Realized heritability of resistance to dicrotophos in greenhouse whitefly

Realized heritability (h ²) of resistance to dicrotophos in greenhouse whitefly,Trialeurodes vaporariorum Westwood, was estimated from a laboratory selection experiment. Five generations of selection increased the LC₅₀ approximately 13-fold. Estimatedh ² of resistance to dicrotophos was 0.40 when calculated with the method of Tabashnik (1992) and 0.35 with the method of Tanaka & Noppun (1989). These results suggest that 35 to 40% of the total phenotypic variation in resistance was caused by additive genetic variation. For thirteen previously reported estimates ofh ² of insecticide resistance in other insect pests, the mean was 0.29. The relatively highh ² of dicrotophos resistance forT. vaporariorum is consistent with rapid resistance development in field populations.     

Baseline susceptibility of persea mite (Acari: Tetranychidae) to abamectin and milbemectin in avocado groves in Southern California

Persea mite, Oligonychus perseae Tuttle, Baker, and Abatiello, susceptibility to abamectin and milbemectin was evaluated in 2003 to determine baseline susceptibility levels in avocado groves in San Diego and Ventura Counties (California, USA) where more than 70% of the state’s avocado production is concentrated. Milbemectin has yet to be used in avocado production in California and abamectin has been available for use since 1999. Baseline susceptibility ratios (in relation to the most susceptible population) of five persea mite field strains to milbemectin varied 2.1- to 2.8-fold at the LC₅₀ and LC₉₀, respectively. The susceptibility of seven field strains to abamectin varied slightly more (2.1- to 3.5-fold) with one strain subjected to seven sprays over the past 4 years showing slight but significant separation of LC₅₀ and LC₉₀’s from the most susceptible strain, which is suggestive of the early stages of resistance to this product. Based on these data, baseline susceptibility levels are proposed that might be used to monitor for future persea mite resistance to these chemicals as their use in California avocado production continues.     

Insecticide resistance in populations of Tuta absoluta (Lepidoptera: Gelechiidae)

1 Control failures of insecticides used against the tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Brazil led to the investigation of the possible occurrence of resistance of this insect pest to abamectin, cartap, methamidophos and permethrin. 2 The insect populations were collected from seven sites in the states of Minas Gerais, Rio de Janeiro, and São Paulo. These populations were subjected to concentration–mortality bioassays using insecticide‐impregnated filter papers. 3 We were unable to obtain a single population which provided a susceptibility standard for all insecticides tested. Therefore, the resistance levels were estimated in relation to the most susceptible population to each insecticide. Resistance to abamectin and cartap were observed in all populations when compared with the susceptible standard population, with resistance ratios ranging from 5.2‐ to 9.4‐fold and from 2.2‐ to 21.9‐fold for abamectin and cartap, respectively. Resistance to permethrin was observed in five populations with resistance ratios ranging from 1.9‐ to 6.6‐fold, whereas resistance to methamidophos was observed in four populations with resistance ratios ranging from 2.6‐ to 4.2‐fold. 4 The long period and high frequency of use of these insecticides against this insect pest suggest that the evolution of insecticide resistance on them has been relatively slow. Alternatively, the phenomenon might be widespread among Brazilian populations of T. absoluta making the finding of suitable standard susceptible populations difficult and leading to an underestimation of the insecticide resistance levels in this pest. 5 Higher levels of resistance to abamectin, cartap and permethrin are correlated with greater use of these compounds by growers. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.     

The stability of tebufenpyrad resistance in two-spotted spider mite (Acari: Tetranychidae) under laboratory conditions

The successful use of chemical rotations to manage insecticide resistance requires reversion between alternate chemical applications. We tested a tebufenpyrad resistant population of Tetranychus urticae Koch after some 55 months laboratory culture without pesticide selection and found LC₅₀ level resistance had dropped from 63.29- to 2.41-fold. However, the population was still heterogeneous with LC₉₉ level resistance at 38.03-fold. It is likely that a lack of reversion contributed directly to the initial tebufenpyrad control failure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Insecticide susceptibility and resistance of Culex tritaeniorhynchus (Diptera: Culicidae) larvae collected from Gwangju,Republic of Korea

