Georghiou GP

References (18)

Title : Biochemical Characterization of the Esterases Al and Bl Associated with Organophosphate Resistance in the Culex pipiens L. - Fournier_1987_Pestic.Biochem.Physiol_27_211
Author(s) : Fournier D , Bride JM , Mouches C , Raymond M , Magnin M , Berge JB , Pasteur N , Georghiou GP
Ref : Pestic Biochem Physiol , 27 :211 , 2015
Abstract : Two esterases, A1 and B1, displaying a high activity in organophosphate (OP) resistant Culex pipiens L. from southern France and in C. quinquefasciatus Say from California, respectively, have been analyzed. Both enzymes are shown to be soluble and to constitute a large proportion of the proteins (1-3% for esterase A1 and 6-12% for esterase B1). The size of native esterase A1 was estimated between 118 and 134 kDa, that of esterase B1 67 kDa. Upon SDS denaturation, esterase B1 leads a single polypeptide of 67 kDa which suggests that it is a monomeric protein; esterase A1 leads also a single polypeptide of 60 kDa suggesting a homodimeric structure of the protein. These observations are discussed with regards to esterase E4 of Myzus persicae Sultz.
ESTHER : Fournier_1987_Pestic.Biochem.Physiol_27_211
PubMedSearch : Fournier_1987_Pestic.Biochem.Physiol_27_211

Title : Selection and characterization of temephos resistance in a population of Aedes aegypti from Tortola, British Virgin Islands - Wirth_1999_J.Am.Mosq.Control.Assoc_15_315
Author(s) : Wirth MC , Georghiou GP
Ref : J Am Mosq Control Assoc , 15 :315 , 1999
Abstract : A collection of Aedes aegypti from Tortola, British Virgin Islands, with a high level of temephos resistance (46.8-fold at the 95% lethal concentration [LC95]) was selected to higher resistance with temephos in the laboratory. After 13 generations of pressure, the temephos resistance ratio increased to 180.6 (LC95), whereas in the absence of selection pressure the resistance ratio declined to 8.5. Relatively low levels of resistance or cross-resistance to other organophosphate and carbamate insecticides, and a high level of resistance to the pyrethroid permethrin were also observed. Synergism tests implicated detoxifying esterases in temephos resistance and the presence of elevated esterase activity was confirmed by biochemical tests; however, no evidence was found of insensitive acetylcholinesterase. Mendelian crosses indicated that temephos resistance was inherited as a monofactorial trait. The presence of high levels of temephos and permethrin resistance in Ae. aegypti has important implications for Aedes control programs.
ESTHER : Wirth_1999_J.Am.Mosq.Control.Assoc_15_315
PubMedSearch : Wirth_1999_J.Am.Mosq.Control.Assoc_15_315
PubMedID: 10480122

Title : Organophosphate resistance in Culex pipiens from Cyprus - Wirth_1996_J.Am.Mosq.Control.Assoc_12_112
Author(s) : Wirth MC , Georghiou GP
Ref : J Am Mosq Control Assoc , 12 :112 , 1996
Abstract : Populations of Culex pipiens were sampled from 8 locations in Cyprus between 1987 and 1993. All population samples generally revealed organophosphate resistance to malathion, temephos, chlorpyrifos, fenthion, dichlorvos, and pirimiphos methyl, in decreasing order of magnitude. Of 7 populations assessed with the carbamate propoxur, all proved to be resistant to different degrees. Of the 6 populations tested with permethrin, 2 were resistant to permethrin. Resistance was associated with the presence of 5 different overproduced esterases (esterases A1, A2, A5, B2, and B5) as well as an insensitive form of acetylcholinesterase. These results are discussed in relation to the ongoing mosquito abatement program in Cyprus and to similar programs in other parts of the world.
ESTHER : Wirth_1996_J.Am.Mosq.Control.Assoc_12_112
PubMedSearch : Wirth_1996_J.Am.Mosq.Control.Assoc_12_112
PubMedID: 8723267

