Mycorrhiza modulates aboveground tri‐trophic interactions to the fitness benefit of its host plant

1. Arbuscular mycorrhiza (AM), the association of AM fungi and plant roots, may alter morphological and physiological attributes of aboveground plant parts and thereby influence plant‐associated organisms such as herbivores and their natural enemies, predators and parasitoids. 2. The interactions between AM and the players of aboveground tri‐trophic systems have mainly been considered in isolation from each other. The effects of AM on aboveground herbivore–carnivore population dynamics and the consequences to plant fitness are unknown. 3. We explored AM‐induced compensatory mechanisms for AM‐promoted proliferation of the herbivorous spider mite, Tetranychus urticae Koch, on whole bean plants, Phaseolus vulgaris L. Vegetative and reproductive plant growth, AM fungal colonisation levels, and mite densities were assessed on spider mite‐infested plants colonised or not by the AM fungus Glomus mosseae Nicol. & Gerd, and harbouring the natural enemy of the spider mites, the predatory mite Phytoseiulus persimilis Anthias‐Henriot or not. 4. AM symbiosis modulated the aboveground tri‐trophic system to the fitness benefit of the plant. AM‐increased plant productivity outweighed the fitness decrease due to AM‐promoted herbivory: at similar vegetative growth, mycorrhizal plants produced more seeds than non‐mycorrhizal plants. 5. AM‐increased spider mite population levels were compensated for by enhanced population growth of the predators and increased plant tolerance to herbivory. 6. AM‐enhanced predator performance looped back to the AM fungus and stabilised its root colonisation levels, providing the first experimental evidence of a mutually beneficial interaction between AM and an aboveground third trophic level natural enemy.     

捕食螨在我国农林害螨生物防治中的应用

捕食螨是农林生产中极具价值的生防作用物。文章对捕食螨在我国农林害螨生物防治中的应用作一综述,内容包括:与释放应用相关的研究(引进与风险评估,饲养、贮存与运输,食性与释放,捕食与繁殖,定殖与扩散,外界影响因子)、几种主要捕食螨(智利小植绥螨Phytoseiulus persimilis、西方盲走螨Typhlodromus occidentalis、伪钝绥螨Amblyseius fallacis、胡瓜钝绥螨A.cucumeris)的应用、释放应用前景与展望等,旨在提高我国的捕食螨研究与应用水平。     

Bt棉田边缘杂草带对棉田内叶螨发生的影响

2003～2004年,在冀南棉区系统研究了棉田边缘杂草带对棉田内叶螨发生的影响。试验设3个处理：转Bt基因棉化防田(使用杀螨剂控制棉叶螨且保留棉田边缘杂草)、转Bt基因棉对照田(保留棉田边缘杂草)和转Bt基因棉除草田(去除棉田边缘杂草)。结果表明,2003年6月28日～8月7日,处理间的叶螨发生量和有螨株率差异明显。2003年叶螨发生高峰期(7月28日),对照田的百株平均螨量达834头,分别是化防田、除草田的9.4倍和11.5倍;对照田的有螨株率的峰值为34.7%,分别高于化防田和除草田6.4%和12%;棉叶螨的总计值,对照田分别是化防田和除草田的5.8倍和5.5倍。2004年7月10日～8月29日,对照田的百株螨量和有螨株率明显高于除草田和化防田。2004年叶螨发生高峰期（8月10日）,对照田的百株平均螨量达1 222头,分别是化防田、除草田的4.3倍和23.4倍;对照田的有螨株率的峰值达100%,分别比除草田和化防田多75%和87%;棉叶螨的总计值,对照田分别是化防田和除草田的4.9和9.7倍。两年中,除草田和化防田的百株螨量和有螨株率峰值出现日期有所不同。对照田内,棉田边缘杂草至所调查的棉株距离同螨害指数呈显著(P＜0.05)或极显著(P＜0.01)的负相关。本研究表明,去除棉田边缘杂草的棉田,叶螨发生始期较晚且发生量较少;棉田边缘杂草到取样点的距离与棉叶螨的为害程度呈直线负相关,距离越近,叶螨的发生为害越重。     

