Strains Of House Fly Research Articles

Evaluation of semiochemical toxicity to houseflies and stable flies (Diptera: Muscidae)

The housefly, Musca domestica L., and stable fly, Stomoxys calcitrans (L.) are cosmopolitan pests of both farm and home environments. Houseflies have been shown to be resistant to a variety of insecticides, and new chemistries are slow to emerge on the market. Toxicities of selected semiochemicals with molecular structures indicative of insecticidal activity were determined against adults from an insecticide-susceptible laboratory strain of houseflies. The three most active semiochemicals were also evaluated against recently colonized housefly and stable fly strains. Nineteen semiochemicals classified as aliphatic alcohols, terpenoids, ketones and carboxylic esters showed toxicity to houseflies and stable flies. Rosalva (LC(50) = 25.98 microg cm(-2)) followed by geranyl acetone and citronellol (LC(50) = 49.97 and 50.02 microg cm(-2)) were identified as the most toxic compounds to houseflies. Permethrin was up to 144-fold more toxic than rosalva on the susceptible strain. However, it was only 35-fold more toxic to the insecticide-tolerant field strain. The compounds generated high toxicity to stable flies, with LC(50) values ranging from 16.30 to 40.41 microg cm(-2). Quantification of LC(50) values of rosalva, citronellol and geranyl acetone against susceptible housefly and field-collected housefly and stable fly strains showed that semiochemicals could serve as potent insecticides for fly control programs.

Nicotinoid and pyrethroid insecticide resistance in houseflies (Diptera: Muscidae) collected from Florida dairies

The housefly, Musca domestica L., continues to be a major pest of confined livestock operations. Houseflies have developed resistance to most chemical classes, and new chemistries for use in animal agriculture are increasingly slow to emerge. Five adult housefly strains from four Florida dairy farms were evaluated for resistance to four insecticides (beta-cyfluthrin, permethrin, imidacloprid and nithiazine). Significant levels of tolerance were found in most field strains to all insecticides, and in some cases substantial resistance was apparent (as deduced from comparison with prior published results). At the LC(90) level, greater than 20-fold resistance was found in two of the fly strains for permethrin and one fly strain for imidacloprid. Beta-cyfluthrin LC(90) resistance ratios exceeded tenfold resistance in three fly strains. The relatively underutilized insecticide nithiazine had the lowest resistance ratios; however, fourfold LC(90) resistance was observed in one southern Florida fly strain. Farm insecticide use and its impact on resistance selection in Florida housefly populations are discussed. Housefly resistance to pyrethroids is widespread in Florida. Imidacloprid resistance is emerging, and tolerance was observed to both imidacloprid and nithiazine. If these insecticides are to retain efficacy, producer use must be restrained.

Unraveling the mystery of spinosad resistance in insects

Spinosad is a new and highly promising insecticide, derived from the bacteria Saccharopolyspora spinosa, with efficacy against a wide range of insects. The mechanism of action of spinosad appears to be unique, with a primary site of attack being the nicotinic acetylcholine receptor (nAChR) and a secondary site of attack being γ-aminobutyric acid (GABA) receptors. Neural nAChRs are composed of five subunits, with a minimum of 2 αs. Each subunit possesses a large N-terminal extracellular domain that includes the acetylcholine (ACh) binding site and four transmembrane domains (M1-4) with M2 contributing most of the amino acids that line the ion channel. Spinosad resistance has been selected for and characterized in several insect species. Generally, resistance is monofactorial, recessive and cannot be overcome by insecticide synergists. Spinosad resistance in the house fly maps to chromosome 1 and three nAChR subunit genes (α5, α6, and β3) are predicted to exist on chromosome 1 based on Drosophila/Musca homology maps. However, cloning and sequencing of Mdα5, Mdα6, and Mdβ3 from susceptible and spinosad resistant strains of house fly found no differences that could be associated with resistance. Unraveling the mystery of spinosad resistance in house flies will require further study.

