Insecticide resistance of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), in mainland China

BACKGROUND: In order to investigate the extent of resistance of oriental fruit fly, Bactrocera dorsalis (Hendel), which is a widespread pest throughout tropical, subtropical and temperate fruit crops, 25 populations of this insect were collected from 13 sites in mainland China in 2007 and 2008. In addition, resistant strains were established that showed increasing development of resistance. RESULTS: Compared with the susceptible strain, one population of B. dorsalis expressed high resistance (RR = 70.4‐fold), 16 populations expressed medium resistance (11.5‐fold < RR < 25.8‐fold) and eight populations had low resistance or remained susceptible (1.4‐fold < RR < 8.9‐fold) to trichlorphon. As regards β‐cypermethrin, one population showed high resistance (RR = 44.0‐fold), nine populations expressed medium resistance (12.2‐fold < RR < 28.4‐fold), 14 populations expressed low or minor resistance (3.0‐fold < RR < 9.7‐fold) and one population remained susceptible (RR = 1.1‐fold). As regards avermectin, five populations had developed high resistance (44.3‐fold < RR < 104‐fold), seven populations expressed medium resistance (11.4‐fold < RR < 38.6‐fold) and three populations expressed low or minor resistance (3.5‐fold < RR < 5.6‐fold). A continuous resistance selection in the laboratory strain showed that the resistance ratios to trichlorphon, β‐cypermethrin and avermectin were 71.6‐fold, 333‐fold and 70.4‐fold respectively. CONCLUSION: The data provided a comprehensive survey of insecticide resistance in Bactrocera dorsalis in mainland China. All results suggested that early resistance management programmes should be established for restoring the efficacy of pesticide‐based control measures. Copyright © 2010 Society of Chemical Industry     

Increased activity and reduced sensitivity of acetylcholinesterase associated with malathion resistance in a field population of the oriental migratory locust, Locusta migratoria manilensis (Meyen)

The susceptibility to malathion, and the activity and sensitivity of acetylcholinesterase (AChE, EC 1.1.1.7) were compared between two populations of the oriental migratory locust, Locusta migratoria manilensis (Meyen) collected from Wudi County of Shandong Province in East China and Huangliu County of Hainan Province in South China. Huangliu population showed 8.5-fold resistance to malathion compared with Wudi population. AChE from Huangliu population showed 4.8-fold higher activity than that from Wudi population toward the model substrate acetylthiocholine (ATC). Kinetic studies indicated that AChE from Huangliu population had 2.6-fold lower affinity, but 5.0-fold higher catalytic activity toward ATC than AChE from Wudi population. Significantly increased activity of AChE in Huangliu population was also confirmed by non-denaturing polyacrylamide gel electrophoresis. Inhibition kinetics revealed that AChE from Huangliu population was 9.8-, 2.4-, 8.0- and 7.7-fold less sensitive to inhibition by paraoxon, malaoxon, chlopyrifos oxon, demeton-S-methyl, respectively, than that from Wudi population. Our studies revealed that a mild resistance to malathion in Huangliu population was associated with reduced sensitivity and increased catalytic activity of AChE. Our results suggest that alterations of AChE may play an important role conferring or contribute to malathion resistance in Huangliu population of the locust.     

Comparative studies of acetylcholinesterases purified from two field populations of the oriental migratory locust (Locusta migratoria manilensis): implications of insecticide resistance

Acetylcholinesterase (AChE) was purified by affinity chromatography from two populations of the oriental migratory locust, Locusta migratoria manilensis (Meyen), collected from Huanghua and Pingshan Counties, Hebei Province of China. The purification factors and yields were 1661-fold and 19.3%, respectively, for the Huanghua population, and 3897-fold and 39.6% for the Pingshan population. Both the purification factor and yield were significantly lower in the Huanghua population than in the Pingshan population. AChE activity was almost completely inhibited by 10⁻⁶ M eserine and BW284C51, but ?5.8% of AChE activity was inhibited by ethopropazine at the same concentration, suggesting that purified AChE from either population was a typical insect AChE. However, AChE purified from the Huanghua population was 62-, 2.0-, and 1.6-fold less sensitive to inhibition by the three organophosphate compounds, chlorpyrifos oxon, demeton-S-methyl, and paraoxon, respectively, than that from the Pingshan population. Significantly lower purification factor and low yield associated with reduced sensitivity of AChE to inhibition by the organophosphates indicated that AChE purified from the Huanghua population was biochemically and pharmacologically different from that of the Pingshan population. Reduced sensitivity of AChE appeared to contribute to organophosphate resistance in the locust from Huanghua County, where insecticides have commonly been used to manage outbreaks of the locust.     

