Mutations in acetylcholinesterase associated with insecticide resistance in the cotton aphid, Aphis gossypii Glover

Two acetylcholinesterase genes, Ace1 and Ace2, have been fully cloned and sequenced from both organophosphate-resistant and susceptible clones of cotton aphid. Comparison of both nucleic acid and deduced amino acid sequences revealed considerable nucleotide polymorphisms. Further study found that two mutations occurred consistently in all resistant aphids. The mutation F139L in Ace2 corresponding to F115S in Drosophila acetylcholinesterase might reduce the enzyme sensitivity and result in insecticide resistance. The other mutation A302S in Ace1 abutting the conserved catalytic triad might affect the activity and insecticide sensitivity of the enzyme. Phylogenetic analysis showed that insect acetylcholinesterases fall into two subgroups, of which Ace1 is the paralogous gene whereas Ace2 is the orthologous gene of Drosophila AChE. Both subgroups contain resistance-associated AChE genes. To avoid confusion in the future work, a nomenclature of insect AChE is also suggested in the paper.     

酶标板法监测棉蚜乙酰胆碱酯酶对杀虫剂的不敏感性

用酶标板法测定了不同浓度有机磷和氨基甲酸酯杀虫剂在反应不同时间内对棉蚜Aphis gossypii乙酰胆碱酯酶(AChE)的抑制作用。结果表明有机磷杀虫剂甲基1605,辛硫磷,久效磷,氧乐果和乙酰甲胺磷对棉蚜AChE均无明显的抑制作用。当用0.01 mol/L灭多威与酶及底物反应1 h对北京棉蚜(敏感)种群AChE的抑制率可达82.4%,与反应2 h 89.4%仅差7%。因此以0.01 mol/L灭多威反应1 h测定棉蚜AChE对它的敏感性是合理的。通过测定北京地区寄主为鼠李和棉花以及山东高密寄主为棉花的棉蚜种群中个体AChE活性的分布和灭多威对其抑制的分布,表明3个棉蚜种群中AChE个体频率的分布差异不大,而灭多威对三个种群个体AChE的抑制率小于30%的个体分别为2.4%、16%和29%。抑制率大于70%的个体分别为72%、33%和1%,与生物测定结果一致。因此,用酶标板法测定棉蚜个体AChE对氨基甲酸酯的不敏感性频率可作为棉蚜对氨基甲酸酯抗性的监测技术,为棉蚜化学防治提供依据。     

禾谷缢管蚜和麦长管蚜玻璃管药膜法敏感毒力基线的建立

【目的】建立禾谷缢管蚜Rhopalosiphum padi（Linnaeus）和麦长管蚜Sitobion avenae（Fabricius）对常用杀虫剂的相对敏感基线。【方法】从田间采集麦蚜在实验室内饲养30代以上,利用玻璃管药膜法测定其对杀虫剂的敏感度,每条毒力基线为2次以上独立测定数据合并后的计算结果。【结果】用玻璃管药膜法建立了包括新烟碱类、吡啶类、氨基甲酸酯类、有机磷类和拟除虫菊酯类共22个药剂品种对禾谷缢管蚜和麦长管蚜3 h的敏感毒力基线。禾谷缢管蚜对新烟碱类药剂吡虫啉和啶虫脒的LC₅₀值分别为0.02和0.007 μg/cm²;对吡啶类药剂吡蚜酮的LC₅₀值为0.124 μg/cm²;对氨基甲酸酯类药剂丁硫克百威、硫双灭多威、灭多威、抗蚜威、西维因的LC₅₀值为0.0026~0.70 μg/cm²;对有机磷类药剂三唑磷、丙溴磷、氧乐果、乐果、马拉硫磷、辛硫磷、敌敌畏、毒死蜱的LC₅₀值为0.005~0.065 μg/cm²;对拟除虫菊酯类药剂三氟氯氰菊酯、高效氯氰菊酯、溴氰菊酯、联苯菊酯、氰戊菊酯、氯氰菊酯的LC₅₀值为0.033~0.240 μg/cm²。麦长管蚜对新烟碱类药剂吡虫啉和啶虫脒的LC₅₀值分别为0.15和0.12 μg/cm²;对吡啶类药剂吡蚜酮的LC₅₀值为0.41 μg/cm²;对氨基甲酸酯类药剂丁硫克百威、硫双灭多威、灭多威、抗蚜威、西维因的LC50值为0.005~0.76 μg/cm²;对有机磷类药剂三唑磷、丙溴磷、氧乐果、乐果、马拉硫磷、辛硫磷、敌敌畏、毒死蜱的LC₅₀值为0.018~0.36 μg/cm²;对拟除虫菊酯类药剂三氟氯氰菊酯、高效氯氰菊酯、溴氰菊酯、联苯菊酯、氰戊菊酯、氯氰菊酯的LC50值为0.20~2.94 μg/cm²。【结论】建立的两种麦蚜对22种杀虫药剂的相对敏感基线,包括当前所有可能用于防治麦蚜的药剂,可以用于以后麦蚜抗药性监测或其他相关研究的参照;禾谷缢管蚜对药剂的敏感度高于麦长管蚜。     

