5种杀螨剂对不同螨态荔枝叶螨的毒力评价和田间防效

为了综合评价常用杀螨剂对荔枝叶螨Oligonychus litchii的室内毒力,在室内分别采用Potter喷雾法、浸叶碟法和浸叶法测定了5种常用杀螨剂对荔枝叶螨成螨、卵和若螨的毒力,并测定了5种杀螨剂对荔枝叶螨的田间防效。室内毒力结果表明:哒螨灵、阿维菌素对荔枝叶螨成螨和若螨有较高的毒力,联苯肼酯对成螨和若螨的毒力较低,而螺螨酯和乙螨唑对成螨基本无活性,对若螨有一定的毒力;5种杀螨剂对卵的毒力大小依次为乙螨唑螺螨酯哒螨灵阿维菌素联苯肼酯。田间防效试验中,15%哒螨灵乳油和1.8%阿维菌素乳油对荔枝叶螨的总体防效较好,药后1 d防效高于70%,药后10 d防效达100%,药后20 d防效仍在90%以上,速效性和持效性均较好;240 g/L螺螨酯悬浮剂和110 g/L乙螨唑悬浮剂对荔枝叶螨药后3 d防效均低于70%,而药后20 d的防效高于90%,说明两药剂速效性较差但持效性较好;43%联苯肼酯悬浮剂药后1、3 d防效低于阿维菌素和哒螨灵,高于螺螨酯和乙螨唑,药后15 d防效开始下降。在田间防治荔枝叶螨时,若荔枝叶螨发生早期、成螨较少时建议施用螺螨酯或乙螨唑,而荔枝叶螨种群中成螨、若螨较多时推荐施用阿维菌素、哒螨灵或联苯肼酯。     

十种杀螨剂对朱砂叶螨不同发育阶段的毒力比较

【目的】为明确不同杀螨剂对朱砂叶螨Tetranychuscinnabarinus不同发育阶段的生物活性。【方法】采用浸渍法分别测定了10种杀螨剂对朱砂叶螨成螨、卵和若螨的毒力。【结果】丁氟螨酯、阿维菌素和联苯肼酯对成螨、卵和若螨的活性均较高;乙螨唑和螺螨酯对卵和若螨活性较高,但对成螨活性明显偏低;甲氰菊酯对成螨和若螨的活性优于卵;唑螨酯、哒螨灵和三唑锡对3种螨态也均具有毒杀作用,但毒力偏低。同一种杀螨剂对若螨的活性均高于成螨和卵,乙螨唑、螺螨酯、联苯肼酯、唑螨酯和炔螨特对卵的活性高于成螨,丁氟螨酯、阿维菌素、甲氰菊酯、哒螨灵和三唑锡对成螨的活性高于卵。【结论】不同杀螨剂对朱砂叶螨不同发育阶段毒力存在较大差异,田间用药防治时应根据害螨发生情况和发生阶段,选择适合的防治药剂。     

4种杀螨剂对二斑叶螨的毒力测定和对少毛钝绥螨的安全性评价

为评价杀螨剂对二斑叶螨Tetranychus urticae Koch的毒力和对少毛钝绥螨Proprioseiopsis asetus Chant的安全性,本文采用叶片喷雾法测定了4种田间常用杀螨剂对少毛钝绥螨和二斑叶螨的毒力,并分析比较了4种杀螨剂对少毛钝绥螨和二斑叶螨的选择毒力。试验结果表明,4种杀螨剂对少毛钝绥螨雌成螨和二斑叶螨雌成螨的毒力选择指数大小依次为：联苯肼酯（10.1261）>阿维菌素（5.4664）＞哒螨灵（3.5293）＞克螨特（2.3615）。联苯肼酯对少毛钝绥螨的毒力选择指数最高,具有中度正向选择性,即联苯肼酯对少毛钝绥螨的毒力明显低于其对二斑叶螨的毒力。阿维菌素、哒螨灵、克螨特对少毛钝绥螨和二斑叶螨的毒力选择指数也都大于1,但都小于10,即这3种杀螨剂对少毛钝绥螨和二斑叶螨都有较低的正向选择性。4种杀螨剂常规使用浓度下对少毛钝绥螨雌成螨的安全系数大小依次为：联苯肼酯>阿维菌素＞哒螨灵＞克螨特。联苯肼酯的安全系数为16.8935～24.4025,阿维菌素的安全系数为5.5782～22.3127,均大于5,表示联苯肼酯和阿维菌素在推荐使用浓度的低浓度情况下,对少毛钝绥螨的安全性高。而15%哒螨灵乳油和73%克螨特乳油的安全系数仅1.1709～1.7564和1.0523～1.5807,在推荐使用浓度的低浓度情况下,对少毛钝绥螨的安全性一般。因此建议在生产中应用少毛钝绥螨进行生物防治时,可优先选用联苯肼酯和阿维菌素配合使用,而不建议使用哒螨灵和克螨特。     

