Toxicity and resistance of field collected Musca domestica (Diptera: Muscidae) against insect growth regulator insecticides

Biochemical and genetic mechanisms in Pieris rapae (Lepidoptera: Pieridae) resistance under emamectin benzoate stress

Pieris rapae (Lepidoptera: Pieridae) poses a significant threat to Brassicaceae crops, leading to substantial losses annually. Repeated insecticide applications are widely used to protect crops and increase the resistance of P. rapae. Exploring the biochemical and molecular basis of insecticide tolerance in P. rapae is crucial for achieving effective insect suppuration and implementing resistance control strategies. In our research, emamectin benzoate (EBZ) resistance was developed in P. rapae strain through selective pressure over 15 generations. Moreover, the biochemical mechanisms underlying resistance to EBZ and its potential cross-resistance to other insecticides were studied. Additionally, the expression levels of cytochrome P450 (CYP450) and glutathione-s-transferase (GST) genes in P. rapae were quantitatively assessed upon exposure to EBZ using real-time PCR. Our data exhibited that the LC50 value of susceptible strain (Sus) and EBZ resistance strain (EBZ-R) were 0.009 and 8.09 mg/L, with a resistance ratio (RR) reaching 898.8-fold. The EBZ-R stain displayed notably low cross-resistance to lambda-cyhalothrin, spinetoram, and cypermethrin. However, it demonstrated a moderate level of cross-resistance to deltamethrin. Conversely, no cross-resistance was noted to chlorantraniliprole and indoxacarb. Notably, enzyme inhibitors of detoxification enzymes revealed that piperonyl butoxide (PBO) and diethyl maleate (DEM) enhanced the EBZ toxicity to the resistant strain, indicating the potential involvement of CYP450 and GST in avermectin resistance. A remarkable enhancement in CYP450 and GST activity was observed in the EBZ-R stain. CYP450 and GST genes are upregulated in the EBZ-R stain compared to the Sus strain, which serves as a basis for comprehending the mechanism behind P. rapae resistance to EBZ. The molecular docking analysis demonstrated that EBZ has a high binding affinity with CYP6AE120 and PrGSTS1 with docking energy values of -20.19 and -22.57 kcal/mol, respectively. Our findings offer valuable insights into crafting efficient strategies to monitor and manage resistance in P. rapae populations in Egypt.

Lethal and Sublethal Effects of Cyromazine on the Biology of Musca domestica Based on the Age-Stage, Two-Sex Life Table Theory

Cyromazine is a triazine insect growth regulator insecticide that is recommended for control of Musca domestica worldwide. Cyromazine is highly effective in causing mortality of M. domestica; however, some aspects of its lethal and sublethal effects on the biology of M. domestica are still unknown. The present study explored lethal and sublethal effects on several biological traits and population parameters of M. domestica. Concentration-response bioassays of cyromazine against third-instar larvae of M. domestica exhibited sublethal and lethal effects from concentrations of 0.03 (LC10), 0.06 (LC25), and 0.14 (LC50) μg/g of a larval medium. Exposure of M. domestica larvae to these concentrations resulted in reduced fecundity, survival, longevity and oviposition period, and delayed development of immature stages (i.e., egg hatch time and larval and pupal durations) in the upcoming generation of M. domestica. The values of population parameters such as intrinsic rate of increase, finite rate of increase, net reproductive rate, age-specific survival rate and fecundity, and age-stage life expectancy and reproductive value, analyzed using the age-stage and two-sex life table theory, were significantly reduced in a concentration-dependent manner in comparison with the control group. In conclusion, the study highlights the significant effects of cyromazine on the biology of M. domestica that could help suppress its population in cases of severe infestations.

Cytotoxic, Scolicidal, and Insecticidal Activities of Lavandula stoechas Essential Oil

