Multiple Resistance and Biochemical Mechanisms of Dicofol Resistance in Tetranychus urticae (Acari: Tetranychidae)

A field colony of Tetranychus urticae (Koch) resistant to dicofol was selected with dicofol successively for 20 generations to produce the DR-20 strain. Resistance and multiple resistance levels of the DR-20 strain to 15 acaricides were determined using a spray bioassay. The DR-20 strain was extremely resistant to dicofol [resistance ratio (RR), 465]. The strain showed extremely strong resistance to acrinathrin (RR, 373) and benzoximate (RR, 197) and strong resistance to bromopropylate (RR, 136), fenbutatin oxide (RR, 65), fenpropathrin (RR, 70), fenpyroximate (RR, 68), and pyridaben (RR, 63). A RR of 11–29 was observed with abamectin, fenazaquin, milbemectin, propagite, and tebufenpyrad. The DR-20 strain exhibited low levels of resistance (RR<3) to azocyclotin and chlorfenapyr. In comparative assays with detoxifying enzymes, the DR-20 strain showed 4.7-fold higher activity in p-nitroanisole-O-demethylation and 1.6-fold higher activities in both α- and β-naphthyl acetate hydrolysis. Synergist experiments with different metabolic inhibitors revealed that piperonyl butoxide, iprobenfos, triphenyl phosphate, and 4, 4-dichloro-α-methyl benzhydrol had little or no synergistic activity in the susceptible and DR-20 strains. These results suggest that employment of certain acaricides with little multiple resistance will be useful for the management of dicofol resistance in the field.     

截形叶螨对哒螨灵、阿维菌素和阿维·哒螨灵的抗性选育和抗性稳定性研究

【目的】明确截形叶螨Tetranychus truncatus Ehara对哒螨灵、阿维菌素和阿维·哒螨灵3种田间常用药剂产生抗性的速率和稳定性,为叶螨的抗性综合治理提供一定的理论依据。【方法】采用室内生测法,对截形叶螨进行药剂的抗性筛选、衰退和再恢复规律研究。【结果】经过连续30代的药剂汰选,截形叶螨对哒螨灵、阿维菌素和阿维·哒螨灵3种药剂产生了不同程度的抗药性,抗性指数分别达到197.50、19.56和12.57;停止喷药后,其抗性都有所下降,其中截形叶螨对哒螨灵的抗性最不稳定,培育至30代后,抗性衰退率达到63.54%,对阿维菌素的抗性较为稳定,抗性衰退率为23.30%;再次恢复用药后,截形叶螨对哒螨灵、阿维菌素和阿维哒螨灵抗性再度回升,以抗哒螨灵品系的抗性恢复最快,药剂汰选30代后,增长率达到了58.47%,阿维·哒螨灵次之(增长率为38.67%),抗阿维菌素的品系抗性恢复最慢,增长率仅为22.86%。【结论】截形叶螨对哒螨灵抗性不稳定,停止用药后,敏感性易恢复,对阿维菌素和阿维·哒螨灵的抗性较稳定,一旦抗性产生不易衰退,故田间应用时应交替轮换用药。     

Genetic analysis and cross-resistance spectrum of a laboratory-selected chlorfenapyr resistant strain of two-spotted spider mite (Acari: Tetranychidae)

A laboratory susceptible strain of Tetranychus urticae was selected with chlorfenapyr resulting in a resistant strain. After 12 cycles of exposure, the resistance ratio (RR) calculated from the LC50s of susceptible and selected strain was 580. The resistant strain was screened with 16 currently used acaricides for cross-resistance. Cross-resistance was detected with amitraz (RR = 19.1), bifenthrin (RR = 1.3), bromopropylate (RR = 7.5), clofentezine (RR = 29.6) and dimethoate (RR = 17.6). No cross-resistance was detected with the new molecules acequinocyl, bifenazate and spirodiclofen. Mortality caused by chlorfenapyr in the F1 progeny from reciprocal crosses between both strains indicated that the mode of inheritance was incomplete recessive. Mortality in F2 progeny indicated that the resistance was under the control of more than one gene. Synergist experiments with S,S,S-tributylphosphorotrithioate (DEF), piperonylbutoxide (PBO) and diethylmaleate (DEM), which are inhibitors of esterases, monooxygenases and glutathion-S-transferases respectively, suggested a major role of esterases in the resistance to chlorfenapyr.     

