Biochemical characterization and purification of esterases from three strains of German cockroach,Blattella germanica (Dictyoptera: Blattellidae)

Three strains of German cockroach, Blattella germanica (L.) showed varying levels of resistance to chlorpyrifos, methyl parathion, propoxur, bendiocarb, and cypermethrin. The general esterase activity was at least twofold higher than susceptible strain. The subcellular distribution studies revealed that the majority of the esterase activity is present in the 100,000g cytosolic fraction. Only a small portion of the activity was membrane bound. Using non-denaturing gel electrophoresis, ten isozymes were identified in German cockroaches. These isozymes were isolated individually from the gels and analyzed for differences in activity. The isozymes E5, E6, and E7 of resistant strains had significantly higher specific activities when compared with the susceptible strain. The purification process using various column chromatography and preparative gel electrophoresis resulted in 9–11% of total esterase recovery. About double the amount of E6 was recovered from the resistant strains when compared with the susceptible strain. Kinetic analyses of E6 did not indicate differences in K_m and V_max values between the resistant and susceptible strains. Also, inhibition of esterase activity by paraoxon, chlorpyrifos, and propoxur did not suggest any structural differences in esterase E6 between strains. The results suggest that the increased production of E6 esterase contributes to insecticide resistance in German cockroaches. The role of E6 may be sequestration of toxic molecules rather than hydrolysis. © 1996 Wiley-Liss, Inc.     

Biochemical characterization of hydrolytic and oxidative enzymes in insecticide resistant and susceptible strains of the German cockroach (Dictyoptera: Blattellidae).

We have identified resistance mechanisms in the German cockroach, Blattella germanica (L.), for propoxur and chlorpyrifos in strains of cockroaches that display multiresistance to several organophosphate and carbamate insecticides. The resistance mechanisms involve the combined effects of increased oxidative and hydrolytic metabolism and both strains are resistant to chlorpyrifos and propoxur. Experiments designed to test for similarity in metabolic enzymes suggest that, although the mechanisms involve similar processes, the enzymes responsible for insecticide detoxification are different in the two strains. Both resistant strains exhibited enhanced activity toward alpha-naphtholic esters relative to a standard susceptible strain; however, analysis of the progeny from resistant X susceptible crosses suggests that this general esterase activity is inherited differently than propoxur or chlorpyrifos resistance. Hybrids of the propoxur-resistant strain displayed the highest activity of all cockroaches tested, in contrast to hybrids of the chlorpyrifos-resistant strain, which were similar to the susceptible strain. Native gel electrophoresis of cytosolic preparations provided further evidence for differences in the pattern of hydrolytic enzymes and inheritance of resistance in the two strains. Analysis of components of the cytochrome P450-dependent monooxygenase system and activities toward model substrates indicate that the two resistance mechanisms also involve different oxidative processes. The propoxur-resistant strain displayed significantly higher levels of total cytochrome P450, but no other components were correlated with resistance. In contrast with the chlopyrifos-resistant strain, which was similar to the susceptible strain in all parameters measured, activity toward model substrates was higher in the propoxur-resistant strain than in any of the other strains and hybrids tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

Strain differences in the response of German cockroaches (Dictyoptera: Blattellidae) to emulsifiable concentrates.

The response of a susceptible and two pyrethroid-resistant field strains of the German cockroach, Blattella germanica, to four emulsifiable concentrates (ECs)--Tempo (cyfluthrin), Demon (cypermethrin), Dursban (chlorpyrifos) LO, and XRM 5184 (chlorpyrifos)--was investigated. Application rates were 0.4, 0.1, 0.5, and 0.5%, respectively. Susceptible cockroaches avoided dried formulations of the pyrethroids Tempo and Demon, but resistant cockroaches did not; avoidance was greater with Demon than with Tempo. Filter papers freshly impregnated (wet) with Demon and Tempo flushed susceptible cockroaches (Demon greater than Tempo). Resistant cockroaches were flushed only by Demon, but less so than susceptible strain cockroaches. No mortality occurred in experiments with the pyrethroids. Dried formulations of Dursban LO and XRM 5184 had little, if any, repellency to nymphs of either the susceptible or resistant strains. Initially (1-3 h), most cockroaches settled on treated papers. Subsequent movement off treated papers was a step in the process leading to knockdown. At 24 h, mortality of susceptible cockroaches was 100% in the experiment with Dursban LO and 95% in the experiment with XRM 5184. Highest mortality in a resistant strain (40%) was in the contact experiment with Dursban LO. In contact repellency and flushing experiments, mortality was higher with Dursban LO than with XRM 5184. Neither chlorpyrifos formulation flushed cockroaches effectively. Mortality in flushing experiments was less than in the contact repellency experiments.     