The susceptibility of Culex tritaeniorhynchus collected from Gwangju, Jeollabuk Province, Republic of Korea (ROK) to insecticides was evaluated under laboratory conditions using ten insecticides (7 pyrethroids and 3 organophosphates) that are currently applied by local public health centers in the ROK. Based on the values of median lethal concentration (LC₅₀), Cx. tritaeniorhynchus larvae were most susceptible to chlorpyrifos (0.006 ppm), fenitrothion (0.022 ppm), fenthion (0.035 ppm) and bifenthrin (0.038 ppm), and were least susceptible to esbiol (1.722 ppm). In comparative resistance tests, the resistance ratios (RRs) of seven insecticides were compared among each other using two strains of Cx. tritaeniorhynchus that were collected from the same locality during 1992 and 2010. Culex tritaeniorhynchus demonstrated significantly increased RRs to pyrethroids over time, while demonstrating decreased RRs among the organophosphates. Among the pyrethroids, permethrin had the highest RR values of 182.1‐ and 833.3‐fold differences, followed by etofenprox with RRs of 138.4‐ and 224.1‐fold differences in values of LC₅₀ and concentration that produced 90% mortality (LC₉₀), respectively. Culex tritaeniorhynchus strains demonstrated the least amount of change in susceptibility to the organophosphates, chlorpyrifos, fenitrothion and fenthion with 0.020‐, 0.019‐ and 0.001‐fold differences in resistance ratios (RRLC₅₀), respectively.     

First detection of <Emphasis Type="Italic">Varroa destructor</Emphasis> resistance to coumaphos in Argentina

In Argentina, studies on Varroa destructor resistance to coumaphos are still unknown. At present, high infestation levels of V. destructor are being detected in colonies of Apis mellifera after treatment with this acaricide. The aim of the present study was to determine the LC₅₀ of coumaphos in V. destructor from four apiaries with high mite density after treatment with coumaphos. The LC₅₀’s were 112, 319, 127 and 133 μg/Petri dish for mites from the four apiaries. Significant LC₅₀ differences were detected between resistant and susceptible mites. LC₅₀ increased 197–559-fold when compared to the corresponding baseline, suggesting the development of resistance. These results are the first report of resistance to coumaphos in V. destructor in Argentina.     

Insecticide resistance in damson-hop aphid, Phorodon humuli in commercial hop gardens in Kent

From 1966 to 1976, samples of Phorodon humuli were collected annually from five commerical hop gardens in Kent and from other hop gardens where problems in control occurred. A susceptible stock was obtained from wild hop growing in northern England in 1969. The samples were cultured in isolation on potted hops and bioassayed against insecticides in common use. The level of resistance to demeton-S-methyl was c. 10X in 1966 after 10 yr use, and more than doubled from 1968–1974 apparently due to the spread of a more resistant type; there was a further increase to c. 50X in 1975–1976. There was also resistance of C. 20–30X to omethoate, 2–7X to methidathion and 4–8X to methomyl. Assays and field results show an increased resistance to methidathion and less certainly to methomyl after 5 yr use. There was no clear change in response to endosulfan. The LC₅₀'s estimated from a single dose and a mean probit slope were found to agree satisfactorily with the LC₅₀'s calculated from serial doses and so should be adequate for monitoring trends in resistance.     

Genetic improvement of Amblyseius finlandicus (Acari: Phytoseiidae): laboratory selection for resistance to azinphosmethyl and dimethoate