Differential expression of CYP6A5 and CYP6A5v2 in pyrethroid‐resistant house flies, Musca domestica

Two cytochrome P450 alleles, CYP6A5 and CYP6A5v2, were isolated from a pyrethroid-resistant house fly stain, ALHF. The two alleles shared 98% similarity in amino acid sequence. To understand the importance of these two alleles in resistance and examine the expression profile of the two alleles between resistant and susceptible strains, quantitative real-time PCR (qRT-PCR) was performed and compared with the Northern blot analysis. We found that qRT-PCR was an efficient method to characterize the expression profiles between these two sequence-closely-related P450 genes between resistant and susceptible houses flies. One of them, CYP6A5v2, was constitutively overexpressed in ALHF house flies compared with susceptible house fly strains. Moreover, this gene was predominantly expressed in the abdominal tissues of ALHF, in which the primary detoxification organs of insects are located. However, there was no significant difference in the expression of CYP6A5 between ALHF and susceptible house flies. The genetic linkage analysis was conducted to determine the possible link between the constitutively overexpressed CYP6A5v2 and insecticide resistance. CYP6A5v2 was mapped on autosome 5, which is correlated with the linkage of resistance in ALHF. Taken together, the study suggests the importance of CYP6A5v2 in increasing metabolic detoxification of insecticides in ALHF. The distinct expression of CYP6A5 and CYP6A5v2 in resistant and susceptible house flies implies the functional difference of theses two genes in house flies and suggests that they are two recently diverged P450 genes presented in a single organism.

Inheritance of beta‐cypermethrin resistance in the housefly Musca domestica (Diptera: Muscidae)

Beta-cypermethrin, a synthetic pyrethroid insecticide, was applied frequently in the control of health pests including houseflies, Musca domestica L., in China. However, different levels of resistance to beta-cypermethrin were monitored in field strains of houseflies. A strain of M. domestica, 4420-fold resistant to beta-cypermethrin after continuous 25 generations of selection, was used in this paper to determine the mode of inheritance of pyrethroid resistance. The estimated realized heritability (h(2)) of beta-cypermethrin resistance was 0.30 in this resistant strain. Results of bioassays showed no significant difference in values of LD(50) and slope of log dose-probit lines between reciprocal progenies F(1) and F'(1), and yielded values of - 0.10 (F(1)) and - 0.11 (F'(1)) for the degree of dominance (D). Chi-square analysis from responses of self-bred and backcross progenies (F(2), BC(1) and BC(2) respectively) indicated that the null hypothesis, a single gene responsible for resistance, was accepted. The minimum number of independent segregation genes was 0.93 for F(1) by Lande's method. It was concluded that beta-cypermethrin resistance in the housefly was inherited as a single, major, autosomal and incompletely recessive factor. These results would provide the basic information for pest management programmes.

Molecular analysis of resistance in a deltamethrin-resistant strain of Musca domestica from China

We investigated the molecular basis of resistance in a strain of house fly (BJD) from Beijing, China. This strain showed 567-fold resistance to commonly used deltamethrin. Flies were 64-fold resistant to deltamethrin synergized by piperonyl butoxide (PBO). The 5′-flanking sequence of the cytochrome P450 gene CYP6D1 in BJD strain had a 15-bp insert as in the LPR strain. Two mutations ( kdr, super-kdr) in the voltage sensitive sodium channel (VSSC) were also detected in the BJD strain. Our results showed that a combination of resistance alleles for CYP6D1 and VSSC existed in deltamethrin resistant house flies in China.

Beta-cypermethrin resistance associated with high carboxylesterase activities in a strain of house fly, Musca domestica (Diptera: Muscidae)

A housefly strain, originally collected in 1998 from a dump in Beijing, was selected with beta-cypermethrin to generate a resistant strain (CRR) in order to characterize the resistance and identify the possible mechanisms involved in the pyrethroid resistance. The resistance was increased from 2.56- to 4419.07-fold in the CRR strain after 25 consecutive generations of selection compared to a laboratory susceptible strain (CSS). The CRR strain also developed different levels of cross-resistance to various insecticides within and outside the pyrethroid group such as abamectin. Synergists, piperonyl butoxide (PBO) and S, S, S-tributyl phosphorotrithioate (DEF), increased beta-cypermethrin toxicity 21.88- and 364.29-fold in the CRR strain as compared to 15.33- and 2.35-fold in the CSS strain, respectively. Results of biochemical assays revealed that carboxylesterase activities and maximal velocities to five naphthyl-substituted substrates in the CRR strain were significantly higher than that in the CSS strain, however, there was no significant difference in glutathione S-transferase activity and the level of total cytochrome P450 between the CRR and CSS strains. Therefore, our studies suggested that carboxylesterase play an important role in beta-cypermethrin resistance in the CRR strain.