Role of esterase enzymes in monitoring for resistance of California red scale, Aonidiella aurantii (Homoptera: Diaspididae), to organophosphate and carbamate insecticides

Eighty-seven populations of California red scale, Aonidiella aurantii (Maskell), from the San Joaquin Valley of California were tested for insecticide resistance by using chlorpyrifos, methidathion, and/or carbaryl in a standard fruit-dip bioassay as well as for general esterase activity by using alpha-naphthyl acetate as a substrate in a colorimetric test. The percentage of individuals that survived a discriminating concentration of methidathion, chlorpyrifos, or carbaryl was significantly correlated with the percentage of individuals showing > 0.4 nmol of esterase activity per minute per microgram of protein in the colorimetric test. Scale survival of the organophosphates showed a higher correlation with esterase activity than survival of carbaryl. These results suggest that the colorimetric test of esterase activity is useful as an indicator of the frequency of organophosphate-resistant and, to a lesser extent, carbamate-resistant individuals in California red scale populations. The results of tests for activity and inhibition of acetylcholinesterase activity suggest that California red scale is using increased amounts of esterase enzymes, including acetylcholinesterase, to sequester organophosphate and carbamate insecticides, rather than modified acetylcholinesterase. Third instars collected from twigs, leaves, and fruit showed similar levels of esterase activity. The colorimetric test of esterase activity is a useful tool to detect organophosphate and carbamate resistance in San Joaquin Valley California red scale because of its speed of testing over a wide range of months, allowing for within-season decision making by citrus growers.     

Alterations in esterases are associated with malathion resistance in Habrobracon hebetor (Hymenoptera: Braconidae)

Biochemical mechanisms of malathion resistance were investigated in a malathion-resistant strain of the parasitoid Habrobracon hebetor Say collected from a farm storage in Kansas. General esterase activities were significantly lower in the resistant strain compared with those in a susceptible strain. However, no significant differences were found in activities of malathion specific carboxylesterase (MCE), glutathione S-transferase and cytochrome P450 dependent O-demethylase activities, cytochrome P450 contents, and sensitivity of acetylcholinesterase to inhibition by malaoxon between the 2 strains. Because MCE was not elevated in the resistant strain, the weak malathion resistance in H. hebetor may result from a different mechanism compared with that hypothesized for some insect species in which reduced general esterase activity is accompanied by an elevated MCE. Decreased esterase activity in the resistant strain suggested that null alleles of some esterases were associated with the resistance. Indeed, E1 and E2, major esterases in the susceptible strain, were not present in the resistant strain on polyacrylamide gels that were stained for esterase activity using the model substrate 1-naphthyl acetate. In contrast, the activity of esterase E3 on the gels was much higher in the resistant strain as compared with that of the susceptible strain. These findings indicate that malathion resistance in H. hebetor is associated with both an increased activity of the esterase E3 and null alleles of the esterases E1 and E2.     

Extracellular Enzyme Activities during Lignocellulose Degradation by Streptomyces spp.: A Comparative Study of Wild-Type and Genetically Manipulated Strains

The wild-type ligninolytic actinomycete Streptomyces viridosporus T7A and two genetically manipulated strains with enhanced abilities to produce a water-soluble lignin degradation intermediate, an acid-precipitable polymeric lignin (APPL), were grown on lignocellulose in solid-state fermentation cultures. Culture filtrates were periodically collected, analyzed for APPL, and assayed for extracellular lignocellulose-catabolizing enzyme activities. Isoenzymes were analyzed by polyacrylamide gel electrophoresis and activity staining on the gels. Two APPL-overproducing strains, UV irradiation mutant T7A-81 and protoplast fusion recombinant SR-10, had higher and longer persisting peroxidase, esterase, and endoglucanase activities than did the wild-type strain T7A. Results implicated one or more of these enzymes in lignin solubilization. Only mutant T7A-81 had higher xylanase activity than the wild type. The peroxidase was induced by both lignocellulose and APPL. This extracellular enzyme has some similarities to previously described ligninases in fungi. This is the first report of such an enzyme in Streptomyces spp. Four peroxidase isozymes were present, and all catalyzed the oxidation of 3,4-dihydroxyphenylalanine, while one also catalyzed hydrogen peroxide-dependent oxidation of homoprotocatechuic acid and caffeic acid. Three constitutive esterase isozymes were produced which differed in substrate specificity toward α-naphthyl acetate and α-naphthyl butyrate. Three endoglucanase bands, which also exhibited a low level of xylanase activity, were identified on polyacrylamide gels as was one xylanase-specific band. There were no major differences in the isoenzymes produced by the different strains. The probable role of each enzyme in lignocellulose degradation is discussed.     

