Strains Of House Fly Research Articles

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

The house fly, Musca domestica, is a serious pest of public health importance with the ability to develop insecticide resistance. The focus of the present study was to evaluate toxicity and resistance of the field collected house flies from Punjab, Pakistan, against insect growth regulator (IGR) insecticides. House flies collected from six different localities exhibited very low levels of resistance to cyromazine, triflumuron, and methoxyfenozide compared with the Lab-susceptible reference strain, with resistance ratios (RRs) ranging between 3.56- to 8.19-fold, 1.45- to 3.68-fold, and 2.20- to 8.60-fold, respectively. However, very low to low levels of resistance were observed for pyriproxyfen and very low to moderate levels for lufenuron with RRs ranged from 4.13- to 11.63-fold to 8.57- to 22.75-fold, respectively. There was a significant correlation between RRs of cyromazine and triflumuron (r = 0.976, p < 0.001), suggesting the possibility for cross-resistance. Susceptibility status of different IGRs in Pakistani strains of house flies is reported here for the first time. The trend observed in decreasing susceptibility towards different IGR insecticides tested will continue unless resistance management practices are followed.

Comparative Effectiveness of Insecticides for Use Against the House Fly (Diptera: Muscidae): Determination of Resistance Levels on a Malaysian Poultry Farm.

In this study, the toxicology of two commercial larvicides--cyromazine (Neporex 50SP) and ChCy (combination of chlorpyrifos and cypermethrin, Naga 505)--and five commercial adulticides--thiamethoxam (Agita 10WG), cyfluthrin (Responsar WP), lambda-cyhalothrin (Icon 2.8EC), fipronil (Regent 50SC), and imidacloprid (Toxilat 10WP)--was examined against the WHO/VCRU (World Health Organization/ Vector Control Research Unit) susceptible strain and the AYTW (Ayer Tawar) field strain of house fly, Musca domestica L. These pesticides were administered topically, in the diet, or as a dry residue treatment on plywood. Probit analysis using at least five concentrations and the concentration that was lethal to 50% (LC(50)) of the organisms was applied to compare the toxicology and resistance levels of the AYTW population to different insecticides. In the larvicide laboratory study, ChCy was more effective than cyromazine, with a significantly lower LC(50) value when administered topically or in the diet, although the AYTW population was susceptible to both larvicides with a resistance ratio (RR) <10. For the adulticide laboratory study, cyfluthrin and fipronil exhibited the lowest LC50 values of the adulticides, indicating that they are both effective at controlling adult flies, although lambda-cyhalothrin showed moderate resistance (RR = 11.60 by topical application; 12.41 by plywood treatment). Further investigation of ChCy, cyromazine, cyfluthrin, and fipronil under field conditions confirmed that ChCy and cyromazine strikingly reduced larval density, and surprisingly, ChCy also exhibited adulticidal activity, which significantly reduced adult fly numbers compared with the control group. Cyfluthrin and fipronil were also confirmed to be effective, with a significant reduction in adult fly numbers compared with the control group.

Selection and Preliminary Mechanism of Resistance to Profenofos in a Field Strain of Musca domestica (Diptera: Muscidae) from Pakistan.

House flies are major insect pests at dairy farms in Pakistan and are mainly controlled with insecticides of different classes, including organophosphates. To develop a better resistance management strategy, a field strain of house flies was selected in the laboratory to study the potential for the development of resistance, possible mechanisms of resistance and cross-resistance to other insecticides. The selection of the field strain with profenofos for five consecutive generations resulted in the LC50 values to increase from 50.49 to 176.03 µg/ml, and the resistance ratio increased from 29.70 to 103.55 as compared with a laboratory-susceptible strain; however, the resistance was decreased significantly when the selected strain was reared for the next five generations without exposure to any insecticide. The profenofos-selected strain (Profen-SEL) showed cross-resistance to chlorpyrifos and deltamethrin but no cross-resistance observed to spinosad. Synergism studies with piperonyl butoxide and S,S,S-tributylphosphorotrithioate indicated that the resistance to profenofos was probably associated with esterase and, possibly, microsomal oxidase activity. Resistance to profenofos in the selected strain suggests that the resistance, owing to instability, could be overcome by switching off profenofos use for few generations in the field or by rotation with different insecticides having different modes of action.