Essential oils (EOs) have recently attracted more interest due to their insecticidal activities, low harmfulness, and rapid degradation in the environment. Therefore, Lavandula steochas (L. steochas) essential oil was assessed for its chemical constituents, in vitro cytotoxicity, and scolicidal, acaricidal, and insecticidal activities. Using spectrometry and gas chromatography, the components of L. steochas EOs were detected. Additionally, different oil concentrations were tested for their anticancer activities when applied to human embryonic kidney cells (HEK-293 cells) and the human breast cancer cell line MCF-7. The oil’s scolicidal activity against protoscolices of hydatid cysts was evaluated at various concentrations and exposure times. The oil’s adulticidal, larvicidal, and repelling effects on R. annulatus ticks were also investigated at various concentrations, ranging from 0.625 to 10%. Likewise, the larvicidal and pupicidal activities of L. steochas against Musca domestica were estimated at different concentrations. The analyses of L. steochas oil identified camphor as the predominant compound (58.38%). L. steochas oil showed significant cytotoxicity against cancer cells. All of the tested oil concentrations demonstrated significant scolicidal activities against the protoscoleces of hydatid cysts. L. steochas EO (essential oil) showed 100% adulticidal activity against R. annulatus at a 10% concentration with an LC50 of 2.34%, whereas the larvicidal activity was 86.67% and the LC50 was 9.11%. On the other hand, the oil showed no repellent activity against this tick’s larva. Furthermore, L. steochas EO achieved 100% larvicidal and pupicidal effects against M. domestica at a 10% concentration with LC50 values of 1.79% and 1.51%, respectively. In conclusion, the current work suggests that L. steochas EO could serve as a potential source of scolicidal, acaricidal, insecticidal, and anticancer agents.

Insecticide resistance to insect growth regulators, avermectins, spinosyns and diamides in Culex quinquefasciatus in Saudi Arabia

BACKGROUND

Culex quinquefasciatus is not only a biting nuisance but also an important vector of fatal diseases. In Saudi Arabia, management measures to control this mosquito and thereby prevent associated disease transmission have focused on insecticides. Nevertheless, information on the resistance status of C. quinquefasciatus is insufficient, especially concerning insecticides containing novel classes of insecticides.

METHODS

We evaluated six insecticides belonging to four classes of insecticides (insect growth regulators [3], avermectins [1], diamides [1] and spinosyns [1]) for toxicity and resistance in eight C. quinquefasciatus populations (from Ishbiliya, Al-Masfa, Al-Masanie, Al-Washlah, Al-Nakhil, Irqah, Al-Suwaidi and Al-Ghanemiya) following World Health Organisation protocols.

RESULTS

Resistance status ranging from susceptibility/low resistance to high resistance, in comparison with the susceptible strain, was detected for cyromazine in the eight C. quinquefasciatus populations: Ishbiliya (resistance ratio [RR] = 3.33), Al-Masfa (RR = 4.33), Al-Masanie (RR = 3.67), Al-Washlah (RR = 2.33), Al-Nakhil (RR = 5.33), Irqah (RR = 7.00), Al-Suwaidi (RR = 21.33) and Al-Ghanemiya (RR = 16.00). All C. quinquefasciatus populations exhibited a high level of resistance to diflubenzuron (RR = 13.33-43.33), with the exception of Al-Nakhil which exhibited moderate resistance (RR = 10.00). Susceptibility/low resistance to high resistance was observed for triflumuron in the eight C. quinquefasciatus populations: Ishbiliya (RR = 0.50), Al-Ghanemiya (RR =  3.00), Al-Suwaidi (RR =  10.00), Al-Masfa (RR =  5.00), Al-Masanie (RR =  10.00), Al-Nakhil (RR =  5.00), Irqah (RR =  5.00) and Al-Washlah (RR =  15.00). Susceptibility/low resistance was assessed for abamectin, chlorantraniliprole and spinosad in all C. quinquefasciatus populations, with RR ranges of 0.25-3.50, 0.17-2.19, and 0.02-0.50, respectively. However, the population collected from Irqah showed high resistance to chlorantraniliprole (RR = 11.93).

CONCLUSIONS

The detection of widespread resistance to insect growth regulators in C. quinquefasciatus highlights an urgent need to establish integrated vector management strategies. Our results may facilitate the selection of potent insecticides for integrated vector management programmes for C. quinquefasciatus.

