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.     

Efficacy of Metarhizium anisopliae in controlling the two‐spotted spider mite Tetranychus urticae on common bean in screenhouse and field experiments

The efficacy of aqueous and emulsifiable formulations of the fungus Metarhizium anisopliae isolate ICIPE78 was evaluated on the population density of Tetranychus urticae infesting common bean plants under screenhouse and field conditions. Synthetic acaricide abamectin was included as a check. Bean plants were artificially infested with T. urticae and allowed to multiply. Three treatments were applied in the screenhouse and 1 treatment in field trials. Mite density was recorded 2 d before spraying and weekly postspraying. The number of pods per plant, number of seeds per pod, and the dry weight of seeds per plant were recorded only in the screenhouse trials. In both screenhouse and field trials, fungal formulations applied at the concentration of 10⁸ conidia/mL and the acaricide reduced the population density of mites as compared to the controls. There were significant differences in T. urticae population densities between the treatments at the various post‐spraying sampling dates. In the screenhouse, the mite densities were near zero from 3‐week postspraying in the treated leaves. At 4‐week postspraying, there were no more leaves in the untreated control (T1) and in the control water + Silwet‐L77 (T2). Fungal formulations were as effective as abamectin in reducing mite densities in both screenhouse and field experiments. There were significant differences in the production parameters during the 2 screenhouse trials, with fungal and abamectin treatments generally having the highest yield. Results of this study underline the potential of the M. anisopliae isolate ICIPE78 as an alternative to acaricides for T. urticae management.     

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.     

Interactions in the biological control of western flower thrips Frankliniella occidentalis (Pergande) and two-spotted spider mite Tetranychus urticae Koch by the predatory bug Orius insidiosus Say on beans

An omnivore shows preference to its preys and thus its control efficiency could be altered in different mix infestation system. The efficiency of Orius insidiosus for biocontrol of either Frankliniella occidentalis or Tetranychus urticae alone or for the two pests in combinations was studied on beans. When only mites or thrips were offered as prey, 1 or 2 O. insidiosus could considerably suppress pest populations at an initial density of 20, 40, and 80 adult female mites, and 100 and 160 thrips larvae, respectively. A single O. insidiosus was able to reduce mite populations by 52.9, 38.7, and 25.8% at initial densities of 20, 40, and 80 mites, respectively, two bugs achieved control levels of 60.6, 63.1, and 38.4%. Releases of 1 and 2 O. insidiosus resulted in corrected mortalities of 62.5 and 87.9%, and 46.3 and 71.9% in F. occidentalis at initial larval densities of 100 and 160, respectively. When two pests were simultaneously offered, the efficiency of O. insidiosus in controlling T. urticae markedly decreased. Furthermore, mite control decreased with increasing T. urticae densities and was also affected by the density of O. insidiosus. The presence of mites at initial densities of 20–80 females did not significantly influence thrips control by O. insidiosus. The presence of F. occidentalis resulted in higher oviposition by O. insidiosus females than the presence of mites, indicating that thrips are a more suitable resource than T. urticae for O. insidiosus. The implications for biocontrol of F. occidentalis and T. urticae are discussed.     

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.     

Entomopathogenic nematodes for biological control of the leafminer,Liriomyza trifolii (Dipt.: Agromyzidae)

In the laboratory, mortality rates of the agromyzid leafminer larvae,Liriomyza trifolii (Burgess), ranged from 48 to 98% by 20 strains and/or species of steinernematid and heterorhabditid nematodes. In the greenhouse, abamectin provided superior control of larval leafminers, killing 100% of them as compared withSteinernema carpocapsae (Weiser) All strain (24 to 43% leafminer mortality) orS. carpocapsae Liriomyza-selected strain (8 to 44% leafminer mortality); the maximum relative humidity (r.h.) ranged between 81 and 91% and the minimum r.h. between 50 and 70%. In the foghouse under high r.h., the commercially available All strain and the Hawaiian isolate ofS. feltiae (Filipjev) MG-14 strain caused 69 and 67% mean mortality, respectively. There was a significant correlation (P<0.01) between nematode mortality of leafminers and r.h., including the mean, standard deviation, and minimum r.h. during the 48 h after treatment. Average r.h. >92% with a standard deviation of <9% r.h. and a minimum of 72% r.h. providedS. carpocapsae All strain mortality rates of leafminers >65%. The major constraint against the use of nematodes against leafminers in the foliar environment is low r.h. The use of nematodes againstL. trifolii can be successful if the r.h. remains high and if nematodes enter leafmines before desiccation, and the nematodes should be integrated with chemical insecticides such as abamectin to manage pesticide resistance inL. trifolii.     