Title : Characterization of resistance to organophosphate, carbamate, and pyrethroid insecticides in field populations of Aedes aegypti from Venezuela - Mazzarri_1995_J.Am.Mosq.Control.Assoc_11_315
Author(s) : Mazzarri MB , Georghiou GP
Ref : J Am Mosq Control Assoc , 11 :315 , 1995
Abstract : Resistance to the organophosphates (OP) temephos, malathion, and pirimiphos methyl, and the carbamate propoxur was found to be low (< 5-fold) in 3 Aedes aegypti populations collected from Falcon and Aragua states of Venezuela. Resistance to chlorpyrifos (OP), permethrin, and lambda-cyhalothrin (pyrethroids) was moderate (7-fold) in both populations. Mechanisms of resistance were investigated with the synergists piperonyl butoxide (mixed function oxidase inhibitor) and S, S, S-tributyl phosphorothioate (DEF, an esterase inhibitor). Nonspecific esterase and oxidase enzymes played a significant role in OP and carbamate resistance, respectively. Resistance to pyrethroid insecticides was not affected by DEF or piperonyl butoxide. This suggested the presence of another mechanism such as altered target site sensitivity (kdr). Biochemical tests showed significantly greater amounts of esterase activity in field strains, whereas insensitive acetylcholinesterase was not involved in either OP or carbamate resistance. These results must be considered in future control programs for Ae. aegypti, because OPs and pyrethroids are currently used in vector control in most countries of Central and South America.
ESTHER : Mazzarri_1995_J.Am.Mosq.Control.Assoc_11_315
PubMedSearch : Mazzarri_1995_J.Am.Mosq.Control.Assoc_11_315
PubMedID: 8551300

Title : Action of Esterase B1 on Chlorpyrifos in Organophosphate-Resistant Culex Mosquitos - Cuany_1993_Pestic.Biochem.Physiol_45_1
Author(s) : Cuany A , Handani J , Berge J , Fournier D , Raymond M , Georghiou GP , Pasteur N
Ref : Pesticide Biochemistry and Physiology , 45 :1 , 1993
Abstract : Esterase B1 activity in Culex pipiens mosquitoes was strongly inhibited by oxidized organophosphates (OP), but not by nonoxidized forms or by carbamates. Inhibition by chlorpyrifos oxon and paraoxon remained total during the 2 hr following the removal of free insecticide molecules, indicating that hydrolysis by esterase B1 is either very slow or absent. This hypothesis was confirmed by comparing the fate of [14C]chlorpyrifos in larvae of strains TEM-R (with the over-produced esterase B1) and MSE (lacking an overproduced esterase). As expected, large quantities of chlorpyrifos oxon were observed in the two strains, but no other metabolite was found in TEM-R. It is concluded that esterase B1 confers resistance at least to diethyl OPs through sequestering rather than metabolism, as is also the case with the overproduced esterase E4 of Myzus persicae.
ESTHER : Cuany_1993_Pestic.Biochem.Physiol_45_1
PubMedSearch : Cuany_1993_Pestic.Biochem.Physiol_45_1

Title : Esterase B1 activity variation within and among insecticide resistant, susceptible and heterozygous strains of Culex quinquefasciatus (Diptera: Culicidae) - Ferrari_1990_J.Econ.Entomol_83_1704
Author(s) : Ferrari JA , Georghiou GP
Ref : J Econ Entomol , 83 :1704 , 1990
Abstract : Amplification of the esterase B1 gene of Culex quinquefasciatus Say results in high titers of an esterase enzyme that confers resistance to organophosphate insecticides. Esterase activity of individuals was measured in samples from an organophosphate resistant strain (Tem-R), a susceptible strain (S-Lb), and their reciprocal F1 progeny. Within-strain variation, as measured by coefficients of variation, was fairly consistent between sexes within strains and among strains (average, 12%). On average, individuals from the Tem-R strain had about 120 times the esterase activity of individuals from the S-Lab strain. The mean esterase activities of the F1 strains were significantly higher than the average of the Tem-R and S-Lab strain mean esterase activities, suggesting enhanced expression of the amplified esterase B1 genes in F1 individuals. Reciprocal F1 strains did not differ significantly in esterase activity or resistance, indicating that maternal effects do not influence either of these measures in these strains. The levels of esterase activity of the strains are discussed in relation to their resistance.
ESTHER : Ferrari_1990_J.Econ.Entomol_83_1704
PubMedSearch : Ferrari_1990_J.Econ.Entomol_83_1704
PubMedID: 2258509