Variation of Musca domestica L. acetylcholinesterase in Danish housefly populations

Anti-cholinesterase resistance is in many cases caused by modified acetylcholinesterase (MACE). A comparison was made of toxicological data and AChE activity gathered from 21 field populations and nine laboratory strains of houseflies, Musca domestica L., to elucidate the best way of generating data to provide advice for management strategies and gathering information for resistance risk assessment on the organophosphates azamethiphos and dimethoate and the carbamate methomyl, which have been the primary insecticides used against adult houseflies in Denmark. Cluster analysis was performed and > 2000 houseflies were assigned to one of three phenotypes based on total acetylcholinesterase activity as well as inhibition by azamethiphos, methomyl or omethoate. A cluster, i.e. a phenotype, with high total AChE activity and high sensitivity to azamethiphos and less sensitivity to inhibition by methomyl and omethoate was shown to be linked to methomyl resistance. It was not possible to define any clusters that could be linked to azamethiphos or dimethoate resistance. The five mutations V180L, G262A, G262V, F327Y and G365A causing anticholinesterase resistance in houseflies were all identified in the Danish housefly strains. The data are very heterogeneous, and a correlation of molecular genetic background and resistance of phenotypes is not obvious with the available data.

Resistance pattern and point mutations of insensitive acetylcholinesterase in a carbamate-resistant strain of housefly ( Musca domestica)

To examine the resistance pattern and point mutations present in the carbamate-resistant strain of housefly (SH-CBR), Musca domestica, from Shanghai, China, the fly’s resistance spectrum and k i ratios to organophosphate (OP) and carbamate (CB) insecticides were determined. The cDNA encoding acetylcholinesterase (AChE) from both a susceptible control strain (SH-S) and the SH-CBR strain of housefly were cloned and sequenced using RT-PCR. Based on two major patterns of target site resistance suggested by Russell et al. [R. J. Russell, C. Claudianos, P. M. Campbell, I. Horne, T. D. Sutherland, J. G. Oakeshott, Two major classes of target site insensitivity mutations confer resistance to organophosphate and carbamate, Pestic. Biochem. Physiol. 79 (2004), 84–93.], the present results indicate a Pattern I resistance: resistance to CBs was greater than that to OPs; the SH-S/SH-CBR k i ratios were also greater for CBs than for OPs. The cDNA was 2079 nucleotides long, encoding a protein of 693 amino acids. The cDNA deduced amino acid sequence of the housefly had a high degree of identity with previously described insect AChEs and exhibited the same structural feature as vertebrate TcAChE. Three mutations in the region of the active site, V261L, G343A, and F408Y, which were identical to those identified in the 77M and YBOL housefly strains, were identified in the AChE from the SH-CBR strain. Additionally, a novel mutation, D422L, was found at the outer surface of the protein where the residue presumably could not interact directly with amino acid residues lining the active site gorge. Homologous modelling of housefly AChE, based on the high resolution crystal structure of fruit fly ( Drosophila melanogaster) AChE, indicated that D422 may be involved in a salt bridge with H341. The distance between D422 and H341 is predicted to be 3.8 Å, and modification of the charge on the side chain of D422 (D to V) would likely affect the profile of the acyl pocket via the Y339 component. Such a structural change in the acyl pocket in the mutant may underlie the decreased affinity of AChE for CBs.