Genetics and mechanism of resistance to deltamethrin in the house fly, Musca domestica L., from Pakistan.

Deltamethrin (a pyrethroid insecticide) has widely been used against the house fly, Musca domestica, a pest found in livestock facilities worldwide. Although, cases of both metabolic and physiological resistance to deltamethrin have been reported in different parts of the world, no studies have been reported to characterize this resistance in house flies from Pakistan. In the present study, we investigated a field strain of house flies for potential to develop resistance to deltamethrin. Also, its stability, possible mechanisms and cross-resistance potential to other insecticides. Before the selection experiments, the field strain showed 8.41-, 3.65-, 8.39-, 2.68-, 19.17- and 5.96-fold resistance to deltamethrin, bifenthrin, lambda-cyhalothrin, chlorpyrifos, profenofos and spinosad, respectively, compared with the reference strain (Lab-susceptible). Continuous selection of the field strain (Delta-SEL) with deltamethrin for six generations (G1-G6) in the laboratory increased the resistance ratio to 176.34 after bioassay at G7. The Delta-SEL strain was reared for the next four generations without exposure to deltamethrin and bioassayed at G11 which revealed that the resistance was stable. The Delta-SEL strain at G7 showed cross-resistance to all other insecticides except spinosad, when compared to the bioassays before the selection experiment (G1). Crosses between Delta-SEL and Lab-susceptible strains revealed an autosomal and incomplete dominant mode of resistance to deltamethrin. A direct test using a monogenic inheritance model revealed that the resistance was governed by more than one factor. Moreover, synergism studies with the enzyme inhibitors PBO and DEF reduced the resistance to deltamethrin in the selected strain up to 2.51- and 2.19-fold, respectively, which revealed that the resistance was possibly due to microsomal oxidase and esterase activity. It is concluded that the resistance to deltamethrin was autosomal and incompletely dominant. The high cross-resistance of bifenthrin, lambda-cyhalothrin, chlorpyrifos and profenofos in the Delta-SEL strain suggests that other insecticides would be necessary to counter the resistance. These results are therefore suggestive for implications in the management of insecticide resistance in house flies.

Thiamethoxam Resistance in the House Fly, Musca domestica L.: Current Status, Resistance Selection, Cross-Resistance Potential and Possible Biochemical Mechanisms.

The house fly, Musca domestica L., is an important ectoparasite with the ability to develop resistance to insecticides used for their control. Thiamethoxam, a neonicotinoid, is a relatively new insecticide and effectively used against house flies with a few reports of resistance around the globe. To understand the status of resistance to thiamethoxam, eight adult house fly strains were evaluated under laboratory conditions. In addition, to assess the risks of resistance development, cross-resistance potential and possible biochemical mechanisms, a field strain of house flies was selected with thiamethoxam in the laboratory. The results revealed that the field strains showed varying level of resistance to thiamethoxam with resistance ratios (RR) at LC50 ranged from 7.66-20.13 folds. Continuous selection of the field strain (Thia-SEL) for five generations increased the RR from initial 7.66 fold to 33.59 fold. However, resistance declined significantly when the Thia-SEL strain reared for the next five generations without exposure to thiamethoxam. Compared to the laboratory susceptible reference strain (Lab-susceptible), the Thia-SEL strain showed cross-resistance to imidacloprid. Synergism tests revealed that S,S,S-tributylphosphorotrithioate (DEF) and piperonyl butoxide (PBO) produced synergism of thiamethoxam effects in the Thia-SEL strain (2.94 and 5.00 fold, respectively). In addition, biochemical analyses revealed that the activities of carboxylesterase (CarE) and mixed function oxidase (MFO) in the Thia-SEL strain were significantly higher than the Lab-susceptible strain. It seems that metabolic detoxification by CarE and MFO was a major mechanism for thiamethoxam resistance in the Thia-SEL strain of house flies. The results could be helpful in the future to develop an improved control strategy against house flies.