Selective and Irreversible Inhibitors of Aphid Acetylcholinesterases: Steps Toward Human-Safe Insecticides

Aphids, among the most destructive insects to world agriculture, are mainly controlled by organophosphate insecticides that disable the catalytic serine residue of acetylcholinesterase (AChE). Because these agents also affect vertebrate AChEs, they are toxic to non-target species including humans and birds. We previously reported that a cysteine residue (Cys), found at the AChE active site in aphids and other insects but not mammals, might serve as a target for insect-selective pesticides. However, aphids have two different AChEs (termed AP and AO), and only AP-AChE carries the unique Cys. The absence of the active-site Cys in AO-AChE might raise concerns about the utility of targeting that residue. Herein we report the development of a methanethiosulfonate-containing small molecule that, at 6.0 µM, irreversibly inhibits 99% of all AChE activity extracted from the greenbug aphid (Schizaphis graminum) without any measurable inhibition of the human AChE. Reactivation studies using β-mercaptoethanol confirm that the irreversible inhibition resulted from the conjugation of the inhibitor to the unique Cys. These results suggest that AO-AChE does not contribute significantly to the overall AChE activity in aphids, thus offering new insight into the relative functional importance of the two insect AChEs. More importantly, by demonstrating that the Cys-targeting inhibitor can abolish AChE activity in aphids, we can conclude that the unique Cys may be a viable target for species-selective agents to control aphids without causing human toxicity and resistance problems.     

Comparison of Anopheles gambiae and Culex pipiens acetycholinesterase 1 biochemical properties

Selection of insensitive acetycholinesterase 1 (AChE1) has occurred in several mosquito species controlled with carbamate (CX) and organophosphate (OP) insecticides. In case of pyrethroid resistance, these insecticides represent an alternative for disease vector control program. Their heavy use in agriculture has selected resistant populations of Anopheles gambiae in West Africa. The evolution of resistance has to be studied to prevent, or at least slow down, the spread of resistant mosquito in wild populations. An. gambiae shares the same resistance mechanism to CX and OP insecticides as Culex pipiens, which was attributed to the G119S substitution in the AChE1 enzyme. By comparing resistant AChE1 from both species, we show here that similar resistance levels are obtained toward 10 insecticides of both classes. Moreover, similar AChE1 activity levels are recorded between either susceptible or resistant mosquitoes of both species. Enzymes belonging to both species seem thus to share identical properties. Consequently, we hypothesize that fitness cost associated with AChE1 insensitivity in C. pipiens mosquitoes should be similar in An. gambiae and thus be used in strategies to control resistant populations where malaria is prevalent.     

The acetylcholinesterase gene and organophosphorus resistance in the Australian sheep blowfly, Lucilia cuprina