Reduced Penetration Rate of Pyraclofos into Housefly, Musca domestica, as a Resistance Mechanism

Ethylacetate was found to be suitable for washing pyraclofos from the insect body in experiments to determine the role of the cuticle in the penetration of pyraclofos into the body, and was recommended as a favorable solvent to study housefly resistance to pyraclofos. Three ml of ethylacetate washed off 99% of pyraclofos from the housefly body surface. The penetration through integument played an important role in resistance mechanism of the housefly to pyraclofos. There were considerable differences in penetration rate, excretion rate, and metabolism of the insect body between the resistant (YBOL) and susceptible (SRS) strains of housefly. In penetration study, the YBOL (resistant) strain showed a slightly greater inhibition of penetration than the SRS strain during 1 h after treatment at both the 8, 000-dpm and 4, 000-dpm treatments. Therefore, the reduced penetration rate of pyraclofos is one of the resistance mechanisms in the YBOL strain of housefly even though there were no significant differences of radioactivity between the YBOL and SRS strains after 2 h. For both 8, 000-dpm and 4, 000-dpm treatments, radioactivity in the YBOL surface extract was somewhat higher than in that of SRS, while radioactivity in the housefly body of SRS was higher than that of YBOL. Excretion rate was faster in the resistant housefly. This suggests that metabolic process might be also one of the resistance mechanisms of housefly to pyraclofos.

Biochemical changes in dehydrogenase, hydroxylase and tyrosinase of a permethrin-resistant strain of housefly larvae, Musca domestica L.

In the present study, a permethrin-resistant strain (ALHF) of housefly was used to understand some enzymic changes in normal biosynthetic pathways after insecticide selection. Aflatoxin B 1 (AFB 1) as a natural substrate was used to verify the changes on the level of cytochrome P450-dependent monooxygenases and oxido-reductase activities in the ALHF strain compared to an insecticide-susceptible strain, aabys. ALHF yielded three major biotransformation products: aflatoxin B 2a (AFB 2a), aflatoxin M 1 (AFM 1), and aflatoxicol (AFL) by larvae. These principal products were also found in aabys. AFL production rate of ALHF larvae was 5-fold lower than that of aabys. Differences between ALHF larvae and aabys in AFM 1 production were found. ALHF did not differ significantly from aabys in AFB 2a production. The levels of 17α- and β-hydroxysteroid dehydrogenase (17α- and β-HSD) were also determined to elucidate which type of dehydrogenase activities could be changed. The cytosolic fraction of ALHF larvae yielded about 2-fold higher 17α-estradiol than that of aabys larvae. In contrast, the microsomal fraction of ALHF larvae produced about 2-fold lower amount of 17α-estradiol than that of aabys larvae. The production rate of microsomal fraction of 17β-estradiol ALHF larvae yielded 3-fold lower than that of aabys larvae. Inhibition studies on 17α-HSD and 17β-HSD activities by pyrethroid insecticides showed that there was no inhibition by pyrethroids on the enzyme activity. Therefore, there seems to be no changes on the enzyme structures. Changes on enzyme expression may occur in ALHF larvae in relation to 17α- or β-HSD. To assess biochemical changes of the cuticle formation phenylalanine 4-hydroxylase and tyrosinase activities were determined. The production rate of tyrosine from phenylalanine in ALHF was about 2-fold higher for larvae than that in aabys. l-(dihydroxylphenyl)alanine (DOPA) content was determined in larvae and ALHF possessed 1.6-fold larger amounts of DOPA than aabys. Tyrosinase activity of ALHF larval preparations showed 1.6-fold higher than aabys. In summary, many enzymic changes were found in ALHF strain compared to aabys strain and these changes may be resulted from the permethrin selection.

The Genetic Basis of Malathion Resistance in Housefly (Musca domestica L.) Strains From Turkey

Organophosphate insecticide (parathion/diazinon) resistance in housefly (Musca domestica L.) is associated with the change in carboxylesterase activity. The product of MdalphaE7 gene is probably playing a role in detoxification of xenebiotic esters. In our research, we have isolated, cloned and sequenced the MdalphaE7 gene from 5 different Turkish housefly strains. High doses of malathion (600 microg/fly) were applied in a laboratory environment for one year to Ceyhan1, Ceyhan2, Adana and Ankara strains while no insecticide treatment was performed in the laboratory to Kirazli strain. Trp251 --> Ser substitution was found in the product of MdalphaE7 gene in all malathion resistant and Kirazli stocks. In addition, we checked the malathion carboxylesterase (MCE), percent remaining activities in acetylcholinesterase (AChE), glutathion-S-transferase (GST), and general esterase activities in all 5 strains used in this study. In comparing with universal standard sensitive control WHO, a high level of MCE and GST activities were observed while lower level of general esterase activities was detected in the tested strains. In addition, a higher percent remaining activities in AChE than WHO susceptible strain were observed in all malathion resistant strains.