药剂对小菜蛾抗性及敏感品系乙酰胆碱酯酶抑制作用比较

采用浸叶法测定了云南通海、元谋和澜沧的小菜蛾plutella xylostella田间种群对常用杀虫剂的抗药性。结果表明,云南上述地区小菜蛾田间种群对各类杀虫剂均产生了不同程度的抗性。对有机磷类药剂的抗药性为1.74~31.1倍;对菊酯类药剂的抗药性为7.41~764倍;对阿维菌素类药剂则产生了 5.60~4.06×104倍的抗性。通过离体和活体试验测定了药剂对小菜蛾头部乙酰胆碱酯酶(AChE)的抑制作用。敌敌畏和灭多威对通海抗性品系AChE离体和活体内的抑制中浓度(I50)分别是敏感品系的209、26.5倍和2.21、2.16倍;敌敌畏对通海小菜蛾种群的离体和活体内抑制中时间(IT50)小于敏感品系,分别是敏感品系的0.32和0.17倍;而灭多威对通海小菜蛾种群的离体和活体内抑制中时间(IT50)则大于敏感品系,分别是敏感品系的1.37和1.74倍。     

Insensitivity of acetylcholinesterase in a field strain of the fall armyworm, Spodoptera frugiperda (J.E. Smith)

Acetylcholinesterase (AChE) was purified from adult heads of the fall armyworm (Spodoptera frugiperda) by using a two-step procedure involving gel filtration on a Sephadex G-200 column and affinity chromatography on a procainamide-ECH Sephadex 4B column. Both susceptible and field strains possessed two AChE isozymes, namely, AChE-1 and AChE-2, with subunit molecular weights of 63.7 and 66.1 kDa. The purified AChE had an apparent K_m value of 33.5 μM and a V_max of 7.07 μmol/min/mg protein in the susceptible strain. The apparent K_m and the V_max were 2.2- and 2.0-fold higher, respectively, in the field strain than in the susceptible strain. The purified AChE from the field strain was 17- to 345-fold less sensitive than that from the susceptible strain to inhibition by carbamates (carbaryl, eserine, methomyl, and bendiocarb) and organophosphates (methyl paraoxon and paraoxon), insensitivity being highest toward carbaryl. The results further support the notion that insensitive AChE played an important role in the insecticide resistance observed in the field strain.     

Status of insecticide resistance in Culex pipiens field populations from north-eastern areas of Italy before the withdrawal of OP compounds

BACKGROUND: Heavy and constant use of organophosphorus (OP) larvicides selected Culex pipiens L. resistant populations through two main mechanisms of genetic resistance, the increased activity of detoxifying esterase and the production of alterate acetylcholinesterase‐1 (AChE1) by G119S mutation. The aim of this study was the assessment of the distribution of Cx. pipiens populations resistant to temephos and chlorpyrifos in the north‐eastern regions of Italy and the occurrence of the insensitive AChE in these populations. Data describe the situation in the last years before European legislation prohibited the use of OP larvicides in mosquito control, up until 2007. RESULTS: For the first time a high level of OP resistance in the samples from Ravenna (182‐fold, 80% A4/B4 or A5/B5 esterases and 38.3% Ester⁵), Emilia Romagna region, was detected; therefore, new data from the Veneto and Friuli Venezia Giulia regions were obtained and reinforced existing knowledge about resistance previously studied along the Adriatic coast. Nearby, in the Villa Verucchio locality, the highest (87.5%) AChE1R was found. CONCLUSION: Cx. pipiens resistance esterases A5/B5 and A4/B4 spread southward along the Adriatic coastal plain while OPs were being used in mosquito control, as confirmed by the first molecular screening of the AChE1 gene in these populations. Copyright © 2010 Society of Chemical Industry     