Amblyseius finlandicus (Oudemans) was selected in the laboratory for resistance to azinphosmethyl and dimethoate by subjecting adult females to increasing concentrations of dried residues of dimethoate and azinphosmethyl on detached bean leaves. The first eight selections were done with dimethoate. Slide-dip bioassays indicated selection with dimethoate increased dimethoate resistance 1.8-fold and azinphosmethyl resistance 2.6-fold. These resistances appeared to be quite stable: a 1.2 to 1.3-fold decrease in resistance ratios was observed in a subculture after 10 months without selections. No decrease was observed after 9 months without selections in a pooled colony that consisted of both resistant and susceptible mites. The dimethoate-selected colony was subsequently selected eight times with azinphosmethyl. About 15 % of the mites survived the last selection round with 2,500 ppm, which is 2.5 times the highest recommended field rate in Finnish apple orchards. At the end of the selection program, based on slide-dip bioassays, the total increase in resistance to dimethoate was about two-fold and to azinphosmethyl about 5.4-fold compared to the unselected base colony from which the selected colony was derived. The LC₅₀ value for azinphosmethyl was 14 times higher in the selected colony (451.3 ppm a.i.) compared to the most susceptible colony tested. A similar level of resistance to both pesticides was achieved after six azinphosmethyl selections on a mixed colony that was initiated by pooling mites from five field-collected colonies and the dimethoate-selected lines. Year-to-year variation in azinphosmethyl LC₅₀ values of the unselected base colony was high, with values varying from 83.8 to 348.7 ppm a.i., demonstrating the need to test a reference strain in each bioassay. Results of the azinphosmethyl selections and the subsequent slide-dip bioassays suggest that the resistant strain could tolerate field rates of azinphosmethyl (300–950 ppm a.i.) used in Finnish apple orchards.     

Differential susceptibility of Cotesia orobenae, a parasitoid of the cross-striped cabbageworm, to commonly used insecticides in Cruciferae

The larval endoparasitoid Cotesia orobenae Forbes (Hymenoptera: Braconidae) is an effective natural enemy of the cross-striped cabbageworm, Evergestis rimosalis (Guenée) (Lepidoptera: Pyralidae), in southwest Virginia. Routine use of insecticides to control Plutella xyostella (L.) and other lepidopterous larvae in commercial plantings of cabbage, cauliflower and broccoli can disrupt populations of C. orobenae, causing localized outbreaks of the cross-striped cabbageworm to occur. Since the use of insecticides is the choice insect pest management tactic of growers in southwest Virginia, we examined the differential susceptibility of this hymenopteran parasitoid to four frequently used pesticides, methomyl (carbamate), permethrin and esfenvalerate (pyrethroids), and Bacillus thuringiensis Berliner subsp. Kurstaki (bacterium). Filter paper dipped into four different concentrations of methomyl, permethrin, and esfenvalerate were left to dry and then exposed to C. orobenae. Two concentrations of B. thuringiensis were also tested by contact bioassay, and an additional test was conducted by mixing B. thuringiensis with honey and water as a food source for the insects. Ten adult parasitoids were exposed to each treatment, replicated 10 times. Significant differences in mortality among insecticides tested (p < 0.05) were found. Most toxic to C. orobenae was permethrin, followed by esfenvalerate and methomyl. The parasitoid was not affected by B. thuringiensis when placed in contact with B. thuringiensis-treated broccoli leaves, or by ingestion of honey mixed with it (p < 0.05).     

Insecticide Susceptibilities of Anopheles sinensis (Diptera: Culicidae) Larvae from Paju-shi, Korea

A study was conducted to determine the susceptibility of Anopheles sinensis larvae, malaria vector, from Paju‐shi (Gyonggi‐do) to 24 pesticides including 11 pyrethroids, 11 organophosphates, 1 pyrazole analogue and another pesticide. The mosquito larvae showed the most highly susceptible to chlorfenapyr with LC₅₀ of 0.0063 ppm followed by spinosad, temephos, fenthion and beta‐cyfluthrin with 0.03, 0.0366, 0.0367 and 0.0998 ppm, respectively, and fluvalinate (>128 ppm) was the least susceptible. Also, 11 pesticides of them were compared with Goyang strain (Gyonggi‐do) of data 1992. The development of resistance was noticed to cypermethrin and permethrin as much of 73.59 and 6.23 folds at LC₅₀, respectively, and also fluvalinate was showed high resistance development. In generally, the pyrethroid insecticides were showed higher development of resistance than organophosphorus insecticides.     