阿维菌素与植物精油复配对朱砂叶螨杀螨的增效作用研究

为了得到对朱砂叶螨(Tetranychuscinnabarinus)具有较好杀螨活性的植物精油与阿维菌素复配配方,并为杀螨剂开发应用提供指导,本研究采用喷雾法测定了柠檬草、广藿香、山鸡椒、亚洲薄荷植物精油及阿维菌素对朱砂叶螨的毒力,分别采用共毒因子法和共毒系数法评价了山鸡椒和亚洲薄荷精油对阿维菌素的增效作用和复配最佳配比.结果表明,柠檬草精油和广藿香精油基本无杀螨活性,山鸡椒精油、亚洲薄荷精油处理朱砂叶螨24h后LC50分别为772.801mg/L和1040.187mg/L.阿维菌素与亚洲薄荷1∶272,1∶679复配具有增效作用.阿维菌素与亚洲薄荷1∶400复配时共毒系数最大,可达160.因此,阿维菌素与亚洲薄荷1∶400复配防治朱砂叶螨具有明显增效作用,这为杀螨剂的开发应用研究提供了参考.     

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。     

苹果害螨室内饲养方法探讨

山楂叶螨和苹果全爪螨均可用育苗器培养的苹果实生苗在室内大量饲养繁殖,营养液可采用改进的Hoagland溶液。试验证明,上述两种叶螨在苹果实生苗、苹果枝条和盆栽苹果树上的产卵量、卵化率、若螨转化为成螨率基本相同;对以上3种寄主上繁殖的苹果叶螨进行毒力测定,其结果基本一致。作者认为,此法可用于杀螨剂的筛选和苹果害螨抗药性测定。     

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。     

截形叶螨药剂防治对比试验

截形叶螨(Tetranychus truncatus Ehara)在云南昆明主要为害大棚花卉,尤其对月季(Rosa chinensis)为害严重。使用玻片浸液法,选用6种化学杀螨剂和1种植物叶面保护剂对该叶螨进行室内药效测定;同时,选取真除螨、主力和植物叶面保护剂等3种杀螨剂实施田间防治试验。结果表明,室内施药48h后,真除螨2 000、3 000倍液杀螨效果达100%;田间喷药3d后,真除螨4 000倍液能达到30%的防治效果,可有效降低害螨数量。建议每年截形叶螨为害严重的5～11月期间,在保护地栽培的月季上连续施用真除螨。害螨发生高峰期前,可使用植物叶面保护剂,减少害螨的取食。     

40种植物丙酮提取物对朱砂叶螨的毒杀活性

为推动植物源杀螨剂的研发进程,采用玻片浸渍法测定40种植物丙酮提取物对朱砂叶螨（Tetranychus cinnabrinus）雌成螨的毒杀活性,以期发现具开发潜力的植物资源。结果表明,沙茴香（Ferula bungeana）、盐肤木（Rhus chinensis）、黄连木（Pistacia chinensis）、紫丁香（Syringa oblata）和南方六道木（Abelia dielsii）等5种植物丙酮提取物对朱砂叶螨的毒杀活性较好;毒力测定表明,沙茴香和盐肤木丙酮提取物对朱砂叶螨的毒杀活性最好,LC₅₀分别为0.08 g·mL^-1和0.09 g·mL^-1。可见,沙茴香和盐肤木可作为植物源杀螨剂研发的候选材料,值得进一步研究。     