A comparative study of the reactivity of acetylcholnesterases of the cattle tick Boophilus microplus and cattle erythrocytes with organophosphorus and carbamate inhibitors

The kinetic constants, K_a (affinity) k₊₂ (acylation), k_a (second order, acylation), and k₊₃ (deacylation) were determined for the reaction of a number of organophosphorus (OP) and carbamate inhibitors with acetylcholinesterase (AChE) from inhibitor-sensitive Yeerongpilly (Y) OP susceptible ticks, relatively insensitiveBiarra (B) and Ridgelands (R) OP-resistant ticks and bovineerythrocytes (Bov). B, R, and Bov AChE exhibited lower affinity for inhibitors than Y AChE. K₊₂ (carbamylation and phosphorylation) decreased in the order Bov ? Y ? B ? R. For inhibitors with markedly different leaving groups there was no clear-cut linear relationship between rates of alkaline hydrolysis and enzymatic hydrolysis (acylation). Decarbamylation and dephosphorylation were rate limiting. The ratios of Y to B to R AChE for V_max and catalytic center activity (substrate hydrolysis) and k₊₃ (carbamate hydrolysis) were very similar. This was a requirement if a lowered deacylating ability was the cause of the reduced catalytic hydrolysis of substrate observed for B and R AChE. Changes to the catalytic sites of B and R AChE are discussed. A strong parallel of these results is drawn with those obtained for spider mite AChE.     

Diagnosis and characterization of insecticide-insensitive acetylcholinesterase in three populations of the sweetpotato whitefly Bemisia tabaci

A biochemical approach was used to characterize acetylcholinesterase (AChE) insecticide insensitivity in several sweetpotato whitefly (Bemisia tabaci; SPW) populations. Discriminating doses of insecticide were established to differentiate between sensitive and insensitive SPW strains and to genotype individual whitefly. This technique was then used to examine the frequency of insensitive AChE alleles in several SPW populations and to isolate a line homozygous for insensitive AChE from a heterogenous B-type population. Inheritance of putative altered AChE genotypes was consistent with the proposed haplo-diploid status of B. tabaci. This biochemical diagnostic was also employed to determine the role of insensitive AChE in the observed resistance profiles of several laboratory populations subjected to different selection regimes. In keeping with previous studies on insecticide resistance in SPW, resistance does not appear to be uniquely associated with the B-type but rather with SPW populations found in crop systems. © 1998 SCI.     

Comparison of acetylcholinesterase from three field populations of Liposcelis paeta Pearman (Psocoptera: Liposcelididae): Implications of insecticide resistance

The toxicological and biochemical characteristics of acetylcholinesterases (AChE) in Liposcelis paeta Pearman were investigated in three field populations collected from Nanyang city of Henan Province (NY), Wuzhou (WZ) and Hezhou (HZ) Cities of Guangxi Province, China. The result of bioassay showed that the LC_50s of the NY (281.4802 mg/m²) and the WZ (285.0655 mg/m²) to dichlorvos were 1.156-fold and 1.171-fold higher than that of the HZ (243.5197 mg/m²), respectively. Compared to NY population, the activity per insect and the specific activity of AChE in WZ and HZ populations were significantly higher, and significant kinetic differences among the three populations were also observed. The apparent Michaelis–Menten constant (K_m) for acetylthiocholine iodide (ATChI) was obviously lower in NY than that in WZ and HZ populations, indicating a higher affinity to the substrate ATChI in the NY population. The affinity to the substrate ATChI between WZ and HZ population was also significantly different. As for V_max, the values of WZ and HZ populations were significantly greater when compared to that for NY population, suggesting a possible over expression of AChE in the former two populations. The inhibition studies of AChE indicated that paraoxon-ethyl, demeton-S-methyl, carbaryl, and eserine all possessed some inhibitory effects on AChE in L. paeta. The results of I_50S suggested that when compared to the other two populations, while AChE from HZ population was less sensitive to paraoxon-ethyl and demeton-S-methyl. The contradiction with the result of the bioassay might be due to the different insecticides used in the bioassay. Although both carbaryl and eserine had excellent inhibitory effects, there was no significant difference among the three populations. The statistical analysis of the bimolecular rate constants (k_i) was consistent with the above situation that carbamates expressed remarkable inhibitory effects. It was noticeable that NY population was most sensitive to carbaryl while least to eserine. The differences in AChE among three populations may attribute to the difference in control practices for psocids between Henan and Guangxi Provinces.     