Screening of tropical fungi producing polyethylene terephthalate-hydrolyzing enzyme for fabric modification

Microfungi were selectively isolated for production of polyethylene terephthalate (PET) fiber-degrading enzymes potentially to be used to modify the surface of polyester fabric. A range of fungi were isolated from plant surfaces and soil samples using a polycaprolactone (PCL) plate-clearing assay technique, and screened for cutinolytic esterase (cutinase) activity. Twenty-two of 115 isolates showed clearing indicating the production of cutinase. The ability of the fungi to produce cutinase in mineral medium (MM) using either potato suberin or PET (1 cm of untreated pre-washed PET fiber) fiber as substrates was assessed based on the hydrolysis of p-nitrophenyl butyrate (p-NPB). All isolates exhibited activity towards p-NPB, isolate PBURU-B5 giving the highest activity with PET fiber as an inducer. PBURU-B5 was identified as Fusarium solani based on its conidial morphology and also nucleotide sequencing from internal transcribed spacer region of the ribosomal RNA gene (rDNA-ITS). Enzymatic modification of PET cloth material properties using crude enzyme from strain PBURU-B5 showed hydrolysis of ester bonds of the PET fiber. The modification of the PET fabric resulted in increase of water and moisture absorption, and general enhancement of hydrophilicity of the fabric, properties that could facilitate processing of fabric ranging from easier dyeing while also yielding a softer feeling fabric for the user.     

Pirimiphos-methyl resistance in two stored product mites, Acarus siro and Acarus farris, as detected by impregnated paper bioassay and esterase activity assays

The response to pirimiphos-methyl, in one strain of Acarus farris and two strains of Acarus siro, was assessed using an impregnated filter paper bioassay and by the selection of adults following exposure to pirimiphos-methyl. It was concluded that one of the strains of A. siro was resistant to pirimiphos-methyl and that a major resistance mechanism was involved. The second strain of A. siro gave a response similar to that of a laboratory strain unexposed to organophosphates and was considered to be susceptible. The A. farris strain responded to selection at the ED50 but not at the ED99, and it was concluded that a minor resistance mechanism is present in this strain. Assays of esterase activity were used to attempt to identify the biochemical mechanisms involved in the resistance detected by the bioassays. The A. farris and susceptible A. siro strains showed similar levels of esterase activity but the esterase activity of the resistant A. siro strain was significantly greater. An increase in esterase activity followed selection of both the A. farris strain and the resistant A. siro strain. An acetylcholinesterase assay showed no significant difference between the susceptible and pirimiphos-methyl selected strains of A. siro. The results suggest that esterases are involved in the resistance to pirimiphos-methyl found in A. siro and A. farris but that in A. siro, at least, other mechanisms may also be present.     

Pharmacodynamics of malathion and carbaryl in susceptible and multiresistant German cockroaches (Dictyoptera: Blattellidae)

Studies with malathion and carbaryl were done to compare toxicity; absorption, metabolism, internal accumulation, and excretion; and in vivo inhibition of acetylcholinesterase (AChE) after topical applications to adult male susceptible (S, Orlando normal) or multiresistant (R, HRDC) German cockroaches, Blattella germanica (L.). Compared with the S strain, R cockroaches were highly resistant to malathion (about 33-fold) and only moderately resistant or tolerant to carbaryl (about 5-fold). Tests with topically applied 14C-labeled malathion and carbaryl indicated that both compounds penetrated rapidly and radioactive products were readily excreted. Rates of absorption or excretion in S and R strains did not differ significantly. Both insecticides were extensively metabolized; each yielded the same array and similar concentrations of metabolites in insects from either strain. In contrast, metabolic detoxification of malathion and carbaryl was significantly greater in R cockroaches when the insects were treated by injection. Strains did not differ significantly in the in vitro inhibition of brain AChE by either malaoxon or carbaryl. However, dramatic differences were observed between strains in the in vivo inhibition of AChE during a 6-h test period after topical treatment with malathion, and moderate but significant differences occurred between strains in the in vivo inhibition of AChE by carbaryl. These data suggest that the strong resistance to malathion and moderate resistance or tolerance to carbaryl in R cockroaches is probably a result of enhanced capability for metabolic detoxification.     