截形叶螨抗哒螨灵品系和敏感品系体内解毒酶活性的变化

【目的】通过对截形叶螨 Tetranychus truncatus Ehara抗哒螨灵品系体内解毒酶活性分析和增效剂与哒螨灵混用的增效作用测定,明确截形叶螨对哒螨灵的抗性动态及抗性机理,获得抗性治理的途径。【方法】采用室内生测法培育截形叶螨抗哒螨灵品系,微量滴度酶标板测定抗性和敏感品系体内解毒酶比活性、米氏常数（K_m）及最大反应速度（V_max）,再用增效醚（PBO）、顺丁烯二酸二乙酯（DEM）和磷酸三甲苯酯（TPP）进行增效作用测定。【结果】室内筛选的截形叶螨对哒螨灵产生了抗性,筛选至49代,抗性倍数达到955.25;PBO,TPP和DEM对哒螨灵药剂有不同程度的增效作用,相对增效系数分别为95.97%, 85.14%和97.37%;抗哒螨灵品系体内的羧酸酯酶（CarE）、谷胱甘肽转移酶（GSTs）、多功能氧化酶（MFO）活性较敏感品系显著性提高（P＜0.05）,酸性磷酸酯酶（ACP）和碱性磷酸酯酶（ALP）的活性与敏感品系差异不大(P>0.05);抗性品系中的CarE,GSTs和MFO 3种解毒酶的米氏常数（K_m）下降,最大反应速度（V_max）高于敏感品系。【结论】截形叶螨对哒螨灵产生抗性可能与其体内CarE,GSTs和MFO 3种解毒酶与底物的亲和力提高和代谢能力增强有关;3种增效剂(PBO, TPP和 DEM)与哒螨灵混用能提高对截形叶螨的毒杀效果。     

Mode of inheritance of resistance to three new acaricides in the Kanzawa spider mite Tetranychus kanzawai Kishida (Acari:Tetranychidae)

The genetics of resistance to three new types of acaricide tebufenpyrad, fenpyroximate and pyridaben was studied by crossing a resistant (R) with a susceptible (S) strain of Tetranychus kanzawai Kishida. The resistance ratios calculated from the LC50s of the R and S strains were 97, 1265 and 134 for tebufenpyrad, fenpyroximate and pyridaben, respectively. The responses to the three acaricides in F1 females from reciprocal crosses between the R and S strains showed that the modes of inheritance of resistance to tebufenpyrad, fenpyroximate and pyridaben were intermediate, incompletely dominant and completely recessive, respectively. Furthermore, the responses of F2 females from the reciprocal crosses indicated that the resistance to the three acaricides was under monogenic control.Exp Appl Acarol 22: 699708 © 1998 Kluwer Academic Publishers     

二斑叶螨对七种杀螨剂的抗药性测定及其机理研究

室内测定了相对敏感种群(S)和抗性种群(R)对常用7种杀螨剂的敏感性,并测定了羧酸酯酶、谷胱甘肽S-转移酶和乙酰胆碱酯酶3种酶的比活力。结果表明:二斑叶螨Tetranychus urticae Koch R种群已对甲氰菊酯和哒螨灵产生了抗性,抗性倍数分别为5.45和105.47。其中,甲氰菊酯对雌成螨的毒力最低(>3000mg/L),已远远超过田间推荐剂量,不宜继续使用。酶活测定结果表明:谷胱甘肽S-转移酶解毒活性的提高是二斑叶螨对甲氰菊酯产生抗性的原因之一;二斑叶螨对哒螨灵抗性的增强可能与羧酸酯酶有关。     