Title : Characterization of amplification core and esterase B1 gene responsible for insecticide resistance in Culex [published erratum appears in Proceedings of the National Academy of Sciences of the United States of America 1990 Jun\;87(11):4411] - Mouches_1990_Proc.Natl.Acad.Sci.U.S.A_87_2574
Author(s) : Mouches C , Pauplin Y , Agarwal M , Lemieux L , Herzog M , Abadon M , Beyssat-Arnaouty V , Hyrien O , de Saint Vincent BR , Georghiou GP
Ref : Proceedings of the National Academy of Sciences of the United States of America , 87 :2574 , 1990
Abstract : Organophosphorus insecticide (OP) resistance in several Culex species is associated with increased esterase activity resulting from amplification of the corresponding structural gene. In Culex pipiens quinquefasciatus, high levels of OP resistance (approximately 800 times) are due to the esterase B1 gene, which is amplified at least 250-fold. This gene has now been sequenced, and the structure of the amplification unit (amplicon) encompassing the structural gene has been partially characterized. The inferred amino acid sequence of the enzyme revealed regions of strong homology with other eukaryotic serine-esterases, such as cholinesterases, which are the target of OPs. The amplicon covers at least 30 kilobases and contains a constant and highly conserved "core" of 25 kilobases. This core carries a single copy of the esterase gene (2.8 kilobases) as well as other sequences that are present as single or low number copies in the genomes of mosquitoes lacking overproduction of the esterase B1 protein. In the amplicon, the esterase gene is framed by two DNA sequences that are repeated in other parts of the genome of resistant mosquitoes and found in the genome of susceptible mosquitoes but not near the esterase B1 gene. It is suggested that these repetitive sequences may have a role in the amplification process.
ESTHER : Mouches_1990_Proc.Natl.Acad.Sci.U.S.A_87_2574
PubMedSearch : Mouches_1990_Proc.Natl.Acad.Sci.U.S.A_87_2574
PubMedID: 2320576
Gene_locus related to this paper: culpi-1este

Title : Esterases A2 and B2 in Culex quinquefasciatus (Diptera: Culicidae): role in organophosphate resistance and linkage - Wirth_1990_J.Med.Entomol_27_202
Author(s) : Wirth MC , Marquine M , Georghiou GP , Pasteur N
Ref : Journal of Medical Entomology , 27 :202 , 1990
Abstract : Two highly active esterases, A2 and B2, were isolated in SeLax, a strain of Culex quinquefasciatus Say from California which demonstrated resistance levels of 19, 14, and 4.3 times to the organophosphate insecticides chlorpyrifos, temephos, and malathion, respectively. Selection of SeLax by temephos during 31 generations increased resistance to this insecticide to 65 times. This resistance was shown to be DEF-suppressible, monofactorial, and strongly associated with the presence of esterases A2 and B2. Although these two esterases are encoded by distinct structural genes, no disjunction was observed when SeLax was crossed to S-Lab, a susceptible strain, or to S54, a strain resistant to organophosphates by means of esterase A1. However, when SeLax was crossed to strain Tem-R, which is resistant to organophosphates because of a highly active esterase B1, all possible recombinants occurred. These results were discussed in relation to the recent discovery that increased activity of B esterases in the genus Culex is caused by gene amplification.
ESTHER : Wirth_1990_J.Med.Entomol_27_202
PubMedSearch : Wirth_1990_J.Med.Entomol_27_202
PubMedID: 2093766