氟化物对家蚕耐氟和氟化物敏感品种幼虫中肠羧酸酯酶及全酯酶活性的影响

为了探讨氟化物在家蚕Bombyx mori体内的代谢途径, 以家蚕耐氟品种T6和氟化物敏感品种734为研究材料, 在5龄幼虫1-7 d内分别添食经50, 100, 200和400 mg/kg NaF溶液浸泡后的新鲜桑叶, 检测家蚕中肠羧酸酯酶（CarE）和全酯酶活性的变化。结果表明： 734添氟组的CarE活性是对照组的1.21~1.98倍, 而T6添氟组约是对照组的0.72~1.10倍。734和T6添氟组的全酯酶活性数值变化规律与其各自对照组相似, 且2品种之间的酶活性数值很相近。2品种在相同浓度下, 不同天数之间的全酯酶活性差异均显著（P＜0.05）。推测氟化物对敏感家蚕中肠CarE有促进作用, 对耐氟家蚕中肠CarE有抑制作用, 但是对全酯酶活性影响不大。     

Effect of synergists on the oral and topical toxicity of azamethiphos to organophosphate-resistant houseflies (Diptera: Muscidae).

Dermal and oral toxicities of azamethiphos were determined in two organophosphate-resistant and one susceptible strain of houseflies, Musca domestica L. The 594vb strain was 1,967-fold more resistant to azamethiphos when compared with the susceptible Chemical Specialties Manufacturers Association (CSMA) strain by dermal application. When the compound was administered orally to the 594vb strain, we observed only a 15-fold resistance. In contrast, the Yachiyo strain, which show 1,500-fold resistance to diazinon and which has known multiple mechanisms for organophosphate resistance, showed only 6-fold resistance to azamethiphos by topical application and 4-fold resistance by oral administration. Azamethiphos administered dermally and orally was equally toxic to the CSMA and Yachiyo strains. However, when azamethiphos was administered to the 594vb strain, the insecticide was 71 times more toxic orally than by the dermal route. This result indicated involvement of a cuticular penetration factor in the resistance mechanism. The effect on azamethiphos toxicity of piperonyl butoxide (PB), an inhibitor of the monooxygenases, and tributylphosphorotrithioate (DEF), an esterase inhibitor, was investigated in the three strains. Pretreatment of the flies with PB, DEF, or PB+DEF before topical application of azamethiphos resulted in a significant decrease in LD50s in all the strains. The degree of synergism, however, varied depending upon the strains and the synergists. Similar results were obtained when azamethiphos was administered orally following pretreatment of the flies with PB+DEF. We attribute the high level of azamethiphos resistance in the 594vb strain partly to increased degradation by oxidative and hydrolytic enzymes. The hydrolytic enzymes are more important, but other factors including reduced cuticular penetration and insensitive acetylcholinesterase may be involved.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced activation is the mechanism of negative cross-resistance to Chlorpyrifos in the Dicofol-IR strain of Tetranychus urticae (Acari: Tetranychidae).

The mechanism responsible for negative cross-resistance to chlorpyrifos was examined in isogenic dicofol susceptible (Orchard-12) and resistant (Dicofol-IR) two-spotted spider mites, Tetranychus urticae Koch. The acetylcholinesterase of both strains was equally sensitive to inhibition by chlorpyrifos oxon. However, the Dicofol-IR strain showed increased oxidative activation of chlorpyrifos to chlorpyrifos oxon relative to the Orchard-12 strain, suggesting this mechanism is responsible for the observed negative cross-resistance.     