Arrestment response of the predatory mite Amblyseius longispinosus to Schizotetranychus nanjingensis webnests on bamboo leaves (Acari: Phytoseiidae, Tetranychidae)

The response of the predatory mite Amblyseius longispinosus (Acari: Phytoseiidae) to the webnest of the spider mite nanjingensis (Acari: Tetranychidae) was examined using two-choice tests in the laboratory. A. longispinosus females were found significantly more often on leaves with webnests than on leaves without webnests and were often observed searching under the webbing. Because spider mites and their eggs were removed from the webnests before experiments, predators responded to stimuli associated with webbing, mite feeding damage and other residues in the webnests.     

Double-stranded RNA analysis of strawberry plants affected by June yellows

Using an improved method for extraction of dsRNA from strawberry leaf tissue, small quantities of several dsRNA species with mol. wt greater than 1.0 × 10⁶were detected in strawberry plants free from known strawberry viruses but affected by June yellows (JY). No such dsRNA species were detected in plants of Fragaria vesca or seven strawberry cultivars known to be free from JY. Neither JY symptoms nor these dsRNA species were detected in healthy strawberry and F. vesca plants graft-inoculated with tissue from JY-affected plants. It is not known whether the JY-associated dsRNA species are those of a causal agent of JY or are a consequence of the JY condition. Nevertheless, the detection of such dsRNA species in plants affected by JY may offer a possible objective method for detecting the incipient condition in symptomless strawberry plants. However, the concentrations of dsRNA in JY-affected plants are very low and dsRNA analysis is thought not to be sufficiently reliable for routine testing of plants. The occurrence of anomalous dsRNA species in extracts from some strawberry plants was caused by dsRNA from two-spotted spider mites (Tetranychus urticae) infesting the plants.     

Molecular identification of four Panonychus species (Acari: Tetranychidae) in Korea,including new records of P. caglei and P. mori

Four species of the genus Panonychus are identified in Korea including two previously known species P. citri (McGregor) and P. ulmi (Koch) and two newly identified species P. mori Yokoyama and P. caglei Mellot. Morphological diagnostics were observed among the four species in the color of dorsal tubercles and in the shape of male aedeagus. The dorsal tubercles of P. citri, P. ulmi, P. mori and P. caglei are red, white, whitish red and light red, respectively. The aedeagi of male adults are diagnostic in sigmoid‐shaped at the distal end and its shape and length was different among four species. Molecular comparison of the internal transcribed spacer 2 (ITS2) sequence of nuclear DNA and cytochrome‐c oxidase subunit I (COI) nucleotide sequence of mitochondrial DNA among the four species showed divergences 8–12% and 9–12%, respectively. Molecular analysis of the ITS2 and COI sequences revealed their divergences were slightly different among four species. In addition, species‐specific primer sets were designed at the base on ITS2 sequences to precisely diagnose these four species at the molecular level.     

Negative interactions between Willamette mites and Pacific mites: possible management strategies for grapes

Willamette mites and Pacific mites are often negatively associated on grape vines. In particular, vineyards with early season infestations of the less damaging Willamette mite rarely develop high populations of the economically important Pacific mite. We report that Willamette mites had a negative effect on Pacific mite populations in both the greenhouse and field. In some experiments, the negative effect was more pronounced when vines had been damaged by previous feeding of Willamette mites and in other experiments concurrent feeding by both mite species was necessary to demonstrate a negative effect. Therefore, we cannot conclude if the mechanism of the response involves induced resistance against Pacific mites, more conventional interspecific competition, or both. Since predators were uncommon in our experiments, predator build up on Willamette mites did not cause the low Pacific mite population that we observed, although this mechanism may be important in many vineyards. Further, larger scale experiments are necesary to determine if growers can introduce Willamette mites to help control Pacific mites.