棉铃虫核型多角体病毒与化学杀虫剂和卵磷脂混用的增效作用

棉铃虫核型多角体病毒(HaNPV)分别与三氟氯氰菊酯、溴氰菊酯、氰戊菊酯、灭净菊酯、灭多威、辛硫磷、甲基对硫磷和乙酰甲胺磷等化学杀虫剂混合饲喂棉铃虫幼虫,统计致死中浓度LC₅₀,计算增效比,测定虫体内与抗性有关的三种重要酶：多功能氧化酶(MFO)、羧酸酯酶(CarE)、乙酰胆碱酯酶(AChE)的活性。研究大豆卵磷脂对HaNPV致病性的影响。结果表明：HaNPV与化学杀虫剂混合饲喂抗性棉铃虫,生测统计增效比均大于1.0,特别是病毒与甲基对硫磷混用,增效比更是达到3.53,表现出良好的增效作用。混剂感染抗性棉铃虫,虫体内MFO的活性比化学杀虫剂单用时降低3～12倍,CarE和AChE的活性也比化学杀虫剂单用时低,HaNPV明显抑制了化学杀虫剂对MFO和CarE的诱导作用。HaNPV与大豆卵磷脂混用,提高了HaNPV对棉铃虫的感染致死率,缩短了致死中时间(LT₅₀)。     

Baseline susceptibility of Helicoverpa armigera,Plutella xylostella,and Spodoptera frugiperda to the meta-diamide insecticide broflanilide

Broflanilide is a novel meta-diamide insecticide that acts as a γ-aminobutyric acid-gated chloride channel allosteric modulator. With its unique mode of action, broflanilide has no known cross-resistance with existing insecticides and is expected to be an effective tool for the management of insecticide resistance. Establishing the baseline susceptibility to this insecticide is an essential step for developing and implementing effective resistance management strategies. Here we evaluated the baseline susceptibility to broflanilide for 3 cosmopolitan lepidopteran pest species, Helicoverpa armigera, Plutella xylostella, and Spodoptera frugiperda. Broflanilide exhibited high activity against populations sampled in the major distribution range of these pests in China, with median lethal concentrations (LC₅₀) ranging between 0.209 and 0.684, 0.076 and 0.336, and 0.075 and 0.219 mg/L for H. armigera, P. xylostella, and S. frugiperda, respectively. Among-population variability in susceptibility to broflanilide was moderate for H. armigera (3.3-fold), P. xylostella (4.4-fold), and S. frugiperda (2.9-fold). The recommended diagnostic concentrations for H. armigera, P. xylostella, and S. frugiperda were 8, 4, and 2 mg/L, respectively. Little or no cross-resistance to broflanilide was detected in 3 diamide-resistant strains of P. xylostella and 1 spinosyns-resistant strain of S. frugiperda. Our results provide critical information for the development of effective resistance management programs to sustain efficacy of broflanilide against these key lepidopteran pests.     

Assessment of insecticide resistance after the outbreak of diamondback moth (Lepidoptera: Plutellidae) in California in 1997

During an outbreak of the diamondback moth, Plutella xylostella (L.), in California in 1997, nine populations were collected from the major broccoli areas throughout the state. Populations were assayed for their susceptibility to currently used materials (Bacillus thuringiensis subsp. kurstaki, permethrin, and methomyl) and to newer materials that had not yet been commercially used in California (spinosad, emamectin benzoate, and chlorfenapyr). For the currently used insecticides, elevated levels of resistance were seen only with permethrin and seven of the nine populations had tolerance ratios (TR) of > 100. With the newer chemistries, TR values were all < 15. To compare potential cross-tolerance, TR values of the currently used insecticides were compared with TR values of the newer insecticides. There were significant relationships found between: methomyl and emamectin benzoate, methomyl and spinosad, and permethrin and spinosad. Further biochemical studies are needed to confirm the actual mechanisms that lead to these relationships and field tests are needed to determine what impact, if any, such TR levels would have on control in the field. These data indicate that resistance to at least one of the commonly used insecticides (permethrin) may have played a role in the outbreak during 1997. However, other factors may have been at least equally important. The winter of 1996-1997 was warmer than normal, and during the period from February through August of 1997 the amount of rainfall was < 50% of normal. Hot and dry conditions are known to be conducive to outbreaks of P. xylostella. These data add to an overall knowledge about the geographic variation of resistance in P. xylostella populations within the United States. They also serve as a baseline for monitoring changes in susceptibility to these newer insecticides and can also help explain the occurrence of outbreaks caused by factors other than insecticide resistance.     