抗性品系棉蚜乙酰胆碱酯酶和羧酸酯酶的变异

用浸叶法测定了采自我国不同地区(泰安、莱阳、南京、北京和安阳)的棉蚜品系Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ对久效磷、甲胺磷、抗蚜威和灭多威等杀虫剂的抗性水平,各棉蚜品系对杀虫剂的抗性依次为Ⅴ>Ⅳ>Ⅲ,Ⅱ>Ⅰ。进一步研究表明,Ⅴ和Ⅳ品系棉蚜乙酰胆碱酯酶对杀虫剂的敏感性显著下降,Ⅱ品系次之,Ⅲ和Ⅰ品系接近于敏感品系。Ⅴ和Ⅳ品系乙酰胆碱酯酶的Km值显著下降,表明酶发生了质的变化。不同棉蚜抗性品系的酯酶（全酯酶和羧酸酯酶）活性均显著升高,其中Ⅲ品系的酯酶活力为Ⅱ品系的2倍。Ⅴ品系羧酸酯酶Km值达2460.4 μmol/L,而Ⅳ品系仅为84.4 μmol/L,该两个品系羧酸酯酶发生了质的变化。研究结果表明,不同抗性程度的棉蚜品系均存在代谢抗性和靶标抗性。低抗水平的棉蚜品系,以代谢抗性为主,靶标抗性为辅;中抗水平的棉蚜品系,抑或由于解毒代谢酶的活性显著增强,也可能由于靶标的敏感性显著下降;而高抗水平的棉蚜品系,依赖于代谢抗性和靶标抗性的联合作用。     

Electrophoretic Pattern of Larval Esterases in Field and Laboratory-selected Strains of the Tobacco Cutworm,Spodoptera litura (Fabricius)

This research was performed to find out and characterize the specific esterase isozymes related to OP and pyrethroid resistance in the tobacco cutworm Spodoptera litura (Fabricius). Two laboratory strains (DSR₅ and CSR₄) of S. litura, selected with deltamethrin and chlorpyrifos-methyl, had higher larval esterase activities than Hamancollected (HC) strain. Ten esterase isozymes were separated in the wild HC strain on 6.5% nondenaturing polyacrylamide gel electrophoresis (pH 8.3), but only 5 of them were detected in the two strains selected with insecticides. The isozymes were designated from E1 to E10 according to their mobility to cathode. E4 was stained more strongly in both laboratory-selected strains than in HC strain. The frequency of E2 in DSR₅ strain was higher than in HC strain. E2 and E4 were proved to be arylesterase and carboxyesterase, respectively, according to enzyme inhibition tests. Thus decreased number and increased intensity of esterase bands in DSR₅ and CSR₄ strain may be associated with insecticide resistance, resulting from selections successively with insecticides for several generations.     

Effects of hydroprene exposure on the physiology and insecticide susceptibility of German cockroaches (Orthoptera: Blattellidae).

We determined nonlethal physiological effects of hydroprene on the German cockroach, Blattella germanica L., and the effects of hydroprene exposure on German cockroach susceptibility to traditional insecticides. Live and dry weights of German cockroach adults exposed as nymphs to the juvenile hormone analog hydroprene increased significantly (6-35%) in both sexes. The change in weight was affected by hydroprene dose and time after adult emergence. Hydroprene treatment did not affect total body lipids and carbohydrates consistently. However, total body urates of males and females increased significantly. The susceptible and multiresistant German cockroach strains were significantly more susceptible to propoxur at the lower hydroprene application rate (0.697 mg per tub) than the untreated cockroaches. Hydroprene application also significantly lowered the LD50 for chlorpyrifos of the multiresistant strain at the lower hydroprene application rate. However, hydroprene failed to affect chlorpyrifos susceptibility of the susceptible strain.     

Overexpressed esterases in a fenvalerate resistant strain of the cotton bollworm, Helicoverpa armigera

Enhanced detoxification is the major mechanism responsible for pyrethroid resistance in Chinese populations of Helicoverpa armigera. Previous work has shown that enhanced oxidation contributes to resistance in the fenvalerate-selected Chinese strain, YGF. The current study provides evidence that enhanced hydrolysis by esterase isozymes also contributes to the resistance in this strain. The average esterase activity of third instar YGF larvae was 1.9-fold compared with that of a susceptible SCD strain. Much of this difference was attributed to isozymes at two zones which hydrolysed the model carboxylester substrate 1-naphthyl acetate and also a 1-naphthyl analogue of fenvalerate. A preparation enriched for enzymes migrating to one of these zones from YGF was shown to hydrolyse fenvalerate with a specific activity of about 2.9 nmol/min/mg. This material was also matched by mass spectrometry with four putative carboxylesterase genes, all of which clustered within a phylogenetic clade of secreted midgut esterases. Quantitative PCR on these four genes showed several-fold greater expression in tissues of YGF compared to SCD but no differences was found in the number of copies of the genes between the strains.     

Esterase B1 activity variation within and among insecticide resistant, susceptible and heterozygous strains of Culex quinquefasciatus (Diptera: Culicidae)

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.     

