Comparison of susceptibility of two populations of Tetranychus urticae Koch to two acaricides,abamectin and propargite

The spider mite, Tetranychus urticae Koch is a serious pest of economically important plants in closed and open area worldwide. The spider mite resistance to acaricide plays a major role in the failure of the chemical control method. Thus, the aim of the current study was to evaluate the efficacy of two acaricides, abamectin and propargite, against two populations (strains) of the spider mite. Results showed that LC₅₀s of the abamectin against susceptible and resistant strains of the spider mite were 0.1 and 2730?ppm, respectively. Whilst LC₅₀s of the propargite against susceptible and resistant strains of the spider mite were 55 and 7199?ppm, respectively. Resistance ratio (RR) calculated as the ratio of resistance LC₅₀/susceptible LC₅₀ showed that RR for abamectin and propargite was 20285 and 130, respectively. The enzyme assay results showed that three mechanisms of MFO, GST and EST are involved in the abamectin resistance of the spider mite. In gel assays, when α-naphthyl acetate was used as substrate, three bands appeared in the gel in which bands E2 and E3 were major bands and E1 was a minor band confirming that α-naphthyl acetate was a better substrate for general esterase activity in the spider mite whereas β-acetate when used for esterase activity, only two faint bands (E1 and E2) were observed. The order of their involvement in the abamectin resistance is EST?>?MFO?>?GST.     

Milbemectin resistance in <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae): selection,stability and cross-resistance to abamectin

Studies on artificial laboratory selections with milbemectin, stability of milbemectin resistance and possible cross-resistance with abamectin were carried out with Tetranychus urticae Koch to provide basic information for a milbemectin resistance management program. Selections for resistance and susceptibility to milbemectin were performed in a population of T. urticae, collected from a commercial chrysanthemum field in the State of São Paulo, Brazil. After six selections for resistance and five selections for susceptibility, susceptible (S) and resistant (R) strains of T. urticae to milbemectin were obtained. The resistance ratio (R/S) at the LC₅₀ reached 409-fold value. The stability of milbemectin resistance was also studied under laboratory conditions, using a population with initial frequency of 75% of resistant mites. The frequencies of milbemectin resistance were evaluated monthly for a period of 7 months. In order to observe possible correlation between milbemectin and abamectin resistance, the frequencies of abamectin resistance were also evaluated for that population, during the same period. The frequency of milbemectin resistance decreased from 75 to 14.5%, while the percentage of abamectin resistant mites decreased from 57 to 9.1%, in 7 months. The frequencies of milbemectin and abamectin resistance were also evaluated in 25 field populations of T. urticae, collected from several crops in the State of São Paulo. The frequencies of milbemectin resistance varied from 4.1 to 89.5%, and of abamectin, from 7.0 to 90.5%. A positive and significant correlation was observed between the frequencies of milbemectin and abamectin resistance, indicating positive cross-resistance between these acaricides. The results indicate that abamectin should be avoided for managing milbemectin resistance in T. urticae. This is the first report on milbemectin resistance in T. urticae in Brazil.     

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。     

Cross-resistance and biochemical mechanisms of abamectin resistance in the B-type Bemisia tabaci

Abstract:  To understand the risk of resistance and the possible mechanisms of resistance to abamectin in B-type Bemisia tabaci (Gennadius) better, a resistant strain of B. tabaci was selected in the laboratory and cross-resistance pattern and resistance mechanisms to abamectin were investigated. The NJ-Abm strain of B. tabaci was derived from a field population (NJ) collected in Nanjing, China in 2002 with 18 generations of selection with abamectin in the laboratory. Compared with the unselected NJ strain, the selected NJ-Abm strain developed 14.5-fold resistance to abamectin and showed significant cross-resistance to emamectin benzoate (4.4-fold) and imidacloprid (3.4-fold), but no cross-resistance to fipronil. The oxidase inhibitor piperonyl butoxide (PBO) and glutathione S -transferase inhibitor diethyl maleate (DEM) produced significant synergism on abamectin in the NJ-Abm strain (with synergistic ratios of 3.9- and 4.1-fold respectively); however, the esterase inhibitor triphenyl phosphate (TPP) did not act synergistically with abamectin. Biochemical analysis confirmed that P450 monooxygenase activity and glutathione S -transferase activity of the NJ-Abm strain were elevated to 2.1- and 2.0-fold, respectively, compared with that of the NJ strain. This indicated that enhanced metabolism mediated by P450 monooxygenase and glutathione S -transferase is likely to be involved in abamectin resistance and cross-resistance to imidacloprid and emamectin benzoate in the NJ-Abm strain.     