Title : Amplification of various esterase B's responsible for organophosphate resistance in Culex mosquitoes -
Author(s) : Raymond M , Beyssat-Arnaouty V , Sivasubramanian N , Mouches C , Georghiou GP , Pasteur N
Ref : Biochemical Genetics , 27 :417 , 1989
PubMedID: 2559713

Title : Genetic association between highly active esterases and organophosphate resistance in Culex tarsalis - Prabhaker_1987_J.Am.Mosq.Control.Assoc_3_473
Author(s) : Prabhaker N , Georghiou GP , Pasteur N
Ref : J Am Mosq Control Assoc , 3 :473 , 1987
Abstract : The genetics of two highly active esterases, A3H and B3H, in a methyl parathion-resistant strain (MP-R) of Culex tarsalis was investigated in relation to organophosphate (OP) resistance. The increased activity of esterase A3 and of esterase B3 is under the control of two distinct and closely linked (approximately 4.4 centimorgans) genes. Each gene possesses two forms, one controlling high activity (A3H or B3H, respectively) and one controlling low activity (A3L or B3L, respectively) of the enzymes. Organophosphate resistance in the MP-R strain is strongly associated with the presence of these highly active esterases. The results are discussed in relation to the present knowledge on the mechanisms responsible for high activity of esterases observed in other OP-resistant mosquitoes of the genus Culex.
ESTHER : Prabhaker_1987_J.Am.Mosq.Control.Assoc_3_473
PubMedSearch : Prabhaker_1987_J.Am.Mosq.Control.Assoc_3_473
PubMedID: 3504931

Title : Amplification of an esterase gene is responsible for insecticide resistance in a California Culex mosquito - Mouches_1986_Science_233_778
Author(s) : Mouches C , Pasteur N , Berge JB , Hyrien O , Raymond M , de Saint Vincent BR , de Silvestri M , Georghiou GP
Ref : Science , 233 :778 , 1986
Abstract : An esterase gene from the mosquito Culex quinquefasciatus that is responsible for resistance to a variety of organophosphorus (OP) insecticides was cloned in lambda gt11 phage. This gene was used to investigate the genetic mechanism of the high production of the esterase B1 it encodes in OP-resistant Culex quinquefasciatus Say (Tem-R strain) from California. Adults of the Tem-R strain were found to possess at least 250 times more copies of the gene than adults of a susceptible strain (S-Lab). The finding that selection by pesticides may result in the amplification of genes encoding detoxifying enzymes in whole, normally developed, reproducing insects emphasizes the biological importance of this mechanism and opens new areas of investigation in pesticide resistance management.
ESTHER : Mouches_1986_Science_233_778
PubMedSearch : Mouches_1986_Science_233_778
PubMedID: 755546

Title : Malathion-specific resistance in Anopheles stephensi from Pakistan - Scott_1986_J.Am.Mosq.Control.Assoc_2_29
Author(s) : Scott JG , Georghiou GP
Ref : J Am Mosq Control Assoc , 2 :29 , 1986
Abstract : A strain of Anopheles stephensi from Pakistan (MalR) was 8.7-fold resistant to malathion and 6.7-fold cross-resistant to phenthoate, but not to other carboxylesters; no cross-resistance to bendiocarb, fenitrothion, permethrin and carbaryl was detected. Resistance was not associated with elevated levels of general esterase activity, as determined by hydrolysis of naphth-l-yl acetate (alpha-NA), but was correlated with higher levels of malathion carboxylesterase (MCE) activity in vitro. The results suggest that a highly specific type of esterase mediated resistance, such as MCE, can best be detected by an enzyme specific assay rather than one for general esterase activity. A new, rapid and sensitive assay for mosquito MCE is given.
ESTHER : Scott_1986_J.Am.Mosq.Control.Assoc_2_29
PubMedSearch : Scott_1986_J.Am.Mosq.Control.Assoc_2_29
PubMedID: 3507466

Title : Joint action of diquat and related one-electron transfer agents with propoxur and fenthion against mosquito larvae -
Author(s) : Georghiou GP , Black AL , Krieger RI , Fukuto TR
Ref : J Econ Entomol , 67 :184 , 1974
PubMedID: 4151605

