混交林和纯竹林与毛竹害螨爆发成灾关系研究

报道在福建省6个不同生态区域内检查10对纯竹林与混交林受南京裂爪螨(Schizotetranychus nanjingensis)、竹缺爪螨(Aponychus corpuzae)、竹刺瘿螨(Aculus bambusae)对毛竹危害情况．结果表明,纯竹林受螨害重,危害指数达22．1％～44．7％,平均35％．混交林受害轻,危害指数为2．7％～28．6％,平均17．5％,混交林与纯竹林之间受害程度经t-测验表明均达到极显著差异．6个样地中纯竹林害螨总量高于其相对的混交林。分别达67．74％、152．47％、299．5％、857．75％、331．67％、26．55％。平均为289．28％;调查混交林天敌竹盲走螨(Typhlodromus bambusae)总量分别比相对纯竹林高95．45％、-18．13％、207．69％、837．5％、190．3％,平均262．5％．纯竹林中益、害螨比例分别达1：27、1：21、1：233、1：282、1：27,平均1：118,而其相对的混交林益、害螨比例为1：12、1：12、1：30、1：3、1：3、1：20,平均1：13．由此可见,纯竹林受螨害程度、害螨总量平均是混交林的2倍,而天敌数量少于相对混交林的2～3倍,益、害螨比例显著低于混交林(t=2．975,P=0．003)．本项研究揭示了由于受人为干扰(集约化管理、劈草、垦复)破坏了毛竹林原有的益螨-害螨-寄主植物之间相对稳定的平衡。导致毛竹害螨种群突发性增长,证明了纯竹林是诱发毛竹害螨爆发成灾成因的重要因素之一。     

Evaluation of Resistance Pattern to Fenpyroximate and Pyridaben in Tetranychus Urticae collected from Ggreenhouses and Apple Orchards using Lethal Concentration-slope Relationship

This study aimed to monitor the present and future developments of the resistance of Tetranychus urticae Koch to fenpyroximate and pyridaben, using the relationship of the LC₅₀ and slope of the concentration-mortality line in a probit model, for the provision of reliable resistance management tactics. Tetranychus urticae populations were collected from 16 commercial greenhouses, where various crops were cultivated, as well as from 10 apple orchards throughout Korea. The resistance to fenpyroximate and pyridaben of each population was estimated by calculating the median lethal concentration (LC₅₀), resistance ratio (RR) and slope of the concentration-mortality regression. Most of the greenhouse populations exhibited moderate levels of resistance, whereas the apple orchard populations showed only low levels, indicating that T. urticae populations in greenhouses were more strongly selected than those in apple orchards. Four population groups were established based on either the habitats (greenhouse and apple orchard) or acaricides (fenpyroximate and pyridaben). To test the hypothesis, “the slope is greatest at low and high levels of resistance,” the slopes were regressed as a function of the LC₅₀, and fitted to a polynomial regression. The polynomial regression model explained this relationship well for the four population groups (p < 0.05), indicating that the development of resistance toward fenpyroximate or pyridaben was consistent with the gradient. A laboratory selection study agreed with the results from both acaricide field populations. These results suggest that the gradient was a good indicator of the susceptibility of T. urticae to genetic variations, which was related to the LC₅₀. The application of these findings is also discussed in relation to the resistance management of T. urticae.     

Population dynamics of Oligonychus afrasiaticus in the southern Arava Valley of Israel in relation to date fruit characteristics and climatic conditions

1 Oligonychus afrasiaticus, the old world date mite, is a serious pest of dates in North Africa and the Near East, including Israel. It attacks and rapidly develops when the fruit is young and green. Mite phenology is affected by date cultivar, but the relationship between fruit characteristics and mite population development is unknown. 2 We report that mite establishment on the main cultivars grown in Israel, ‘Medjool’, ‘Barhi’ and ‘Deglet Noor’, began only when the water content of the fruit increased to ≥ 84%. Fruit bunch architecture and resistance to penetration, as well as sugar composition and content, were not key factors in mite establishment. 3 Later in the season, when total sugar levels reached ≥ 150 mg/g fresh fruit weight, total soluble solids comprised 15% and water content decreased to ≤ 75%, mite populations declined. 4 Yearly climatic variations could be responsible for phenological asynchrony between the pest and fruit development.     