Efficacy of insecticide mixtures against a resistant strain of house fly (Diptera: Muscidae) collected from a poultry farm

House flies (Musca domestica L.) are key pests of poultry and are managed worldwide with a variety of insecticides. However, extensive and injudicious use of insecticides has led to the development of resistance in many insect pests. Insecticide mixtures can increase the efficacy of the product and/or delay the development of resistance, thus making them a useful tool for pest control. In addition to their efficacy when used alone, mixtures of emamectin benzoate, spinosad or nitenpyram with either lambda-cyhalothrin or profenofos were assessed against a susceptible strain of house flies collected from poultry farms. The analysis revealed that combination indices for lambda-cyhalothrin/emamectin benzoate and lambda-cyhalothrin/spinosad mixtures were significantly >1, indicating an antagonistic effect. In contrast, the indices for all the tested ratios of lambda-cyhalothrin/nitenpyram were significantly < 1, suggesting a synergistic effect. For mixtures containing profenofos, combination indices varied significantly. For example, synergism was observed in a 1:1 mixture containing lambda-cyhalothrin and emamectin benzoate, but antagonism occurred when a higher proportion of the latter insecticide was used. Conversely, synergism in a mixture containing profenofos and nitenpyram was observed only when a lower proportion of the second insecticide was used. The present results suggest that ideal insecticide mixtures must be empirically determined and alternative strategies such as mosaics, rotations and cultural control should be considered for the management of the house fly.

On the Estimation of a Univariate Gaussian Distribution: A Comparative Approach

Estimation of the unknown mean, μ and variance, σ2 of a univariate Gaussian distribution given a single study variable x is considered. We propose an approach that does not require initialization of the sufficient unknown distribution parameters. The approach is motivated by linearizing the Gaussian distribution through differential techniques, and estimating, μ and σ2 as regression coefficients using the ordinary least squares method. Two simulated datasets on hereditary traits and morphometric analysis of housefly strains are used to evaluate the proposed method (PM), the maximum likelihood estimation (MLE), and the method of moments (MM). The methods are evaluated by re-estimating the required Gaussian parameters on both large and small samples. The root mean squared error (RMSE), mean error (ME), and the standard deviation (SD) are used to assess the accuracy of the PM and MLE; confidence intervals (CIs) are also constructed for the ME estimate. The PM compares well with both the MLE and MM approaches as they all produce estimates whose errors have good asymptotic properties, also small CIs are observed for the ME using the PM and MLE. The PM can be used symbiotically with the MLE to provide initial approximations at the expectation maximization step.

Expression of xenobiotic metabolizing cytochrome P450 genes in a spinosad-resistant Musca domestica L. strain.

BackgroundSpinosad is important in pest management strategies of multiple insect pests. However, spinosad resistance is emerging in various pest species. Resistance has in some species been associated with alterations of the target-site receptor, but in others P450s seems to be involved. We test the possible importance of nine cytochrome P450 genes in the spinosad-resistant housefly strain 791spin and investigate the influence of spinosad on P450 expression in four other housefly strains.ResultsSignificant differences in P450 expression of the nine P450 genes in the four strains after spinosad treatment were identified in 40% of cases, most of these as induction. The highly expressed CYP4G2 was induced 6.6-fold in the insecticide susceptible WHO-SRS females, but decreased 2-fold in resistant 791spin males. CYP6G4 was constitutively higher expressed in the resistant strain compared to the susceptible strain. Furthermore, CYP6G4 gene expression was increased in susceptible WHO-SRS flies by spinosad while the expression level did not alter significantly in resistant fly strains. Expression of CYP6A1 and male CYP6D3 was constitutively higher in the resistant strain compared to the susceptible. However, in both cases male expression was higher than female expression.Conclusion CYP4G2, CYP6A1, CYP6D3 and CYP6G4 have expressions patterns approaching the expectations of a hypothesized sex specific spinosad resistance gene. CYP4G2 fit requirements of a spinosad resistance gene best, making it the most likely candidate. The overall high expression level of CYP4G2 throughout the strains also indicates importance of this gene. However, the data on 791spin are not conclusive concerning spinosad resistance and small contributions from multiple P450s with different enzymatic capabilities could be speculated to do the job in 791spin. Differential expression of P450s between sexes is more a rule than an exception. Noteworthy differences between spinosad influenced expression of P450 genes between a field population and established laboratory strains were shown.