Monitoring of Housefly [Musca Domestica] Population Abundance in Alexandria Governorate and Assessment of its Susceptibility towards some Commonly Used Insecticides

This study was conducted to monitor the housefly “M usca domestica” population abundance in different districts of Alexandria Governorate throughout one year from January to December 2002. Also, it determined the susceptibility of housefly against different currently used insecticides by Ministry of Health and Population [namely malathion and azamethiphos against adults and chlorpyriphos against larvae]. In addition, it evaluated the effect of a botanical compound; neem oil against both adults and larvae as an alternative insecticide. The data demonstrated that the highest housefly abundance was observed in El-Amreya and West Districts with mean grid count of 75.0±40.8 and 72.9±46.3, respectively. The lowest housefly abundance was observed in Borg El-Arab and East Districts with mean grid count of 37.7±19.7 and 39.5±28.1, respectively. The order of housefly population abundance in different districts of Alexandria Governorate was as follows: El-Amreya > West > El-Montaza > Middle > El-Gomrok > East > Borg El-Arab. Also, the abundance of housefly was greatly affected by temperature fluctuation where there were two peaks observed in Spring and Autumn while there were two depressions in Summer and Winter. There was a negative significant correlation between housefly abundance and both shadow and wind. As regards the susceptibility of housefly towards tested insecticides, the LD50 of malathion against adult insect using topical application for laboratory strain was 0.0199 mg/fly wile in case of field strain, it was 0.0363 mg/fly [1.824 times more than that of laboratory strain]. As regards azamethiphos using diet treatment, the LC50 for laboratory strain was 0.0281% while it was 0.0312% for field strain [1.11 times more than that of laboratory strain]. The EC50 of chloropyriphos using diet treatment against first instar larvae of field strain of housefly was 3.50 ppm. The most prominent toxic affected of neem oil emulsion was noticed in larval stage where EC50 for laboratory strain was 1982.9 ppm, while it was 2045.3 ppm for field strain. Neem oil had no toxic effect on adult housefly by either topical application or diet treatment. In conclusion, the study reported no resistance of housefly against the tested compounds.

Cross-resistance potential of fipronil in Musca domestica.

The toxicity of fipronil to insecticide-susceptible houseflies and the cross-resistance potential of fipronil were determined for six insecticide-resistant laboratory housefly strains by topical application and feeding bioassay. The insecticide-resistant strains represented different levels and patterns of resistance to pyrethroids, organophosphates, carbamates and organochlorines. Five strains were almost susceptible to fipronil in feeding bioassay with resistance factors at LC50 between 0.36 and 3.0. Four of these strains were almost susceptible to topically applied fipronil (resistance factors at LD50 were 0.55, 0.83, 3.3 and 2.5, respectively), whereas one strain was 13-fold resistant to topically applied fipronil. A highly gamma-HCH-resistant strain, 17e, was 430-fold resistant to fipronil in topical application bioassay and 23-fold resistant in feeding bioassay at LD50/LC50. We also tested the toxicity of fipronil in a feeding bioassay and gamma-HCH in topical application bioassay on thirteen housefly field populations. Eleven of the field populations had resistance factors for fipronil ranging from 0.98 to 2.4 at LC50, whereas two populations were 4.0- and 4.6-fold resistant to fipronil. The resistance level to gamma-HCH at LD50 in the field populations ranged from 1.8- to 8.1-fold. The two strains showing fipronil resistance were 3.4- and 8.1-fold resistant to gamma-HCH. Fipronil and gamma-HCH toxicities were positively correlated in the field populations. Biochemical assays of esterase, glutathione S-transferase and cytochrome P450 monooxygenase indicated that the low fipronil resistance observed in laboratory and field strains could be caused by elevated detoxification or be due to a target-site resistance mechanism with cross-resistance to gamma-HCH.

