Investigating the effectiveness of feeding deterrents against the southern corn rootworm, using behavioral bioassays and toxicity testing

Leaf-disk feeding tests were conducted to determine the effect of various chemicals on southern corn rootworm, Diabrotica undecimpunctata howardi Barber, larval feeding. Ethanolic extracts of plant seeds from the family Meliaceae were all highly active feeding deterrents, while hexane extracts were ineffective as deterrents. In leaf disk feeding tests, the fungicide thiram (tetramethylthiuram disulfide), as technical material or formulated as thiram 50% or 75% (AI) was also an effective feeding deterrent. In choice tests, all thiram-based deterrents were equally effective, while in no-choice tests, thiram-75 was most effective at preventing feeding. Thiram-75 was also effective in protecting corn seedlings in a soil bioassay mimicking the field environment. It was determined that the formulation of thiram-75 used in these tests had been contaminated with 0.87% dieldrin (by weight). The contaminated thiram-75 had a toxic action, as well as a deterrent effect on southern corn rootworm larvae and both factors contributed to overall feeding inhibition. Toxicity was not found in technical thiram or in thiram-50. The mode(s) of action of the various deterrents are discussed in relation to screening procedures.

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Resumé Des expériences de consommation avec et sans choix ont été utilisées pour déterminer l'effet de différentes substances sur la prise de nourriture par D. undecimpunctata howardi Barber. Des disques de feuilles de Zea mays avec dissuadants ont été présentés à des chenilles du troisième stade; l'état des disques a été examiné au bout de 3,6 et 24 h dans les expériences de choix et de 48 et 72 h en absence de choix.Les extraits éthanoliques (1% dans l'éthanol) de Méliacées sont tous très efficaces, tandis que ceux à l'hexane (1% dans le pentane) sont inefficaces. Le thiram (disulfure de tétraméthylethiuram) utilisé comme matériel technique, à 50% ou à 75%, est lui aussi efficace (à 0,5% ou 1% dans l'acétone). Lorsqu'il y a choix tous les thirams sont aussi dissuasifs, alors qu'en absence de choix le thiram 75% paraît le plus efficace. Lorsque ce dernier est contaminé par 0,87% en poids de dieldrine, il est efficace lors d'expériences simulant le sol du champ. La contamination par la dieldrine rend le thiram 75 toxique autant que dissuadant. Cette toxicité n'est pas observée sur le thiram technique ou le thiram 50. Les modes d'action des différents dissuadants sont discutés.

     

The inhibitory effects of the cysteine protease inhibitor, oryzacystatin, on digestive proteases and on larval survival and development of the southern corn rootworm (Diabrotica undecimpunctata howardi)

At least eight proteolytic activities have been identified in the midgut contents of larval Southern corn rootworm (Diabrotica undecimpunctata howardi). Around 70% of protease activity could be arrested by the cysteine protease inhibitors E-64 and chicken egg-white cystatin, while the aspartic acid protease inhibitor pepstatin caused 30% inhibition. The cysteine protease activity was found to be highly sensitive to inhibition by both chicken egg-white cystatin and the rice cystatin, oryzacystatin I. Oryzacystatin I, expressed as a fully functional fusion protein in E. coli, was found to strongly inhibit larval gut protease activity. This recombinant oryzacystatin, incorporated into artificial diet at concentrations of 10 mM and above, caused significant decreases in larval survival and weight gain. E-64 was also shown to cause a significant antimetabolic in vivo effect. These results demonstrate the great potential for cysteine protease inhibitors, such as oryzacystatin, as tools for exploitation in the control of the Southern corn rootworm.     

