Volatile spider-mite pheromone and host-plant kairomone, involved in spaced-out gregariousness in the spider mite Tetranychus urticae

ABSTRACT. From the host plant-spider mite complex Phaseolus lunatus—Tetranychus urticae Koch a volatile chemical is emitted that acts as a kairomone for the predatory mite Phytoseiulus persimilis Athias-Henriot (Sabelis et al. , 1984a). This kairomone is apparently a byproduct of a vital physiological process and/or it has a function in the biology of the spider mite as well.
The spider mite—host plant complex also emits a volatile spider-mite dispersing pheromone. This is shown in the present study where spider mites were introduced into an odour patch on a horizontal screen in a vertical airflow olfactometer. When spider-mite infested leaves of Lima bean are offered, the spider mites walk mainly straight and soon reach the edge of the screen. On the other hand, when clean Lima bean leaves are offered, the mites walk tortuously most of the time and reach the edge of the screen much later. Artificially damaged plants elicit the same response as undamaged plants. Differences in spider-mite behaviour are observed in the vertical airflow olfactometer when odour of either clean or spider-mite infested leaves is offered. A comparison of the behaviour in these two situations with that when no odour was offered suggests that Lima bean leaves emit a volatile kairomone that activates T. urticae and makes them return after losing the stimulus. A Y-tube olfactometer experiment confirms the existence of this kairomone.
At a low ratio of dispersing pheromone to plant kairomone, the spider mites behave as if only kairomone is present, walking mainly tortuously. At a high ratio they disperse. No aggregation-pheromonal effect is observed.
The possibility that the spider-mite dispersing pheromone acts as a kairomone for P. persimilis is discussed.     

Development of two spotted spider mite (Acari: Tetranychidae) populations on strawberry and raspberry cultivars

Five strawberry (Fragaria sp.) and five raspberry (Rubus ideaus L.) cultivars were evaluated for resistance to two spotted spider mite (Tetranychus urticae Koch.). Two methods of assessing the development of two spotted mite populations using detached leaves were compared. The number of eggs laid and mites which developed were compared. The strawberry cvs Hapil and Pegasus had significantly greater development of two spotted mite populations than the cvs Rhapsody, Symphony and Elsanta. The raspberry cv. Joan Squires had higher populations of two spotted mite whilst the raspberry cv. Leo the least, when compared with cvs Glen Clova, Glen Moy and Glen Prosen. Differences were observed in oviposition sites and mite distribution when comparing raspberries with strawberries. The method of assessing the populations development of two spotted mite which involved maintaining the cut leaf stem in water may be of potential use for studying population dynamics of both two spotted mite and possible predators over extended periods of time.     

Inter- and intra-population variations in diapause attribute of the two-spotted spider mite,Tetranychus urticae Koch,in Japan

Populations of the two-spotted spider mite, Tetranychus urticae Koch collected from various localities and from various host plants in Japan showed wide variations in diapause attribute. Diapause percentages at 18°C/9L15D varied from nearly 100% in the north to 0% in the south-west. At intermediate latitudes the mites showed wide inter-population variations. Populations on herbaceous hosts in vinyl- or glass-houses gave significantly lower incidence of diapause than those on roses and deciduous fruit trees. Presence of winter hosts and better host quality under protected environments seemed to favour non-diapausing mites. The temperature threshold for diapause expression also varied widely among local populations. Northern populations consistently had higher and less variable thresholds than populations at intermediate latitudes with thresholds between 15 and 18°C. Inbred lines derived from a population in Kyoto exhibited a wide variation in diapause percentage at 18°C. These results show that diapause in T. urticae is a quantitative threshold trait and that populations in central Japan consist of a variety of genotypes with different diapause traits. This might provide a genetic source for adaptation to local and temporal variations in environmental conditions.     

A reappraisal of Athoracophorus bitentaculatus,with comments on the validity of genus Reflectopallium (Gastropoda: Athoracophoridae)

Abstract

The slug Athoracophorus bitentaculatus (Quoy & Gaimard, 1832) is redescribed from material collected in the northern third of the North Island of New Zealand. Its anatomy is described and figured, local variation in the condition of the lateral grooves and mantle is figured, and supplementary information on its biology and distribution is given. Its identity and taxonomy are discussed in the context of earlier work on the species. Evidence is presented for the reduction of Reflectopallium Burton, 1963 to synonymy with Athoracophorus Gould, 1852. A revised key to New Zealand and subantarctic genera of Athoracophoridae is given.     

二斑叶螨抗螺螨酯品系GST基因的克隆与表达分析

【目的】揭示二斑叶螨Tetranychus urticae对螺螨酯的分子抗性机理。【方法】利用RT-PCR克隆了二斑叶螨的谷胱甘肽-S-转移酶（glutathione S-transferase, GST)基因 cDNA 全长序列, 采用生物信息学软件分析了克隆基因的编码蛋白特性; 利用实时荧光定量PCR 方法分析GST基因在二斑叶螨的螺螨酯抗性与敏感品系中的表达差异。【结果】克隆获得的谷胱甘肽-S-转移酶2个基因分别被命名为TuGSTd1和TuGSTd2 (GenBank登录号分别为： KC445659和KC445660)。序列分析发现, TuGSTd1的开放阅读框长度为648 bp, 编码215个氨基酸, 分子量约为24.47 kDa, 理论等电点为5.49; TuGSTd2的开放阅读框为648 bp, 编码215个氨基酸, 分子量约为24.57 kDa, 理论等电点为6.33。系统发育分析表明这两个基因与桔全爪螨Panonychus citri Delta家族的GST基因的氨基酸序列一致性为93%。实时荧光定量PCR 结果表明, TuGSTd1和TuGSTd2在二斑叶螨抗螺螨酯品系中的相对表达量分别为敏感品系的5.60和3.75 倍。【结论】 GST基因在二斑叶螨抗螺螨酯品系中的相对表达量均显著高于敏感品系, 据此推测GST基因的过量表达可能与其对螺螨酯的抗性形成有关。     