Thermal effects on the development of <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis> (Hendel) (Diptera: Tephritidae) and model validation in Taiwan

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a major polyphagous insect pest with a worldwide distribution. The effects of temperature on stage-specific development in B. dorsalis were investigated at eight constant temperatures (13.0 °C, 14.4 °C, 16.2 °C, 19.5 °C, 23.8 °C, 27.7 °C, 31.8 °C and 34.8 °C). B. dorsalis developed successfully from the egg stage to the adult stage at all the tested temperatures, except at the lowest temperatures (13.0 °C and 14.4 °C). Stage-specific lower developmental thresholds and thermal constants were determined using linear regression. The lower and higher temperature threshold (TL and TH, respectively) were estimated using the Sharpe-Schoolfield-Ikemoto model. The lower developmental threshold and thermal constant from egg to adult emergence were 9.8 °C and 325.5 degree-days, respectively. The intrinsic optimum temperatures of the egg, larval, pupal and egg to pupal stage were 20.7 °C, 21.8 °C, 21.1 °C, and 22.4 °C, respectively. The temperature range of the B. dorsalis total immature stage from TL to TH was 20.4 °C (13.8 °C - 34.2 °C). The stage-specific developmental completion of B. dorsalis was determined using a two-parameter Weibull function. The daily adult emergence frequency of B. dorsalis was estimated in relation to adult age and temperature using non-linear developmental rate functions and the Weibull function. The date of cumulative 50% adult emergence estimated using non-linear functions was approximately one day earlier than the experimentally observed date. Thermal performance was compared among B. dorsalis populations from different locations.     

Molecular and biochemical mechanisms of organophosphate resistance in laboratory-selected lines of the oriental fruit fly (Bactrocera dorsalis)

Genetic and biochemical factors leading to resistance to various organophosphate (OP) based insecticides were studied in lines selected for OP-resistance in the oriental fruit fly Bactrocera dorsalis. Lines were separately selected for resistance to naled, trichlorfon, fenitrothion, fenthion, formothion, and malathion. Overall, these lines showed increased resistance ratios ranging from 13.7- to 814-fold relative to a susceptible (S) line. Also, in these newly selected lines the same three point mutations in the ace gene, previously identified in resistance studies and designated as I214V, G488S and Q643R, were found. As expected, the enzyme from the resistant lines showed lower overall activity and reduced sensitivity to inhibition by fenitrothion, methyl-paraoxon and paraoxon compared to the wild type acetylcholinesterase (AChE) enzyme. The apparent V_max values for esterase from the resistant lines were 1.2-3.69 times higher than that of the S line. Although only the naled-, trichlorfon- and fenthion-r lines showed lower esterase affinities (based on apparent K_m values) compared with the S line, all of the V_max/K_m ratios were higher in the resistant lines compared to that of the S line. The OP-resistant lines also displayed an overall similar pattern of isozyme expression, except for one additional band found only in the naled-r line and one band that was absent in the trichlorfon-, malathion-, and fenthion-r lines. Our results also show that overall, multiple examples of high OP resistance in selected lines of B. dorsalis exhibiting the same genetic alterations in the ace gene seen previously resulted in different effects on esterase enzyme activity in relation to various OP compounds.     

Triazophos resistance mechanisms in the rice stem borer (Chilo suppressalis Walker)