Permethrin resistance in Aedes aegypti (Linnaeus) collected from Kuala Lumpur,Malaysia

Permethrin resistance status of a laboratory strain, a permethrin-selected strain and three field strains of Aedes aegypti collected in Kuala Lumpur, Malaysia were evaluated using three standard laboratory bioassays: WHO larval bioassay, WHO adult mosquito bioassay, and mixed function oxidase (MFO) enzyme microassay. The LC₅₀ values of field strains from the WHO larval bioassay did not differ significantly. The highest LC₅₀ value was from the Taman Melati field strain (0.39 mg/L). The resistance ratio for the permethrin-selected strain and the field strains ranged from 1.86 fold to 5.57 fold. Pre-exposure to piperonyl butoxide (PBO) in the WHO adult bioassay and MFOs enzyme microassay reduced the LT₅₀ values and reduced the mean optical density of elevated oxidase activity (0.28–0.42) at 630 nm. The LC₅₀ or LT₅₀ values and the level of oxidases were significantly correlated (r = 0.825; p< 0.05). This study confirmed the presence of permethrin resistance in these mosquito populations.     

Acaricidal and biological activities of Titanium dioxide and Zinc oxide nanoparticles on the two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae) and their side effects on the predatory mite,Neoseiulus californicus (Acari: Phytoseiidae)

The excessive application of pesticides raises environmental pollution levels, necessitating the need to identify alternative substances that do not cause ecological damage. In this context, the toxicity and residual efficacy of titanium dioxide (TiO₂) and zinc oxide (ZnO) nanoparticles (NPs) compared to abamectin against adult females of T. urticae was evaluated under laboratory and greenhouse conditions. In addition, the effects of tested NPs on the biological parameters of T. urticae as well as their side effects on the predatory mite, Neoseiulus californicus were examined. In laboratory bioassays, LC₅₀ values of TiO₂ and ZnO NPs were 5.82 and 7.09 mg L^–1, respectively, compared to 4.90 mg L^–1 in abamectin 72 hr post-treatment. TiO₂ and ZnO NPs had a prolongation effect on both the developmental and reproductive durations with mean life spans of 33.18 ± 0.72 days and 30.53 ± 0.82 days in the case of TiO₂ and ZnO NPs, respectively, compared to 24.65 ± 0.53 days in the normal case. Treated T. urticae females produced lesser fecundities (10–22 eggs less than the normal mean) and decreased hatchability rates. The highest mortality percentages in T. urticae populations were 92.4 % and 90.0 % after 24 h of spraying with TiO₂ and ZnO NPs, respectively, compared to 98.4 % in abamectin. In contrast, tested NPs demonstrated less toxicity in N. californicus populations with no phytotoxicity on treated leaves. This study is the first in Egypt to investigate the NPs control of T. urticae mites infesting cucumber plants and the effects on their biology and natural enemies.     