Protease activities in the midgut of Western corn rootworm (Diabrotica virgifera virgifera LeConte)

The Western corn rootworm is one of the most economically important pests in corn. One possibility for controlling this pest is the cultivation of transgenic corn expressing Bacillus thuringiensis (Bt) toxins, such as Cry3A, Cry34Ab1/Cry35Ab1, and Cry3Bb1. However, widespread cultivation of the resulting Bt corn may result in the development of resistant pest populations. The Bt toxins are processed by proteases in the midgut of susceptible insects. Thus, protease activity studies were conducted using the midgut juice (pH 5.75) from third instars larvae of the susceptible Western corn rootworm. As a result, the activities of the serine endopeptidases trypsin, chymotrypsin, elastase, cathepsin G, plasmin, and thrombin; the cysteine endopeptidases cathepsin L, papain, cathepsin B, and cathepsin H; the aspartic endopeptidase pepsin; the metallo endopeptidase saccharolysin; the exopeptidase aminopeptidase, and the omegapeptidase acylaminoacylpeptidase were detected. These results are of basic interest but also lead to reference systems for the identification of protease-mediated resistance mechanisms in potentially resistant individuals.     

Whorl and pollen-shed stage application of Beauveria bassiana for suppression of adult western corn rootworm

The corn rootworm complex is the most damaging insect pest of corn (Zea mays L.). This study was conducted to determine the efficacy of whorl and pollen-shed stage applications of a granular formulation of Beauveria bassiana (Balsamo) Vuillemin for control of adult western corn rootworm (Diabrotica virgifera virgifera Le Conte). The effect of application time (whorl-stage, pollen-shed) and plant surface exposed (leaves and leaf collars; silks; leaves, leaf collars, and silks) on level of beetle fungal infection were investigated. In addition, the number of colony forming units of B. bassiana in the corn leaf collar area was quantified. In the three years (1998–2000) of the study, application of B. bassiana at whorl-stage did not significantly increase beetle fungal infection. Beauveria bassiana applied to plants at pollen-shed in 1998 resulted in a significant increase in beetle infection with 51% of beetles from treated plants infected and 6.0% from control plants. Similar applications at pollen-shed in 1999 and 2000 resulted in very low infection levels. Beauveria bassiana application at pollen-shed stage significantly increased the number of colony forming units per leaf collar during all years of the study. Beetle infection with B. bassiana did not differ consistently among plant surface to which beetles were exposed for either application. Increased fungal load in leaf collars was not correlated with increased levels of adult infection. Increased rates of B. bassiana and application when beetles are present on the plants are likely needed to significantly increase infection rates.     

Comparative susceptibility of larval instars and pupae of the western corn rootworm to infection by three entomopathogenic nematodes

As a first step towards the development of an ecologically rational control strategy against western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte, Coleoptera: Chrysomelidae) in Europe, we compared the susceptibility of the soil living larvae and pupae of this maize pest to infection by three entomopathogenic nematode (EPN) species. In laboratory assays using sand-filled trays, Heterorhabditis bacteriophora Poinar and H. megidis Poinar, Jackson & Klein (both Rhabditida: Heterorhabditidae) caused comparable mortality among all three larval instars and pupae of D. v. virgifera. In soil-filled trays, H. bacteriophora was slightly more effective against third larval instars and pupae, and H. megidis against third larval instars, compared to other developmental stages. In both sand and soil, Steinernema feltiae (Filipjev) (Rh.: Steinernematidae) was least effective against second instars. In conclusion, all larval instars of D. v. virgifera show susceptibility to infection by all three nematodes tested. It is predicted that early application against young larval instars would be most effective at preventing root feeding damage by D. v. virgifera. Applications of nematodes just before or during the time period when third instars are predominant in the field are likely to increase control efficacy. According to our laboratory assays, H. bacteriophora and H. megidis appear to be the most promising candidates for testing in the field. I. Hiltpold similarly contributed to this paper as the first author.     