Acetylcholinesterase (AChE), encoded by the Ace gene, is the primary target of organophosphorous (OP) and carbamate insecticides. Ace mutations have been identified in OP resistants strains of Drosophila melanogaster. However, in the Australian sheep blowfly, Lucilia cuprina, resistance in field and laboratory generated strains is determined by point mutations in the Rop-1 gene, which encodes a carboxylesterase, E3. To investigate the apparent bias for the Rop-1/E3 mechanism in the evolution of OP resistance in L. cuprina, we have cloned the Ace gene from this species and characterized its product. Southern hybridization indicates the existence of a single Ace gene in L. cuprina. The amino acid sequence of L. cuprina AChE shares 85.3% identity with D. melanogaster and 92.4% with Musca domestica AChE. Five point mutations in Ace associated with reduced sensitivity to OP insecticides have been previously detected in resistant strains of D. melanogaster. These residues are identical in susceptible strains of D. melanogaster and L. cuprina, although different codons are used. Each of the amino acid substitutions that confer OP resistance in D. melanogaster could also occur in L. cuprina by a single non-synonymous substitution. These data suggest that the resistance mechanism used in L. cuprina is determined by factors other than codon bias. The same point mutations, singly and in combination, were introduced into the Ace gene of L. cuprina by site-directed mutagenesis and the resulting AChE enzymes expressed using a baculovirus system to characterise their kinetic properties and interactions with OP insecticides. The K(m) of wild type AChE for acetylthiocholine (ASCh) is 23.13 microM and the point mutations change the affinity to the substrate. The turnover number of Lucilia AChE for ASCh was estimated to be 1.27x10(3) min(-1), similar to Drosophila or housefly AChE. The single amino acid replacements reduce the affinities of the AChE for OPs and give up to 8.7-fold OP insensitivity, while combined mutations give up to 35-fold insensitivity. However, other published studies indicate these same mutations yield higher levels of OP insensitivity in D. melanogaster and A. aegypti. The inhibition data indicate that the wild type form of AChE of L. cuprina is 12.4-fold less sensitive to OP inhibition than the susceptible form of E3, suggesting that the carboxylesterases may have a role in the protection of AChE via a sequestration mechanism. This provides a possible explanation for the bias towards the evolution of resistance via the Rop-1/E3 mechanism in L. cuprina.     

Duplication of theAce.1 locus inCulex pipiens mosquitoes from the Caribbean

InCulex pipiens mosquitoes, AChE1 encoded by the locusAce.1 is the target of organophosphorus and carbamate insecticides. In several resistant strains homozygous forAce.1 ^RR , insensitive AChE1 is exclusively found. An unusual situation occurs in two Caribbean resistant strains where each mosquito, at each generation, displays a mixture of sensitive and insensitive AChE1. These mosquitoes are not heterozygotes,Ace.1 ^RS , as preimaginal mortalities cannot account for the lethality of both homozygous classes. This situation is best explained by the existence of twoAce.1 loci, coding, respectively, a sensitive and an insensitive AChE1. Thus, we suggest that in the Caribbean a duplication of theAce.1 locus occurred before the appearance of insecticide resistance at one of the two copies.     

棉铃虫AChE不同分子型对抑制剂的敏感度及其与抗药性的关系(英文)

在分离到的棉铃虫AChE五种不同的分子型中 ,2 .1s和 8.7sAChE抗性品系对毒扁豆碱的敏感度明显低于敏感品系 ,成虫头部I50 值分别相差 1 86.3和 84.8倍 ,幼虫I50 值分别相差 1 0 1 0 倍和 1 0 5 倍。幼虫 5.3sAChE对毒扁豆碱的敏感度抗性品系和敏感品系相差达 1 2 3倍 ,而成虫则没有差异。研究结果表明 2 .1s、5.3s和 8.7sAChE敏感度降低可能是造成棉铃虫对有机磷和氨基甲酸酯类杀虫药剂产生抗性的主要原因     

Mutations of acetylcholinesterase1 contribute to prothiofos-resistance in Plutella xylostella (L.)

Insensitive acetylcholinesterase (AChE) is involved in the resistance of organophosphorous and carbamate insecticides. We cloned a novel full-length AChE cDNA encoding ace1 gene from adult heads of the diamondback moth (DBM, Plutella xylostella). The ace1 gene encoding 679 amino acids has conserved motifs including catalytic triad, choline-binding site and acyl pocket. Northern blot analysis revealed that the ace1 gene was expressed much higher than the ace2 in all examined body parts. The biochemical properties of expressed AChEs showed substrate specificity for acetylthiocholine iodide and inhibitor specificity for BW284C51 and eserine. Three mutations of AChE1 (D229G, A298S, and G324A) were identified in the prothiofos-resistant strain, two of which (A298S and G324A) were expected to be involved in the prothiofos-resistance through three-dimensional modeling. In vitro functional expression of AChEs in Sf9 cells revealed that only resistant AChE1 is less inhibited with paraoxon, suggesting that resistant AChE1 is responsible for prothiofos-resistance.     