Insecticide Sensitivity of Acetylcholinesterase from a Korean Housefly ( Musca domestica) Strain to Organophosphates

Acetylcholinesterase (AChE) was purified, by affinity chromatography, from adult heads of the housefly ( Musca domestica) (GSNU strain) known to have mutated AChE gene. The purified AChE showed a single peak in capillary electrophoresis with an overall yield of 42% representing 957-fold purification and a specific activity of about 290 μ mol/min/mg. It hydrolyzed acetylthiocholine iodide better than S-butyrylthiocholine iodide or propionylthiocholine iodide. AChE-specific inhibitors, BW284C51 and eserine, significantly inhibited the purified AChE, but a butyrylcholinesterase-specific inhibitor, ethopropazine, did not. The housefly AChE was separated into membrane-bound and soluble forms. In vitro inhibition assays with seven organophophates, except for EPN, showed no significant difference between the crude and the purified AChE. Molecular forms of the housefly AChE did not affect the enzyme sensitivity to chlorpyrifos. Inhibition rate (%) of the AChE from the housefly was shown lower than that of the susceptible housefly strain (SRS) to trichlorfon and chlorpyrifos possibly because of the mutated amino acids of the AChE gene.

Susceptibility of Spinosad in Musca domestica (Diptera: Muscidae) Field Populations

The toxicity of spinosad was determined in one susceptible and five insecticide-resistant laboratory strains of house fly, Musca domestica L. Spinosad was relatively slow-acting, but highly toxic to house flies. In a feeding bioassay, spinosad LC50 at 72 h was 0.51 microg of spinosad per gram of sugar, making it 6.3- and 3.5-fold more toxic to house flies compared with azamethiphos and methomyl, respectively. In topical application bioassay, the LD50 at 48 h of spinosad in susceptible house flies was 40 ng per 20 mg of house fly, making spinosad less toxic than the pyrethroid bioresmethrin synergized by piperonyl butoxide and the organophosphate dimethoate. The insecticide-resistant laboratory strains had resistance factors to spinosad at LC50 in feeding bioassay from 1.5 to 5.5 and at LD50 in topical application bioassay from 2.5 to 4.7, indicating that in house fly cross-resistance to the major insecticide classes will not initially be of major concern for the use of spinosad for house fly control. The toxicity of spinosad was also evaluated against 31 field populations of house flies collected from livestock farms across Denmark. The field populations were 2.2- to 7.5-fold resistant to spinosad at 72 h in feeding bioassay, but based on steep slopes in the bioassay and the limited variation of spinosad toxicity against the various field populations, we consider the field populations to be spinosad-susceptible. We propose a diagnostic dose of 12 microg of spinosad per gram of sugar in feeding bioassay with impregnated sugar for determination of resistant house flies, which is 10x the LC95 of the susceptible strain WHO and approximately = 2x the LD95 of the field populations. Spinosad showed no substantial cross-resistance to the pyrethroid bioresmethrin synergized by piperonyl butoxide, the anticholinesterases dimethoate, azamethiphos, methomyl, and spinosad in house fly field populations.

Susceptibility of Spinosad in <I>Musca domestica</I> (Diptera: Muscidae) Field Populations