不同猎物饲喂对南方小花蝽捕食量和喜好性的影响

为探讨南方小花蝽对不同猎物的捕食喜好性,室内用西花蓟马、蚕豆蚜、二斑叶螨、混合饲料(同时饲喂3种猎物)分别饲喂南方小花蝽驯化两代,研究了4种饲喂处理的南方小花蝽初孵若虫、5龄若虫和雌成虫对西花蓟马、蚕豆蚜和二斑叶螨的捕食量和喜好性。结果显示不同猎物饲喂处理驯化的南方小花蝽1龄若虫对同一种猎物的捕食量和喜好性均不存在显著差异。南方小花蝽5龄若虫和雌成虫对某种猎物的捕食量因前期取食的猎物种类不同而有显著差异。南方小花蝽5龄若虫和雌成虫均表现出对西花蓟马2龄若虫的正喜好性。蚕豆蚜饲喂处理的5龄若虫和雌成虫对蚕豆蚜表现出正喜好性,除二斑叶螨饲喂处理外其余3种处理的南方小花蝽5龄若虫和雌成虫均表现出对二斑叶螨的负喜好性。以上结果表明4种饲喂驯化处理的南方小花蝽1龄若虫的喜好性不受前期取食猎物的影响,但5龄若虫和雌成虫对前期取食过的猎物的喜好性增强,存在一定的学习行为。     

Screening of Some Crude Plant Extracts for Their Acaricidal and Insecticidal Efficacies

Methanol extracts from 28 samples of 22 plant species in 17 different plant families were tested at 10, 000 ppm for evaluating their insecticidal and acaricidal activities against Tetranychus urticae Koch, Aphis gossypii Glover, Myzus persicae Sulzer, Trialeurodes vaporariorum (Westwood), and Panonychus citri (McGregor). In a test with T. urticae, extracts from Albizzia coreana twig and Pyracantha angustifolia leaf possessed potent acaricidal activities. Reproduction of T. urticae for three days significantly decreased in the extract treatments of Gardenia jasminoides, Ficus carica, and Albizzia coreana twigs. Though slight repellent activities against T. urticae were obtained from extracts of Camellia japonica seed, G. jasminoides peel and fruits, Ligustrum japonicum leaves, A. coreana twig, and Machilus thunbergii leaves in 24 h after treatment, but tended to decrease in 72 h. Extracts of F. carica leaves and G. jasminoides fruits had potent insecticidal activities against M persicae and A. gossypii. Methanol extracts of F. carica leaves possessed insecticidal activity against T. vaporariorum. In a field test with P. citri, extracts from C. japonica seeds, A. coreana leaves, Ranunculus japonicus leaves and roots, an Houttuynia cordata leaves exhibited acaricidal activities.     

Differences in the susceptibility of five herbivore species and developmental stages to tomato resistance induced by methyl jasmonate treatment

We compared the susceptibility of five herbivores to tomato resistance induced by methyl jasmonate (MeJA) treatment. We tested for lethal effects against five herbivores (Spodoptera litura, Mamestra brassicae, Frankliniella occidentalis, Tetranychus urticae, and Henosepilachna vigintioctopunctata) at various MeJA concentrations. The mortality of all five herbivores increased significantly with increasing MeJA concentration. The 25 % lethal concentration was 0.03 μM for both first-instar larvae of S. litura and third-instar larvae of M. brassicae, 0.51 μM for third-instar larvae of S. litura, 0.76 μM for adult T. urticae, 2.4 μM for first-instar larvae of F. occidentalis, and 5.7 μM for first-instar larvae of H. vigintioctopunctata. Thus, the degree of susceptibility to MeJA-induced resistance of tomato was first-instar larvae of S. litura = third-instar larvae of M. brassicae > third-instar larvae of S. litura ≈ adult T. urticae > first-instar larvae of F. occidentalis > first-instar larvae of H. vigintioctopunctata. Mortality of first-instar larvae of M. brassicae was >90 % at all concentrations. Mortality of fourth-instar larvae of H. vigintioctopunctata (<7 %) was similar to that of the control at all MeJA concentrations. We also detected statistically significant weight loss of the surviving lepidopteran larvae, increased larval duration of F. occidentalis and H. vigintioctopunctata, and reduced egg production by T. urticae grown on MeJA-treated tomato, suggesting that the MeJA-induced resistance can control these herbivores, but effectiveness is different on different species and growth stage. Feeding by both M. brassicae and H. vigintioctopunctata larvae activated JA-inducible genes in tomato.     