二斑叶螨为害对草莓叶片H2O2、MDA含量以及部分防御酶活性的影响

本文旨在探究二斑叶螨Tetranychus urticae为害对草莓Fragaria×ananassa Duch.叶片内过氧化氢（H2O2）、丙二醛（MDA）含量以及部分防御酶活性的影响。在草莓苗上接种不同数量（5~25头）的二斑叶螨,分别在接种后的24 h、48 h和72 h取样,分析草莓叶片内H2O2、MDA的含量以及部分防御酶的活性。结果显示,二斑叶螨为害的草莓叶片内H2O2和MDA的含量以及超氧化物歧化酶（SOD）的活性随着时间的延长而呈现先升后降的趋势,在二斑叶螨持续为害草莓叶片24 h、48 h和72 h时,受损草莓叶片中H2O2的含量均显著高于对照（P<0.05）,不同密度二斑叶螨为害的草莓叶片中H2O2的含量均显著高于对照（P<0.05）,但与取食时间关系不大。当为害时间达到48 h时,MDA的含量和SOD的活性均达到最高峰,此时它们均与二斑叶螨的密度密切相关。当二斑叶螨为25头/叶时,MDA的含量和SOD的活性分别约是对照的3.6倍和10倍。过氧化物酶（POD）和过氧化氢酶（CAT）的活性随时间延长不断升高,均在二斑叶螨为害72 h时达到最高峰。同时,二斑叶螨的为害时间和为害密度之间存在一定的交互作用。以上结果表明草莓叶片主要通过调节其体内H2O2和MDA的含量以及各种防御酶活性的变化,对二斑叶螨的为害产生应激反应。     

Jasmonic acid induces the production of gerbera volatiles that attract the biological control agent Phytoseiulus persimilis

Jasmonic acid (JA) is a plant hormone that is involved in the induction of plant defence in response to herbivore attack. We studied the effect of exposure of gerbera leaves to JA on indirect plant defence, i.e. attraction of natural enemies of herbivores. Treatment of gerbera leaves with JA or feeding damage by the herbivorous spider mite Tetranychus urticae, both induced the production of a complex odour blend that attracts the predatory mite Phytoseiulus persimilis. This phytoseiid predator is a very effective biological control agent of the spider mite T. urticae. Comparison of headspace composition of gerbera leaves exposed to either JA or T. urticae revealed a large degree of resemblance, but some quantitative and qualitative differences were recorded. The major chemical group in both treatments is formed by the terpenoids which quantitatively comprised up to 80% of the total odour blend. These terpenoids included (E)-4,8-dimethyl-1,3,7-nonatriene, (E)--ocimene and linalool that are known to attract P. persimilis. Aldehydes, alcohols, esters and ketones, together with nitrogenous compounds formed the remaining constituents of the odour blend. The induction of predator attractants in plants by JA may be applied in biological control programs, which is discussed in this paper.     

Variability in susceptibility among cucumber and tomato strains of Tetranychus urticae Koch to 2-tridecanone from tomato trichomes: effects of host plant shift

The effects of secondary plant compounds on different host races/strains of a herbivorous arthropod are not easy to interpret based on dose–response tests alone. This difficulty arises because the responses in a population to a given dose are dictated not only by genetic factors, but also by factors such as feeding history, age and plant. To discriminate between these possibilities different strains of a herbivorous mite (Tetranychus urticae Koch) were exposed to one relevant toxin from glandular hairs on tomato (the methyl ketone, 2-tridecanone) and these strains had a known feeding history on either or both of two host plants (tomato and cucumber). It was hypothesized that tomato is a relatively hostile host plant to spider mites partly due to methyl ketones from glandular hairs and that consequently there will be stronger selection on the tomato strains than on the cucumber strains. However, the expected differences between the tomato and cucumber strains did not show up; three spider mite strains collected from tomato and two strains collected from cucumber appeared to be equally susceptible to 2-tridecanone. This unexpected result cannot result from selection for resistance to 2-tridecanone, but it may be the consequence of cross-resistance to other ketones in cucumber or the bio-accumulation (i.e. metabolic load) of 2-tridecanone prior to the toxicity test. To test this hypothesis, one of the tomato strains was released on cucumber for different time intervals and one of the cucumber strains on tomato. It was found that the resistance of the tomato strain to 2-tridecanone increased 6 months after transfer to cucumber. This increased resistance cannot be the result of selection because 2-tridecanone is absent from cucumber. Hence, it may be due either to selection for resistance to another ketone in cucumber, possibly leading to cross-resistance, or to the absence of 2-tridecanone bioaccumulation on cucumber. Transfer of the cucumber strain from cucumber to tomato also increased the resistance to 2-tridecanone. As this was accompanied by high mortality directly after the transfer, selection for resistance may have played a role. Alternatively, the increased resistance may be due to induction of resistance to secondary plant compounds of tomato, including 2-tridecanone. In conclusion, experiments on host plant transfer show that the tomato strain and the cucumber strain are not equal in their resistance to 2-tridecanone.