六种常用杀虫剂对八种蚜虫的选择毒性

作者自1982年开始研究了乐果、氧化乐果、抗蚜威、氰戊菊酯、溴氰菊酯和氯氰菊酯等6种杀虫剂对8种蚜虫的选择毒性.以桃粉大尾蚜Hyalopterus amygdali Blanchard为标准,氧化乐果对桃粉大尾蚜和瓜蚜Aphis gossypii Glover之间的选择毒性指数最高为163.77,乐果和抗蚜威分别是373.24和34.70,而氰戊菊酯仅为1.37.氰戊菊酯最高的选择毒性指数是在桃粉大尾蚜和麦长管蚜Sitobionavenae(F.)之间,也只有6.86,有机磷和氨基甲酸酯杀虫剂对不同蚜虫的选择毒性与乙酰胆碱酯酶(AChE)对巯基试剂(DTNB)的敏感度有明显的相关性,说明其选择毒性与AChE的巯基结合部位有关.同时还发现,抗蚜威对洋槐蚜Aphis robiniae Macchiati和瓜蚜AChE的1₅₀值与其LC₅₀值表现一致.这些都说明了这两类杀虫剂对不同种蚜虫的选择毒性与AChE有关.氰戊菊酯和溴氰菊酯对蚜虫的选择毒性与α-乙酸萘酯羧酸酯酶的活性具有明显的相关性,而与β-乙酸萘酯羧酸酯酶的活性则无任何关系.氯氰菊酯的选择毒性与上述两种酯酶的活性没有任何相关性.     

杀虫药剂抗性家蝇品系乙酰胆碱酯酶基因的特征分析

乙酰胆碱酯酶(AChE)是有机磷和氨基甲酸酯类杀虫药剂的作用靶标,这两大类杀虫药剂的广泛应用导致了昆虫对抗性的选择。靶标的修饰是某些昆虫产生抗性的分于机理,这种抗性是和AChE的变更型相关的,这些变更型的酶显示出对杀虫药剂的不被感性。利用RT-PCR和Streptavidin偶联磁珠技术从两种抗性家蝇(Musca domestica)品系D3和Kash中分别分离了AChE基因并测定了其按苷酸颅序。eDNA的可读框长2082bp．由此推导出了AChE的氨基酸顺序,通过与敏感家蝇品系Cooper的比较,发现了一些核苷酸顺序差异和4个氨基酸点突变,其中3个替代可能与杀虫药剂不敏感性有关。这一结果表明D3和Kash均属于CH₂抗性类型。     

Comparative inhibition kinetics for acetylcholinesterases extracted from organophosphate resistant and susceptible strains of Boophilus microplus (Acari: Ixodidae)

In this study, acetylcholinesterases (AChEs) were extracted from two Mexican Boophilus microplus strains that demonstrated resistance to the organophosphate (OP) acaricide, coumaphos, in bioassay. The rate of inhibition of the extracted AChEs by the diethyl-OP paraoxon was determined for two resistant strains and two susceptible strains of B. microplus. The time to inhibition of 50% AChE activity was approximately two-fold greater for the resistant strains. Kinetic analysis of the interaction of the resistant AChEs with paraoxon revealed reduced bimolecular reaction constants (ki). Apparent conformational changes in the AChE of the resistant strains were reflected in reduced Km and Vmax values. The bimolecular reaction constants (ki) of the resistant strains were most affected by a slower rate of enzyme phosphorylation (k2).     

Genetic diversity and insecticide resistance of Myzus persicae (Hemiptera: Aphididae) populations from tobacco in Chile: evidence for the existence of a single predominant clone

The tobacco-feeding race of Myzus persicae (Sulzer), formerly known as M. nicotianae Blackman, was introduced into Chile during the last decade. In order to evaluate the genetic diversity and insecticide resistance status of Chilean tobacco aphid populations, a field survey was conducted in 35 tobacco fields covering a 300 km latitudinal survey. The populations sampled were characterized using microsatellite markers and morphometric multivariate analysis. Insecticide resistance levels were assessed through a microplate esterase assay and the mutation status of the kdr gene. All samples collected corresponded to the same anholocyclic aphid genotype, and showed morphological variation within the range expected for the tobacco-feeding race of M. persicae. Esterase activity showed the level and variability expected for an R1 clone lacking mutations in the sodium channels (susceptible kdr), thus corresponding to a type slightly resistant to organophosphate and carbamate, and susceptible to pyrethroid insecticides.     

