The distribution of a typhlocybine leafhopper, Ribautiana ulmi (Homoptera: Cicadellidae) on a specimen wych elm tree

ABSTRACT.

• 1 Higher numbers of feeding and resting Ribautiana ulmi (L.) were found on the more highly illuminated areas of the canopy of a wych elm tree, Ulmus glabra Huds. cv. Camperdownii.
• 2 Higher numbers were also found on the basal leaves of each branch when compared with the distal leaves, and on exposed areas of individual leaves when compared with the shaded areas which they overlapped.
• 3 Leaf thickness, tannin concentrations and leaf toughness were greater, and water content lower, in leaves from exposed areas of the canopy than from shaded ones.
• 4 R.ulmi feeds selectively on the contents of the palisade mesophyll cells, and therefore was assumed to ingest the highest available levels of tannins.

     

Lumicella,a new genus of the tribe Empoascini (Hemiptera,Cicadellidae, Typhlocybinae) from China

Lumicella rotundata gen. et sp. n. is described based on specimens from Fujian Province, China. Habitus photos and illustrations of male genitalia of this new species are provided. Differences between the new genus and closely related genera are discussed.     

Comparison of transmission abilities of four Cicadulina species vectors of maize streak virus from Nigeria

Four Cicadulina species [Cicadulina arachidis China, Cicadulina dabrowskii Webb, Cicadulina mbila (Naude), and Cicadulina storeyi China (Homoptera: Cicadellidae)] found during field surveys in 1997–1999 across five ecological zones in Nigeria were reared in screenhouses and females were used in a study to compare their abilities to transmit Maize streak virus (Geminiviridae: genus Mastrevirus) from maize to maize using the susceptible variety Pool 16. The results showed that for both acquisition access feeding periods (AAP) and inoculation access feeding periods (IAP), transmission efficiencies decreased in the following order: C. storeyi > C. mbila > C. arachidis > C. dabrowskii. The transmission efficiencies of these vectors increased with longer feeding periods, as the means of susceptible test plants that showed Mastrevirus symptoms for both acquisition and IAPs were higher for 24 and 48 h than for 1 and 2 h for all four species studied. The epidemiological implications of these differences in transmission abilities are discussed.     

Maize seedling morphology and defence hormone profiles,but not herbivory tolerance,were mediated by domestication and modern breeding

We addressed whether Zea seedling morphology relevant to performance, defence hormone profiles and tolerance of a phloem‐feeding, specialist herbivore were affected by two processes, plant domestication and modern breeding. Domestication effects were inferred through comparisons between Balsas teosintes (Zea mays parviglumis) and landrace maizes (Z. mays mays), and modern breeding effects through comparisons between landrace maizes and inbred maize lines. Specifically, we compared seedling forms (a composite measure of leaf length, average stem diameter, shoot wet weight, shoot dry weight, total root length, root wet weight, and root dry weight), shapes (forms scaled by seedling dry weight, a proxy for seedling size), and defence hormone profiles among Balsas teosinte and landrace and inbred line maizes, exposed or unexposed to feeding by Dalbulus maidis. Our results suggested that domestication as well as modern breeding strongly mediated both seedling form and shape. Form was more similar between landrace and inbred maize than between Balsas teosinte and landrace maize, suggesting that domestication affected seedling form more than modern breeding. In contrast, shape was more similar between Balsas teosinte and landrace maize than between landrace and inbred maizes, suggesting that modern breeding affected seedling shape more than domestication. Additionally, seedling shoot : root ratios appeared to have been mediated by domestication, but not by modern breeding. In broad terms, individual seedling structures relevant to seedling ecology in wild or managed environments, such as leaf and root lengths, and shoot and root masses, were enlarged with domestication and reduced with modern breeding. Herbivory did not affect seedling shape, but had a weak effect on form so that seedlings were slightly larger in the absence versus presence of D. maidis. Also, both domestication and modern breeding seem to have mediated seedling hormone profiles, with breeding more strongly mediating profiles than domestication. Jasmonic acid isoleucine (JA‐Ile) and salicylic acid (SA) were induced by herbivory in both teosinte and maize. The hormone profiles assays collectively suggested that domestication and modern breeding altered constitutive levels of SA, abscisic acid and JA‐related (JA‐Ile and oxo‐phytodienoic acid) hormone levels in seedlings, particularly by increasing the levels of SA and decreasing those of JA‐related hormones. Altogether, our results suggested that maize domestication and modern breeding significantly altered seedling form, shape, ecologically relevant morphological traits (e.g. leaf and root lengths, and shoot and root masses) and hormonal defences, but not tolerance of D. maidis herbivory.     