A field population of the rice stem borer (Chilo suppressalis Walker) with 203.3-fold resistance to triazophos was collected. After 8-generation of continuous selection with triazophos in laboratory, resistance increased to 787.2-fold, and at the same time, the resistance to isocarbophos and methamidophos was also enhanced by 1.9- and 1.4-fold, respectively, implying some cross-resistance between triazophos and these two organophosphate insecticides. Resistance to abamectin was slightly enhanced by triazophos selection, and fipronil and methomyl decreased. Synergism experiments in vivo with TPP, PBO, and DEM were performed to gain a potential indication of roles of detoxicating enzymes in triazophos resistance. The synergism results revealed that TPP (SR, 1.92) and PBO (SR 1.63) had significant synergistic effects on triazophos in resistant rice borers. While DEM (SR 0.83) showed no effects. Assays of enzyme activity in vitro demonstrated that the resistant strain had higher activity of esterase and microsomal O-demethylase than the susceptible strain (1.20- and 1.30-fold, respectively). For glutathione S-transferase activity, no difference was found between the resistant and the susceptible strain when DCNB was used as substrate. However, 1.28-fold higher activity was observed in the resistant strain when CDNB was used. These results showed that esterase and microsomal-O-demethylase play some roles in the resistance. Some iso-enzyme of glutathione S-transferase may involve in the resistance to other insecticides, for this resistant strain was selected from a field population with multiple resistance background. Acetylcholinesterase as the triazophos target was also compared. The results revealed significant differences between the resistant and susceptible strain. The V_max and K_m of the enzyme in resistant strain was only 32 and 65% that in the susceptible strain, respectively. Inhibition tests in vitro showed that I₅₀ of triazophos on AChE of the resistant strain was 2.52-fold higher. Therefore, insensitive AChE may also involved in triazophos resistance mechanism of rice stem borer.     

Synergism of resistance to phosalone and comparison of kinetic properties of acetylcholinesterase from four field populations and a susceptible strain of Colorado potato beetle

The susceptibility to phosalone and biochemical characteristics of acetylcholinesterase (AChE) were compared between susceptible (SS) strain and four field populations of Colorado potato beetle (CPB) collected from commercial potato fields of Hamedan Province in west of Iran. Bioassays involving topical application of phosalone to fourth instars revealed up to 252 fold resistance in field populations compared with the SS strain. Synergism studies showed that although esterase and/or glutathione S-transferase metabolic pathways were present and active against phosalone, they were not selected for and did not have a major role in resistance. It is likely that piperonyl butoxide (PBO) reduced phosalone toxicity by inhibiting bio-activation of phosalone. The affinity (K_m) and hydrolyzing efficiency (V_max) of AChE to selected substrates, namely, acetylthiocholine iodide (ATC), propionylthiocholine iodide (PTC), and butyrylthiocholine iodide (BTC) were examined. AChE inhibition by higher substrate concentration was evident only in the SS strain. In resistant field populations, Aliabad (Aa), Bahar (B) and Dehpiaz (Dp), substrate inhibition at higher concentrations was not seen. There was no definite optimal concentration found for any of the substrates examined. When ATC, PTC, and BTC were used as substrate, the reaction rates of AChE from Yengijeh (Yg) population increased as the concentration of all three substrates were increased, but were almost constant at concentration of ATC ? 3.98, PTC ? 2.8, and BTC ? 5 mM. The susceptible form of AChE had the most efficient ATC hydrolysis but very low BTC hydrolysis activity. In contrast, AChEs from field populations elicited relatively reduced ATC hydrolysis, but relatively increased BTC hydrolysis. The in vitro inhibition potency of some organophosphates (OPs), on AChEs of the field populations and SS strain was determined. The rank order from the most potent inhibitor to the least as determined by their bimolecular reaction constants (K_i) was ethyl paraoxon > diazoxon > methyl paraoxon for AChE from Aa, B, Dp, and Yg populations, respectively, whereas the rank order for the susceptible strain was methyl paraoxon > ethyl paraoxon > diazoxon.     

Phosphine-induced walking response of the lesser grain borer (Rhyzopertha dominica)

BACKGROUND: In spite of the intensive worldwide use of phosphine against stored-product insects, its potential sublethal effects on targeted insect species is seldom recognised and may compromise the efficacy of this fumigant, particularly against phosphine-resistant insects. Therefore, the behavioural response of three populations of the lesser grain borer Rhyzopertha dominica (Coleoptera: Bostrichidae) to sublethal phosphine exposure was assessed. RESULTS: Concentration-mortality bioassays with phosphine confirmed the resistance status of the insect populations studied, with levels of phosphine resistance of 40.8-fold and 85.7-fold compared with the susceptible population. Regarding walking behaviour, determined using a digital video-tracking system, the phosphine-resistant populations were less active than the susceptible population. In addition, sublethal phosphine exposure decreased the walking activity of all three populations. CONCLUSION: Phosphine exposure decreased walking ativity. Such reduced walking activity is likely to lower the respiration rate, thereby minimising phosphine uptake. As higher phosphine resistance was also associated with reduced walking activity, phosphine-resistant populations may resist phosphine fumigation even more efficiently on account of this behavioural trait, further aiding their physiological resistance, and should be a matter of concern. Copyright © 2012 Society of Chemical Industry     