二化螟对杀螟硫磷产生抗性的机理

本文就二化螟Ckilo suppressalis Walker对杀螟硫磷抗性发生的机理进行了较为全面的研究。活体增效作用研究表明,脱叶磷(DEF)和氧化胡椒基丁醚(PBO)对抗性种群可分别增效1.3和34.8倍。这表明了多功能氧化酶(MFO)活性增强,而似乎与水解酶的活性无关。对寓体解毒酶的进一步研究表明,抗性和敏感种群的非特异性酯酶活力无明显差异,但羧酸酮酶(CarE,加入10^-4mol/L的毒扁豆碱)和MFO的活力在抗性种群中有所增高。R种群幼虫CarE活力分别是s的2.42和2.92倍(以a-和β-乙酸萘酯为底物);R种群幼虫MFO的O-脱甲基作用的活力为s幼虫的1.43倍(以对硝基茴香醚为底物);R幼虫乙酰胆碱酯酶(AChE)对乙酰胆碱的活力是s的1.3倍,两者相差不大。但从米氏常数K_m)和最大反应速度(V_max)看,R幼虫是s幼虫的1.9和1.6倍;以对氧磷为抑制剂的R幼虫150是s幼虫的2倍。这些表明了R和s的AChE是不同的。研究结果还表明,二化螟对杀螟硫磷抗性的机理至少包括：(1)CarE活性的增高;(2)MFO的O-脱甲基活力的增高和(3)AChE敏感性的降低等。     

二化螟对杀螟硫磷产生抗性的机理

本文就二化螟Ckilo suppressalis Walker对杀螟硫磷抗性发生的机理进行了较为全面的研究。活体增效作用研究表明,脱叶磷(DEF)和氧化胡椒基丁醚(PBO)对抗性种群可分别增效1.3和34.8倍。这表明了多功能氧化酶(MFO)活性增强,而似乎与水解酶的活性无关。对寓体解毒酶的进一步研究表明,抗性和敏感种群的非特异性酯酶活力无明显差异,但羧酸酮酶(CarE,加入10^-4mol/L的毒扁豆碱)和MFO的活力在抗性种群中有所增高。R种群幼虫CarE活力分别是s的2.42和2.92倍(以a-和β-乙酸萘酯为底物);R种群幼虫MFO的O-脱甲基作用的活力为s幼虫的1.43倍(以对硝基茴香醚为底物);R幼虫乙酰胆碱酯酶(AChE)对乙酰胆碱的活力是s的1.3倍,两者相差不大。但从米氏常数K_m)和最大反应速度(V_max)看,R幼虫是s幼虫的1.9和1.6倍;以对氧磷为抑制剂的R幼虫150是s幼虫的2倍。这些表明了R和s的AChE是不同的。研究结果还表明,二化螟对杀螟硫磷抗性的机理至少包括：(1)CarE活性的增高;(2)MFO的O-脱甲基活力的增高和(3)AChE敏感性的降低等。     

Resistance mechanisms to mitochondrial electron transport inhibitors in a field-collected strain of Tetranychus urticae Koch (Acari: Tetranychidae)

A Belgian field strain (MR-VP) of Tetranychus urticae (Koch) (Acari: Tetranychidae) exhibits different levels of resistance to four frequently used METI (mitochondrial electron transport inhibitor)-acaricides, i.e. tebufenpyrad, fenpyroximate, pyridaben and fenazaquin. Resistance factors for these compounds were 184, 1547, 5971 and 35, respectively. A 23.5-fold increase in 7-ethoxy-4-trifluoromethylcoumarin O-deethylation activity suggested that metabolic resistance through elevated levels of cytochrome P450 dependent monooxygenase-activity is a possible resistance mechanism.However, synergism studies with different metabolic inhibitors revealed some contrasting resistance mechanisms between the METI-acaricides. Tebufenpyrad resistance could only be synergized after pre-treatment with the monooxygenase inhibitor piperonyl butoxide (PBO), whereas pyridaben resistance was strongly synergized both by PBO and the esterase inhibitor S,S,S-tributylphosphorotrithioate (DEF). Resistance levels to fenpyroximate could neither be suppressed by PBO nor by DEF. Although METI-acaricides are structurally related, these findings probably reflect a different role of esterases and mono-oxygenases in metabolic detoxification between these compounds. The overall lack of synergism by diethylmaleate (DEM) suggests that glutathione-S-transferases are not an important factor in resistance to METIs.Reciprocal crosses between susceptible females and resistant males showed no maternal effect, and resistance to METI-acaricides was inherited generally as a dominant trait. Backcrosses with F1 females revealed striking differences in the mode of inheritance. Although resistance to fenpyroximate and pyridaben was under monogenic control, resistance to tebufenpyrad was under control of more than one gene.     