Impact of a natural enemy overwintering refuge and its interaction with the surrounding landscape

1. Egg parasitoids in the genus Anagrus (Hymenoptera: Mymaridae) are important mortality factors for grape leafhoppers ( Erythroneura elegantula ; Homoptera: Cicadellidae) in California vineyards, yet must overwinter in habitats external to these vineyards. Existing evidence suggests that French prune trees, which harbour the overwintering host Edwardsiana prunicola , planted adjacent to vineyards may enhance early-season abundance of Anagrus.
2. Anagrus overwintering in French prune tree refuges were labelled with the trace element rubidium in four separate experiments. Rubidium-labelled Anagrus were captured in adjacent vineyards in two of the experiments, confirming that French prune trees contribute to early-season Anagrus populations. Anagrus from refuges were captured at the most distant sampling positions, 100 m from refuges.
3. Use of rare element labelling has, for the first time, enabled the relative contribution of different sources to early-season colonization by this parasitoid to be quantified. Refuges contributed 1% and 34% of Anagrus colonizing two of the experimental vineyards, respectively. The remainder originated from overwintering habitats external to the French prune/vineyard system.
4. The spatial patterns of Anagrus originating from external overwintering habitats suggest that the French prune trees are generating a 'windbreak effect'. Anagrus dispersing within the windstream colonized vineyards at a higher-than-average rate immediately downwind of refuges.
5. The amount of colonization by Anagrus from external overwintering habitats was apparently related to the distance to presumed overwintering habitats. These findings demonstrate that both the number of natural enemies emerging from a refuge and the composition of the surrounding landscape are important in determining the impact of local, small-scale habitat manipulations.     

Importance of color stimuli in host-finding by Dalbulus leafhoppers

The importance of color stimuli in host-finding by Dalbulus maidis (DeLong & Wolcott), D. gelbus DeLong, and D. quinquenotatus DeLong & Nault (Homoptera: Cicadellidae) was determined by comparing pre- and post-contact responses of leafhoppers to maize seedlings (Zea mays L.) with those to vertical models varying in hue or value (total amount of reflected light). For each species, more contacts were made with maize by jumping/flying than by walking, and both sexes remained on maize for similar times after contact. When presented simultaneously with seven models (vertical wooden rods) painted in different colors, each species made more contacts with yellow. Yellow also received more contacts when it was present in a group of four colors. There were no differences in contacts made with the yellow model by jumping/flying or by walking for D. maidis and D. gelbus, but D. quinquenotatus made more contacts by jumping/flying than by walking. If yellow was not present in the group, the color reflecting maximally between 500–580 nm received more contacts compared to the other three colors. Responses to a series of neutrals indicated contacts were elicited primarily because of hue, and not changes in value. Yellow also elicited tenure as long or significantly longer than other colors after contact with a model. For each species, there were no differences in tenure between males and females on models. The importance of color stimuli in host-finding by Dalbulus leafhoppers is suggested to be influenced by differences in flight behavior and habitat stability of field hosts.

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Résumé Nous avons examiné l'importance de la couleur dans la découverte de l'hôte, en comparant au laboratoire les réactions avant et après contacts avec des plants de maïs,-à 4 feuilles-, et avec des leurres peints présentant des différences de nuance ou de quantité de lumière réfléchie, chez 3 espèces de Dalbulus: D. maidis,-spécialiste du maïs-, D. gelbus,-qui consomme le maïs et Tripsacum, et D. quinquenotatus,-spécialiste de Tripsacum. Les espèces entrent en contact avec le maïs plus en voltigeant que par la marche, mâles et femelles séjournant plusieurs heures après être entrés en contact. En utilisant des leurres végétaux,-des morceaux de bois verticaux peints de différentes couleurs-, une forte réponse au jaune, due à la teinte plus qu'à l'intensité, a été mise en évidence. Il n'y a pas de différence dans les contacts après voltige ou après marche avec des leurres jaunes pour D. maidis et D. gelbus, tandis que chez D. quinquenotatus, ils sont plus fréquents après voltige. Ces 3 espèces de Dalbulus continuent à être influencées par la couleur après contact, puisque chaque espèce reste plus longtemps sur le jaune que sur les autres couleurs. L'importance de la stimulation par la couleur dans la découverte des hôtes par Dalbulus est semble-t-il due au comportement de vol et à la stabilité de l'habitat dans la nature.