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

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

Pyriproxyfen induces lethal and sublethal effects on biological traits and demographic growth parameters in Musca domestica

Musca domestica is a global insect-pest of human beings and animal agriculture. Pyriproxyfen, a juvenile hormone analog, has shown its potential for effective management of M. domestica. However, lethal and sublethal effects of pyriproxyfen on biological traits and demographic growth parameters of M. domestica are still unknown. The present study investigated the effects of lethal and sublethal concentrations on different biological traits of M. domestica for two generations i.e., exposed parents (F0) and their offspring (F1). Concentration-response bioassays revealed that concentrations of pyriproxyfen that caused 50% (LC₅₀), 25% (LC₂₅), 10% (LC₁₀) and 2% (LC₂) mortality of M. domestica were estimated as 0.12, 0.06, 0.03 and 0.01 μg/g, respectively. In the F0 generation, exposure of 3^rd instar larvae to these concentrations resulted in a reduced pupation rate, lengthened pupal stage duration, light weight pupae and reduction in adult emergence in a concentration-dependent manner. In the case of F1 generation, similar trend was observed for pupation rate, pupal stage duration, and total developmental period (i.e., egg to adult); however, pupal weight was affected at LC₁₀, LC₂₅, LC₅₀ levels, and adult emergence at only LC₂₅ and LC₅₀ levels. The values of demographic growth parameters, analyzed through age-stage, two-sex life table theory, were significantly decreased at all the levels of pyriproxyfen compared with control. This study highlights that pyriproxyfen has the potential to suppress the population of M. domestica through its lethal and sublethal effects and presents an empirical basis from which to consider management decisions for chemical control in the field.

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

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

Evaluation of triflumuron and pyriproxyfen as alternative candidates to control house fly, Musca domestica L. (Diptera: Muscidae), in Riyadh city, Saudi Arabia

This study was conducted to determine the susceptibility and resistance of some house fly strains of Musca domestica L. to the insect growth regulator insecticides triflumuron and pyriproxyfen in some locations in Riyadh city. Field-collected strains of M. domestica L. from five sites in Riyadh city that represented five slaughterhouse sites where flies spread significantly were tested against triflumuron and pyriproxyfen. Triflumuron LC₅₀ values for the five collected strains ranged from 2.6 to 5.5 ppm, and the resistance factors (RFs) ranged from 13-fold to 27-fold that of the susceptible laboratory strain. Pyriproxyfen LC₅₀ values for the field strains ranged from 0.9 to 1.8 ppm with RFs of 3-fold to 5-fold. These results indicate that pyriproxyfen is an effective insecticide to control house flies and should be used in rotation with other insecticides in the control programs applied by Riyadh municipality.

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

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

Sub-lethal aquatic doses of pyriproxyfen may increase pyrethroid resistance in malaria mosquitoes

BACKGROUND

Pyriproxyfen (PPF), an insect growth hormone mimic is widely used as a larvicide and in some second-generation bed nets, where it is combined with pyrethroids to improve impact. It has also been evaluated as a candidate for auto-dissemination by adult mosquitoes to control Aedes and Anopheles species. We examined whether PPF added to larval habitats of pyrethroid-resistant malaria vectors can modulate levels of resistance among emergent adult mosquitoes.

METHODOLOGY

Third-instar larvae of pyrethroid-resistant Anopheles arabiensis (both laboratory-reared and field-collected) were reared in different PPF concentrations, between 1×10-9 milligrams active ingredient per litre of water (mgAI/L) and 1×10-4 mgAI/L, or no PPF at all. Emergent adults escaping these sub-lethal exposures were tested using WHO-standard susceptibility assays on pyrethroids (0.75% permethrin and 0.05% deltamethrin), carbamates (0.1% bendiocarb) and organochlorides (4% DDT). Biochemical basis of pyrethroid resistance was investigated by pre-exposure to 4% PBO. Bio-efficacies of long-lasting insecticide-treated nets, Olyset® and PermaNet 2.0 were also examined against adult mosquitoes with or without previous aquatic exposure to PPF.

RESULTS

Addition of sub-lethal doses of PPF to larval habitats of pyrethroid-resistant An. arabiensis, consistently resulted in significantly reduced mortalities of emergent adults when exposed to pyrethroids, but not to bendiocarb or DDT. Mortality rates after exposure to Olyset® nets, but not PermaNet 2.0 were also reduced following aquatic exposures to PPF. Pre-exposure to PBO followed by permethrin or deltamethrin resulted in significant increases in mortality, compared to either insecticide alone.

CONCLUSIONS

Partially-resistant mosquitoes exposed to sub-lethal aquatic concentrations of PPF may become more resistant to pyrethroids than they already are without such pre-exposures. Studies should be conducted to examine whether field applications of PPF, either by larviciding or other means actually exacerbates pyrethroid-resistance in areas where signs of such resistance already exist in wild the vector populations. The studies should also investigate mechanisms underlying such magnification of resistance, and how this may impact the potential of PPF-based interventions in areas with pyrethroid resistance.