Soil amelioration effects on peanut growth,yield and quality

Summary In order to study the reasons for poor peanut (Arachis hypogaea L.) performance on an Avalon medium sandy loam, a three year field study was undertaken to investigate the effects of lime and gypsum applications on growth, yield and quality. Rates of up to 2,400 kg agricultural lime/ha/annum significantly increased soil pH (1N KCl) and exch. Ca and decreased levels of exch. Al and Al saturation in the soil (0–150 mm). The effect of the same rates of gypsum was much less marked, only exch. Ca increasing and Al saturation decreasing to any substantial extent. In the absence of lime (i.e. even where gypsum was applied). nodulation was poor and the plants developed a general chlorosisc. 90 days after planting. Liming markedly improved nodulation whereas annual applications of gypsum had the opposite effect. Liming significantly increased the hay, pod and kernel yields by up to 73, 105 and 117%, respectively. On average, gypsum applications had no significant effects. Liming increased shelling percentage, the percentage mature pods, 100-kernel mass and protein concentration in the kernel, and decreased the incidence of pops and kernels with black plumule. Applications of gypsum had little effect on quality except for a decreased incidence of black plumule. It appeared that the improved crop performance with liming resulted from a reduction in Al toxicity which improved nodulation. Calcium deficiency did not appear to be a major cause of poor peanut growth and quality in the unameliorated soil.     

Soil potassium mobility and uptake by corn under differential soil moisture regimes

This study examined the effects of soil moisture on soil K mobility, dynamics of soil K, soil K fixation, plant growth and K uptake. A pot experiment, with and without corn (Zea maysL.), was conducted over a 16-d duration using a Yolo silt loam treated with two soil moisture regimes, i.e. constant moisture vs. wetting–drying (W–D) cycles. Soil K dynamics were determined using both ion exchange resin and direct extraction of soil solution. Soil K mobility increased significantly with soil moisture content (θ_v) and there was a positive curvilinear relationship between θ_v and effective diffusion coefficient (D_e), suggesting that more K⁺ can diffuse to the plant roots at sufficient soil moistures. Increase in D_e could be attributed to the decrease of impedance factor. During W–D cycles, soil solution K concentration increased as soil solution volume decreased, but soil solution K and NH₄ ⁺-extractable K pools decreased. In the constant moisture regime, available K pools decreased over the 16-d duration, but to a lesser extent than in W–D regime. The W–D cycles significantly enhanced K fixation and reduced available K pools in the soil in contrast to the constant moisture regime. Potassium fixation by the soil showed a biphasic pattern under the W–D regime, with a rapid fixation within the first 2 d after re-wetting, followed by a slower fixation. In the soil with constant moisture, K fixation was rapid during the first 8 h after wetting the soil, and then proceeded so slowly that no significant K fixation was observed after 4 d. The W–D cycles decreased root and shoot growth and K uptake by corn compared to constant moisture condition. Our results support the hypothesis that W–D cycles enhance soil K fixation, reduce soil K mobility and plant growth, and therefore reduce plant K⁺ uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Population response of the twospotted spider mite,Tetranychus urticae, to host phenology in corn and peanut

In northeastern North Carolina, outbreaks ofTetranychus urticae Koch on commercial corn and peanut plantings were observed to coincide with flowering and fruiting of the crop host. In greenhouse studies, when equal mite numbers were started on plants in either vegetative or reproductive growth stages, populations increased significantly more after 3–4 weeks on reproductive plants of both corn and peanut. This direct response of mite populations to differences in plant phenology appears to be an important component in the population dynamics ofT. urticae. The importance of this effect in understanding mite outbreaks on corn and peanut is discussed, especially in reference to the corn-peanut agroecosystem in North Carolina.

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Réponse de populations deTetranychus urticae Koch., aux phénologies du maïs et de l'arachide

Résumé Les populations de tétraniques sont souvent associées à la floraison et à la fructification des plantes attaquées. Dans les agrosystèmes maïsarachide du N.E. de la Caroline du Nord, l'augmentation rapide de populations deT. urticae a été observée lors de la maturation des épis mâles du maïs et du maximum de floraison de l'arachide. Bien que ces observations suggèrent une relation causale avec la phénologie des plantes hôtes, il est difficile de déterminer dans les conditions de la nature si l'augmentation des populations d'acariens sur les stades reproducteurs des plantes est due à une réponse à la phénologie des cultures ou à une autre cause, comme le passé de la population ou une immigration. Des expériences ont été réalisées dans une serre pour mettre en évidence l'action de la phénologie du maïs et de l'arachide sur les populations d'acariens en maîtrisant ces autres hypothétiques facteurs. Des effectifs identiques d'acariens femelles ont été libérés sur des plantes à des stades tant végétatifs que reproductifs, et ensuite laissés sans interventions pendant plusieurs semaines, au bout desquelles les effectifs sur chaque plante ont été dénombrés. Sur les deux hôtes, les populations sur plante à un stade reproducteur avaient augmenté significativement plus que sur les plantes de même espèce à un stade végétatif. Ces résultats montrent queT. urticae répond directement à des différences entre plantes à un stade végétatif et à un stade reproductif. Cette réponse semble jouer un rôle important dans la dynamique des populations deT. urticae.