小菜蛾对定虫隆抗性种群的选育及交互抗性研究

用昆虫生长调节剂(insect growth regulator,简称IGR)定虫隆(chlorfluazuron)对源自深圳田间的小菜蛾(SZ-S)Plutella xylostella(L.)在室内进行抗性种群选育,经过8代饲养和6次药剂汰选,获得抗性种群(CH-R),与相对敏感种群Sz—S比较,抗性指数(R1)为23.78倍。CH-R种群在去除选择压力条件下饲养5代,抗性逐渐下降。抗性汰选前后分别测定了10种药剂的剂量—死亡毒力回归线,发现CH—R抗性种群对三氟氯氰菊酯、氯氰菊酯、辛硫磷、喹硫磷、灭多威、磺胺脲类衍生物—杀螨隆、微生物杀虫剂Bt和齐墩螨素无明显交互抗性,抗性倍数为0.4-1.7;对两种沙蚕毒素类杀虫剂杀螟丹和杀虫丹的敏感性却有所上升,有负交互抗性趋势。活体增效剂试验表明,增效醚(PBO)和三苯基磷酸酯(TPP)对定虫隆均有一定的增效活性,PBO的增效比最高为29倍,能够完全抑制对定虫隆的抗性,说明多功能氧化酶可能是主导抗性机制之一。     

Determination of acaricide resistance allele frequencies in field populations of Tetranychus urticae using quantitative sequencing

Resistances to monocrotophos, fenpropathrin and abamectin in Tetranychus urticae are primarily conferred by reduced sensitivities of respective target sites [i.e., acetylcholinesterase (TuAChE), voltage-sensitive sodium channel (TuVSSC) and glutamate-gated chloride channel (TuGluCl)], which are due to point mutations (G228S and F439W in TuAChE; L1022V in TuVSSC; G323D in TuGluCl). As a population-based genotyping technique, a quantitative sequencing (QS) protocol was developed for the determination of the resistance-associated mutation frequencies in T. urticae. Standard prediction equations revealed high correlation coefficients (r² = 0.993–0.999), demonstrating that the resistant nucleotide signal ratio is highly proportional to the resistance allele frequencies. The lower and higher detection limits for the four resistance mutations were 3.7–13.1% (7.8 ± 3.3%) and 89.4–97.3% (93.3 ± 3.2%), respectively, suggesting that QS can be employed as a preliminary monitoring tool for the detection of resistance allele frequencies, which ranged approximately 7.8–93.3% at the 95% confidence level. The QS was successfully employed for the determination of resistance allele frequencies in 26 T. urticae populations. The two TuAChE mutations responsible for monocrotophos resistance were almost saturated in most field populations. The TuVSSC L1022V mutation tentatively associated with fenpropathrin resistance was also found in 9 field populations. However, the TuGluCl G323D mutation conferring abamectin resistance was found only in one field population, suggesting that abamectin resistance is not yet widespread. The QS protocol, as an alternative to traditional bioassays, will greatly facilitate resistance monitoring of T. urticae.     

Effects of abamectin and deltamethrin to the foragers honeybee workers of Apis mellifera jemenatica (Hymenoptera: Apidae) under laboratory conditions

This study aimed at evaluating the toxicity of some insecticides (abamectin and deltamethrin) on the lethal time (LT₅₀) and midgut of foragers honeybee workers of Apis mellifera jemenatica were studied under laboratory conditions. The bees were provided with water, food, natural protein and sugar solution with insecticide (concentration: 2.50 ppm deltamethrin and 0.1 ppm abamectin). The control group was not treated with any kind of insecticides. The mortality was assessed at 1, 2, 4, 6, 12, 24, 48, and 72 hour (h) after insecticides treatment and period to calculate the value of lethal time (LT₅₀). But the samples the histology study of midgut collected after 24 h were conducted by Scanning Electron Microscope. The results showed the effects of insecticides on the current results show that abamectin has an adverse effect on honeybees, there is a clear impact on the lethal time (LT₅₀) was the abamectin faster in the death of honeybee workers compared to deltamethrin. Where have reached to abamectin (LT₅₀ = 21.026) h, deltamethrin (LT₅₀ = 72.011) h. However, abamectin also effects on cytotoxic midgut cells that may cause digestive disorders in the midgut, epithelial tissue is formed during morphological alterations when digestive cells die. The extends into the internal cavity, and at the top, there is epithelial cell striated border that has many holes and curves, abamectin seems to have crushed the layers of muscle. Through the current results can say abamectin most toxicity on honeybees colony health and vitality, especially foragers honeybee workers.     