Permethrin resistance associated with inherited genes in a near-isogenic line of Musca domestica

BACKGROUND

Permethrin has been used frequently in the control of Musca domestica worldwide including Pakistan, with reports of resistance development in different field strains. A near-isogenic line of M. domestica with permethrin resistance (Perm-R) was constructed to elucidate mode of inheritance and cross-resistance analyses.

RESULTS

Toxicity responses of reciprocal progenies F1 and F1' showed no significant difference in median lethal dose (LD₅₀ ) values, suggesting that permethrin resistance was inherited in an autosomal fashion with neither sex linkage nor maternal effects in the Perm-R strain of M. domestica. Degree of dominance was 0.6 and 0.7 for F1 and F1' progenies, respectively, which suggests that permethrin resistance was expressed as an incompletely dominant trait. Chi-square analyses for self-bred (F2), and backcross progenies (BC1, BC2, BC3 and BC4) revealed significant differences between the observed and expected mortality, indicating the possibility of multiple genes responsible for permethrin resistance. Moreover, the Perm-R strain did not show cross-resistance to propoxur, chlorpyrifos, profenofos or spinetoram.

CONCLUSION

Permethrin resistance in the Perm-R strain of M. domestica was inherited as autosomal, incompletely dominant and governed by more than one gene. Lack of cross-resistance between permethrin and propoxur, chlorpyrifos, profenofos or spinetoram provides an opportunity for rotational use of these insecticides in the control of M. domestica. These data could help to manage M. domestica and the problem of permethrin resistance.

Posttreatment temperature influences toxicity of insect growth regulators in Musca domestica

Musca domestica is one of the major cosmopolitan pests in livestock facilities because it can be both a nuisance and a vector of pathogens to animals. Currently, treatment of animal manure with insect growth regulator (IGR) insecticides is among major practices to control M. domestica throughout the year over wide-ranging environmental temperatures. Fluctuation in daily or seasonal temperature is one of the most established factors impacting toxicity of insecticides against insect pests. In this study, the effect of posttreatment temperature (range, 20-36 °C) on the toxicity of eight IGRs: five chitin synthesis inhibitors (cyromazine, diflubenzuron, lufenuron, novaluron, triflumuron), two juvenile hormone analogs (methoprene, pyriproxyfen), and one ecdysone agonist (methoxyfenozide), was investigated against M. domestica. The toxicity of lufenuron and novaluron increased by 1.78 times over the range of 20-28 °C, and 2.25 and 1.83 times, respectively, over the range of 28-36 °C, with an overall increase by 4.00 and 3.26 times, respectively (i.e., positive temperature coefficient). In contrast, the toxicity of diflubenzuron, pyriproxyfen, and triflumuron decreased by 1.43, 1.89, and 2.10 times, respectively, over the range of 20-28 °C, and 1.70, 2.00, and 1.95 times, respectively, over the range of 28-36 °C, with an overall decrease by 2.43, 3.78, and 4.10 times, respectively. The toxicity of cyromazine, methoprene, and methoxyfenozide did not change significantly. Overall, these data will help stakeholders to choose appropriate insecticides for M. domestica control depending on the prevailing environmental temperature and to avoid misuse of insecticides that ultimately lead to environmental safety.

Evaluation of Eugenol and (E)-Cinnamaldehyde Insecticidal Activity Against Larvae and Pupae of Musca domestica (Diptera: Muscidae)

Musca domestica L., 1758, is an important mechanical vector of several pathogens for humans and livestock, making it essential to study new alternatives of more efficient and safer control for this dipteran. This study evaluated the toxicity of the phenylpropanoids eugenol and (E)-cinnamaldehyde on its life stages. A contact test with 10 repetitions (n = 10) was performed for each substance concentration on each post-embryonic immature life stage. Both substances presented insecticidal activity on the immature life stages of the dipteran, and secondary effects on development caused by sublethal concentrations. Larvicidal activity was shown from the 1.25 mg/ml concentration by eugenol and from 2.5 mg/ml by (E)-cinnamaldehyde, and both substances had a 100% larval treatment efficacy (LTE) from the 5mg/ml concentration. For pupal treatment, (E)-cinnamaldehyde differed from the control from the 10 mg/ml concentration (P < 0.05), and both phenylpropanoids caused malformation in adults from 10 mg/ml. The highest pupal treatment efficacy (PTE) was obtained from the 30 mg/ml concentration, 67.2% for (E)-cinnamaldehyde, and 32% for eugenol. The products tested in this study showed high larvicidal potential, and both presented pupicidal effects and caused malformation in adults from treated pupae.