不同杀虫剂对西花蓟马的室内毒力及田间药效

【目的】西花蓟马是一种世界性的危险性入侵害虫,筛选防治西花蓟马的有效药剂可为生产中科学用药提供依据。【方法】通过室内毒力测定和田间药效试验,测定了2种化学药剂和8种生物药剂对西花蓟马成虫的致死中浓度(LC_(50))和药后不同时期的防治效果。【结果】室内毒力测定依据LC_(50)值将各药剂对西花蓟马的敏感性由高到低依次排序为乙基多杀菌素(0.1958 mg·L~(-1))、印楝素(0.9399 mg·L~(-1))、苦参碱(1.2483 mg·L~(-1))、阿维菌素(1.8096 mg·L~(-1))、高效氯氰菊酯(4.4458 mg·L~(-1))、藜芦碱(10.7628 mg·L~(-1))、鱼藤酮(18.1898 mg·L~(-1))、吡虫啉(46.3964 mg·L~(-1))、松脂酸钠(131.5214 mg·L~(-1))、苏云金杆菌(446.2318 mg·L~(-1));田间药效试验发现,乙基多杀菌素和吡虫啉防治西花蓟马均表现出较强的速效性和持效性,药后1～14 d的防效分别可达84%和73%以上;其次是藜芦碱,药后1～14 d的防效可达48.15%～61.37%;高效氯氰菊酯的防效较低,药后14 d的防效为46.22%;生物药剂阿维菌素、苏云金杆菌、苦参碱、印楝素的速效性均较低,但防效随施药后时间的延长而逐渐上升;鱼藤酮持效性最低。【结论】乙基多杀菌素和吡虫啉可推荐为生产中防治西花蓟马的首选药剂,植物源药剂藜芦碱和生物药剂阿维菌素可作为交替使用药剂。     

A population model for two-spotted spider mite Tetranychus urticae and its predator Metaseiulus occidentalis

A population simulation model that was developed for the fruit tree red spider mite (Panonychus ulmi Koch) and its phytoseiid predator (Amblyseius potentillae Garman) (Rabbinge, 1976) was adapted to Metaseiulus occidentalis Nesbitt and Tetranychus urticae Koch. The model uses life-table data for T. urticae and M. occidentalis and M. occidentalis' numerical and functional responses. The assumptions made in the model were tested by comparing the model outcome with the results of an independent greenhouse experiment. Sensitivity analyses were also done to evaluate the implicit assumptions of the model and to determine the relative importance of the rates and parameters used. Results of the sensitivity analysis showed that time of release is critical for rapid control of the prey population. Predator-prey release ratios and frequency of releases are relatively less important. Differences in functional and numerical response and predator dispersal rate also seem relatively less important than proper timing of releases.

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Zusammenfassung Ein Simulationsmodell, das für die Populationen der Obstbaumspinnmilbe (Panonychus ulmi Koch) und ihren Feind (Amblyseius potentillae Garman) entwickelt worden war (Rabbinge, 1976), wurde Metaseiulus occidentalis Nesbitt und Tetranychus urticae Koch angepasst. Das Modell verwendet Life-table Daten für T. urticae und M. occidentalis sowie die numerischen und funktionalen Reaktionen von M. occidentalis. Die im Modell gemachten Annahmen wurden getestet, indem das Modellergebnis mit den Resultaten eines unabhängigen Gewächshausversuchs verglichen wurde. Die Sensitivitätsanalyse zeigte, dass der Zeitpunkt der Freilassung entscheidend ist für eine rasche Begrenzung der Wirtspopulation. Das Räuber-Wirtverhältnis und die Häufigkeit der Freilassung sind weniger wichtig. Unterschiede in der numerischen und funktionalen Reaktion und die Ausbreitungsgeschwindigkeit scheinen ebenfalls weniger wichtig zu sein als der richtige Zeitpunkt der Freilassung.

     

Loss of residual activity of abamectin on foliage against adult hymenopteran parasitoids

The residual activity of abamectin against adult maleCotesia plutellae Kurdj. (Hym.:Braconidae) appeared to be markedly less on freshly sprayed Chinese cabbage (Brassica chinensis var. pekinensis cv Up Top) leaves compared with residues on glass. The residual activity of abamectin against adult maleDiadegma semiclausum Hellén (Hym.:Ichneumonidae) was also shown to decline rapidly on Chinese cabbage with no detectable activity remaining two days after spraying with concentrations in excess of the recommended field rates. The residual activity of abamectin against both species appeared to be consistently greater on Chinese cabbage compared with common cabbage (B. oleracea var. capitata cv Wheeler’s Imperial).     