     

Assessing host specificity of a classical biological control agent against western corn rootworm with a recently developed testing protocol

Celatoria compressa (Wulp) (Diptera: Tachinidae), a parasitoid of adult chrysomelid beetles in the subtribe Diabroticina in North America, has been selected as a candidate for classical biological control of the alien invader, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae: Galerucinae), into Europe. We conducted host specificity testing to evaluate the fundamental host range of C. compressa and potential risks to native European coleopteran species. Nine potential non-target beetles were tested for host selection with D. v. virgifera in no-choice tests, sequential no-choice tests, choice tests and sequential choice tests in small experimental arenas in a quarantine laboratory. The nine representative non-target species were selected for experimentation based on (1) ecological host range information of C. compressa, (2) ecological similarities to D. v. virgifera, (3) close phylogenetic/taxonomic relationships, (4) safeguard considerations, (5) morphological similarities, geographical distributions, overlap of temporal occurrences with D. v. virgifera and C. compressa, and (6) accessibility and availability. Of the potential nine non-target hosts tested, gravid C. compressa only parasitized a few red pumpkin beetles, Aulacophora foveicollis (Chrysomelidae: Galerucinae), regardless of the presence or absence of D. v. virgifera. However, C. compressa significantly preferred D. v. virgifera (44.6% parasitized) over A. foveicollis (2.7%) in choice tests. Of the 1110 A. foveicollis tested among all experiment types, only 23 were parasitized and only one C. compressa successfully developed from the parasitism, demonstrating that A. foveicollis is a poor host. In conclusion, C. compressa has a fundamental host range restricted to the subtribes Diabroticina and Aulacophorina, and would therefore be unlikely to have a direct impact on indigenous species in Europe.     

Dispersal and spatial distribution of western corn rootworm larvae in relation to root phenology

• 1 Despite the increasing economic importance of root feeding pests such as the western corn rootworm (WCR) Diabrotica virgifera virgifera, basic parameters about their below ground biology are only partly understood. The present study investigated the dispersal and distribution of WCR larvae in the maize root system during their development at two growth stages of maize (BBCH 13–14 and BBCH 17–18).
• 2 Dispersal of the WCR larvae increased as they developed; the larvae moved off their original place of emergence and into deeper soil layers. Overall, changes in the horizontal distribution of the larvae were more extensive than changes in the vertical distribution.
• 3 The spatial analysis of distance indices revealed that the larvae had an aggregative distribution throughout their development. The feeding site of larvae in the root system was determined by the stage of larval development. Initially, WCR larvae started feeding in close proximity to their emergence location and moved to more developed root tissue towards the end of their development.
• 4 Differences in root phenology mainly influenced the distribution of the larvae at the end of their development, when larvae exhibited increased vertical movement at a later growth stage of maize.
• 5 The mechanisms of these distributional changes and the implications for the management of WCR larvae are discussed, especially with regard to chemical control, because fewer larvae are expected to be targeted at a later growth stage of maize.

     

Influence of predator density on nonindependent effects of multiple predator species

Interactions between multiple predator species are frequent in natural communities and can have important implications for shared prey survival. Predator density may be an important component of these interactions between predator species, as the frequency of interactions between species is largely determined by species density. Here we experimentally examine the importance of predator density for interactions between predator species and subsequent impacts on prey. We show that aggressive interactions between the predatory shore crabs Carcinus maenas and Hemigrapsus sanguineus increased with predator density, yet did not increase as fast as negative interactions between conspecifics. At low density, interactions between conspecific and heterospecific predators had similar inhibitory impacts on predator function, whereas conspecific interference was greater than interference from heterospecifics at high predator density. Thus the impact of conspecific interference at high predator density was sufficient in itself that interactions with a second predator species had no additional impact on per capita predation. Spatial and temporal variability in predator density is a ubiquitous characteristic of natural systems that should be considered in studies of multiple predator species.     