Progress and prospects of arthropod chitin pathways and structures as targets for pest management

Chitin is a structural component of the arthropod cuticular exoskeleton and the peritrophic matrix of the gut, which play crucial roles in growth and development. In the past few decades, our understanding of the composition, biosynthesis, assembly, degradation, and regulation of chitinous structures has increased. Many chemicals have been developed that target chitin biosynthesis (benzoyphenyl ureas, etoxazole), chitin degradation (allosamidin, psammaplin), and chitin regulation (benzoyl hydrazines), thus resulting in molting deformities and lethality. In addition, proteins that disrupt chitin structures, such as lectins, proteases, and chitinases have been utilized to halt feeding and induce mortality. Chitin-degrading enzymes, such as chitinases are also useful for improving the efficacy of bio-insecticides. Transgenic plants, baculoviruses, fungi, and bacteria have been engineered to express chitinases from a variety of organisms for control of arthropod pests. In addition, RNA interference targeting genes involved in chitin pathways and structures are now being investigated for the development of environmentally friendly pest management strategies. This review describes the chemicals and proteins used to target chitin structures and enzymes for arthropod pest management, as well as pest management strategies based upon these compounds, such as plant-incorporated-protectants and recombinant entomopathogens. Recent advances in RNA interference-based pest management, and how this technology can be used to target chitin pathways and structures are also discussed.

Comparative laboratory and field study of biorational insecticides for Culicoides biting midge management in larval developmental sites

An appropriate management strategy of bluetongue vectors should include larvicidal treatments in their larval development sites utilizing active substances with low environmental impact. A selection of biorational insecticides with potential against dipteran larvae was assayed in the laboratory against field collected Culicoides larvae including C. cataneii, C. circumscriptus, and C. imicola, determining their median lethal concentrations in water and mud/water substrate. The efficacy of formulations containing the insect growth regulators pyriproxyfen and cyromazine, the botanical insecticide azadirachtin, and the entomopathogenic bacteria Bacillus thuringiensis israelensis and Brevibacillus laterosporus, was also assessed in field conditions in a comparative study conducted in sheep farm larval development sites, including treatments with the organophosphate temephos. Significant larvicidal properties were associated with the various insecticides evaluated in the laboratory assays and in field trials, although with different levels of effectiveness. While temephos was confirmed to be an effective broad spectrum larvicidal substance, B. laterosporus appeared to be the most effective among entomopathogens, while insect growth regulators combined a good efficacy to a long-lasting residual effect in the field. Everything considered, the use of these biorational insecticides alone or in combination with larval habitat manipulation techniques appears to be a promising method to complement integrated biting midge management programs.

Resistance Status to Deltamethrin, Permethrin, and Temephos Along With Preliminary Resistance Mechanism in Aedes aegypti (Diptera: Culicidae) From Punjab, Pakistan

The use of insecticides such as deltamethrin, permethrin, and temephos has been a primary tool to manage Aedes aegypti (Linnaeus) in Punjab province, Pakistan; however, recent reports of control failure necessitate monitoring insecticide resistance. For this reason, we evaluated 12 field strains of Ae. aegypti from Punjab for resistance against deltamethrin, permethrin, and temephos along with underlying resistance mechanisms. For deltamethrin, high level of resistance was observed in Rawalpindi, Faisalabad, Sheikhupura, Lahore, Pattoki, and Kasur strains (RRLC50 > 10-fold); moderate level of resistance in Sargodha, Gujranwala, and Sialkot strains (RRLC50 = 5- to 10-fold), and low level of resistance in Okara, Multan, and Sahiwal strains (RRLC50 < 5-fold). In the case of permethrin, high level of resistance was found in all the field strains, except the Okara strain that exhibited moderate resistance. For temephos, five field strains, viz. Faisalabad, Rawalpindi, Kasur, Lahore, and Gujranwala, showed high level of resistance; five strains, viz. Sheikhupura, Sialkot, Pattoki, Sahiwal, and Okara, showed moderate resistance, and two strains from Multan and Sargodha showed low resistance to temephos. Synergism bioassays implementing piperonyl butoxide and S,S,S-tributylphosphorotrithioate exhibited a nonsignificant effect on synergizing toxicity of deltamethrin and permethrin in all field strains except the Lahore strain, suggesting the possible role of target-site resistance mechanism. However, both synergists had a significant effect on synergizing toxicity of temephos in all field strains, suggesting the possibility of metabolic-based mechanism of insecticide resistance. In conclusion, the study confirmed the presence of resistance to deltamethrin, permethrin, and temephos in the studied field strains of Ae. aegypti from Punjab, Pakistan.

