Influence of microarthropod abundance and climatic factors on weight loss and mineral nutrient contents of Eucalyptus leaf litter during decomposition

Summary Densities of the different taxa of microarthropods per gram of litter in litter bags varied widely from the rainy to the dry season. Collembola and Acarina constituted more than 86% of the total microarthropods, and occurred in significantly greater numbers in the coarse-mesh bags than the fine-mesh bags. There were no fauna in the litter of suspended bags. The average weight loss was greater in the coarse-mesh bags (50.4%) than in the fine-mesh bags (44.5%), and the suspended bags (7.4%). Similarly, the concentrations of N and Ca were greater in the litter of coarse-mesh bags compared to that of the fine-mesh bags. In contrast, the concentrations of P and K were comparatively lower in coarse-mesh bags. The mass loss of litter showed a negative linear correlation with the total Collembola and with litter temperature. The N concentrations in the litter in both the mesh bags showed negative correlations with the abundance of total Collembola, and with that of Lepidocyrtus sp. and Sminthuridae, and rainfall. The N concentration in the litter in the coarse-mesh bags was positively correlated with the total number of arthropods but, surprisingly, was negatively correlated with the total number of Acarina. The concentration of Ca showed negative correlations with rainfall and litter moisture only. The P concentration showed positive correlations with total Collembola, with Lepidocyrtus sp. and Sminthuridae in both the mesh bags, with rainfall in the fine-mesh bags, and with total microarthropods in the coarse-mesh bags.     

Litter microarthropod responses to canopy herbivory,season and decomposition in litterbags in a regenerating conifer ecosystem in Western Oregon

Summary The microarthropod community response to season, change in foliage litter quality during decomposition, and manipulated canopy herbivory by insects was measured in litterbags under 10-year-old Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, in western Oregon. Collembola accounted for 35% of the total fauna, oribatid mites for 29%, and fungivorous actinedids for 22%.The community structure was affected by responses to canopy defoliation, season, and changes in litter quality. Of 33 taxa, three were significantly more abundant under trees subject to lepidopteran defoliation (20% foliage removal), compared to other treatments, indicating responses to defoliator-induced changes in litter environment. Most taxa (23) showed seasonal fluctuations in abundance related to the seasonal pattern of temperature and precipitation and to the pattern of N and Ca mobilization from litterbags. Five taxa showed significant longterm trends in abundance, indicating responses to changes in litter quality, perhaps a loss of P and K.These data indicate that microarthropod communities respond qualitatively to environmental changes, including canopy defoliation. The qualitative changes can affeet decomposition processes.     

辽宁老秃顶子北坡森林土壤蜱螨共有度的海拔梯度变化

在老秃顶子自然保护区北坡海拔700～1320m地段,从低海拔到高海拔设置12块样地,并采用Jaccard指数,对不同蜱螨目(Acarina)土壤动物群落间物种共有度的海拔梯度变化进行了分析.结果表明,不同海拔蜱螨群落间物种的共有度,无论以哪一生活层的螨类来表达,基本都以与其最相邻的群落间为最高.中气门亚目(Mesostigmata)、甲螨亚目(Oribatida)、蜱螨目(Acarina)螨类的共有度,均随着海拔差的增加呈下降趋势,但并不与植被情况完全吻合,低海拔群落间甲螨亚目、蜱螨目共有度大于高海拔,而中气门亚目则相反.     

Effects of a sulfonylurea herbicide on soil microarthropods

 The short-term effects on soil microarthropods of the herbicide triasulfuron, belonging to the chemical class of sulfonylureas, were evaluated in two fields which had never been treated with sulfonylureas, and were cultivated with winter wheat. In particular, the effects of single applications at rates corresponding to two- (rate 2) and sixfold (rate 6) the recommended agricultural rate (7.5 g active ingredient ha^–1) were analysed and compared with controls. The changes in the populations of the main groups of microarthropods were evaluated. Rate 2 had very low effects, whereas rate 6 produced a significant decrease in the number of microarthropods, Acarina and Collembola in the surface soil layer (0–7.5 cm). The Collembola were analysed at the species level. Statistical analysis revealed significant differences only for a few species, and only after treatment with the highest rate of triasulfuron. Finally, the results of the field tests were compared to those of laboratory tests carried out previously, which examined the effects of the same herbicide on a collembolan species. Received: 11 November 1998     

双低储粮虫螨群落组成研究

1990～1992年对四川合川和广安县小麦双低仓虫螨群落组成调查表明,腐食酪螨及书虱为粮仓虫螨群落优势种群。模拟双低储藏与实仓调查结果一致。     

新腾岛螨属一新种(蜱螨亚纲：腾岛螨科)

 记述了腾岛螨科新腾岛螨属一新种--云南新腾岛螨(Neoteneriffiola yunnanensis sp.nov).编制了新腾岛螨属分种检索表。     

湖南省植绥螨小志(一)

本文记述了湖南省17种植绥螨的形态特征、分类地位、栖息植物和采集地点。     

新腾岛螨属一新种(蜱螨亚纲: 腾岛螨科)