Phenotypic- and Genotypic-Resistance Detection for Adaptive Resistance Management in Tetranychus urticae Koch

Rapid resistance detection is necessary for the adaptive management of acaricide-resistant populations of Tetranychus urticae. Detection of phenotypic and genotypic resistance was conducted by employing residual contact vial bioassay (RCV) and quantitative sequencing (QS) methods, respectively. RCV was useful for detecting the acaricide resistance levels of T. urticae, particularly for on-site resistance detection; however, it was only applicable for rapid-acting acaricides (12 out of 19 tested acaricides). QS was effective for determining the frequencies of resistance alleles on a population basis, which corresponded to 12 nonsynonymous point mutations associated with target-site resistance to five types of acaricides [organophosphates (monocrotophos, pirimiphos-methyl, dimethoate and chlorpyrifos), pyrethroids (fenpropathrin and bifenthrin), abamectin, bifenazate and etoxazole]. Most field-collected mites exhibited high levels of multiple resistance, as determined by RCV and QS data, suggesting the seriousness of their current acaricide resistance status in rose cultivation areas in Korea. The correlation analyses revealed moderate to high levels of positive relationships between the resistance allele frequencies and the actual resistance levels in only five of the acaricides evaluated, which limits the general application of allele frequency as a direct indicator for estimating actual resistance levels. Nevertheless, the resistance allele frequency data alone allowed for the evaluation of the genetic resistance potential and background of test mite populations. The combined use of RCV and QS provides basic information on resistance levels, which is essential for choosing appropriate acaricides for the management of resistant T. urticae.     

Oral delivery of double-stranded RNA induces prolonged and systemic gene knockdown in Metaseiulus occidentalis only after feeding on Tetranychus urticae

Metaseiulus (=Typhlodromus or Galendromus) occidentalis is an important biological control agent. Functional genomic studies on this predator have been hampered by the lack of reverse genetic tools such as RNA interference (RNAi). In the current study, we evaluated possible RNAi responses in M. occidentalis females by feeding double-stranded RNA (dsRNA) of RpL11, RpS2, RpL8, or Pros26.4 genes in 20 % sucrose solution. Females needed to subsequently feed on two-spotted spider mites (Tetranychus urticae) to elicit a nearly complete loss of egg production. The corresponding gene knockdown was robust, long-term, and was observed in the very few eggs produced (systemic or parental RNAi). Interestingly, dsRNA-mediated gene knockdown could not be induced if these predators were provided only the sucrose diet after ingesting dsRNAs; T. urticae had to be provided to elicit the RNAi response. However, the spider mite diet was not needed for sustaining the dsRNA-mediated gene knockdown once it commenced. Oral delivery of dsRNA will be a valuable tool for efficient genome-wide functional screens in this important predatory mite.     

Absorption and cannibalism: do phytoseiids conserve egg resources when prey densities decline rapidly?

The number of eggs oviposited or left in the opisthosomas of dead mites (total eggs) was assessed for Metaseiulus occidentalis (Nesbitt), Neoseiulus fallacis (Garman), Typhlodromus pyri Scheuten or Amblyseius andersoni Chant when each was caged with either (1) no Tetranychus urticae Koch, (2) only odours of T. urticae, (3) ten eggs of M. occidentalis or (4) ten nymphs of M. occidentalis (T. pyri for M. occidentalis). The total eggs for the no prey versus odour tests did not differ within species; the levels were the greatest for N. fallacis > T. pyri > A. andersoni > M. occidentalis. Among treatments, egg means did not differ for M. occidentalis but they did for N. fallacis and T. pyri and similar trends were seen for A. andersoni. Egg means were usually less for mites held with ten predator nymphs than mites held with ten predator eggs or with no prey. Were adult females with nymphs absorbing rather than ovipositing their eggs or dying with them in their opisthosomas? Activity levels (walking) for adult females were no more for mites held with nymphs versus no food. The data indicated that interference by nymphs was not increasing the energy use of females and thus reducing egg levels. However, tests with ten nymphs, one egg and no adult female had egg losses from nymphal predation that could account for fewer eggs in cage tests. Overall, no evidence for absorption was found. If it occurs, it must be among younger eggs or mites exposed to less rapid prey losses than were the mites tested here; in addition, other stimuli may cause absorption. The total eggs in sticky-tape tests were greatest for N. fallacis > M. occidentalis > T. pyri > A. andersoni. Cage versus stick-tape data differed most for M. occidentalis because of cannibalism. All four mites cannibalized eggs but M. occidentalis did most rapidly and extensively. When starved, it laid all of its eggs before the other three species did. Such behaviours may enhance survival of M. occidentalis when prey become scarce.     