朱砂叶螨抗药性监测

本文采用药膜法建立了朱砂叶螨Tetranychus cinnabarinus（Boisduval）对5种杀螨剂的敏感基线,并对6个不同地理种群的朱砂叶螨进行了抗药性监测,结果表明：5种药剂杀螨活性由高到低分别为阿维菌素〉丁氟螨酯〉氧化乐果〉炔螨特〉甲氰菊酯,其对朱砂叶螨雌成螨的LC50值分别为0.08、2.19、67.89、201.19和605.27mg/L;朱砂叶螨各地理种群已对甲氰菊酯和炔螨特产生了低、中水平的抗性,其抗性倍数分别介于2.93～16.22与4.85～14.35之间,其中云南种群对这2种杀螨剂抗性最高,对氧化乐果与丁氟螨酯处于敏感性降低阶段,其抗性倍数分别介于2.35～4.26与1.56～2.11之间,对阿维菌素还未产生明显抗性;对阿维菌素和甲氰菊酯的增效剂生物测定结果表明,三类解毒酶系（多功能氧化酶、谷胱甘肽S-转移酶和酯酶）都不同程度地参与了朱砂叶螨抗药性的形成。     

Monitoring pyrethroid resistance in field collected Blattella germanica Linn. (Dictyoptera: Blattellidae) in Indonesia

The German cockroach, Blattella germanica , is a major and the most common pest in public areas in Indonesia. Although intensive control measures have been carried out to control the populations of this pest, results have been far from successful, which is believed to be because of its resistance to insecticides. A standard World Health Organization (WHO) glass jar test was carried out to determine the resistance level of this insect to pyrethroid insecticides, the most commonly used insecticides for cockroach control in Indonesia. A susceptible S1 strain collected from Tembagapura Papua was compared with four strains collected from Bandung, West Java: strain S2, from a local restaurant; strain S3, from the Bandung train station; and strains S4 and S5, from two different hotels. All strains showed low resistance to the pyrethroid, except the S5 strain, which had a Resistance Ratio (RR)₅₀ of 95 for permethrin. The addition of piperonyl butoxide (PBO) suggests that the detoxifying enzyme mixed function oxidases (MFO) played an important role in the development of resistance to permethrin in the S5 strain, suggested by the high Synergist Ratio (SR) of 70.4. However, the low level of resistance to cypermethrin was not affected by PBO, suggesting that other mechanisms of pyrethroid resistance are involved. Our study is the first report of German cockroach resistance to permethrin in Indonesia, and the findings can be used in formulating potential strategies for cockroach resistance management.     

ESTMATION OF REALIZED HERITABILITY OF RESISTANCE TO FENPROPATHRIN, ABAMECTIN, PYRIDABEN AND THEIR MIXTURES IN ACARICIDE-SELECTED STRAINS OF TETRANYCHUS CINNABARINUS (BOIDUVAL)

Abstract Threshold trait analysis was used to estimate realized heritability (h²) of resistance to five acaricides (three single acaricide and two mixtures) and resistance risk in Tetranychus cinnabarinus (Boiduval). Tetranychus cinnabarinus collected from the field of Beibei, Chongqing reared more than 60 generations under pesticide free conditions and considered susceptible. Successively selected for about 30 generations, the strain had a 65.55-, 5.82-, 1.23-, 5.20- and 1.42-fold increase in resistance to fenpropathrin, abamectin, pyridaben, pyridaben-abamectin (pyridaben: abamectin = 7.4:0.1, m/m) and fenpropathrin-abamectin (fenpropathrin: abamectin = 8.9:0.1, m/m), respectively. The realized heritability of resistance to fenpropathrin, abamectin, pyridaben, pyridaben-abamectin (pyridaben: abamectin = 7.4:0.1, m/m) and fenpropathrin-abamectin (fenpropathrin: abamectin = 8.9:0.1, m/m) is 0.2167, 0.0967, 0.0130, 0.0800 and 0.0172, respectively. Under the selected condition, a 10-fold increase in resistance would be expected 15 generations for fenpropathrin, 34 generations for abamectin, 333 generations for pyridaben, 42 generations for pyridaben-abamectin (pyridaben: abamectin = 7.4:0.1, m/m) and 200 generations for fenpropathrin-abametcin (fenpropathrin: abamectin = 8.9:0.1, m/m). The highest resistance risk of the five acaricides in Tetranychus cinnabarinus was fenpropathrin, then abamection, pyridaben-abamectin (pyridaben: abamectin = 7.4: 0.1, m/m), fenpropathrin- abamectin (fenpropathrin: abamectin = 8.9:0.1, m/m) and that to pyridaben was the lowest. The mixture of pyridaben and abamectin is not useful in delaying development of resistance in the pest to the two single acaricide while the mixture of fenpropathrin and abamectin could do it.     