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Résumé E. willametti et T. pacificus sont souvent antagonistes dans les vignobles. En particulier, dans les vignobles contaminés tôt dans la saison par E. willametti,-dont les dégâts sont moins conséquents-, on observe rarement des populations élevées de T. pacificus, dont les dégâts sont économiquement importants. Nous avons constaté que E. Willametti a réduit les populations de T. pacificus, tant en serres qu'à l'extérieur. Dans quelques cas, l'effet antagoniste était plus marqué quand les vignes avaient été préalablement endommagées par l'alimentation de E. willametti. Dans d'autres expériences, la compétition alimentaire entre les deux espèces d'acariens était nécessaire pour produire un effet antagoniste. Cependant, nous ne pouvons pas en conclure que la réponse implique une résistance induite contre T. pacificus, ou une compétition interspécifique plus classique, ou les deux à la fois. Puisque les prédateurs étaient rares dans nos expériences, une explosion des prédateurs sur E. willametti n'a pu provoquer le faible niveau de population observé avec T. pacificus, bien qu'un tel méchanisme puisse être important dans certains vignobles. Quoi qu'il en soit, des expériences à plus grande échelle sont nécessaires pour déterminer si les vignerons peuvent introduire Eotetranychus willametti afin de limiter les populations de Tetranychus pacificus.

     

New species and new record of Tetranychus Dufour from Australia, with a key to the major groups in this genus based on females (Acari: Prostigmata: Tetranychidae)

A new species of spider mite, Tetranychus bunda sp. n., is described and illustrated from Australia. It was found damaging the foliage of Desmodium tortuosum (Sw.) DC. (Fabaceae) in Darwin, Northern Territory. In addition, the geographical range of Tetranychus fijiensis Hirst is extended to include Australia. This species was found in the Northern Territory feeding on frangipani ( Plumeria sp., Apocynaceae), betel palm ( Areca catechu L., Arecaceae) and Macarthur feather palm ( Ptychosperma macarthurii [H. Wendl. ex Veitch] (H. Wendl. ex Hook. f., Arecaceae)). Details of the biology of T. bunda sp. n. and T. fijiensis are given. A key to the major groups of Tetranychus Dufour of the world, based on females, is presented and species known to occur in Australia are outlined.     

山楂叶螨在苹果不同品种上的生长发育及繁殖

室内试验结果表明 ,山楂叶螨TetrancychusvienensisZacher在苹果不同品种上的生长发育和繁殖有较大的差异。其中在红星上存活率高 ,发育速度快 ,生殖力强 ;而在秦冠上存活率低、发育速度慢、生殖力低。对山楂叶螨种群年结龄构的分析表明 ,卵在种群中所占比例较高 ,而成虫所占比例甚低 ,建议在对其进行防治时选用杀卵力强的药剂     

The possibilities for control of two‐spotted spider mite Tetranychus urticae on field‐grown strawberries in the UK by predatory mites

The potential of two species of predatory phytoseiid mites to control the two‐spotted spider mite, Tetranychus urticae, on unprotected field‐grown strawberries in the UK was investigated. Typhlodromus pyri, a native species, was able to control T. urticae in some circumstances, but was less effective under hot, dry conditions. Natural colonization by this species is likely to be too slow in plantations of 1–2 years life. Attempts to introduce this predator to strawberry fields on cut apple shoots were unsuccessful. The exotic predator Phytoseiulus persimilis, which is available from commercial sources, gave very good control of T. urticae when released onto strawberry plants in June. A release earlier in the year was less successful, so to prevent early build‐up of mites and possible plant damage it may sometimes be necessary to reduce spider mite numbers early in the year with an acaricide, before a later release of P. persimilis. The success of this integrated control strategy was demonstrated.     