Oribatid mites reveal that competition for resources and trophic structure combine to regulate the assembly of diverse soil animal communities

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Importance of ambient saturation deficits in an epizootic of the fungus Neozygites floridana in cassava green mites (Mononychellus tanajoa)

The mite-pathogenic fungus Neozygites floridana Fisher (Entomophthorales: Neozygitaceae) is considered to have potential for the biological control of the cassava green mite, Mononychellus tanajoa (Bondar). However, its activity is sporadic and laboratory data suggest a strong dependence on night-time saturation deficits for transmission. We report on an epizootic of this fungus in a mite population in northeastern Brazil. During the epizootic, host populations appeared to be limited by a combination of the pathogen and a predatory mite Neoseiulus idaeus (Acari: Phytoseiidae). When temperatures increased, the epizootic finished and the host population began to grow. Abiotic conditions could not explain the variation in host mortality following pickup of infective propagules in this epizootic. However, night-time saturation did help to explain the variation in transmission from infective cadavers to newly killed hosts. This supports laboratory observations that horizontal transmission between hosts is determined mainly by saturation deficits, while the process of infection is little affected by abiotic conditions. A further field observation was the near-absence of resting spores in dead mites (ca. 0.1% of cadavers), suggesting that the pathogen population was unsuccessful in producing inoculum to infect future M. tanajoa populations. The implications are that this pathogen will only be effective as a biological control agent in periods of high relative humidity, and establishment in new areas may be limited by resting spore formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Positive association between thrips and spider mites in seedling cotton

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Spider mite (Acari: Tetranychidae) mitochondrial COI phylogeny reviewed: host plant relationships,phylogeography, reproductive parasites and barcoding

The past 15 years have witnessed a number of molecular studies that aimed to resolve issues of species delineation and phylogeny of mites in the family Tetranychidae. The central part of the mitochondrial COI region has frequently been used for investigating intra- and interspecific variation. All these studies combined yield an extensive database of sequence information of the family Tetranychidae. We assembled this information in a single alignment and performed an overall phylogenetic analysis. The resulting phylogeny shows that important patterns have been overlooked in previous studies, whereas others disappear. It also reveals that mistakes were made in submitting the data to GenBank, which further disturbed interpretation of the data. Our total analysis clearly shows three clades that most likely correspond to the species T. urticae, T. kanzawai and T. truncatus. Intraspecific variation is very high, possibly due to selective sweeps caused by reproductive parasites. We found no evidence for host plant associations and phylogeographic patterns in T. urticae are absent. Finally we evaluate the application of DNA barcoding.     

Spatial Distribution of Galls Caused by <Emphasis Type="Italic">Aculus tetanothrix</Emphasis> (Acari: Eriophyoidea) on Arctic Willows

The distribution of galls caused by Aculus tetanothrix (Acari: Eriophyoidea) on three Salix species was studied. The factors influencing this distribution were analysed, i.e. willow species, study area and shoot length. Spatial pattern of gall distribution within the shoot was also examined. The study was conducted in Russia, Kola Peninsula. Densities of galls caused by A. tetanothrix differed significantly among willow species. Considerably higher gall density was recorded in the White Sea coast than in the Khibiny Mountains. This may be explained by the influence of a milder maritime climate that favors mite occurrence compared to a harsh and variable mountain climate that limits mite abundance. There was no relationship between the gall density and the shoot length. The highest density of galls was recorded on the inner offshoots; within the offshoot, there was a maximum density on the fifth leaf. This pattern was repeatable for all shoots studied, independent of the study area, willow species and length of shoots, suggesting the optimal conditions for A. tetanothrix exist on leaves in the middle part of a shoot. This distribution pattern may be an effect of the trade-off between the costs and benefits resulting from leaf quality and mite movement along the shoot. This hypothesis, however, needs to be tested experimentally.