Insecticide toxicity, synergism and resistance in the German cockroach (Dictyoptera: Blattellidae)

The toxicity of synergism of and resistance to insecticides in four strains of German cockroach, Blattella germanica (L.), were investigated. Toxicity of nine insecticides by topical application to the susceptible strain varied greater than 2,000-fold, with deltamethrin (LD50 = 0.004 micrograms per cockroach) and malathion (LD50 = 8.4 micrograms per cockroach) being the most and least toxic, respectively. Resistance to pyrethrins (9.5-fold) in the Kenly strain was unaffected by the synergists piperonyl butoxide (PBO) or S,S,S-tributylphosphorotrithioate (DEF), suggesting that the metabolism is not involved in this case. Malathion resistance in the Rutgers strain was suppressible with PBO, implicating oxidative metabolism as a resistance mechanism. The Ectiban-R strain was resistant to all the pyrethroids tested, and cypermethrin resistance was not suppressible with PBO or DEF. These findings support results of previous studies that indicated this train has a kdr-like mechanism. Bendiocarb resistance in both the Kenly and Rutgers strains was partially suppressed by either PBO or DEF, suggesting that oxidative and hydrolytic metabolism are involved in the resistance. Trends between the effects of the synergists on the susceptible versus resistant strains are discussed.     

褐飞虱抗甲胺磷品系的交互抗性和抗性生化机制

用甲胺磷筛选的褐飞虱Nilaparvata lugens品系（R）,对甲胺磷的抗性达到43.74倍,对马拉硫磷、二嗪磷、异丙威、仲丁威及醚菊酯都表现出一定的交互抗性,而对氰戊菊酯和吡虫啉的交互抗性不显著。为了研究褐飞虱对甲胺磷抗性和对其它药剂交互抗性产生的机制,进行了活体增效试验和离体生化实验。用2 μg/头的增效剂预处理试虫的活体增效实验结果显示,在甲胺磷筛选品系（R）中, TPP(triphenyl phosphate, 磷酸三苯酯)对甲胺磷的增效倍数达到4.54,TPP对马拉硫磷、二嗪磷、仲丁威、异丙威都表现出一定的增效作用,增效比分别为2.76、2.07、2.17和1.64;PBO(piperonyl butoxide,胡椒基丁醚)对甲胺磷、马拉硫磷和醚菊酯有一定的增效作用;DEM(diethyl meteate, 顺丁烯二酸二乙酯)的增效作用不明显。研究离体情况下增效剂对三种解毒酶活性的影响发现,TPP对R品系酯酶活力抑制作用很强（抑制率69.04%）,PBO对多功能氧化酶（MFO）具有一定的抑制作用（抑制率29.30%）,而TPP和PBO在F品系和S品系中对酯酶和MFO的抑制作用都较小;DEM在三个品系中对谷胱甘肽-S-转移酶的抑制作用都很小。由此可见,酯酶在褐飞虱对甲胺磷的抗性中起最主要作用,在马拉硫磷、二嗪磷、异丙威和仲丁威的交互抗性中起很重要作用;MFO可能在甲胺磷抗性和醚菊酯、马拉硫磷的交互抗性中起一定作用。     

Cross-resistance, inheritance, and biochemistry of mitochondrial electron transport inhibitor-acaricide resistance in Tetranychus urticae (Acari: Tetranychidae).