Geographical Variations in Life Histories of House Flies, Musca domestica (Diptera: Muscidae), in Punjab, Pakistan

Musca domestica Linnaeus is an important public health pest with the ability to adapt to diverse climates. Assessment of variations in biology and life-history traits of insects along geographical gradients is important for a successful management plan in different regions. We investigated life-history traits and life table parameters of M. domestica from six different geographical regions of Punjab, Pakistan: Rahim Yar Khan (RYK), Bahawalpur (BWP), Multan (MTN), Lahore (LHR), Gujrat (GJT), and Murree (MRE). Overall, M. domestica from localities of lower latitude and elevations with higher mean temperatures completed their development faster than those from localities of higher latitude and elevations with lower mean temperatures. The immature developmental time was the longest for the MRE population that was collected from higher latitude and elevation with cooler climate, whereas the shortest for the RYK population from lower latitude with warmer climate. Pupal weights were heavier for the RYK, BWP, and MTN populations, all were from the lowest latitude and elevations with warmer climate, compared with rest of the field populations. Similarly, rate of adult eclosion, fecundity, egg hatching, longevity, and life table parameters such as intrinsic rate of population increase, mean relative growth rate, net reproductive rate, and biotic potential were significantly higher for the RYK, BWP, and MTN populations compared with the GJT, LHR, and MRE populations of M. domestica. The current results will probably be of importance when planning management of M. domestica in different geographical regions of Pakistan.

Susceptibility survey of Ommatissus lybicus (de Bergevin) populations against deltamethrin and fenitrothion in Oman

Despite of extensive application of insecticides, severe infestation of date palms is reported with Ommatissus lybicus every year. The development of insecticide resistance in the field strains receiving heavy pesticide regimes can be a reason for unsuccessful control. Seventeen field strains of O. lybicus from Oman were appraised for resistance against deltamethrin and fenitrothion in years 2017 and 2018. Eleven field strains depicted susceptibility (RR < 3-fold) while six strains expressed minor (RR = 3–5-fold) to low level (RR = 5–10-fold) of resistance against deltamethrin when compared with lab-susceptible strain. In case of fenitrothion, fourteen field strains exhibited minor to low level of resistance and only two showed susceptibility. Intermediate resistance (RR = 10–40-fold) was also reported in one field strain against fenitrothion. A significant but low resistance (RR = 7.86-fold) was observed in a lab strain selected with deltamethrin for resistance development mechanism studies. The deltamethrin-selected strain exhibited minor resistance development (RR = 3.13-fold) against fenitrothion. Significant reduction in resistance was observed with higher toxicity values when the two pesticides were tested along with piperonyl butoxide (PBO) against all the field collected dubas bug strains. Higher susceptibility of field strains to deltamethrin suggest it a suitable alternate candidate to deter resistance development in O. lybicus.

Realized heritability of resistance to deltamethrin in a field strain of Musca domestica Linnaeus (Diptera: Muscidae)

A deltamethrin selected field strain of the house fly, Musca domestica, was used to assess realized heritability (h²) and risk for resistance development to deltamethrin. The estimated value of h² was 0.27 with phenotypic standard deviation σ_p = 0.56 and selection differential S = 0.64. The intensity of deltamethrin selection had a direct effect on the rate of resistance development in the selected strain. Assuming the h² value = 0.27 for six generations under selection pressure, a tenfold increase in the LC₅₀ values has been expected in only 8-4 generations at the selection intensity 50-90%, respectively. In conclusion, the estimated values of h² and the projected rate of deltamethrin resistance revealed a strong and rapid potential of the M. domestica strain to develop resistance against deltamethrin. Therefore, this insecticide should be used cautiously in the field.

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.