Adaptation of Musca domestica L. Field Population to Laboratory Breeding Causes Transcriptional Alterations

BackgroundThe housefly, Musca domestica, has developed resistance to most insecticides applied for its control. Expression of genes coding for detoxification enzymes play a role in the response of the housefly when encountered by a xenobiotic. The highest level of constitutive gene expression of nine P450 genes was previously found in a newly-collected susceptible field population in comparison to three insecticide-resistant laboratory strains and a laboratory reference strain.ResultsWe compared gene expression of five P450s by qPCR as well as global gene expression by RNAseq in the newly-acquired field population (845b) in generation F1, F13 and F29 to test how gene expression changes following laboratory adaption. Four (CYP6A1, CYP6A36, CYP6D3, CYP6G4) of five investigated P450 genes adapted to breeding by decreasing expression. CYP6D1 showed higher female expression in F29 than in F1. For males, about half of the genes accessed in the global gene expression were up-regulated in F13 and F29 in comparison with the F1 population. In females, 60% of the genes were up-regulated in F13 in comparison with F1, while 33% were up-regulated in F29. Forty potential P450 genes were identified. In most cases, P450 gene expression was decreased in F13 flies in comparison with F1. Gene expression then increased from F13 to F29 in males and decreased further in females.ConclusionThe global gene expression changes massively during adaptation to laboratory breeding. In general, global expression decreased as a result of laboratory adaption in males, while female expression was not unidirectional. Expression of P450 genes was in general down-regulated as a result of laboratory adaption. Expression of hexamerin, coding for a storage protein was increased, while gene expression of genes coding for amylases decreased. This suggests a major impact of the surrounding environment on gene response to xenobiotics and genetic composition of housefly strains.

Autosomal male determination in a spinosad‐resistant housefly strain from Denmark

The housefly, Musca domestica L., is a global pest and has developed resistance to most insecticides applied for its control. The insecticide spinosad plays an important role in housefly control. Females of the Danish housefly strain 791spin are threefold more resistant to spinosad than males in this strain. The factor responsible for spinosad resistance in the strain is unknown, but previous studies suggest a role of cytochrome P450s for detoxification of spinosad. Sex determination in the housefly is controlled by a male-determining factor (M), either located on the Y chromosome or on one of the five autosomes (I to V). The authors performed a series of crosses and backcrosses, starting with cross of 791spin and the susceptible reference strain aabys (bearing morphological mutations on each autosome). These flies were evaluated for gender and bioassayed to determine levels of resistance to spinosad. Sex determination in 791spin is due to a male factor on autosome 3. The most likely explanation for the differentiation of spinosad resistance between males and females is a recessive spinosad resistance factor on autosome III.

Resistance to conventional insecticides in Pakistani populations of Musca domestica L. (Diptera: Muscidae): a potential ectoparasite of dairy animals

The house fly, Musca domestica L., is an important hygienic pest of humans and dairy animals with the potential to develop resistance to most chemical classes of insecticides. Six adult house fly strains from dairy farms in Punjab, Pakistan were evaluated for resistance to selected insecticides from organochlorine, organophosphate, carbamate and pyrethroid classes. For a chlorocyclodiene and two organophosphates tested, the resistance ratios (RR) at LC50 were in the range of 5.60-22.02 fold for endosulfan, 7.66-23.24 fold for profenofos and 2.47-7.44 fold for chlorpyrifos. For two pyrethroids and one carbamate, the RR values at LC50 were 30.22-70.02 for cypermethrin, 5.73-18.31 for deltamethrin, and 4.39-15.50 for methomyl. This is the first report of resistance to different classes of insecticides in Pakistani dairy populations of house flies. Regular insecticide resistance monitoring programs on dairy farms are needed to prevent field control failures. Moreover, integrated approaches including the judicious use of insecticides are needed to delay the development of insecticide resistance in house flies.