Resistance of the twospotted spider mite, Tetranychus urticae Koch, to acaricides acting as mitochondrial electron transport inhibitors (METIs) is an increasing problem. Because of their high levels of cross-resistance to all commercially available METI-acaricides, a Japanese strain (AKITA) and an English strain (UK-99) of T. urticae were investigated in detail. Larvae of both strains, AKITA and UK-99, showed 1,100- and 480-fold resistance against pyridaben, 870- and 45-fold resistance against fenpyroximate, and 33- and 44-fold resistance against tebufenpyrad, respectively, in a foliar spray application bioassay compared with the susceptible strain GSS. These resistance factors remained stable even when maintained in the laboratory without further selection. Furthermore, strain AKITA showed cross-resistance to dicofol. The METI resistant strains AKITA and UK-99 showed 2.4- and 1.7-fold enhanced O-ethoxycoumarin O-deethylation (cytochrome P450) activity. Increased oxidative metabolism of the METI-acaricides in the resistant strains could be partially suppressed in vivo by the monooxygenase-inhibitor piperonyl butoxide. Reciprocal crosses of homozygous, diploid females and hemizygous, haploid males of strains GSS (susceptible) and AKITA (resistant) revealed that resistance to pyridaben and fenpyroximate was inherited incompletely dominant with slight differences between maternal and paternal inheritance. This is the first attempt to mechanistically describe METI-acaricide resistance in T. urticae. The implications for resistance management strategies are discussed.     

朱砂叶螨对甲氰菊酯、阿维菌素,哒螨灵及其混剂抗性遗传力的分析(英文)

采用域性状分析法 ,估算了朱砂叶螨对 5种杀螨剂 (3种单剂和 2种混剂 )的抗性现实遗传力 ,并对 5种药剂的抗性风险进行了评估。把采自重庆北碚田间的朱砂叶螨种群 ,在室内不施药情况下饲养 6 0余代 ,以此作为抗性筛选的敏感品系。分别单一连续汰选近 30代 ,朱砂叶螨对甲氰菊酯、阿维菌素、哒螨灵、哒螨 -阿维 (哒螨灵 :阿维菌素 =7 4 :0 1,m m)和甲氰 -阿维 (甲氰菊酯 :阿维菌素 =8 9:0 1,m m)的抗性分别达 6 5 5 5、5 82、1 2 3、5 2 0和 1 4 2 倍 ;抗性现实遗传力分别为 0 2 16 7、0 0 96 7、0 0 130、0 0 80 0和 0 0 172。在实验室选择条件下 ,预计抗性增长 10倍时 ,甲氰菊酯、阿维菌素、哒螨灵、哒螨 -阿维 (哒螨灵 :阿维菌素 =7 4 :0 1,m m)和甲氰 -阿维 (甲氰菊酯 :阿维菌素 =8 9:0 1,m m)分别需要 15、34、333、4 2和 2 0 0代。甲氰菊酯抗性风险较高 ,其次是阿维菌素、哒螨 -阿维 (哒螨灵 :阿维菌素 =7 4 :0 1,m m)、甲氰 阿维 (甲氰菊酯 :阿维菌素 =8 9:0 1,m m) ,哒螨灵抗性风险较低。混剂哒螨 阿维 (哒螨灵 :阿维菌素 =7 4 :0 1,m m)不能延缓朱砂叶螨对两单剂哒螨灵和阿维菌素的抗性发展 ,而混剂甲氰 阿维 (甲氰菊酯 :阿维菌素 =8 9:0 1,m m)却能有效延缓朱砂叶螨对两单剂     

棉铃虫对氰戊菊酯抗性遗传分析

本文采用剂量对数-死亡机率值回归线(LD-P线)分析法, 利用室内选育的棉铃虫 Heliccverpa armitera(Hubner)对氰戊菊酯抗性晶系和敏感品系,研究了棉铃虫对氰戊菊酯的抗性遗传规律。结果表明,棉铃虫对氰戊菊酯的抗性为多基因遗传,其主要基因为不完全显性,抗性不属性连锁遗传。利用增效剂对抗性机理进行的研究表明,多功能氧化酶(MFO)是棉铃虫对氰戊菊酯产生抗药性的主要因子,因此,可以推断多功能氧化酶基因为不完全显性。     

Thiamethoxam Resistance in the House Fly,Musca domestica L.: Current Status,Resistance Selection,Cross-Resistance Potential and Possible Biochemical Mechanisms