A tryptophan in the bottleneck of the catalytic gorge of an invertebrate acetylcholinesterase confers relative resistance to carbamate and organophosphate inhibitors

Amphioxus, an invertebrate chordate, has two acetylcholinesterases (AChEs): cholinesterase 1 (ChE1) and cholinesterase 2 (ChE2). ChE1 is up to 329-fold more resistant to a variety of carbamate and organophosphate inhibitors, including a number of insecticides, when compared with ChE2. One difference between the two enzymes is at the position homologous to Phe331 in Torpedo AChE. In Torpedo AChE, this residue is a component of the hydrophobic subsite and defines one side of the bottleneck in the catalytic gorge of the enzyme. In ChE1, the homologous residue is Trp353; in ChE2, it is Phe353. We used site-directed mutagenesis to investigate the proposal that the resistance of ChE1 to inhibition by carbamates and organophosphates was due to this difference, creating a ChE1 W353F mutant to widen the bottleneck. The mutation virtually abolishes the difference in sensitivity to the inhibitors. The ChE1 W353F mutant is only 2- to 3-fold more resistant than ChE2 to carbamates and is actually 2.5- to 10-fold more sensitive to inhibition by organophosphates. The differences in resistance are due to different affinities of the enzymes for the inhibitors, not different reactivities. Molecular modeling supports the proposal that the difference in inhibition is due to the width of the bottleneck of the gorge. Our results have implications for insecticide resistance in insects, in particular mosquitoes and aphids.     

INSECTICIDE RESISTANCE OF COTTON APHID IN NORTH CHINA

Abstract  The cotton aphid ( Aphis gossypii Glover) is one of the most important pests infesting cotton in the cotton areas of North China. Since 1953 organophosphorus insecticides such as parathion and systox have been used to control the aphids for keeping up good yield of cotton. After several years. the concentration and the amount of spray were increasing in the field. In the early 1980's highly effective pyrethroid insecticides such as decis and sumicidin were largely imported into China. When first used 2. 5% decis emulsion was diluted in the ratio from 1:10000 to 1: 12000. However in 1985 the resistance of cotton aphid to pyrethroids increased by 171 times in general, 3230 times in some cotton fields. Thus it has prompted us to investigate the mechanism of resistance to insecticides and to search for the strategy to control the resistant aphids.
Experiments showed that the use of synergists including SV₁ (O, O-diethyl, O-phenyl phos-phorothionate) and PB has given evidence indicating mixed function oxidases (MFO). α-NA esterases and α-NA carboxylesterase are involved in the formation of resistance. The results also showed that the sensitivity of AChE to paraoxon in resistant aphids was lower than that in susceptible aphids.
Experiments showed that SV₁ was particularly synergistic to organophosphorus or pyrethroid insecticides and had played an excellent role in overcoming the resistance of cotton aphids to insecticides.     

Genetic diversity of the cotton aphid Aphis gossypii in the unstable environment of a cotton growing area

1 Spatial and temporal habitat heterogeneity represented by annual crops is a major factor influencing population dynamics of phytophagous insect pests such as the cotton aphid Aphis gossypii Glover. We studied the effects of instability of the cotton agroecosystem resulting from the temporary availability of the plant resource and the repeated use of insecticides on the genetic variability of the cotton aphids.
2 Samples of A. gossypii were collected in cotton plots, treated or not with insecticides and from vegetable crops (Malvaceae, Cucurbitaceae and Solanaceae) within the cotton growing area of northern Cameroon. The genetic structure of the samples was assessed using eight microsatellite markers. Insecticide resistance was estimated through the detection of two mutations in the ace -1 gene that are associated with insensitivity of acetylcholinesterase to carbamate and organophosphate insecticides.
3 The results obtained show that both host plants and insecticides act in genetic structuring of A. gossypii . Ninety-three percent of aphids collected on cotton were characterized by the same microsatellite multilocus genotype, Burk1 , which also displays the insecticide resistant alleles.
4 During the dry season, the cotton crop season after, the genotype Burk1 was principally found on two other malvaceous cultivated plants, rosella and okra, acting as suitable reservoir plants. The ability of the cotton aphid to move among asynchronous suitable habitats in response to changes in resource availability enables the pest to exploit unstable cropping systems. An understanding of the cotton aphid life system may aid to improve strategies for integrated resistance management.     