免耕对北方旱作玉米土壤水分及物理性质的影响

通过2006-2008年的田间试验,研究了北京地区免耕与传统翻耕条件下土壤水分的时空动态及其对土壤相关物理性质的影响.结果表明：研究期间,免耕和翻耕地0～100 cm土层的土壤贮水量随时间及降水变化的趋势一致,但免耕地的土壤贮水量在不同时刻以及不同降雨条件下均高于翻耕地,增幅在2.7%～30.3%,降雨相对充分条件下土壤贮水量的增量有所增加,但免耕在相对缺水的地区更值得推广;免耕地0～100 cm土层的平均土壤含水量明显高于传统翻耕,增幅在3.4%～12.8%,其中表层（0～20 cm）和底层（80～100 cm）的水分增量明显高于中间层次,最高增量可达22.2%;免耕覆盖的耕作方式可通过降低土壤容重、提高土壤孔隙度、促进土壤水稳性团聚体的形成等作用来提高土壤的保水能力和水分利用效率,进而促进作物增收.与对照相比,免耕3年后土壤水分利用率和春玉米产量分别较传统翻耕提高13.3%和16.4%.     

Feeding and ovipositing on plants by an omnivorous insect predator

Omnivory (i.e., feeding at more than one trophic level) is common in many ecological communities. To date, most studies of omnivory have focused on systems that include omnivores that feed on several prey items, primarily in aquatic systems. Yet, many terrestrial insect predators feed not only on prey but also on plants. The difference between systems with plant-feeding omnivores and those with exclusively prey-feeding omnivores calls for special attention. The first step towards understanding the interactions between plant-feeding omnivores and their prey is to determine how omnivores respond to variations in plant properties. In this study, I investigated two major aspects of the interactions between the plant-feeding predatory bug Orius insidiosus and four host plants of its prey; the behavioral aspect, in which plants are selected for oviposition and the physiological aspect, in which plants differ in their suitability for the insect's growth, survival, and reproduction. No prey was offered to the omnivore during any of the experiments, but older nymphs and adults were fed prey eggs prior to their use in the experiments. Data show that O. insidiosus females almost completely rejected corn leaves for oviposition; nymph and adult survival was highest on bean; and female fecundity was higher on bean than tomato, pepper or corn foliage. the significance of the apparent ability of O. insidiosus to discriminate among plants and the observed correlation between oviposition preference and offspring performance in bean and in corn is discussed.     

Soil carbon sequestrations by nitrogen fertilizer application, straw return and no-tillage in China's cropland

Soil as the largest global carbon pool has played a great role in sequestering the atmospheric carbon dioxide (CO₂). Although global carbon sequestration potentials have been assessed since the 1980s, few investigations have been made on soil carbon sequestration (SCS) in China's cropland. China is a developing country and has a long history of agricultural activities. Estimation of SCS potentials in China's cropland is very important for assessing the potential measures to prevent the atmospheric carbon rise and predicting the atmospheric CO₂ concentration in future. After review of the available results of the field experiments in China, relationships between SCS and nitrogen fertilizer application, straw return and no‐tillage (NT) practices were established for each of the four agricultural regions. According to the current agricultural practices and their future development, estimations were made on SCS by nitrogen fertilizer application, straw return and NT in China's cropland. In the current situation, nitrogen fertilizer application, straw return and zero tillage can sequester 5.96, 9.76 and 0.800 Tg C each year. Carbon sequestration potential will increase to 12.1 Tg C yr⁻¹ if nitrogen is fertilized on experts' recommendations. The carbon sequestration potentials of straw return and NT can reach 34.4 and 4.60 Tg C yr⁻¹ when these two techniques are further popularized. In these measures, straw return is the most promising one. Full popularization of straw return can reduce 5.3% of the CO₂ emission from fossil fuel combustion in China in 1990, which meets the global mean CO₂ reduction requested by the Kyoto Protocol (5.2%). In general, if more incentive policies can be elaborated and implemented, the SCS in China's cropland will be increased by about two times. So, popularization of the above‐mentioned agricultural measures for carbon sequestration can be considered as an effective tool to prevent the rapid rise of the atmospheric CO₂ in China.     