Effects of artificial migration of susceptible individuals on resistance and fitness of a fenitrothion-resistant strain of Musca domestica (L.) Diptera

Migration of susceptible individuals from untreated areas to populations that have developed insecticide resistance is one of the most important processes that can significantly delay or even prevent the development of resistance against insecticides. Fitness parameters of susceptible and resistant insect populations and changes in fitness following susceptible population migration have a crucial place in this process, as they determine the permanence and spread of susceptible alleles in the absence of insecticides. In this study, we investigated changes in resistance levels and fitness characteristics after introducing individuals from the ancestral susceptible strain in an equal ratio to a housefly (Musca domestica) strain artificially selected against fenitrothion, an organophosphate insecticide. We measured fitness parameters such as pre-adult development time, fecundity, fertility, and survival. Compared to the susceptible strain, the resistant strain had slower development time, but there were not any significant differences for fecundity, fertility, and survival. The level of resistance decreased gradually with 2 generations of susceptible migration. Development times were faster in both migration strains compared to the resistant strain. In addition, we detected a fitness reduction in fecundity, fertility, and female survival after the first generation of migration, but this reduction was alleviated after the second generation of migration. In conclusion, these findings indicate that fenitrothion resistance in Musca domestica has important fitness costs related with development time, and these costs are mitigated with susceptible migration.

Monitoring of Five Different Insecticide Resistance Status in Turkish House Fly Musca domestica L. (Diptera: Muscidae) Populations and the Relationship Between Resistance and Insecticide Usage Profile

The objective of this study is to assess the resistance status and yearly changes involved for house fly populations from six cities in Turkey. Field strains of house fly (Musca domestica L. Diptera: Muscidae) were collected in 2004-2006 from cow farms (Antalya, İzmir) and garbage dumps (Adana, Ankara, İstanbul, Şanlıurfa) in Turkey. The resistance levels of first and two generation offspring were determined against five insecticides (cypermethrin, cyphenothrin, deltamethrin, permethrin and fenitrothion). While the highest resistance level for pyrethroid was determined for Antalya 2005 strain (851.97 Cypermethrin) and lowest resistance level for Şanlıurfa 2004 strain (2.06 Permethrin), the highest fenitrothion resistance was found in Şanlıurfa 2004 strain (50.37) and lowest fenitrothion resistance was found in Adana 2004 strain (6.45). Our results showed that pyrethroid resistance levels were very high and determined a decreasing trend for Antalya and İstanbul strains and an increasing trend for Adana and Şanlıurfa strain for all tested pyrethroid insecticides from 2004 to 2006. Although cypermethrin and cyphenothrin resistance showed a decreasing trend, deltamethrin and permethrin showed an increasing trend for the Izmir strain from 2004 to 2006. The same trend was also determined for the Ankara strain except for permethrin. Fenitrothion resistance was determined to be lower than pyrethroids, but these levels were still high. Flies from cow farms were generally more resistant than those from garbage dumps. Our results also revealed the presence of strong selective pressure on the populations.

Pyriproxyfen and House Flies (Diptera: Muscidae): Effects of Direct Exposure and Autodissemination to Larval Habitats

Pyriproxyfen is an insect growth regulator with juvenile hormone-like activity that has potential uses for dipterans that are difficult to manage with conventional insecticides, such as house flies (Musca domestica L.). The objectives of this study were to determine the efficacy of this insect growth regulator against house flies using variety of delivery systems and target life stages, including an evaluation of the potential for autodissemination by female flies to larval development sites. Adult female house flies exposed to filter paper (3.75% active ingredient) or sugar treated with pyriproxyfen (0.01-0.1%) produced significantly fewer F1 pupae than untreated flies. Adult emergence from pupae was unaffected. In contrast, treatment of larval rearing medium with 0.35 ml/cm2 of a 12 mg pyriproxyfen/liter preparation had no effect on the number of pupae developing from eggs but markedly inhibited adult emergence from those pupae. There was little difference in susceptibility between an insecticide-susceptible and a wild strain of house fly. The LC50 for inhibiting fly emergence of dust formulations in diatomaceous earth incorporating commercial pyriproxyfen products ranged from 8 to 26 mg/liter, with little difference among products. Compared with untreated flies, significantly fewer pupae were produced at concentrations > 0.5% and no adults were produced at concentrations > 0.05% pyriproxyfen. When gravid females were exposed for 1 h to treated fabric (6 mg pyriproxyfen/cm2) and allowed to oviposit in rearing media containing eggs, sufficient pyriproxyfen was autodisseminated to reduce adult emergence from those eggs by > 99%. Intermittent contact with treated fabric over 2 d reduced adult emergence by 63-76%.