The toxicity of spinosad was determined in one susceptible and five insecticide-resistant laboratory strains of house fly, Musca domestica L. Spinosad was relatively slow-acting, but highly toxic to house flies. In a feeding bioassay, spinosad LC50 at 72 h was 0.51 microg of spinosad per gram of sugar, making it 6.3- and 3.5-fold more toxic to house flies compared with azamethiphos and methomyl, respectively. In topical application bioassay, the LD50 at 48 h of spinosad in susceptible house flies was 40 ng per 20 mg of house fly, making spinosad less toxic than the pyrethroid bioresmethrin synergized by piperonyl butoxide and the organophosphate dimethoate. The insecticide-resistant laboratory strains had resistance factors to spinosad at LC50 in feeding bioassay from 1.5 to 5.5 and at LD50 in topical application bioassay from 2.5 to 4.7, indicating that in house fly cross-resistance to the major insecticide classes will not initially be of major concern for the use of spinosad for house fly control. The toxicity of spinosad was also evaluated against 31 field populations of house flies collected from livestock farms across Denmark. The field populations were 2.2- to 7.5-fold resistant to spinosad at 72 h in feeding bioassay, but based on steep slopes in the bioassay and the limited variation of spinosad toxicity against the various field populations, we consider the field populations to be spinosad-susceptible. We propose a diagnostic dose of 12 microg of spinosad per gram of sugar in feeding bioassay with impregnated sugar for determination of resistant house flies, which is 10x the LC95 of the susceptible strain WHO and approximately = 2x the LD95 of the field populations. Spinosad showed no substantial cross-resistance to the pyrethroid bioresmethrin synergized by piperonyl butoxide, the anticholinesterases dimethoate, azamethiphos, methomyl, and spinosad in house fly field populations.

Determination of Malathion and Diazinon Resistance by Sequencing the Md E7 Gene from Guatemala, Colombia, Manhattan, and Thailand Housefly (Musca domestica L.) Strains

Organophosphate (OP) insecticides (parathion/diazinon) resistance in housefly (Musca domestica L.) is associated with the change in carboxylesterase activity. The product of alpha E7 gene, which is a member of alpha-esterase gene cluster, is probably playing a role in detoxification of the xenobiotic esters. In parathion/diazinon resistant M. domestica species Gly137 to Asp substitution was found in the active center of the product of alpha E7 gene. In malathion (an OP) resistant M. domestica strains Trp251 to Ser substitution was identified in the active center of the Md alpha E7. In our research, to understand the allelic diversity of the Md alpha E7, the gene was partially sequenced from four different housefly strains from different localities (Guatemala, Manhattan (USA), Colombia (USA) and Thailand). It was found out that; in Thailand strain one allele has Cys residue at the position of 251, the other allele contains a Trp for the same site. In Colombia strain, one allele has Asp137, the other allele contains a Gly residue at this point. The Manhattan and Guatemala strains have Asp137 and Trp251 residues on their both alleles at these two different positions.

Evolutionary plasticity of monooxygenase-mediated resistance

The cytochrome P450 monooxygenases are an important metabolic system involved in the detoxification of xenobiotics, and are thus one of the major mechanisms by which insects evolve insecticide resistance. However, comparatively little is known about the evolutionary constraints of this insecticide resistance mechanism. We investigated the genetic basis of resistance in a strain of house fly (NG98) from Georgia, USA that had evolved 3700-fold resistance to the pyrethroid insecticide permethrin, and compared this to other permethrin resistant strains of house flies from the US and Japan. Resistance in NG98 was due to kdr on autosome 3 and monooxygenase-mediated resistance on autosomes 1, 2, and 5. These results indicate that the genes which evolve to produce monooxygenase-mediated resistance to permethrin are different between different populations, and that the P450 monooxygenases have some degree of plasticity in response to selection. Monooxygenase-mediated resistance appears to evolve using different P450s, and possibly different regulatory signals controlling P450 expression, even in strains selected with the same insecticide.

Insecticide Resistant Strains of House Flies (Musca domestica) Show Limited Cross-Resistance to Chlorfenapyr

The toxicity of chlorfenapyr was evaluated against susceptible and pyrethroid resistant strains (laboratory and field collected) of house fly (Musca domestica L.). In one laboratory strain no cross-resistance was detected, 2.3-fold cross-resistance was detected in another strain, and a 2-fold negative cross-resistance was found in two strains. In field collected populations cross-resistance levels were also low (1.2- to 1.6-fold). These results suggest that the initial utility of chlorfenapyr for house fly control would not likely be compromised by cross-resistance, and that not all strains that have enhanced monooxygenase-mediated resistance will have negative cross-resistance to chlorfenapyr. The P450 isoform responsible for the activation of chlorfenapyr is discussed.