Controlling fungi that colonize eggs of the western corn rootworm in the laboratory

Females of the polyphagous, ectoparasitoid, Exeristes roborator (F.) (Hymenoptera: Ichneumonidae), learned an olfactory stimulus associated with an artificial host microhabitat in the laboratory. In a two-choice olfactometer, females previously given hosts only in association with one stimulus showed a greater tendency to visit exclusively, and spend time in, chambers containing a source of that stimulus, than control females. Learning of olfactory cues could act in conjunction with learning of visual cues to allow the parasitoid to identify accurately microhabitats that experience has taught it contain hosts. It could also allow the parasitoid to identify these resources when visual cues are not available.

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Résumé Nous avons supposé que les femelles polyphages de l'ichneumonide ectoparasite, E. roborator (F.), pourraient apprendre les stimuli olfactifs liés au microhabitat artificiel dans lequel elles avaient attaqué leur hôte. 4 lots de femelles ont été placés dans des conditions différentes: le microhabitat des hôtes du premier lot était du Parafilm imprégné d'odeur de pomme; celui des hôtes du second était un Parafilm non traité. Les hôtes des lots témoins 3 et 4 étaient présentés respectivement avec les deux microhabitats et sans aucun microhabitat. Placées dans un olfactomètre statique contenant du Parafilm traité à la pomme et du Parafilm vierge, des femelles du lot 1 ont eu tendance à ne visiter que l'enceinte contenant du Parafilm traité à la pomme, elles ont passé environ 75% de leur temps dans cette enceinte. A l'opposé, les femelles des 3 autres lots ont eu tendance à ne visiter que l'enceinte sans odeur de pomme, et elles n'ont passé que 34 à 46% de leur temps dans l'enceinte traitée à la pomme. Les différences entre les réactions du lot 1 et des autres lots sont significatives, mais entre les lots 2, 3 et 4, elles ne le sont pas. Une expérience témoin confirme que les préférences des femelles du lot 1 ne sont pas innées; E. roborator a donc appris à reconnaitre les stimuli olfactifs du microhabitat sentant la pomme. L'apprentissage des signaux olfactifs liés au microhabitat de l'hôte pourrait s'effectuer seul ou en relation avec l'apprentissage de signaux visuels permettant au parasitoïde d'identifier avec précision les microhabitats d'un hôte convenable.

     

花生种子相关促生菌分离鉴定及功能评价

【背景】利用微生物促进植物健康生长是农业可持续发展的重要方向之一,而种子相关的促生菌可在植物生命周期早期与植物相互作用,对植物健康生长具有重要意义。【目的】发掘与利用种子相关促生菌的前提是筛选获得促生菌菌种资源,验证其益生能力,为其进一步应用与机理研究提供依据与支持。【方法】以花生种子为研究对象,从种子表面及种子内部分离纯化多株菌,测定菌株的固氮、解磷、解钾、吲哚乙酸合成和铁载体合成等促生能力,并验证菌株对常见植物病原菌的生长抑制特性;通过16S rRNA基因序列进行系统发育分析,确定分类地位;通过生物膜形成能力及根际定殖能力测定菌株在植物根际的生存能力;最后通过催芽及盆栽试验测定菌株对花生种子发芽及幼苗生长的影响。【结果】从花生种子表面、种子内和胚根内分离筛选到41株菌,均有吲哚乙酸合成能力,其中35株有固氮能力,2株有铁载体分泌能力,14株有植物病原菌生长抑制能力。各选一株为代表的菌株,即PS3、PE5和PR5,经16S rRNA基因序列比对分析鉴定为芽孢杆菌属(Bacillus)。PS3、PE5和PR5均可在MSgg液体培养基表面形成褶皱较强的生物膜,也可在花生根际形成有效定殖。催芽试验结果表明经过促生菌浸种后花生种子萌发率明显提高,在第2天时,PS5将发芽率由14.17%提高至38.33%,PE5发芽率提高至30.83%,PR5发芽率提高至39.17%。三株菌能够明显促进花生幼苗生长,PS5对花生幼苗苗高、根长、鲜重和干重分别提高21.82%、22.20%、37.11%和35.64%,PE5分别提高17.45%、18.93%、26.10%和21.18%,PR5分别提高23.11%、23.92%、38.66%和37.47%。【结论】筛选获得的花生种子相关促生菌,具有促进植物生长的潜力,明显促进种子萌发及幼苗生长,是良好的促生菌生物资源,具有较好的应用潜力。     