Investigating the potential of selected natural compounds to increase the potency of pyrethrum against houseflies Muscadomestica (Diptera: Muscidae)

A study was undertaken to determine the efficacy of seven natural compounds compared with piperonyl butoxide (PBO) in synergising pyrethrum, with the intention of formulating an effective natural synergist with pyrethrum for use in the organic crop market. Discriminating dose bioassays showed PBO to be significantly more effective at synergising pyrethrum in houseflies than the seven natural compounds tested, causing 100% mortality in insecticide-susceptible WHO and resistant 381zb strains of housefly. The most effective natural synergists against WHO houseflies were dillapiole oil, grapefruit oil and parsley seed oil, with 59, 50 and 41% mortality respectively, compared with 18% mortality with unsynergised pyrethrum. Against 381zb houseflies, the most effective natural synergists were parsley seed oil and dillapiole oil. Esterase inhibition by the natural compounds and PBO in vitro showed no correlation with pyrethrum synergism in vivo, whereas the inhibition of oxidases in vitro more closely correlated with pyrethrum synergism in vivo. Dillapiole oil and parsley seed oil showed the greatest potential as pyrethrum synergists. PBO remained the most effective synergist, possibly owing to its surfactant properties, enhancing penetration of pyrethrins. The results suggest the involvement of oxidases in pyrethroid resistance in houseflies, with the efficacy of synergists showing a high correlation with inhibition of oxidases.

Spinosad resistance in female Musca domestica L. from a field‐derived population

Bait-formulated spinosad is currently being introduced for housefly (Musca domestica L.) control around the world. Spinosad resistance was evaluated in a multiresistant field population and strains derived from this by selection with insecticides. Constitutive and spinosad-induced expression levels of three cytochrome P450 genes, CYP6A1, CYP6D1 and CYP6D3, previously reported to be involved in insecticide resistance, were examined. In 2004 a baseline for spinosad toxicity of Danish houseflies where all field populations were considered to be susceptible was established. In the present study, females of a multiresistant field population 791a were, however, 27-fold spinosad resistant at LC(50), whereas 791a male houseflies were susceptible. Strain 791a was selected with spinosad, thiamethoxam, fipronil and imidacloprid, resulting in four strains with individual characteristics. Selection of 791a with spinosad did not alter spinosad resistance in either males or females, but counterselected against resistance to the insecticides thiamethoxam and imidacloprid targeting nicotinic acetylcholine receptors. A synergist study with piperonyl butoxide, as well as gene expression studies of CYP6A1, CYP6D1 and CYP6D3, indicated a partial involvement of cytochrome P450 genes in spinosad resistance. This study reports female-linked spinosad resistance in Danish houseflies. Negative cross-resistance was observed between spinosad and neonicotinoids in one multiresistant housefly strain. Spinosad resistance involved alterations of cytochrome P450 gene expression.

Investigations of the constitutive overexpression of CYP6D1 in the permethrin resistant LPR strain of house fly ( Musca domestica)

House fly ( Musca domestica) CYP6D1 is a cytochrome P450 involved in metabolism of xenobiotics. CYP6D1 is located on chromosome 1 and its expression is inducible in response to the prototypical P450 inducer phenobarbital (PB) in insecticide susceptible strains. Increased transcription of CYP6D1 confers resistance to permethrin in the LPR strain, and this trait maps to chromosomes 1 and 2. However, the constitutive overexpression of CYP6D1 in LPR is not further increased by PB and the non-responsiveness to PB maps to chromosome 2. It has been suggested that a single factor on chromosome 2 could be responsible for both the constitutive overexpression and lack of PB induction of CYP6D1 in LPR. We examined the PB inducibility of CYP6D1v1 promoter from LPR using dual luciferase reporter assays in Drosophila S2 cells and found the CYP6D1v1 promoter was able to mediate PB induction, similar to the CYP6D1v2 promoter from the insecticide susceptible CS strain. Therefore, variation in promoter sequences of CYP6D1v1 and v2 does not appear responsible for the lack of PB induction of CYP6D1v1 in LPR; this suggests an unidentified trans acting factor is responsible. HR96 has been implicated in having a role in PB induction in Drosophila melanogaster and M. domestica. Therefore, house fly HR96 cDNA was cloned and sequenced to examine if this trans acting factor is responsible for constitutive overexpression of CYP6D1v1 in LPR. Multiple HR96 alleles ( v1– v10) were identified, but none were associated with resistance. Expression levels of HR96 were not different between LPR and CS. Thus, HR96 is not the trans acting factor responsible for the constitutive overexpression of CYP6D1 in LPR. The identity of this trans acting factor remains elusive.