     

An attachment tip and pili-like structures in insect- and plant-pathogenic spiroplasmas of the class Mollicutes

Ultrastructural studies using scanning electron microscopy (SEM), negative-staining transmission electron microscopy (TEM), and thin-sectioning TEM on four species of Spiroplasma, in vitro and/or in vivo, indicated that their helices commonly possess one tapered end (tip structure) and one blunt or round end. These tip structures appeared morphologically different from the rest of the helix, exhibiting an electron-dense conical or rod-shaped core. In thin sections of the midgut of the leafhopper Dalbulus elimatus, the tip structures of Spiroplasma kunkelii in the midgut lumen were mostly aligned between microvilli, perpendicular to the apical plasma membrane of epithelial cells. These tip structures appeared frequently attached or closely apposed to the plasma membrane, in which cup-shaped invaginations close to the tips were observed. Pleomorphic forms of spiroplasma, enclosed in membranous vesicles, were found in the cytoplasm of the midgut epithelial cells. These findings suggest that the tip structure may be involved in the orientation and attachment of spiroplasma helices in relation to their host cells, and thus may be functionally comparable to the attachment organelle of mycoplasmas. Additionally, pili-like structures were observed by negative-staining TEM on the surface of Spiroplasma melliferum, and in thin sections of S. kunkelii infecting the leafhopper vector Dalbulus gelbus. Abbreviations CSS Corn stunt spiroplasma - SEM Scanning electron microscopy - TBS Tris-buffered saline - TEM Transmission electron microscopy     

轻中度石漠化地区不同土地利用类型叶蝉群落结构及动态

轻中度石漠化地区生态环境较为脆弱,昆虫是生态系统中的重要角色。以叶蝉作为指示生物,在轻中度石漠化地区选取刺梨林、核桃林、玫瑰园、桃林、李子林以及草地6种不同土地利用类型的样地进行叶蝉标本采集,分析6类样地中叶蝉群落的物种组成、相似性、多样性、均匀度和丰富度等特征及其与各地理要素之间的关系。同时还分析了不同月份叶蝉群落的物种组成、多样性、均匀度和丰富度等指数的变化趋势。结果如下：共鉴定叶蝉11亚科52属。拟竹叶蝉属Bambusananus Li&Xing、顶斑叶蝉属Empoascanara Distant和小绿叶蝉属Empoasca Walsh是各样地的优势类群,共占69.4%。尤其是小绿叶蝉属Empoasca,在不同样地中个体数都是最多,占总采集数量的44.6%。Shannon-Wiener多样性指数表现为：刺梨林 > 草地 > 核桃林 > 李子林 > 桃树林 > 玫瑰园;Pieluo均匀性指数则是：草地 > 刺梨林 > 李子林 > 桃树林 > 核桃林 > 玫瑰园,Simpson优势度指数为：玫瑰园 > 李子林 > 草地 > 刺梨林 > 桃树林 > 核桃林。温度是影响叶蝉群落个体数量的重要环境因子之一,气压和湿度等环境因子则与之无明显相关性。结果表明在生态环境脆弱的轻中度石漠化地区,草地和刺梨林两种土地利用类型的叶蝉个体数与类群数较为丰富,是较为合适的喀斯特生态环境修复的土地利用类型,研究结果将对石漠化治理和喀斯特轻-中度石漠化地区生态恢复技术集成与示范具有重要指导意义。     

Effects of bund crops and insecticide treatments on arthropod diversity and herbivore regulation in tropical rice fields

Ecological engineering using vegetable or flower strips is promoted as a potential pest management strategy in irrigated rice. Farmers in the Philippines often plant rice levees (bunds) with vegetables, particularly string beans (Vigna unguiculata [L.] Walpers) to supplement income, but without considering the potential for pest management. This study examines the effects of planted bunds on rice herbivores and their natural enemies. We compared arthropods in (a) rice fields that had string beans planted on bunds, (b) fields without string beans and without any insecticide applications and (c) fields without string beans but with insecticide treatments (standard practice). Rice yield was similar across all treatments; however, the vegetation strips produced an extra 3.6 kg of fresh string bean pods per metre of bund. There were no apparent increases in major natural enemy groups in fields with string beans compared to fields with conventional bunds. Fields with insecticide treatments had higher damage from leaffolders (Lepidoptera: Pyralidae). The sprayed fields also had lower parasitism of planthopper eggs and fewer predatory dragonflies and damselflies (Odonata). Furthermore, the mortality of planthopper (Delphacidae: Hemiptera) and stemborer (Pyralidae) eggs by parasitoids and predators was density dependent only in the unsprayed fields (with and without string beans). Our results demonstrate that planting string beans on rice bunds improves the productivity of rice farms, but our ecological engineering system did not appreciably affect natural enemy or herbivore abundance; however, chemical insecticides adversely affected pest regulatory ecosystem functions leading to higher pest damage.