Title : Carbamate resistance in mosquitos. The metabolism of propoxur by susceptible and resistant larvae of Culex pipiens fatigans - Shrivastava_1970_Bull.World.Health.Organ_42_931
Author(s) : Shrivastava SP , Georghiou GP , Metcalf RL , Fukuto TR
Ref : Bulletin of the World Health Organization , 42 :931 , 1970
Abstract : Toxicity tests on Culex pipiens fatigans with propoxur (o-isopropoxyphenyl methylcarbamate) and carbofuran (2,2-dimethyl-2,3-dihydrobenzofuranyl-7-methylcarbamate) indicated that both compounds are fast-acting insecticides. Transfer of treated larvae to fresh water results in their partial recovery from knockdown.Propoxur is metabolized by resistant and susceptible larvae by their homogenate-reduced nicotinamide-adenine dinucleotide phosphate (NADPH(2)) enzyme system and by the microsome-plus-soluble fraction of mouse-liver extracts to at least 10 organosoluble metabolites with the isopropoxy group intact. The major metabolites, which are primarily hydroxylation products or the result of degradation of these products, have tentatively been identified as: acetone plus o-hydroxyphenyl methylcarbamate, 2-isopropoxy-5-hydroxyphenyl methylcarbamate, 2-isopropoxyphenyl carbamate, and 2-isopropoxyphenyl N-hydroxymethylcarbamate. Upon incubation of water-soluble products from treated larvae with beta-glucosidase, beta-glucuronidase, aryl sulfatase and acid phosphatase, the conjugates are hydrolysed, liberating mainly hydroxylated carbamates.The results indicate that slower absorption as well as faster detoxification by hydroxylation mechanisms, together with conjugation with polar molecules and elimination, are major factors in resistance of mosquito larvae to substituted-aryl methylcarbamate insecticides.
ESTHER : Shrivastava_1970_Bull.World.Health.Organ_42_931
PubMedSearch : Shrivastava_1970_Bull.World.Health.Organ_42_931
PubMedID: 5312255

Title : Carbamate-resistance in mosquitos. Selection of Culex pipiens fatigans Wiedemann (=C. quinquefasciatus Say) for resistance to Baygon - Georghiou_1966_Bull.World.Health.Organ_35_691
Author(s) : Georghiou GP , Metcalf RL , Gidden FE
Ref : Bulletin of the World Health Organization , 35 :691 , 1966
Abstract : The authors investigated the rate of development and other characteristics of Baygon-resistance in Culex pipiens fatigans (=C. quinquefasciatus) recently colonized from Southern California. Selective pressure against the larvae (strain L) for 35 generations resulted in 25.4-fold resistance in larvae, but only 3-fold and 4.8-fold resistance in adults, as determined by contact and topical application, respectively. Conversely, selective pressure on adults (strain A) for 24 generations resulted in 8.4-fold (contact) and 5.3-fold (topical) resistance in adults, but only 2.7-fold resistance in larvae. About 10% of strain A adults survived 1-hour contact exposure even when the concentration of Baygon was increased 100-fold. This was not due to enhanced phototropism in this stage. Larvae of strain L metabolized (14)C-labelled Baygon at a rate 2.5-fold greater than the non-selected strain. Cross-resistance in strain L to carbamates closely related to Baygon was high, but was extremely low to remotely related carbamates.The authors consider the relatively slow rate of development of resistance to Baygon, the reduced expressivity of the resistance character in adults, and its specificity for the selective agent and for closely related carbamates to be encouraging indications as to the usefulness of this class of compounds for mosquito control.
ESTHER : Georghiou_1966_Bull.World.Health.Organ_35_691
PubMedSearch : Georghiou_1966_Bull.World.Health.Organ_35_691
PubMedID: 5297803