Selection for Resistance to Imidacloprid in the House Fly (Diptera: Muscidae)

The house fly, Musca domestica L. (Diptera: Muscidae), continues to be a primary pest of livestock facilities worldwide. This pest also has shown a propensity for pesticide resistance development when under high selection pressures. In this study the house fly strain FDm was created by a 20% contribution from each of five colonies collected from dairies in Florida with known imidacloprid resistance. The FDm strain was used to evaluate the level ofimidacloprid resistance after five selections near the LC70 value of each selected generation. Overall, the mean selection mortality was 72.7, with males being considerably more susceptible than females. The unselected (F0) FDm strain showed considerable susceptibility to imidacloprid after its creation, compared with the five parental strains. Between 9500 and 14,000 virgin house flies were used in each selection. After the fifth and final selection, a 331-fold increase in imidacloprid resistance at the LC70 was observed over the parental FDm strain. In parallel studies, the FDm strain showed increasing tolerance of the commercial imidacloprid product QuickBayt. These results suggest that livestock producers should use caution when choosing pesticides and consider rotating fly baits, as is encouraged with other pesticide treatment regimes on farms.

Insecticidal potency of novel compounds on multiple insect species of medical and veterinary importance

Vector-borne diseases continue to present significant threats to human, animal and plant health. Mosquitoes, houseflies, sand flies and stable flies are well-known vectors of several human and animal pathogens. The toxicity of selected semiochemicals with molecular structures indicative of insecticidal activity was determined against these insect species with the aim of developing novel insecticides toxic to multiple insect species. Three semiochemicals, namely beta-damascone, cyclemone A and melafleur, showed remarkable toxicity to three mosquitoes, Aedes aegypti L., Ae. albopictus (Skuse) and Anopheles quadrimaculatus Say, the housefly, Musca domestica L., the stable fly, Stomoxys calcitrans L., and the sand fly, Lutzomyia shannoni (Dyar). The chemicals were equally toxic to several field-collected permethrin-tolerant housefly strains. When formulated as 500 mL L(-1) emulsifiable concentrates, the chemicals demonstrated stability and toxicity on filter paper and camouflage military fabrics, with persistence up to 8 days under laboratory conditions. The chemicals were equally effective under field conditions when evaluated on unpainted plywood panels, although a higher dosage was required under field conditions to achieve similar efficacy. Laboratory quantification of LC(50) values and field efficacy of three semiochemicals as formulated compounds on mosquitoes, houseflies, stable flies and sand flies showed that these semiochemicals could serve as potent insecticides for multiple insect species.

Low expression of nicotinic acetylcholine receptor subunit Mdα2 in neonicotinoid‐resistant strains of Musca domestica L.

Neonicotinoid action as well as resistance involves interaction with nicotinic acetylcholine receptors (nAChRs). In the housefly, neonicotinoid resistance also involves cytochrome P450, as indicated by bioassay with synergist as well as altered expression. In bioassay, synergism was only partial and indicated possible target-site resistance. The nAChR α2 subunit is important in neonicotinoid toxicity to insects, and gene expression of the Mdα2 subunit was investigated in field populations and laboratory strains of neonicotinoid-resistant and insecticide-susceptible houseflies, Musca domestica L. The genomic sequence covering exon III-VII of Mdα2 was analysed for mutations. Gene expression profiling of Mdα2 revealed notable differences between neonicotinoid-resistant and insecticide-susceptible houseflies. On average, the neonicotinoid-resistant field population 766b and the imidacloprid selected strain 791imi had 60% lower copy numbers of Mdα2 compared with the susceptible reference strain. Sequencing of exon III-VII of the Mdα2, encoding acetylcholine binding-site regions and three out of four transmembrane domains, did not reveal any mutations explaining the increased neonicotinoid tolerance in the strains examined. Previous discoveries and the results of this study suggest that the neonicotinoid resistance mechanism in Danish houseflies involves both cytochrome P450 monooxygenase-mediated detoxification and reduced expression of the nAChR subunit α2.