The house fly, Musca domestica L., is an important ectoparasite with the ability to develop resistance to insecticides used for their control. Thiamethoxam, a neonicotinoid, is a relatively new insecticide and effectively used against house flies with a few reports of resistance around the globe. To understand the status of resistance to thiamethoxam, eight adult house fly strains were evaluated under laboratory conditions. In addition, to assess the risks of resistance development, cross-resistance potential and possible biochemical mechanisms, a field strain of house flies was selected with thiamethoxam in the laboratory. The results revealed that the field strains showed varying level of resistance to thiamethoxam with resistance ratios (RR) at LC₅₀ ranged from 7.66-20.13 folds. Continuous selection of the field strain (Thia-SEL) for five generations increased the RR from initial 7.66 fold to 33.59 fold. However, resistance declined significantly when the Thia-SEL strain reared for the next five generations without exposure to thiamethoxam. Compared to the laboratory susceptible reference strain (Lab-susceptible), the Thia-SEL strain showed cross-resistance to imidacloprid. Synergism tests revealed that S,S,S-tributylphosphorotrithioate (DEF) and piperonyl butoxide (PBO) produced synergism of thiamethoxam effects in the Thia-SEL strain (2.94 and 5.00 fold, respectively). In addition, biochemical analyses revealed that the activities of carboxylesterase (CarE) and mixed function oxidase (MFO) in the Thia-SEL strain were significantly higher than the Lab-susceptible strain. It seems that metabolic detoxification by CarE and MFO was a major mechanism for thiamethoxam resistance in the Thia-SEL strain of house flies. The results could be helpful in the future to develop an improved control strategy against house flies.     

烟粉虱对拟除虫菊酯杀虫剂的抗性机理

通过增效剂生物测定、生化分析以及钠离子通道基因ⅡS4-6 cDNA片段的RT-PCR扩增,探讨了烟粉虱Bemisia tabaci（Gennadius）对拟除虫菊酯杀虫剂的抗性机理。结果表明：对于采自田间的6个烟粉虱抗性品系,磷酸三苯酯（TPP）和胡椒基丁醚（PBO）对氯氰菊酯、溴氰菊酯、氯氟氰菊酯和甲氰菊酯均有显著的增效作用,而DEM对4种拟除虫菊酯杀虫剂均无明显的增效作用。烟粉虱抗性品系的α-NA羧酸酯酶和β-NA羧酸酯酶活性分别是敏感品系的2.16～2.65倍和1.22～1.41倍,抗性品系的谷胱甘肽S转移酶活性与敏感品系没有差异,表明羧酸酯酶和多功能氧化酶在烟粉虱对拟除虫菊酯类杀虫剂的抗性中具有重要的作用,而谷胱甘肽S转移酶与抗性无关。通过RT-PCR克隆了6个烟粉虱田间抗性品系的钠离子通道结构域ⅡS4-6 cDNA片段的序列（420 bp）,发现与敏感品系相比,有2个位点发生突变,分别为L925I突变和I917V突变,L925I突变在所有6个烟粉虱田间抗性种群中均有发生,该位点突变已被证实与拟除虫菊酯类杀虫剂密切相关,表明神经不敏感性可能是烟粉虱对拟除虫菊酯产生抗性的另一个重要因子。     

Diagnosis of amitraz resistance in Brazilian populations of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) with larval immersion test

Among the ectoparasites of cattle, Rhipicephalus (Boophilus) microplus (Canestrini) (Acari: Ixodidae) remains a major cause of economic losses to livestock. The chemical control with acaricides is still the most efficient method available to control ticks. The aims of this study were to diagnose resistance to amitraz in 16 tick populations from the States of São Paulo (14) and Paraná (2), using the larval immersion technique (LIT), and evaluate the effect of synergists [piperonyl butoxide (PBO), diethyl maleate (DEM), triphenyl phosphate (TPP)] on amitraz resistant and susceptible strains of cattle tick. Most of the evaluated populations (68.7 %) showed to be resistant to amitraz, with resistance ratios ranging from 2.14 to 132. The results suggest that the test procedure by LIT is sensitive and adequate for detection and monitoring of amitraz resistance in cattle tick. No synergistic effect was observed for the synergists PBO, DEM and TPP, on the amitraz resistant (Poa) strain of cattle tick, indicating that increased detoxification metabolism was not involved in this resistance.