Mortality and knockdown effects of imidacloprid and methomyl in house fly (Musca domestica L., Diptera: Muscidae) populations

In this study, the knockdown and mortality effects of imidacloprid and methomyl were investigated. The residual surface applications were carried out to determine the knockdown effects (KDt₅₀ and KDt₉₅) and mortality (LD₅₀ and LD₉₅) induced by each insecticide. For mortality comparisons, the susceptible house fly (Musca domestica L., Diptera: Muscidae) of a WHO population and three natural field‐collected M. domestica populations from Turkey were used. In conclusion, it was found that the resistance to imidacloprid and methomyl was significantly higher in the field populations when compared to the susceptible population from WHO. The results showed that applicators and pest management decision‐makers should control and conduct an integrated pest management strategy by including biological agents to prevent the development of high levels of resistance in the field populations.     

Effects of Insecticides on Movement,Nictation, and Infectivity of Steinernema carpocapsae

Movement, nictation, and infectivity of Steinernema carpocapsae strain All were compared for ensheathed (EnJ) and desheathed (DeJ) infective juveniles exposed to the insecticides acephate, dichlorvos, methomyl, oxamyl, or permethrin. Nematode response to various solutions included normal sinusoidal movement, uncoordinated motion, twitching, convulsion or formation of a pretzel shape, an inactive "S" posture with fine twitching, or a quiescent straight posture. The DeJ displayed these movements at lower concentrations of each insecticide than did EnJ. In petri dish bioassays, insecticide-treated EnJ caused generally lower mortality in the common cutworm, Spodoptera litura, than did EnJ alone but caused greater insect mortality than did insecticides alone. Nematode response to chemicals was more clearly demonstrated by nictating behavior than by the movement bioassay. Nictation of DeJ was suppressed by the test chemicals at low concentrations, except for acephate and permethrin. Nictating EnJ or DeJ, regardless of chemical treatment, killed host insects faster than did non-nictating juveniles. Insecticides that enhance nictating behavior at certain concentrations may be used for mixed applications with nematodes.     

First report of amitraz and cypermethrin resistance in Rhipicephalus sanguineus sensu lato infesting dogs in Mexico

Engorged female Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae) were collected from dogs in the state of Yucatán, Mexico. Fourteen tick populations were collected from dogs at seven veterinary clinics, four residential homes and three cattle farms. The larval immersion test was used in the progeny of collected adult females to test susceptibility to amitraz and cypermethrin. Dose–mortality regressions, 50% lethal concentrations (LC₅₀), confidence intervals and slope were estimated by probit analysis. For amitraz, 12 tick populations (85.7%) were classified as resistant and low inter‐population variation in the phenotypic level of resistance was evident [resistance ratios (RRs) at LC₅₀: 1.0–13.0]. For cypermethrin, 12 tick populations (85.7%) were classified as resistant and substantial inter‐population variation in the phenotypic level of resistance was evident (RRs at LC₅₀: 1.0–104.0). Thus, amitraz resistance in R. sanguineus s.l. is common, but generally occurs at low levels; however, alarmingly high levels of cypermethrin resistance are present in R. sanguineus s.l. populations in dogs in Yucatán, Mexico. The intensive use of both acaricides to control ectoparasites on dogs is likely to lead to more serious resistance problems that may cause high levels of control failure in the future.     

Determination of LC50 of permethrin acaricide in semi-engorged females of the tick Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae)

Currently, the most efficient and widely used method of tick control still is the treatment with acaricides, especially permethrin (active ingredient of the Advantage^® Max3, Bayer), a pyrethroid with neurotoxic action. Due to the wide use of this acaricide in the control of the tick Rhipicephalus sanguineus, this study carried out laboratorial procedures to determine the LC₅₀ (lethal concentration fifty) of permethrin in semi-engorged females of R. sanguineus. Based on the result of 14 dilutions of permethrin in distilled water and later Probit analysis, the LC₅₀ of permethrin for R. sanguineus was 2062 ppm (1549-2675 ppm). This work can be used as a protocol with other chemicals, to determinate the LC₅₀, basic procedure for studies of control, resistance and behavior of ticks treated with acaricides, especially the brown dog tick R. sanguineus. Also, the knowledge of the LC₅₀ provides information on the potency of chemicals, the sensitivity of Arthropods to them and even estimates on pest control.     