Insecticide resistance status of the codling moth Cydia pomonella (Lepidoptera: Tortricidae) from Greece

The codling moth Cydia pomonella L. is controlled mostly with chemical insecticides in Greece and control failures have been reported. However, there are no insecticide resistance studies in the country as yet. We examined the insecticide resistance status of 33 and 38 populations of fifth-instar non-diapausing and diapausing larvae, respectively by applying bioassays, biochemical and DNA diagnostics. Diagnostic concentrations of azinphos-methyl, phosalone, deltamethrin, thiacloprid, fenoxycarb, tebufenozide, methoxyfenozide and diflubenzuron were used in bioassays. Almost all populations showed reduced susceptibility to at least one insecticide and approximately half of them to all insecticides examined compared to a laboratory susceptible strain used as reference. However, only one out of six populations tested showed reduced susceptibility in ovicidal tests with fenoxycarb. Cross-resistances were observed among most insecticides, except from the pairs fenoxycarb–phosalone and thiacloprid–phosalone, in non-diapausing larvae. The more obvious biochemical marker associated with the reduced susceptibility observed in both larval instars was elevated cytochrome P₄₅₀ polysubstrate monooxygenases activity, followed by elevated glutathione-S-transferase activity and reduced carboxylesterases activity. Neither sodium channel nor AChE known resistance mutations were found in any of the approximately 1000 individuals of each larval instar screened with diagnostic PCR. Actions for Integrated Resistance Management and application of alternative control methods are discussed.     

Target site insensitivity and mutational analysis of acetylcholinesterase from a carbofuran-resistant population of Colorado potato beetle, Leptinotarsa decemlineata (Say)

The BERTS strain of Colorado potato beetle (CPB) was found to be highly resistant to N-methyl carbofuran but relatively susceptible to azinphosmethyl. N-Methyl carbofuran resistance was found to correlate well with acetylcholinesterase (AChE) insensitivity. In becoming resistant to N-methyl carbofuran, the AChE of the BERTS strain became more sensitive to N-propyl carbofuran inhibition. This negative cross-insensitivity correlated well to the increased relative toxicity of the BERTS strain to N-propyl carbofuran compared to the susceptible SS strain. BERTS beetles were sorted into BERTS-R and BERTS-S substrains using their AChE activity profiles. Sequence comparisons of AChE cDNAs from the two substrains revealed the presence of the point mutation that results in the S291G substitution previously found in the AChE of the azinphosmethyl-resistant AZ-R strain of CPB. A novel mutation present only in BERTS-S CPB, however, resulted in an additional I392T substitution in the AChE and apparently reverses the resistance conferring properties of the S291G substitution.     

Mapping of clubroot (Plasmodiophora brassicae) resistance in canola (Brassica napus)

Clubroot disease, caused by Plasmodiophora brassicae, has become a major problem in the production of cruciferous crops worldwide. In this study, a population of 121 doubled haploid (DH) lines derived from a crossing between a resistant and a susceptible canola (Brassica napus) genotype was subjected to phenotypic and genotypic studies to determine the inheritance and location of the resistance gene(s). After inoculation with pathotype 3 of P. brassicae, the lines showed a 1:1 segregation ratio for resistance, indicating that resistance in this population is controlled by a single gene. Fifteen PCR‐based markers that were known to be linked to clubroot resistance (CR) genes were screened against genomic DNA from parents and resistant and susceptible bulks. Marker GC1680, linked to the CR gene CRa, exhibited polymorphism between the parents and between the resistant and susceptible bulks. CRa target primers were used to amplify fragments from the two parents and the resultant sequences were compared. A high degree of sequence similarity was found between the parents in the nucleotide binding site domain of CRa. In contrast, sequence polymorphisms were detected in the leucine‐rich repeat (LRR) domain. One pair of primers that amplify a band from the LRR region of the resistant parent but not the susceptible parent was used to screen the DH population. Amplicons were obtained from 60 of the 61 resistant lines and two of the 60 susceptible lines; thus, three recombinants were found. Based on these results, a resistance locus linked to CRa was found.     