昆明地区鲜切花产区朱砂叶螨抗药性监测

采用玻片浸渍法测定了昆明地区花卉朱砂叶螨Tetranychus cinnabarinus(Boisduval)对阿维菌素、甲氨基阿维菌素苯甲酸盐、溴虫腈、丁醚脲、炔螨特和哒螨灵的抗性。结果表明,昆明北郊和呈贡地区玫瑰上的朱砂叶螨雌成螨对阿维菌素与甲氨基阿维菌素苯甲酸盐产生了极高的抗药性,阿维菌素对2个地区的朱砂叶螨的LC50分别为40.25mg·L-1和19.67mg·L-1,相对毒力指数分别为敏感品系的2441.08倍和1192.86倍;甲氨基阿维菌素苯甲酸盐对其LC50分别为118.18mg·L-1和9.24mg·L-1,相对毒力指数是敏感品系的2805.73倍和219.35倍。昆明北郊的朱砂叶螨对溴虫腈的相对毒力指数是敏感品系的2371.40倍,呈贡和晋宁分别为162.01倍和173.38倍。丁醚脲对北郊、呈贡和晋宁朱砂叶螨的LC50分别为244.58mg·L-1、385.41mg·L-1和54.93mg·L-1,相对毒力指数在3.01倍～21.10倍之间。北郊、呈贡和晋宁的朱砂叶螨种群对炔螨特和哒螨灵的LC50分别为155.39mg·L-1、424.49mg·L-1和62.70mg·L-1,其相对毒力指数是敏感品系的6.45倍、17.63倍和2.60倍。朱砂叶螨对药剂抗药性水平趋势从高到低为:阿维菌素、甲氨基阿维菌素苯甲酸盐>溴虫腈、丁醚脲>炔螨特、哒螨灵,抗性最高的地区为昆明北郊,晋宁相对较低。     

Farmer knowledge,attitude and practice on cotton (Gossypium hirsutum L.) pest resistance management strategies in Zimbabwe

Cotton is an important cash crop and a means of survival for Zimbabwe’s smallholder farmers who are located in the semi-arid areas. However, it is plagued by a wide variety of pests. The cotton industry in Zimbabwe came up with sustainable pest management strategies which include within the season rotation of bollworm pesticides, a closed season and acaricide rotation scheme. The land reform programme brought new players in the cotton industry and it was critical to determine their knowledge on the pest management strategies. A survey was conducted to determine farmer knowledge, practice and perception on the resistance management strategy. Responses indicated that both communal and new farmers based their spray on egg counts. Communal farmers knew when to use pyrethroids compared to new farmers. Farmers observed the acaricide rotation scheme although they use some non acaricide pesticides. More than half of the new farmers could not say which acaricides were in the acaricide scheme. The majority of the farmers reported that they adhered to the closed season although field observation revealed otherwise. A significantly higher number of new farmers knew when to slash cotton compared to communal farmers. Knowledge of acaricides was not common among farmers. Use of pyrethroids was not limited to 1 February onwards as stipulated in the cotton pest resistance management strategy. The results suggest the need for training among the cotton farmers especially the new farmers or refresher courses among the communal farmers.     

Modeling survival of experimentally virus-infected laboratory animals

Although survival analysis is a well-established mathematical discipline, there seem to be almost no attempts in survival modeling for experimentally virus-infected laboratory animals. We have taken up a stochastic approach originally developed by Shortley in the sixties and have applied it to three different types of experimental data: to virus titer determination, to the dose dependence of the mean survival time and to single survival curves. Experience concerning parameter estimation is reported and new ways of working with the model parameters are proposed. A standard mean survival time is defined and suggested as a new quantitative measure of virulence. Moreover, for the comparison of two experiments for which the amount of virions inoculated is kept fixed, but for which other parameters may vary, a new scheme of systematizing survival data from experimentally virus-infected laboratory animals is proposed. It is very likely that the model can be also applied to cancer survival data or any other infectious pathogen.     

New methods for the assessment of mite numbers and results obtained for several textile objects

Summary The assessment of mite numbers in textile objects is important with regard to measures aimed at mite control. The standard method is to take a dust sample and to separate the mites from the dust by means of flotation. The results of mite assessment can be improved using methods based on the natural mobility of the mites; the so-called Mobility Test makes use of the intrinsic movement tendencies of the mites, whereas the Heat Escape Method uses the mobility of the mites in connection with the effects of heat. An example concernig two jackets shows the difference in results of mite assessment when using the conventional method (dust sample and flotation) on the one hand, and the new methods (Mobility Test and Heat Escape Method) on the other. It is shown that the conventional method can only supply relative mite numbers. The new methods also enable the user to monitor more efficiently the use of acaricide agents in mite control. This is demonstrated using the example of two beds and a carpet taken from a children's bedroom. The considerably higher numbers of mites suggest that the risk of the occurence of mite allergens and their penetration into the indoor air is even greater than previously assumed.     