Resistance to acaricides in Italian strains of <Emphasis Type="Italic">Tetranychus urticae</Emphasis>: toxicological and enzymatic assays

Problems with Tetranychus urticae are frequently reported in protected crops in Italy, particularly in roses where many introduced acaricides show a progressive loss of effectiveness. We have conducted bioassays to assess the response of some Italian strains of T. urticae to a number of acaricides. These include compounds that were widespread and frequently used in the past, but also some recently registered compounds. We investigated two T. urticae strains collected from rose growers where control failures were reported (SAN and PSE), together with a strain collected from unsprayed vegetables (BOSA). Adult females of the rose strains (SAN and PSE) were resistant to tebufenpyrad (Resistant Ratio—RR, RR₅₀ = 48.4 and 163.6) and fenpyroximate (RR₅₀ = 74.1 and 25.9) when compared to the susceptible BOSA strain. Lethal concentrations for these products were higher than the registered field rate. The PSE strain proved to be highly resistant to abamectin (RR₅₀ = 1,294.1). Variation in bifenazate susceptibility was detected amongst strains, but LC₉₀ values of SAN and PSE were still in the range of the registered field rate. In egg bioassays, the SAN and PSE strains exhibited high resistance levels to clofentezine (RR₅₀ = 66,473 and 170,714), hexythiazox (RR₅₀ = 70,244 and 159,493) and flufenoxuron (RR₅₀ = 61.9 and 117.9). But the recently introduced ovi/larvicides etoxazole and spirodiclofen exhibited high activity on all strains. The activity of detoxifying enzymes such as esterases, glutathione-S-transferases (GSTs) and cytochrome P450 monooxygenases (MFOs) was determined in these strains as a preliminary attempt to identify potential resistance mechanisms. Enzymatic assays showed that the rose strains exhibited 2.66 and 1.95-fold increased MFOs activity compared to the susceptible strain. Assays for GSTs revealed that only the SAN strain exhibited a significantly higher activity. In contrast, only the PSE strain showed a significant higher hydrolysis of 1-naphthyl acetate.     

Monitoring of acaricide resistance of Tetranychus urticae (Acari: Tetranychidae) from Korean apple orchards

Tetranychus urticae populations were collected from ten commercial apple orchards and their susceptibilities to 12 acaricides were tested using a leaf disc bioassay. The resistance of each T. urticae population was reported as the LC₅₀ value, the resistance ratio (RR) and the slope of the probit–concentration regression. Cross resistances of T. urticae populations were estimated using the Spearman's rank correlation coefficient. Most local populations showed low resistance levels (RR ≤ 10). Development of resistance to METI and pyrethroid acaricides differed among local populations. The highest RR value (154.6) was found in the Uiseong population to tebufenpyrad. The Geochang population was highly resistant, especially to METI and pyrethroid acaricides. T. urticae populations collected from Suwon, Chungju, Yeongju and Geochang showed moderate resistance (10 < RR ≤ 40) to more than two acaricides. Resistance ratios to abamectin, chlorfenapyr, fenbutatin-oxide and milbemectin were low (RR ≤ 10) in all populations. The LC₅₀ values of abamectin, chlorfenapyr, fenbutatin-oxide and milbemectin ranged from 0.06 to 0.2 mg/l, from 0.67 to 3.38 mg/l, from 10.12 to 40.85 mg/l and from 0.47 to 3.01 mg/l, respectively. We discuss possible cross-resistance to acaricides using Spearman's rank correlation coefficient.     