Oxydemeton-methyl resistance, mechanisms, and associated fitness cost in green peach aphids (Hemiptera: Aphididae)

Susceptibility to oxydemeton-methyl and imidacloprid, and the inhibitory effects of oxydemeton-methyl and some organophosphate compounds on acetylcholinesterase (AChE) and carboxylesterase activity were studied in two populations (Karaj and Rasht) of green peach aphids, Myzus persicae (Sulzer). Results show that the Karaj population was resistant to oxydemeton-methyl but susceptible to imidacloprid. The esterase activity of the resistant and susceptible populations suggests that one of the resistance mechanisms to oxydemeton-methyl was esterase-based. The inhibition assay shows that the AChE of the Karaj population is less sensitive to oxydemeton-methyl and paraoxon derivatives. Regarding the paraoxon derivatives, the smaller paraoxon side chain is more potent against the modified AChE than against the AChE from the susceptible strain. Fertility life table parameters of green peach aphid populations resistant and susceptible to oxydemeton-methyl also were studied under laboratory conditions. The standard errors of the population growth parameters were calculated using the Jackknife method. Results showed that susceptible strain exhibits a significantly higher r(m) than the resistant strain, probably because the resistant strain had a higher generation time than the susceptible strain. These results suggested that the resistant Karaj strain may be less fit than the susceptible strain.     

Biochemical basis of organophosphate and carbamate resistance in Asian citrus psyllid

The Asian citrus psyllid, Diaphorina citri Kuwayama, is a worldwide pest of citrus, which vectors the putative causal pathogen of huanglongbing. Current management practices warrant continuous monitoring of field populations for insecticide resistance. Baseline activities of acetylcholinesterase (AChE), general esterase, and glutathione S-transferase as well as sensitivity of AChE to selected organophosphate and carbamate insecticides were established for a susceptible laboratory strain (Lab) and compared with several field populations of D. citri from Florida. The specific activity of AChE in various D. citri populations ranged from 0.77 to 1.29 microM min(-1) mg of protein(-1); the Lab strain was characterized by the highest activity. Although reduced AChE sensitivity was observed in the Lab strain compared with field populations, overlap of 95% confidence intervals of I50 values (concentration required for 50% AChE activity inhibition) suggests no significant difference in AChE sensitivity among all populations tested for a given insecticide. There was no significant evidence of target site insensitivity in field populations that were exposed to the selected organophosphate and carbamate insecticides tested. The specific activity of general esterase and glutathione S-transferase was lowest in the Lab strain and was generally comparable to that of the field populations evaluated. The current data provide a mode-of-action specific baseline for future monitoring of resistance to organophosphate and carbamate insecticides in populations of D. citri.     

Two different genes encoding acetylcholinesterase existing in cotton aphid (Aphis gossypii).

Two acetylcholinesterase (AChE) genes, Ace1 and Ace2, have been cloned from cotton aphid, Aphis gossypii Glover, using the rapid amplification of cDNA ends (RACE) technique. To the best of our knowledge, this should be the first direct molecular evidence that multiple AChE genes exist in insects. The Ace1 gene was successfully amplified along its full length of 2371 bp. The open reading frame is 2031 bp long and encodes 676 amino acids (GenBank accession No. AF502082). The Ace2 gene was amplified as a mega-fragment of 2130 bp lacking part of 5'-end untranslated region (UTR). The open reading frame is 1992 bp long and ecodes a protein of 664 amino acids (GenBank accession No. AF502081). Both genes have the conserved amino acids and features shared by the AChE family, but share only 35% identity in amino acid sequence. The Ace1 gene is highly homologous to the AChE gene of Schizaphis graminum (AF321574) with 95% identity, and Ace2 to that of Myzus persicae (AF287291) with 92% identity. Phylogenetic analysis showed that the two cloned AChEs of A. gossypii are different in evolution. The phylogenetic tree generated by the PHYLIP program package inferred that AChE2 of A. gossypii is a more ancestral form of AChE. Homology modeling of structures using Torpedo californica (2ACE_) and Drosophila melanogaster (1Q09:A) native acetylcholinesterase structure as main template indicated that the two AChEs of Aphis gossypii might have different three-dimensional structures. Alternative splicing of Ace1 near the 5'-end resulting in two proteins differing by the presence or absence of a fragment of four amino acids is also reported.