. The heritability values were 0.112, 0.075, 0.084, 0.008, and 0.052 for fipronil, emamectin benzoate, spinosad, acetamiprid, and chlorpyrifos, respectively. It was concluded that fipronil resistance in M. domestica was autosomally inherited, incompletely dominant, and polygenic. These findings would be helpful for the better and successful management of M. domestica.

Increased fitness and realized heritability in emamectin benzoate-resistant Chrysoperla carnea (Neuroptera: Chrysopidae)

The common green lacewing Chrysoperla carnea is a key biological control agent employed in integrated pest management (IPM) programs for managing various insect pests. A field collected population of C. carnea was selected for emamectin benzoate resistance in the laboratory and fitness costs and realized heritability were investigated. After five generations of selection with emamectin benzoate, C. carnea developed a 318-fold resistance to the insecticide. The resistant population had a relative fitness of 1.49, with substantially higher emergence rate of healthy adults, fecundity and hatchability and shorter larval duration, pupal duration, and development time compared to the susceptible population. Mean population growth rates; such as the intrinsic rate of natural population increase and biotic potential were higher for the emamectin benzoate selected population compared to the susceptible population. The realized heritability (h(2)) value of emamectin benzoate resistance was 0.34 in emamectin benzoate selected population of C. carnea. Chrysoperla species which show resistance to insecticides makes them compatible with those IPM systems where emamectin benzoate is employed.