淡色库蚊酯酶等位基因及其在自然种群中的频率分布

酯酶基因扩增所产生的酯酶活性升高是库蚊Culex pipiens对有机磷杀虫剂抗性的主要机理之一。采用分子杂交技术和限制性酶切片段长度多态性(RFLP)分析,已鉴定出多种酯酶等位基因类型。该文通过酯酶基因特异性片段的PCR扩增及扩增片段的酶切片段分析,对淡色库蚊Culex pipiens pallens四种有机磷抗性品系的酯酶等位基因进行分型,并测定分析自然种群中不同酶型的频率分布。研究结果表明：PCR分型方法具有快速、准确的特点。不同的有机磷杀虫剂对酯酶等位基因具有明显的选择作用。双硫磷品系为B₁型;毒死蜱和敌百虫品系为B₂型;马拉硫磷品系为B₁型和B₁/B₂杂合型。不同地区采集的种群表现出不同的酶型频率分布。该文就杀虫剂对酯酶等位基因选择作用及自然种群的酶型频率分布进行了讨论。     

Characterization of esterases in malathion-resistant and susceptible strains of the pteromalid parasitoid Anisopteromalus calandrae

General esterase, malathion-specific carboxylesterase, phosphotriesterase, glutathione S-transferase, cytochrome P-450-dependent monooxygenase activity, and target site sensitivity were compared in malathion-resistant (R) and malathion-susceptible (S) strains of the parasitoid Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae). Activity against -naphthyl acetate was not significantly different in male and female wasps for either strain. General esterase activity ranged from 1.2-fold to 2.5-fold higher in the R strain compared with the S strain, but these differences between strains were not consistent. Based on V_max/K_m ratios estimated for a number of analogs of four substrates (-naphthyl acetate, β-naphthyl acetate, 4-methylumbelliferyl acetate, and p-nitrophenyl acetate) there was no evidence that general esterase activity was elevated or reduced in the R strain. Malathion-specific carboxylesterase (MCE) activity, determined by using 2,3-¹⁴C-malathion as substrate, was 10- to 30-fold higher in the R strain compared with that in the S strain. The MCE has a pH optima at about pH 7, is cytosolic, and is labile upon storage at −80°C. MCE activity could be recovered from native 10% PAGE gels and IEF–PAGE gels (pI=5.2), but the peak of MCE activity also contained the major peak of activity against -naphthyl acetate. There was no evidence for major involvement of phosphotriesterase, glutathione S-transferase, monooxygenase, or altered acetylcholinesterase in the resistance. These data suggest that an increased activity of a MCE in the R strain is the probable major mechanism conferring resistance to malathion in A. calandrae. This study provides the first characterization of a biochemical resistance mechanism in a parasitoid with a high level of resistance to an organophosphate insecticide.     

甜菜夜蛾不同龄期幼虫对药剂的敏感性及其与酶活力的关系

【目的】明确甜菜夜蛾Spodoptera exigua(Hübner)不同龄期幼虫对甲氨基阿维菌素苯甲酸盐和毒死蜱的敏感性及其与羧酸酯酶、多功能氧化酶、谷胱甘肽S-转移酶和乙酰胆碱酯酶活性的相关性。【方法】采用室内生物测定方法检测甜菜夜蛾不同龄期幼虫对药剂的敏感性,并检测了不同龄期幼虫体内羧酸酯酶、多功能氧化酶、谷胱甘肽S-转移酶和乙酰胆碱酯酶的活力。【结果】在所测定的5个龄期中,随龄期增加,敏感性逐渐降低,其中1~5龄幼虫对甲氨基阿维菌素苯甲酸盐的LC50分别为0.1010、0.3561、0.7568、1.4325和8.4390 mg/L,对毒死蜱的LC50分别为27.4632、46.8495、87.5222、129.3217和1 356.6770 mg/L。单头幼虫的羧酸酯酶、多功能氧化酶、谷胱甘肽S-转移酶和乙酰胆碱酯酶活力随虫龄的增加而提高,与龄期间对药剂的敏感性呈负相关(由于外源化合物摄入量减少,5龄单头幼虫的多功能氧化酶活力略有降低)。【结论】甜菜夜蛾不同龄期幼虫对药剂的敏感性存在非常明显的差异,在田间防治中,应选择对杀虫剂敏感性较高的低龄幼虫作为最佳防治时期。