The Effect of Patch Size and Persistence of Host Plants on the Development of Acaricide Resistance in the Two-spotted Spider Mite Tetranychus Urticae (Acari: Tetranychidae)

Spatial and temporal characteristics of host plants can influence the population biology of the herbivores feeding on them. In this study, I examined the effect of variation in host plant characteristics on the development of acaricide resistance in the two-spotted spider mite Tetranychus urticae, a widely distributed agricultural pest. This investigation examined the geographic variation in the degree of resistance to two new types of acaricide, pyridaben and fenpyroximate. From mortality tests at field-level concentrations of the acaricides, many populations collected from fruit trees and roses had a high frequency of resistant individuals for acaricides while almost all populations collected from herbaceous crops had low frequencies of resistant individuals. These results, combined with those from a previous allozyme study, indicate that patch size and persistence of host plants regulate the population structure of the mites including gene flow between populations and, by extension, the development of acaricide resistance.     

Influence of acaricide resistance on cattle-fever tick (Boophilus spp.) infestations in semi-arid thornshrublands: a simulation approach

Cattle-fever tick (Boophilus microplus and B. annulatus) populations that develop acaricide resistance become more difficult to control or eradicate. We used a simulation model to assess the direct and indirect effects of interactions among season, habitat type, grazing strategy, and acaricide resistance on the ability to eradicate Boophilus infestations in semi-arid thornshrublands of Texas, USA. Season of infestation appeared to have the strongest effect, with infestations begun on 27 September (autumn) tending to die out sooner than those begun on 1 March (spring) and to remain undetected. Habitat type had the next strongest effect, with infestations surviving much longer as canopy cover increased from uncanopied buffelgrass (Cenchrus ciliaris) habitats to mesquite (Prosopis glandulosa)-canopied grass habitats. Acaricide resistance had a moderate effect; as expected, highly resistant tick populations survived longer than those with no acaricide resistance. The importance of grazing strategy varied with changes in habitat type: as canopy cover increased, infestation duration increased faster under continuous grazing than under rotational grazing strategies. Importance of grazing strategy also varied with acaricide resistance: detected tick populations with no and slight acaricide resistance subjected to acaricide treatments tended to survive longer under rotational grazing than continuous grazing, due to reduced contact with a treated host. Populations with moderate and high resistance behaved more like untreated populations, tending to survive longer under continuous, rather than rotational, grazing, because they experienced less mortality on a treated host. Assuming acaricide treatments at 2-week intervals and maintenance of cattle in infested pastures, results indicate that, for each habitat type, infesting ticks have a threshold of acaricide resistance below which one can eradicate them faster with continuous grazing than with rotational grazing. As canopy cover increases, this threshold appears to shift from high resistance (in grass) to slight resistance (in mesquite).     

Double-leaf-disk residue assay for assessing the toxicity of repellent acaricides to spider mites (Acari: Tetranychidae)

A closed double-leaf-disk (DLD) assay is presented which prevents escape (runoff) of spider mites and exposes them to treated leaf tissue during the entire test period. The physiological (direct) toxicity of acaricide residue can be estimated with this assay without the interference of behavioral factors. In contrast, runoff is often a major component of the total mortality in open single-leaf-disk (SLD) assays, in addition to direct mortality. Fenpropathrin, a highly repellent pyrethroid acaricide, caused primarily runoff and little direct mortality in SLD assays withPanonychus ulmi (Koch). When runoff and direct mortality were combined, concentration-response lines andlc ₅₀ values were identical to those obtained with the closed DLD assay. Assays with the organotin fenbutatin oxide gave similar results, suggesting that the runoff response should be included when estimating the residual toxicity of these compounds with the standard SLD assay. In fact, excluding runoff mortality from the analysis may underestimate the toxicity of foliar residue. Providing residue-free non-leaf surface inside the DLD cage caused a shift to the right of the concentration-response line, resulting in higherlc ₅₀s. The DLD assay can be employed for mite species which are difficult to confine, and in toxicological studies of repellent or irritating acaricides. This assay may be particularly useful for elucidating the relationship between physiological toxicity and mite behavior in response to acaricide residue.Technical Paper 9167 of the Oregon State University Agricultural Experiment State, Corvallis, Oregon, USA.     