Dispersal and gene flow of pesticide resistance traits in phytoseiid and tetranychid mites

Dispersal and gene flow of pesticide resistance traits in phytoseiid and tetranychid mites are discussed relative to their biologies and resistance management. The focus is on deciduous fruit-tree crops whereTyphlodromus pyri Scheuten andMetaseiulus occidentalis (Nesbitt) can effectively control spider mite pests. Oregon populations ofM. occidentalis were more dispersive thanT. pyri, as evidenced by movement to small apple trees placed inside and outside of commercial apple orchards. This difference was corroborated by the spatial distributions of organophosphate resistance in populations from sprayed orchards and nearby unsprayed habitats:T. pyri showed patchy, local patterns of resistance whileM. occidentalis showed more regional, homogeneous trends. Gene flow among populations was estimated from allozymic variation ofT. pyri. Intra- and inter-population genetic variation was high enough to prevent population differentiation. Thus, allozymic estimates of gene flow were higher than that indicated by pesticide resistance patterns.Dispersal inTetranychus urticae Koch is also discussed relative to resistance evolution. Immigration of resistant phenotypes from crops or other sprayed habitats can increase the frequency of resistance. Immigration of susceptible individuals from surrounding unsprayed habitat into a sprayed crop can slow resistance or lead to its reversion, depending on the level of gene flow between populations. Dispersal within crops can have the same effect if susceptibles come from a refuge. In pears, immigration of susceptibleT. urticae from nearby habitat and groundcover aided in reversion of organotin resistance. Experiments on resistance management tactics forT. urticae are discussed.     

Multiple resistance mechanisms to abamectin in the two-spotted spider mite

The two-spotted spider mite, Tetranychus urticae, is one of the most destructive pests of various orchard trees and garden plants. Biochemical mechanisms of abamectin resistance in two T. urticae strains (PTF, 239-fold resistance; AbaR, ca. 4753-fold resistance) were investigated. The involvement of both esterase (Est) and mixed function oxidase (MFO) in abamectin resistance was suggested by synergistic bioassays, in which median lethal time (LT₅₀) values were significantly reduced by pretreatment with triphenyl phosphate (TPP) and piperonyl butoxide, respectively. Detoxification enzyme assays confirmed that Est and MFO were related to abamectin resistance as metabolic factors. Moreover, some Est bands on a native isoelectric focusing gel were specifically inhibited by TPP, implying their association with resistance. Pretreatment with verapamil in synergistic bioassays did not reduce the LT₅₀ to abamectin, suggesting that the ABC transporter is not likely involved in resistance. However, enhanced MFO and Est activities in the AbaR strain were not enough to account for the extremely high level of abamectin resistance, which suggests the involvement of additional resistance mechanisms, such as target site insensitivity.     

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.     

Predation capacity,development and reproduction of the southern African flower bugs Orius thripoborus and Orius naivashae (Hemiptera: Anthocoridae) on various prey

The little-studied species Orius thripoborus (Hesse) and Orius naivashae (Poppius) (Hemiptera: Anthocoridae) have potential as biological control agents of thrips pests in southern Africa, but may also hold promise for the control of other harmful arthropods. In this study, the predation capacity, development, reproduction and growth rates of both predatory species on the key pests Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), Tetranychus urticae Koch (Acari: Tetranychidae) and Myzus persicae nicotianae Blackman (Hemiptera: Aphididae) were examined under laboratory conditions. Female adults of O. thripoborus and O. naivashae fed on 24 and 18 F. occidentalis 2nd instars, and 15 and 21 T. urticae eggs per day, respectively. Developmental and reproductive parameters of both Orius species were most favorable on F. occidentalis. Their intrinsic rates of increase (r_m) were highest when fed on F. occidentalis, averaging 0.123 and 0.131 females/female/day for O. thripoborus and O. naivashae, respectively. On the other prey, O. thripoborus showed significantly higher r_m-values than O. naivashae. Overall, r_m-values on M. persicae nicotianae were higher than on T. urticae, although differences were only significant for O. thripoborus. For O. naivashae, the estimated intrinsic rates of increase on the tested non-thrips prey were slightly negative. Our findings indicate the potential of both Orius spp. as biocontrol agents of thrips, whereas only O. thripoborus appears to hold promise for the suppression of aphids and spider mites as well.     

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.