Acaricidal activity of spinosad and abamectin against two-spotted spider mites

Spinosad is a bioinsecticide with a high degree of selective toxicity towards insects of different orders, but its toxicity towards the two-spotted spider mite (TSSM), Tetranychus urticae Koch (Acari: Tetranychidae) is under debate. In this study, we compared the acaricidal properties of spinosad with the commercial bioacaricide abamectin on the life stages of TSSM. Adulticide and ovicide bioassays were performed on a susceptible laboratory strain using direct spraying of leaf disks with five rates of spinosad (20, 25, 30, 35 and 40 mg/l), five rates of abamectin (0.125, 0.25, 0.5, 1 and 2.5 mg/l), sublethal concentrations or a combination of spinosad and abamectin. Both adulticidal and ovicidal effects of spinosad against T. urticae in the laboratory were apparent, based on morality rates of the adults, reduction of female fecundity and death of offspring. Abamectin was also found to significantly reduce female fecundity and killed offspring when applied directly on the eggs. Interestingly, sublethal concentrations of spinosad reduced female fecundity stronger than abamectin. When a mixture of spinosad and abamectin was applied at LC_50, mortality was 74%, fecundity reduction was comparable to abamectin alone and egg hatching rate was lower than by either compound alone. In conclusion, spinosad was more harmful than abamectin for TSSM life stages and the combined application is recommended.     

High γ-aminobutyric acid content, a novel component associated with resistance to abamectin in Tetranychus cinnabarinus (Boisduval)

An abamectin-resistant strain of Tetranychus cinnabarinus (Boisduval) (Rf = 25.3) was selected in laboratory. We compared the γ-aminobutyric acid (GABA) content in abamectin-susceptible T. cinnabarinus individuals with that in resistant individuals and investigated its relationship to abamectin resistance. High performance liquid chromatography (HPLC) was used to ascertain GABA content in abamectin-susceptible (SS) and resistant (AR) strains of T. cinnabarinus. The results indicate that GABA content in the AR was significantly higher than that in the SS (1.39-fold). AR individuals treated with a sublethal dose of abamectin did not show significant differences in GABA levels compared with AR individuals that were not treated with abamectin. However in the SS, abamectin treated individuals had a significantly higher GABA content than those that were untreated (1.52-fold). Individuals in the SS that survived from selection with LC₉₅ of abamectin (SS-AR) showed significantly higher GABA levels compared to SS (1.41-fold). Similarly, progenies of the SS-AR parental generation (SS-ARF₁) also showed increased GABA levels (1.51-fold) compared to SS. In addition, behavioral observations have shown that all individuals from the AR, SS-AR and SS-ARF₁, which had more GABA content than the SS, demonstrated a significant decrease in crawling speed compared with SS individuals. This observation is consistent with excessive GABA levels had inhibitory effect on the central nervous system. Thus, we postulate that increasing GABA content in T. cinnabarinus is associated with resistance against abamectin.     

Residual contact vial bioassay for the on-site detection of acaricide resistance in the two-spotted spider mite

To develop a less technique-dependent bioassay technique that can be conveniently used by practitioners or farmers in the field for the monitoring of acaricide resistance of the two-spotted spider mite, Tetranychus urticae Koch, a residual contact vial (RCV) method was established using a 5-ml glass vial coated with acaricides. The RCV bioassay procedures were optimized by using abamectin and tebufenpyrad, two widely used acaricides. The diagnostic concentrations causing 100% mortality within 8 h post-treatment in a susceptible strain of T. urticae was set at 30 and 60 ppm for abamectin and tebufenpyrad, respectively. The vial-coated pesticides were stable at least one year when stored at ? 20 °C as determined by HPLC. There was no significant difference in the bioassay results in repeated RCV bioassay by three different experimenters, indicating its high reproducibility and reliability. RCV-based resistance monitoring of 15 field populations of mites revealed that abamectin resistance begins to spread but tebufenpyrad resistance is already prevalent in Korea. The RCV diagnostic kit, when used by practitioners or farmers on site, should provide crucial information for the selection of most suitable acaricides for different field populations of T. urticae.     