光照时间对双尾新小绥螨生长发育及种群参数的影响

【目的】为了进一步明确光照时间对双尾新小绥螨Neoseiulus bicaudus Wainstein生长发育的影响。【方法】在实验室恒温条件下,采用生命表研究方法,研究在不同光照时间下,双尾新小绥螨捕食土耳其斯坦叶螨的生长发育情况。【结果】双尾新小绥螨在不同光照时间段下均能完成世代周期。在光照时数小于12 h时,从卵发育至成螨的各个发育阶段所需时间均呈缩短趋势,当光照时数大于16 h后各个发育阶段所需的时间又呈增长趋势。产卵期在12L︰12D光照时数下最长为20.74 d,且同其他光照条件均存在显著性差异(P<0.05)。产卵后期、寿命、总产卵量均表现在16L︰8D光照时数下最长,分别为11.93 d、31.05 d和42.4粒。双尾新小绥螨种群的净增值率(R_0)在16L︰8D时达到最大值33.88,在8L︰16D时最低为14.97。【结论】光照时间在12~16 h范围内最适合双尾新小绥螨生长发育。     

Photoperiodic time measurement in the spider mite Tetranychus urticae: A novel concept

To explain photoperiodic induction of diapause in the spider mite Tetranychus urticae a new theoretical model was developed which took into account both the hourglass and rhythmic elements shown to be present in the photoperiodic reaction of these mites. It is emphasized that photoperiodic induction is the result of time measurement as well as the summation and integration of a number of successive photoperiodic cycles: the model, therefore, consists of separate ‘clock’ and ‘counter’ mechanisms. In current views involvement of the circadian system in photoperiodism is interpreted in terms of the hypothesis that the photoperiodic clock itself is based on one or more circadian oscillators. Here a different approach has been chosen as regards the role of the circadian system in photoperiodism: the possibility, previously put forward by other authors, that some aspect of the photoperiodic induction mechanism other than the clock is controlled by the circadian system was investigated by assuming a circadian influence on the photoperiodic counter mechanism. The derivation of this ‘hourglass timer oscillator counter’ model of photoperiodic induction in T. urticae is described and its operation demonstrated on the basis of a number of diel and nondiel photoperiods, with and without light interruptions.     

External coincidence and photoperiodic time measurement in the spider mite Tetranychus urticae

The incidence of diapause in the spider mite Tetranychus urticae was predicted for various photoperiodic regimes, according to the external coincidence model of photoperiodic time measurement. A phase response curve was constructed for the hypothetical photoperiodic oscillator in these mites: entrainment of this photoperiodic oscillator to a variety of ‘complete’ and ‘skeleton’ photoperiods was calculated using a transformation method for circadian rhythms. The external coincidence model proved adequate to describe experimental results with T. urticae in ‘complete’ photoperiods (T = 24 hr), symmetrical ‘skeleton’ photoperiods (T = 24 hr), asymmetrical ‘skeleton’ photoperiods (T = 24 hr) (night-interruption experiments), and ‘resonance’ experiments, in which the light component of a light/dark cycle was held constant at 8 hr and the dark component was varied over a wide range in successive experiments, providing cycles with period lengths up to 92 hr. The external coincidence model proved inadequate to explain results obtained in a ‘T-experiment’ with T. urticae comprising 1 hr pulses of light in a cycle of LD1:17.5 (T = 18.5 hr) with the first pulse of the train starting at different circadian phases. The validity and limitations of the external coincidence model as an explanation of photoperiodic time measurement in T. urticae are discussed in view of the above results.     

Feeding History Affects the Response of the Predatory Mite Typhlodromus Kerkirae (Acari: Phytoseiidae) to Volatiles of Plants Infested with Spider Mites

The response of adult females of the predatory mite Typhlodromus kerkirae (Acari: Phytoseiidae) to volatiles emitted from bean leaves infested with Tetranychus urticae (Acari: Tetranychidae) or from leaves of Oxalis corniculata infested with Petrobia harti (Acari: Tetranychidae) was studied in the laboratory using a Y-tube olfactometer. Typhlodromus kerkirae females reared from larvae through to adults on T. urticae and pollen of Vicia faba responded to volatiles of bean leaves infested with T. urticae, either when they had a choice between infested and non-infested bean leaves or between bean leaves infested with T. urticae and O. corniculata leaves infested with P. harti. However, they did not respond when they had been reared only on the carotenoid-deficient pollen of V. faba. Female T. kerkirae that had been reared from larva to the tenth day of adult life on T. urticae and subsequently fed for 1 week on V. faba pollen did not respond to volatiles of bean leaves infested with T. urticae. In contrast, those that had been reared on V. faba pollen to the tenth day of adult life and subsequently fed for 1 week on T. urticae responded to volatiles of infested bean leaves.     