Insecticide resistance status of Aedes aegypti (L.) from Colombia

BACKGROUND: To evaluate the insecticide susceptibility status of Aedes aegypti (L.) in Colombia, and as part of the National Network of Insecticide Resistance Surveillance, 12 mosquito populations were assessed for resistance to pyrethroids, organophosphates and DDT. Bioassays were performed using WHO and CDC methodologies. The underlying resistance mechanisms were investigated through biochemical assays and RT‐PCR. RESULTS: All mosquito populations were susceptible to malathion, deltamethrin and cyfluthrin, and highly resistant to DDT and etofenprox. Resistance to lambda‐cyhalothrin, permethrin and fenitrothion ranged from moderate to high in some populations from Chocó and Putumayo states. In Antioquia state, the Santa Fe population was resistant to fenitrothion. Biochemical assays showed high levels of both cytochrome P450 monooxygenases (CYP) and non‐specific esterases (NSE) in some of the fenitrothion‐ and pyrethroid‐resistant populations. All populations showed high levels of glutathione‐S‐transferase (GST) activity. GSTe2 gene was found overexpressed in DDT‐resistant populations compared with Rockefeller susceptible strain. CONCLUSIONS: Differences in insecticide resistance status were observed between insecticides and localities. Although the biochemical assay results suggest that CYP and NSE could play an important role in the pyrethroid and fenitrothion resistance detected, other mechanisms remain to be investigated, including knockdown resistance. Resistance to DDT was high in all populations, and GST activity is probably the main enzymatic mechanism associated with this resistance. The results of this study provide baseline data on insecticide resistance in Colombian A. aegypti populations, and will allow comparison of changes in susceptibility status in this vector over time. Copyright © 2011 Society of Chemical Industry     

Non-target-site-based resistance to ALS-inhibiting herbicides in six Bromus rigidus populations from Western Australian cropping fields

BACKGROUND: Bromus rigidus is a common weed species that has increased in cropping fields owing to limited control options. During a random field survey in Western Australia, six B. rigidus populations that had survived in‐crop weed control programmes were collected. The study aimed to determine the resistance profile of these six populations. RESULTS: Based on dose–response studies, all six B. rigidus populations had a low‐level resistance to sulfosulfuron and sulfometuron (both sulfonylurea herbicides) while remaining susceptible to herbicides with other modes of action. ALS in vitro activity assays revealed no differences in enzyme sensitivity between susceptible and resistant populations, while the use of malathion (a cytochrome P450 inhibitor) in combination with sulfosulfuron caused the resistant populations to behave like the susceptible population. CONCLUSION: This study established that these six B. rigidus populations have a low‐level resistance to the ALS‐inhibiting sulfonylurea herbicides, but are able to be controlled by other herbicide modes of action. The low‐level, malathion‐reversible resistance, together with a sensitive ALS, strongly suggest that a non‐target‐site enhanced metabolism is the mechanism of resistance. Copyright © 2012 Society of Chemical Industry     

Metabolic resistance mechanisms to phosalone in the common pistachio psyllid, Agonoscena pistaciae (Hem.: Psyllidae)

The common pistachio psyllid, Agonoscena pistaciae, is the most damaging pest of pistachio in Iran, and is generally controlled by insecticides belonging to various classes especially, phosalone. The toxicity of phosalone in nine populations of the pest was assayed using the residual contact vial and insect-dip methods. The bioassay results showed significant discrepancy in susceptibility to phosalone among the populations. Resistance ratio of the populations to the susceptible population ranged from 3.3 to 11.3. The synergistic effects of TPP, PBO and DEM were evaluated on the susceptible and the most resistant population to determine the involvement of esterases, mixed function oxidases and glutathione S-transferases in resistance mechanisms, respectively. The level of resistance to phosalone in the resistant population was suppressed by TPP, PBO and DEM, suggesting that the resistance to phosalone is mainly caused by esterase detoxification. Biochemical enzyme assays revealed that esterase, glutathione S-transferase and cytochrome P450 monooxygenase activities in the resistant population was higher than that in the susceptible. Glutathione-S-transferases play a minor role in the resistance of the pest to phosalone.