The G126S substitution in mitochondrially encoded cytochrome b does not confer bifenazate resistance in the spider mite Tetranychus urticae

Several genetic variants of the cd1- and ef-helices of the Q_o site of mitochondrial cytochrome b have been associated with bifenazate resistance in the spider mite Tetranychus urticae, an important crop pest around the world. Maternal inheritance of bifenazate resistance has provided strong evidence for the involvement of many of these mutations alone or in combination. A number of populations highly resistant to bifenazate were uncovered that carried the G126S substitution in combination with other target-site mutations. This G126S mutation has therefore been investigated in several studies in the context of resistance evolution and the development of diagnostic markers. However, experimental data that link bifenazate resistance with the presence of the G126S mutation without additional cd1- and ef-helices mutations, remain very limited. Here, we genotyped 38 T. urticae field populations for cytochrome b and uncovered nine field populations with a fixed or segregating G126S substitution without other target-site mutations in the conserved cd1- and ef-helices of the cytochrome b Q_o pocket. Toxicity bioassays showed that all nine field populations were very susceptible to bifenazate, providing strong evidence that G126S alone does not confer bifenazate resistance. These findings also implicate that previous T. urticae populations with G126S found to be low to moderately resistant to bifenazate, evolved alternative mechanisms of resistance, and more importantly, that this mutation cannot be used as a molecular diagnostic for bifenazate resistance.

     

Spider mite resistance to miticides in South Carolina strawberry and implications for improved integrated pest management

Tetranychus urticae Koch (Acari: Tetranychidae), twospotted spider mite, is a major secondary pest of strawberry and can cause significant yield loss. Tetranychus urticae is typically controlled using miticides, which has led to rapid resistance development. In South Carolina (USA), extension agents and growers have reported field failures of miticides (inadequate pest suppression), but resistance has not been quantitatively determined. In 2018, we determined the level of miticide resistance of six T. urticae populations found on strawberry across South Carolina. We examined efficacy of all miticides registered for use on US strawberry by conducting an initial diagnostic bioassay at 20% of the maximum labeled field rate. Any population?×?active ingredient combination resulting in?<?55% mortality was identified as ‘potentially resistant’ and concentration–response bioassays were then conducted to calculate LC₅₀ values for an individual population. These values were compared with those of a known-susceptible laboratory population to calculate resistance ratios (RR). Our results indicate that examined South Carolina populations of T. urticae from strawberry were highly resistant to bifenthrin (RR?=?100–60,000) and there was reduced susceptibility to fenbutatin-oxide (RR?=?25–123). The 'Sardinia' population had decreased abamectin susceptibility (RR?=?25). No resistance to hexythiazox, etoxazole, acequinocyl, bifenazate, fenpyroximate, spiromesifen, or cyflumetofen was found. Based on available data, it appears that miticide resistance is not a likely cause of field failures and issues related to application error and coverage should be investigated. Overall, this work supports the need to reduce the use of broad-spectrum pesticides and older products, in favor of newer miticide chemistries due to resistance issues.

     

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.     

Status and preliminary mechanism of resistance to insecticides in a field strain of housefly (Musca domestica,L)

Resistance profiles of houseflies (Gol-RR) collected from a field in Golmud city, Qinghai province, China, were determined for seven insecticides using topical bioassays. Resistance ratios of >1219.51, 153.17, >35.43, 6.12, 3.24, 1.73, and 0.86-fold were obtained for propoxur, cypermethrin, imidacloprid, indoxacarb, chlorpyrifos, fipronil, and chlorfenapyr, respectively, relative to a laboratory susceptible strain (SS). Synergism experiments showed that piperonyl butoxide (PBO), triphenylphosphate (TPP), and diethyl maleate (DEM) increased propoxur toxicity by >105.71, >7.88, and >5.15-fold in the Gol-RR strain, compared with 5.25, 2.00, and 1.39-fold in the SS strain, indicating the involvement of P450 monooxygenases, esterases, and glutathione-S-transferase in conferring resistance. Although cypermethrin resistance was significantly suppressed with PBO, TPP, and DEM in the Gol-RR strain, the synergistic potential of these agents to cypermethrin was similar in the SS strain, demonstrating that metabolism-mediated detoxification was not important for conferring resistance to cypermethrin in the Gol-RR strain. However, the three agents did not act synergistically with imidacloprid, indicating that other mechanisms may be responsible for the development of resistance to this insecticide. Acetylcholinesterase (AChE) activity was 13.70-fold higher in the Gol-RR than in the SS strain, suggesting the properties of the AChE enzyme were altered in the Gol-RR strain. Thus, rotation of chlorfenapyr insecticide with other agents acting through a different mode with minimal/no resistance could be an effective resistance management strategy for housefly.     