Walking,feeding and intraspecific interaction of larvae of Metaseiulus occidentalis,Typhlodromus pyri,Neoseiulus fallacis and Amblyseius andersoni held with and without eggs of Tetranychus urticae

Larvae of Metaseiulus occidentalis (Nesbitt), Typhlodromus pyri Scheuten, Neoseiulus fallacis (Garman) and Amblyseius andersoni Chant exhibited different activity levels when held on apple leaf or on tile arenas and given or not given eggs of Tetranychus urticae Koch and water (tiles only). M. occidentalis larvae held without prey exhibited high levels of walking (includes searching) during 24 hours of evaluation, whereas M. occidentalis larvae held with prey fed quickly and then became less active. Fed larvae of M. occidentalis were less active on leaves than tile. Larvae of T. pyri on leaves had a very low frequency of walking, almost never fed and quickly assumed a resting position during development. While much less active than M. occidentalis, fed and unfed T. pyri larvae walked more on tiles than leaves before resting. Larvae of N. fallacis and A. andersoni fed at low rates and were similarly active on tiles and leaves. Free water increased walking by M. occidentalis, A. andersoni and T. pyri on tile but not N. fallacis. M. occidentalis larvae interacted 5–7 times more often than larvae of the other three species. Cannibalism or scavenging was rarely seen and then only for M. occidentalis larvae. Larvae of all four mites walked, fed and interacted much more in the first 12 hours than the second 12 hours of tests, except unfed M. occidentalis. Unfed M. occidentalis larvae did not molt to protonymphs but unfed larvae of the other three species did. Unfed and fed protonymphs of all four species walked more at 4 hours after molting than larvae at 12–24 hours. Unfed and fed protonymphs of T. pyri or A. andersoni had similar walking frequencies, but unfed protonymphs of N. fallacis were more active than fed ones. Trends in larval activities are discussed relative to the life history of each species.     

Interspecific competition counteracts negative effects of dispersal on adaptation of an arthropod herbivore to a new host

Dispersal and competition have both been suggested to drive variation in adaptability to a new environment, either positively or negatively. A simultaneous experimental test of both mechanisms is however lacking. Here, we experimentally investigate how population dynamics and local adaptation to a new host plant in a model species, the two‐spotted spider mite (Tetranychus urticae), are affected by dispersal from a stock population (no‐adapted) and competition with an already adapted spider mite species (Tetranychus evansi). For the population dynamics, we find that competition generally reduces population size and increases the risk of population extinction. However, these negative effects are counteracted by dispersal. For local adaptation, the roles of competition and dispersal are reversed. Without competition, dispersal exerts a negative effect on adaptation (measured as fecundity) to a novel host and females receiving the highest number of immigrants performed similarly to the stock population females. By contrast, with competition, adding more immigrants did not result in a lower fecundity. Females from populations with competition receiving the highest number of immigrants had a significantly higher fecundity than females from populations without competition (same dispersal treatment) and than the stock population females. We suggest that by exerting a stronger selection on the adapting populations, competition can counteract the migration load effect of dispersal. Interestingly, adaptation to the new host does not significantly reduce performance on the ancestral host, regardless of dispersal rate or competition. Our results highlight that assessments of how species can adapt to changing conditions need to jointly consider connectivity and the community context.     

Condensed tannins of cotton leaves

Some primitive races of cotton (Gossypium hirsutum) are almost immune to spider mites. These strains contain condensed tannins of about 20% of dry wt. The tannins accumulate in leaves and their concentration increases in successive leaves until about the 10th true leaf. The upper leaves maintain this quantity until early fall. The condensed tannins give a moderate astringency to the leaf, and are mixed polymers hydrolysing in acidic digests to 1 part cyanidin and 4 parts delphinidin.