Pyrethroid resistance in Anopheles gambiae s.s. and Anopheles arabiensis in western Kenya: phenotypic,metabolic and target site characterizations of three populations

Field and laboratory investigations revealed phenotypic, target site and metabolic resistance to permethrin in an Anopheles gambiae s.s. (Diptera: Culicidae) population in Bungoma District, a region in western Kenya in which malaria is endemic and rates of ownership of insecticide‐treated bednets are high. The sensitivity of individual An. gambiae s.l. females as indicated in assays using World Health Organization (WHO) test kits demonstrated reduced mortality in response to permethrin, deltamethrin and bendiocarb. Estimated time to knock‐down of 50% (KDT₅₀) of the test population in Centers for Disease Control (CDC) bottle bioassays was significantly lengthened for the three insecticides compared with that in a susceptible control strain. Anopheles arabiensis from all three sites showed higher mortality to all three insecticides in the WHO susceptibility assays compared with the CDC bottle assays, in which they showed less sensitivity and longer KDT₅₀ than the reference strain for permethrin and deltamethrin. Microplate assays revealed elevated activity of β‐esterases and oxidases, but not glutathione‐S‐transferase, in An. gambiae s.s. survivors exposed to permethrin in bottle bioassays compared with knocked down and unexposed individuals. No An. arabiensis showed elevated enzyme activity. The 1014S kdr allele was fixed in the Bungoma An. gambiae s.s. population and absent from An. arabiensis, whereas the 1014F kdr allele was absent from all samples of both species. Insecticide resistance could compromise vector control in Bungoma and could spread to other areas as coverage with longlasting insecticide‐treated bednets increases.     

Seasonal fluctuation in susceptibility to insecticides within natural populations of Drosophila melanogaster: empirical observations of fitness costs of insecticide resistance

To investigate genetic variation and seasonal fluctuation in susceptibility to insecticides, natural populations of Drosophila melanogaster were collected from Katsunuma in mid summer and late fall for two consecutive years. After isofemale lines of each population collected in each season had been established in a laboratory, the susceptibility of each line to five insecticides, including permethrin, malathion, prothiophos, fenitrothion, and DDT, was examined. Lines of each population exhibited the broad ranges of variation in susceptibility to all chemicals. Comparison between populations in different seasons indicated that genetic variation in susceptibility to organophosphates fluctuated in consistency with the population size, in which the susceptibility increased in fall. In addition, highly significant correlations were observed among responses to organophosphates, and the correlations also fluctuated with seasons. On the other hand, genetic variation in susceptibility to permethrin and DDT was less fluctuated. These results suggest that not only a common resistance factor for organophosphate resistance but also different resistance factor(s) for each insecticide could be involved within a natural population, and that the fluctuation observed in the susceptibility to organophosphates could be associated with fitness costs of organophosphate resistance factor(s).     

Evaluation of Resistance Pattern to Fenpyroximate and Pyridaben in Tetranychus Urticae collected from Ggreenhouses and Apple Orchards using Lethal Concentration-slope Relationship

This study aimed to monitor the present and future developments of the resistance of Tetranychus urticae Koch to fenpyroximate and pyridaben, using the relationship of the LC₅₀ and slope of the concentration-mortality line in a probit model, for the provision of reliable resistance management tactics. Tetranychus urticae populations were collected from 16 commercial greenhouses, where various crops were cultivated, as well as from 10 apple orchards throughout Korea. The resistance to fenpyroximate and pyridaben of each population was estimated by calculating the median lethal concentration (LC₅₀), resistance ratio (RR) and slope of the concentration-mortality regression. Most of the greenhouse populations exhibited moderate levels of resistance, whereas the apple orchard populations showed only low levels, indicating that T. urticae populations in greenhouses were more strongly selected than those in apple orchards. Four population groups were established based on either the habitats (greenhouse and apple orchard) or acaricides (fenpyroximate and pyridaben). To test the hypothesis, “the slope is greatest at low and high levels of resistance,” the slopes were regressed as a function of the LC₅₀, and fitted to a polynomial regression. The polynomial regression model explained this relationship well for the four population groups (p < 0.05), indicating that the development of resistance toward fenpyroximate or pyridaben was consistent with the gradient. A laboratory selection study agreed with the results from both acaricide field populations. These results suggest that the gradient was a good indicator of the susceptibility of T. urticae to genetic variations, which was related to the LC₅₀. The application of these findings is also discussed in relation to the resistance management of T. urticae.