Molecular mechanisms conferring asymmetrical cross-resistance between tebufenozide and abamectin in Plutella xylostella

Based on the confirmation of asymmetrical cross-resistance between abamectin and tebufenozide in Plutella xylostella, the present work proved that the cytochrome P450 monooxygenase plays a decisive role in cross-resistance, and the expression of various cytochrome P450 (CYP450) genes in different strains was surveyed to elucidate the molecular basis of the underlying mechanisms. Enzyme analysis showed the activity of cytochrome P450 monooxygenase was notable enhanced in the strains resistant to both tebufenozide (3.07-fold) and abamectin (3.37-fold), suggesting that the enhancement of cytochrome P450 monooxygenase is the main detoxification mechanism responsible for the cross-resistance. CYP4M7 (64.58-fold) and CYP6K1 (41.97-fold) had extremely high expression levels in the Teb-R strain, selected using tebufenozide, which was highly resistant to tebufenozide (RR 185.5) and moderately cross-resistant to abamectin (RR 41.0). When this strain was subjected to further selection using abamectin, the resultant Aba-R strain showed a higher expression of CYP6K1 (60.32-fold). However, the expression of CYP4M7 was reduced (10.62-fold). Correspondingly, the Aba-R strain became more resistant to abamectin (RR 593.8) and less resistant to tebufenozide (RR 28.0). Therefore, we concluded that the over expression of CYP4M7 was the main cause for tebufenozide resistance, and that CYP6K1 mainly conferred abamectin resistance. The asymmetrical cross-resistance occurred because tebufenozide selection not only enhanced the expression of CYP4M7, but also that of CYP6K1. This is the first report on the molecular mechanism of asymmetrical cross-resistance between insecticides.     

棉蚜啶虫脒抗性种群交互抗性和增效剂增效作用的研究

【目的】明确棉蚜Aphis gossypii Glover啶虫脒抗性品系与其它杀虫剂的交互抗性现状以及增效剂的增效作用,为延缓和治理棉蚜对啶虫脒的抗性提供依据。【方法】采用单头反选育和群体汰选的方式,获得了棉蚜啶虫脒敏感和抗性品系;采用叶片药膜法测定了13种杀虫剂对啶虫脒的交互抗性以及增效剂对啶虫脒的增效作用。【结果】经过室内棉蚜敏感和抗性品系的筛选,获得了相对抗性倍数为82.33倍的棉蚜啶虫脒抗性品系。棉蚜啶虫脒抗性品系的交互抗性谱的研究表明,交互抗性倍数小于5的药剂为:吡蚜酮,甲基阿维菌素;交互抗性倍数在5~10倍的药剂为:噻虫嗪,联苯菊酯,毒死蜱,马拉硫磷,丙溴磷,辛硫磷;交互抗性倍数在10~15倍的药剂为:硫丹,阿维菌素,高效氯氰菊酯,三唑磷,氧化乐果;交互抗性倍数大于1 5倍的药剂为:吡虫啉。增效剂实验表明,TPP和PBO在啶虫脒敏感品系中增效作用不明显,但在抗性品系中增效作用显著。在啶虫脒抗性品系中的增效比为1.77、1.61,在啶虫脒敏感品系中的增效比为1.02、1.03。DEM在啶虫脒抗性、敏感品系中的增效作用均不明显,增效比为1.04、1.02。TPP和PBO对啶虫脒有很好的增效作用。以室内棉蚜敏感品系(LC_(50)为0.180 mg/L)为基础,对新疆各主要棉区的棉蚜种群进行了啶虫脒药剂的抗性调查,结果表明新疆各主要棉区棉蚜对啶虫脒的相对抗性倍数为6.1~22.0倍。【结论】由此说明新疆主要棉区棉蚜对啶虫脒具有一定的抗性风险,生产中可以利用无交互抗性的吡蚜酮和甲基阿维菌素来治理抗性棉蚜种群。