记述了腾岛螨科新腾岛螨属一新种——云南新腾岛螨（Ｎｅｏｔｅｎｅｒｉｆｆｉｏｌａｙｕｎｎａｎｅｎｓｉｓｓｐ．ｎｏｖ）．编制了新腾岛螨属分种检索表     

Phoretic mites of three bark beetles (<Emphasis Type="Italic">Pityokteines</Emphasis> spp.) on Silver fir

The species composition and abundance of phoretic mites of the bark beetles Pityokteines curvidens, P. spinidens, and P. vorontzowi on Silver fir (Abies alba) were investigated in 2003 at two locations (Trakoscan and Litoric) in Croatia. Stem sections and branches from A. alba trees infested by Pityokteines ssp. were collected and incubated in rearing cages. Bark beetles emerging from the stem sections and branches were examined for photetic mites. A total of ten mite species were documented for the first time as associates of Pityokteines spp. on A. alba. These included Dendrolaelaps quadrisetus, Ereynetes scutulis, Histiostoma piceae, Paraleius leontonychus, Pleuronectocelaeno japonica, Proctolaelaps hystricoides, Schizostethus simulatrix, Tarsonemus minimax, Trichouropoda lamellose, and Uroobovella ipidis. T. minimax was the most frequent phoretic mite of all the three scolytines and U. ipidis was also common, whereas, the other mite species occurred less frequently. The species spectrum and relative abundance of mite associates were similar for all three Pityokteines species. Another species, Pleuronectocelaeno barbara was commonly found phoretic on P. curvidens, captured in pheromone traps in 2005 at the location Litoric. Furthermore, two previously collected mite specimens from Switzerland, phoretic on P. curvidens, were identified as Nanacarus sp. and Bonomia sp. The records from Croatia and Switzerland in the present study increase the number of known mite associates of Pityokteines spp. from one previously documented species to 14 species. None of the phoretic mites found in the survey in Croatia appear to have the potential to be used for biological control of Pityokteines spp., although the feeding habits are unknown for many species recorded.     

Field mesocosms for assessing biotic processes in soils: How to avoid side effects

Field mesocosms can overcome the simplicity and deficiencies of laboratory based experimental designs. This study deals with a number of possible side effects of a mesocosm technique that involves deep-freezing of soil monoliths to eliminate soil fauna, wrapping in nets of various mesh-size to control faunal immigration and replanting in the field. We used Berlese-Tullgren sets in the field to directly inoculate mesocosms with microarthropods. After 6 months of exposure, the number of collembolans equalled control level whereas immigration and inoculation of oribatids accounted for only 30% of the control. The number of ciliates, their distribution into feeding groups, and the numbers of nematodes, tardigrades and rotifers were not significantly affected by the elimination of mesofauna. We also did not detect significant treatment specific effects on microclimatic conditions within the litter layer of the mesocosms. Furthermore, we compared the monolith approach with a technique using sieved soil as a time-saving alternative. Water capacity and infiltration rate of mesocosms made of sieved soil did not differ from mesocosms made of monoliths, but NH₄⁺ losses were significantly higher in sieved soil when defaunated by deep-freezing. We conclude that the investigated mesocosm technique has little side effects and recommend the use of monoliths in mesocosm studies.

Résumé

La mise en œuvre de mésocosmes au champ peut être une alternative pour pallier la simplicité et aux imperfections des expérimentations en laboratoire. Cette étude aborde les différents effets secondaires potentiellement générés par une approche en mésocosmes, impliquant successivement i) une défaunation des monolithes de sol par congélation intense, ii) leur enrobage au moyen d'une toile de vide de mailles dans le but de contrôler l'immigration de la faune, iii) leur replacement au champ. À l'aide d'appareils de Berlèse-Tullgren utilisés sur place, les mésocosmes ont été ensuite directement inoculés avec les micro-arthropodes extraits. Après 6 mois d'incubation, l'abondance des collemboles est similaire à celle observée initialement dans le sol témoin alors que l'abondance des oribates, par immigration et inoculation, atteint seulement 30% de l'abondance observée dans le sol témoin. L'élimination de la mésofaune n'a pas affecté le nombre de ciliés et leur distribution dans les différents groupes trophiques, ni le nombre de nématodes, de tardigrades et de rotifères. De même, nous n'avons pas mis en évidence de manière significative d'effets secondaires, spécifiques au prétraitement des monolithes sur les conditions microclimatiques régnant au sein de la couche de litière dans les mésocosmes. L'approche en monolithes de sol est aussi comparée avec une approche par tamisage du sol, en tant que technique alternative permettant un gain de temps. La capacité de rétention en eau et le taux d'infiltration mesurés dans les mésocosmes constitués de sol tamisé et ceux constitués de monolithes de sol ne différent pas, mais les pertes en NH₄⁺ sont significativement plus élevées dans les mésocosmes faits de sol tamisé, après l'étape de défaunation par forte congélation. Nous concluons que la technique mésocosme proposée ici présente peu d'effets secondaires et nous recommandons l'utilisation de monolithes de sol pour des études en mésocosmes.