Author(s) : Georghiou GP , Garber MJ
Ref : Bulletin of the World Health Organization , 32 :181 , 1965
Abstract : In view of the increasing importance of carbamic acid esters in insect control, the authors have conducted studies on the inheritance of carbamate-resistance in the housefly Resistance to Isolan (1-isopropyl-3-methyl-5-pyrazolyl dimethylcarbamate) in carbamate-selected strains is inherited as a partially dominant major single factor, without sex linkage or appreciable cytoplasmic influence. Inclusion of piperonyl butoxide as a synergist with Sevin (1-naphthyl methylcarbamate), Zectran (4-dimethylamino-3,5-xylyl methylcarbamate), or m-isopropylphenyl methylcarbamate also produced evidence of monofactorial inheritance.In contrast, resistance to Isolan and to a combination of Sevin and piperonyl butoxide in a ronnel-selected strain is inherited in a pattern suggestive of a polygenic system.The results obtained are discussed in the light of previously established data on the rate of development, stability and regression of carbamate-resistance.
ESTHER : Georghiou_1965_Bull.World.Health.Organ_32_181
PubMedSearch : Georghiou_1965_Bull.World.Health.Organ_32_181
PubMedID: 14310905

Title : Toxicity of certain new compounds to insecticide-resistant houseflies - Georghiou_1965_Bull.World.Health.Organ_33_479
Author(s) : Georghiou GP , Metcalf RL , Von Zboray EP
Ref : Bulletin of the World Health Organization , 33 :479 , 1965
Abstract : Houseflies in poultry ranches in certain areas of California are now resistant to most insecticides licensed for use in these establishments, and this resistance problem appears likely to spread to other areas in the future. The authors have therefore studied the contact and oral toxicity of 19 new compounds that have shown interesting properties against resistant flies. These compounds were selected from among several hundred submitted by various laboratories for evaluation under a co-operative programme sponsored by the World Health Organization.Five compounds were found to be as toxic to three insecticide-resistant strains as to a susceptible strain, and showed strikingly steep log-dosage/probit mortality lines against the resistant strains. The authors suggest that these compounds be further studied for fly control in field trials.
ESTHER : Georghiou_1965_Bull.World.Health.Organ_33_479
PubMedSearch : Georghiou_1965_Bull.World.Health.Organ_33_479
PubMedID: 5294994

Title : The comparative toxicity of phosphoramidothionates and phosphoramidates to susceptible and insecticide-resistant houseflies and mosquitos - March_1964_Bull.World.Health.Organ_30_71
Author(s) : March RB , Georghiou GP , Metcalf RL , Printy GE
Ref : Bulletin of the World Health Organization , 30 :71 , 1964
Abstract : Studies of the comparative toxicity of a number of homologous X-chlorophenyl phosphoramidothionates and phosphoramidates and related analogues to susceptible and insecticide-resistant houseflies (Musca domestica L.) and mosquitos (Culex pipiens quinquefasciatus Say and Anopheles albimanus Wied.) have shown that the 2,4,5-trichlorophenyl series is the most active and the 4-chlorophenyl series the least active. Toxicity decreases in general with increasing chain length of the alkoxy and alkylamido moieties, maximum toxicity residing in methoxy, ethoxy, amido, methylamido, and ethylamido homologues. Toxicity is greatest to the susceptible strain but the alkylamido and X-chlorophenyl structures confer toxicological advantages from the standpoint of relative effectiveness against organophosphorus-resistance and organophosphorus vigour-tolerance. Many of the phosphoramidates are less toxic than their phosphoramidothionate analogues, probably due to less favourable physical properties.Certain of these compounds show promise against both susceptible and insecticide-resistant housefly adults and it is suggested that they be further evaluated in broad-spectrum field trials. Although some show promise as mosquito larvicides, in general the introduction of an alkyl-amido group markedly decreases residual toxicity from a filter-paper residue to mosquito adults in comparison with the corresponding dialkoxy analogues.
ESTHER : March_1964_Bull.World.Health.Organ_30_71
PubMedSearch : March_1964_Bull.World.Health.Organ_30_71
PubMedID: 14122443