Spinosad resistance affects biological parameters of Musca domestica Linnaeus

Musca domestica is one of the major cosmopolitan insect pests of public health importance. Spinosad is considered an eco-friendly insecticide used for the management of M. domestica and other pests of significant concern. Cases of resistance against spinosad in M. domestica have been reported from some parts of the world; however, there are no reports of any negative effects of spinosad resistance on the fitness/biological parameters of M. domestica. To investigate fitness costs, a near isogenic M. domestica resistant strain (Spin-R) was constructed using Spin-UNSEL-susceptible and Spin-SEL-resistant strains sharing a close genetic background. We found significantly reduced rates of adult eclosion, fecundity, egg hatching, survival, and lengthened developmental time in the Spin-R strain. Moreover, the values of different fitness parameters like biotic potential, mean relative growth rate, intrinsic rate of natural increase, and net reproductive rate, were also significantly reduced in the Spin-R strain, which reflect fitness costs most probably linked with spinosad resistance. The presence of fitness costs suggests likely instability of resistance to spinosad in M. domestica, which can be reverted by relaxing spinosad selection pressure and rotation with alternate insecticides. The wise use of insecticides will ultimately help to manage resistance in this pest and minimize environmental pollution.

Trichlorfon and spinosad resistance survey and preliminary determination of the resistance mechanism in Pakistani field strains of Bactrocera dorsalis

The use of insecticides has been a primary tool to manage Bactrocera dorsalis in Pakistan; however, recent reports of field control failures necessitate mapping out the insecticide resistance problem. Therefore, eight field strains from Pakistan, were evaluated for their resistance against trichlorfon and spinosad. Compared with a reference strain, six field strains showed high levels of resistance to trichlorfon, while two field strains expressed intermediate resistance. In case of spinosad, five field strains fell in the susceptible range, whereas, the rest of the strains represented minor resistance. Correlation analysis between LD₅₀ values of trichlorfon and spinosad of all the field strains revealed non-significant association, suggesting the possibility of lack of cross-resistance between both insecticides. Synergism bioassays implementing S,S,S-tributylphosphorotrithioate (DEF) and piperonyl butoxide (PBO) revealed that the LD₅₀ values of trichlorfon in the presence of either DEF or PBO in seven field strains were significantly reduced. However, DEF and PBO had a non-significant effect on synergizing spinosad toxicity. The results revealed resistance to trichlorfon in field strains of B. dorsalis, which might be metabolic-based. Absence or minor resistance to spinosad and lack of cross-resistance to trichlorfon, suggest that spinosad could be a potential candidate for managing B. dorsalis.

Resistance to Selected Pyrethroid Insecticides in the Malaria Mosquito, Anopheles stephensi (Diptera: Culicidae), From Punjab, Pakistan

Pyrethroids are commonly used insecticides in malaria control programs; however, insecticide resistance limits the benefits gained by using these insecticides. In the present study, we assessed the resistance status for different pyrethroids of the malaria mosquito vector, Anopheles stephensi Liston (Diptera: Culicidae), in the Punjab province, Pakistan. Bioassays were conducted using diagnostic doses following standard World Health Organization protocols: 0.05% λ-cyhalothrin, 0.75% permethrin, 0.15% cyfluthrin, 0.05% deltamethrin, and 0.1% cypermethrin. Field collected An. stephensi from four localities in Punjab (Khanewal, Multan, Lodhran, and Bahawalpur) were reared in the laboratory, and non-blood-fed females were used in the bioassays. An. stephensi from all the study sites except Khanewal were found to be susceptible to permethrin and deltamethrin. Resistance or potential resistance to cypermethrin, λ-cyhalothrin and cyfluthrin was observed from all the study sites. The median and 95% knockdown times (KDT50 and KDT95) estimates for all the tested insecticides also showed similar responses. In conclusion, the study revealed resistance to selected pyrethroids in An. stephensi from some parts of Punjab, Pakistan, underscoring the need to devise a resistance management strategy for effective control of this important malaria vector.