Emergent multiple predator effects in an experimental microbial community

Studies on multiple predator effects have typically focused on metazoans. Here we examined the effects of multiple consumers on bacteria. Specifically, we investigated the separate and combined effects of two common bacterivorous ciliates, Colpidium striatum and Paramecium caudatum, on a simple bacterial assemblage. Non-additive multiple predator effects emerged for all bacterial species significantly affected by grazing, where bacterial responses in the two-consumer treatment cannot be predicted by summing the separate effects of the two consumers. Some species showed risk reduction (observed responses less than expected), whereas others showed risk enhancement (observed responses larger than expected). We attributed risk alteration to the interference between the two consumers. Contradictory to theoretical predictions, total bacterial abundance in the two-consumer treatment did not differ from single-consumer treatments and consumer-free controls, due largely to risk reduction and compensatory responses within the bacterial assemblage. Decomposition of particulate organic matter was greater in the two-consumer treatment than the Paramecium single-consumer treatment, but did not differ among other treatments. These results suggest that the presence of multiple consumers may have unexpected impacts on the structure and functioning of bacterial communities.     

The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities

The prevalence of non-indigenous species (NIS) in southern California embayments was assessed from 123 Van Veen grab samples collected in nine bays and harbors during the summer of 1998. NIS occurred in all but two samples. They accounted for only 4.3% of the 633 taxa but contributed 27.5% of the abundance. There was no significant difference in the proportion of NIS abundance among ports harboring large vessels, small boat marinas, and areas where boats were not moored. Three species accounted for 92% of the NIS abundance: a spionid polychaete worm Pseudopolydora paucibranchiata, a mytilid bivalve Musculista senhousia, and a semelid bivalve Theora ubrica. The NIS did not appear to have a negative impact at the overall community level since NIS abundance was positively correlated with the abundance and richness of other species. This may be due to biogenic structures built by P. paucibranchiata and M. senhousia that enhance the abundances of other macrofauna.     

干酪乳杆菌干预对花生过敏小鼠模型的免疫调节作用

【目的】研究干酪乳杆菌(Lactobacillus casei)Zhang在预防及治疗花生过敏方面的作用。【方法】构建小鼠花生过敏模型,饲喂L.casei Zhang,并检测血清中IgE、IgG1和IgG2a抗体,粪便中组胺和IgA抗体,细胞因子和CD4+Foxp3+Tregs细胞的含量。【结果】与模型组相比,口服L.casei Zhang的实验组小鼠血清过敏原特异性的IgG2a和粪便总IgA抗体水平有所上调,花生过敏症状及Th2型反应(血清总IgE、特异性IgE、粪便组胺和IL-4水平等指标)明显降低。L.casei Zhang的摄入对血清IgG1抗体和其他细胞因子(IL-10、IL-12及IFN-γ)的表达水平没有明显影响,而IFN-γ/IL-4的比例及实验组脾脏和肠系膜淋巴结中CD4~+Foxp3~+Tregs细胞的表达增加。【结论】L.casei Zhang能促使Th2优势反应向Th1方向转变,从而起到预防和治疗花生过敏的作用。