A model to test how ticks and louping ill virus can be controlled by treating red grouse with acaricide

Ticks are the most important vectors of disease‐causing pathogens in Europe. In the U.K., Ixodes ricinus L. (Ixodida: Ixodidae) transmits louping ill virus (LIV; Flaviviridae), which kills livestock and red grouse, Lagopus lagopus scoticus Lath. (Galliformes: Phasianidae), a valuable game bird. Tick burdens on grouse have been increasing. One novel method to reduce ticks and LIV in grouse may be acaricide treatment. Here, we use a mathematical model parameterized with empirical data to investigate how the acaricide treatment of grouse might theoretically control ticks and LIV in grouse. Assuming a situation in which ticks and LIV impact on the grouse population, the model predicts that grouse density will depend on deer density because deer maintain the tick population. In low deer densities, no acaricide treatment is predicted to be necessary because abundances of grouse will be high. However, at higher deer densities, the model predicts that grouse densities will increase only if high numbers of grouse are treated, and the efficacy of acaricide is high and lasts 20 weeks. The qualitative model predictions may help to guide decisions on whether to treat grouse or cull deer depending on deer densities and how many grouse can be treated. The model is discussed in terms of practical management implications.     

The effects of acaricide treatment of sheep on red grouse Lagopus lagopus scotica tick burdens and productivity in a multi‐host system

Ixodes ricinus (Ixodida: Ixodidae) ticks are of economic and pathogenic importance across Europe. Within the uplands of the U.K., management to reduce ticks is undertaken to benefit red grouse Lagopus lagopus scotica (Galliformes: Phasianidae). Management strategies focus on the acaricide treatment of domestic sheep Ovis aries (Artiodactyla: Bovidae), but the effectiveness of this is less certain in the presence of wild hosts, particularly red deer Cervus elaphus (Artiodactyla: Cervidae) and mountain hare Lepus timidus (Lagomorpha: Leporidae). This study examines the effects of sheep management on grouse tick burdens and productivity using sites with a range of wild host densities. Sites at which applications of acaricide were more frequent had lower tick burdens; this relationship was similar on sites with a range of deer densities. However, no direct link was detected between acaricide treatment interval and grouse productivity. Sites with higher deer densities had higher grouse tick burdens and lower productivity [mean ± standard error (SE) young : adult ratio: 1.2 ± 0.2] compared with sites with lower deer densities (mean ± SE young : adult ratio: 1.8 ± 0.1). Sites with higher grouse brood sizes and higher proportions of hens with broods were also those with higher mountain hare abundance indices. This study highlights the importance of the frequent treatment of sheep with acaricide to reduce tick burdens on grouse, even in the presence of wild hosts.     

Controlling tick-borne diseases through domestic animal management: a theoretical approach

Vector-borne diseases are of global importance to human and animal health. Empirical trials of effective methods to control vectors and their pathogens can be difficult for practical, financial and ethical reasons. Here, therefore, we use a mathematical model to predict the effectiveness of a vector-borne disease control method. As a case study, we use the tick-louping ill virus system, where sheep are treated with acaricide in an attempt to control ticks and disease in red grouse , an economically important game bird. We ran the model under different scenarios of sheep flock sizes, alternative host (deer) densities, acaricide efficacies and tick burdens. The model predicted that, with very low deer densities, using sheep as tick mops can reduce the tick population and virus prevalence. However, treatment is ineffective above a certain threshold deer density, dependent on the comparative tick burden on sheep and deer. The model also predicted that high efficacy levels of acaricide must be maintained for effective tick control. This study suggests that benignly managing one host species to protect another host species from a vector and pathogen can be effective under certain conditions. It also highlights the importance of understanding the ecological complexity of a system, in order to target control methods only under certain circumstances for maximum effectiveness.     

Do pathogens become more virulent as they spread? Evidence from the amphibian declines in Central America

The virulence of a pathogen can vary strongly through time. While cyclical variation in virulence is regularly observed, directional shifts in virulence are less commonly observed and are typically associated with decreasing virulence of biological control agents through coevolution. It is increasingly appreciated, however, that spatial effects can lead to evolutionary trajectories that differ from standard expectations. One such possibility is that, as a pathogen spreads through a naive host population, its virulence increases on the invasion front. In Central America, there is compelling evidence for the recent spread of pathogenic Batrachochytrium dendrobatidis (Bd) and for its strong impact on amphibian populations. Here, we re-examine data on Bd prevalence and amphibian population decline across 13 sites from southern Mexico through Central America, and show that, in the initial phases of the Bd invasion, amphibian population decline lagged approximately 9 years behind the arrival of the pathogen, but that this lag diminished markedly over time. In total, our analysis suggests an increase in Bd virulence as it spread southwards, a pattern consistent with rapid evolution of increased virulence on Bd''s invading front. The impact of Bd on amphibians might therefore be driven by rapid evolution in addition to more proximate environmental drivers.