Toxicity and Sublethal Effects of Cantharidin on Musca domestica (Diptera: Muscidae)

The house fly, Musca domestica L. (Diptera: Muscidae), is a major pest of medical and veterinary importance all over the world. Management efforts for house flies are usually compromised owing to their resistance to many groups of conventional insecticides. Cantharidin, a natural toxin produced by meloid beetles, is a biopesticide with a reported toxicity to some insect pests including house flies. However, the effects of cantharidin on biological and fitness parameters of house flies have not yet been investigated. In the present study, we investigated the toxicity and sublethal effects of cantharidin on biological parameters of house flies for two consecutive generations. The results revealed that the values of LC50, LC25, LC10, and LC2 against house flies were to be 2.45, 1.23, 0.66, and 0.30 mg/liter, respectively. Sublethal effects of these concentrations on the development and reproduction parameters of house flies revealed that cantharidin reduced population growth by affecting pupation rate, adult emergence, and by lengthening developmental time. The female ratio, fecundity, egg hatching, and survival of adult flies were significantly reduced at LC2, LC10, LC25, and LC50 of cantharidin when compared with the control group. Furthermore, the increase in concentration of cantharidin had a significant effect on reducing the mean values of mean relative growth rate, net reproductive rate (Ro), intrinsic rate of natural increase (rm), and biotic potential (bp). In conclusion, the results of this study revealed the toxicity of cantharidin against house flies and the adverse effects of sublethal concentrations on biological parameters which may have positive implications for effective management of house flies.

Effects of pyriproxyfen on wild populations of the housefly, Musca domestica, and compatibility with its principal parasitoids

BACKGROUND

The housefly, Musca domestica L., is an important pest of animal agriculture. Effective fly management requires integration of manure management, mass trapping, biological control, and selective insecticide use. Insecticidal control of houseflies is difficult due to the rapidity of resistance development, yet the insect growth regulator pyriproxyfen (PPF) is one of few insecticides that may still be effective. Here, we tested the susceptibility of wild housefly populations in the USA and in Israel to PPF, as well as the effect of PPF on housefly parasitoids of the genera Muscidifurax and Spalangia.

RESULTS

Most housefly populations from both countries were completely eliminated at PPF concentrations of 100 mg kg^-1 (USA) and 600 mg kg^-1 (Israel). One population from each country exhibited initial levels of PPF tolerance. PPF efficacy significantly decreased in cow manure. Emergence rates of parasitoids developing in PPF-treated hosts at concentrations of ≥600 mg kg^-1 were significantly affected, whereas other fitness parameters were moderately to non-affected.

CONCLUSIONS

PPF is still an effective tool for housefly control, but resistance management practices should be employed to avoid resistance. PPF is compatible with principal housefly parasitoids at concentrations <600 mg kg^-1 , and is suitable for use in integrated pest management. © 2017 Society of Chemical Industry.

Cyromazine resistance in a field strain of house flies, Musca domestica L.: Resistance risk assessment and bio-chemical mechanism

Developing resistance management strategies for eco-friendly insecticides is essential for the management of insect pests without harming the environment. Cyromazine is a biorational insecticide with very low mammalian toxicity. Resistance to cyromazine has recently been reported in house flies from Punjab, Pakistan. In order to propose a resistance management strategy for cyromazine, experiments were planned to study risk for resistance development, possibility of cross-resistance and bio-chemical mechanisms. A field strain of house flies with 8.78 fold resistance ratio (RR) to cyromazine was re-selected under laboratory conditions. After seven rounds of selection (G1-G7), the RR values rapidly increased from 8.8 to 211 fold. However, these values declined to 81fold when the cyromazine selected (CYR-SEL) strain was reared without selection pressure, suggesting an unstable nature of resistance. The CYR-SEL strain showed lack of cross-resistance to pyriproxyfen, diflubenzuron, and methoxyfenozide. Synergism bioassays using enzyme inhibitors: piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF), and metabolic enzyme analyses revealed increased activity of carboxylesterase (CarE) and mixed-function oxidase (MFO) in the CYR-SEL strain compared to the laboratory susceptible (Lab-susceptible) strain, suggesting the metabolic resistance mechanism responsible for cyromazine resistance in the CYR-SEL strain. In conclusion, risk of rapid development of cyromazine resistance under consistent selection pressure discourages the sole reliance on cyromazine for controlling house flies in the field. The unstable nature of cyromazine resistance provides window for restoring cyromazine susceptibility by uplifting selection pressure in the field. Moreover, lack of cross-resistance between cyromazine and pyriproxyfen, diflubenzuron, or methoxyfenozide in the CYR-SEL strain suggest that cyromazine could be rotated with these insecticides whenever resistance crisis occur in the field.