Habitat and food specificity in aphidophagous predators

Current knowledge of the processes underlying prey location and choice by aphidophagous predators is reviewed by considering the succession of behavioural mechanisms required for the predator to obtain prey. The predator may locate areas where prey are likely to be found by responding to physical aspects of the habitat, or to semiochemicals produced by the host plant. The predator may then respond to visual or olfactory cues to locate the aphid prey. The predator's readiness to attack and consume aphids is influenced by any behavioural or chemical defence strategies, and by the palatability or nutrient value of the aphids. Toxic allelochemicals ingested by aphids from their host plant may have a detrimental effect on predators.     

Challenges,achievements and opportunities in allelopathy research

Abstract

Allelopathy is defined as the suppression of any aspect of growth and/or development of one plant by another through the release of chemical compounds. Although allelopathic interference has been demonstrated many times using in vitro experiments, few studies have clearly demonstrated allelopathy in natural settings. This difficulty reflects the complexity in examining and demonstrating allelopathic interactions under field conditions. In this paper we address a number of issues related to the complexity of allelopathic interference in higher plants: These are: (i) is a demonstrated pattern or zone of inhibition important in documenting allelopathy? (ii) is it ecologically relevant to explain the allelopathic potential of a species based on a single bioactive chemical? (iii) what is the significance of the various modes of allelochemical release from the plant into the environment? (iv) do soil characteristics clearly influence allelopathic activity? (v) is it necessary to exclude other plant interference mechanisms?, and (vi) how can new achievements in allelopathy research aid in solving problems related to relevant ecological issues encountered in research conducted upon natural systems and agroecosystems? A greater knowledge of plant interactions in ecologically relevant environments, as well as the study of biochemical pathways, will enhance our understanding of the role of allelopathy in agricultural and natural settings. In addition, novel findings related to the relevant enzymes and genes involved in production of putative allelochemicals, allelochemical persistence in the rhizosphere, the molecular target sites of allelochemicals in sensitive plant species and the influence of allelochemicals upon other organisms will likely lead to enhanced utilization of natural products for pest management or as pharmaceuticals and nutraceuticals. This review will address these recent findings, as well as the major challenges which continue to influence the outcomes of allelopathy research.     

邻苯二甲酸对萝卜种子萌发、幼苗叶片膜脂过氧化及渗透调节物质的影响

华北地区是我国玉米的主产区,玉米秸秆还田不仅可有效改善土壤理化性状、提高土壤生物有效性,还会在腐解过程中释放出目前公认的化感物质——酚酸类物质,邻苯二甲酸是玉米秸秆腐解液中的主要酚酸类物质。从玉米秸秆还田过程中主要腐解产物(邻苯二甲酸)对蔬菜作物的化感效应角度进行了研究,为量化秸秆还田量及构建粮-菜轮作制度探寻化感效应依据。试验以萝卜为蔬菜材料,通过配置4个浓度(0.05、0.5、1.0、2.0 mmol/L)的邻苯二甲酸溶液,模拟玉米秸秆还田条件,以清水为对照,研究主要腐解产物邻苯二甲酸对萝卜种子萌发、幼苗生长、膜脂过氧化作用及渗透调节物质的影响。结果表明:(1)萝卜不同生育期对邻苯二甲酸化感效应的响应程度不同。在0.05-1 mmol/L浓度范围内,邻苯二甲酸处理促进了萝卜种子萌发,但随着处理浓度的增大,促进作用减弱;浓度达到2 mmol/L时对萝卜种子萌发具有抑制效果。(2)邻苯二甲酸0.05mmol/L处理,促进了萝卜幼苗干鲜物质积累,幼苗根系生长,其中根系长度和根系表面积分别比对照提高42.03%、38.36%,显著高于清水对照;植株体内超氧化物歧化酶(Superoxide dismutase, SOD)活性增大,过氧化物酶(Peroxidase, POD)、过氧化氢酶(Catalase, CAT)活性降低,膜脂过氧化产物丙二醛(Malonaldehyde, MDA)含量与对照无显著差异。(3)当邻苯二甲酸浓度超过0.5 mmol/L时,萝卜幼苗脂质过氧化伤害加剧,体内MDA含量急剧增加,代谢与生理功能出现紊乱,正常生长及干鲜物质积累受到显著抑制。邻苯二甲酸浓度达到2 mmol/L时,叶片数较对照降低了36.51%;根系长度、根系表面积及根尖数降幅分别为64.46%、40.20%、41.28%。(4)对于渗透调节物质的影响,邻苯二甲酸处理促进了萝卜幼苗叶片可溶性糖含量的增加,但随着处理浓度的升高其促进作用逐渐减弱;可溶性蛋白含量随着邻苯二甲酸处理浓度的升高表现出逐渐减少的趋势,分别较对照降低了12.82%、14.88%、21.58%、24.73%。因此,华北地区实施玉米-萝卜轮作模式,从化感效应角度研究玉米秸秆量化还田,应将土壤中邻苯二甲酸浓度控制在0.5 mmol/L范围以内,以防止邻苯二甲酸浓度过高对萝卜幼苗生长的抑制作用。     

Effects of the mixotrophic flagellate Ochromonas sp. on colony formation in Microcystis aeruginosa

The aim of this study was to investigate the interactions between the cyanobacteria (Microcystis aeruginosa) and the potential grazer (Ochromonas sp.) with regard to colony formation. Two kinds of treatments were carried out: (i) In the dialyse experiment Microcystis aeruginosa and Ochromonas sp. were physically separated by a dialyse tubing. (ii) In the contact experiment interactions between Microcystis aeruginosa, heterotrophic bacteria and Ochromonas sp. in different concentrations were investigated. In one treatment where the predator Ochromonas sp. came in direct contact with Microcystis, aggregates were formed.In the contact experiment, there were some interactions between the predator Ochromonas sp. and the two groups of prey, Microcystis aeruginosa and heterotrophic bacteria. When exposed to a low initial Ochromonas sp. concentration, Microcystis aeruginosa decreased and then remained stable in concentration. Ochromonas sp. switched to feed on heterotrophic bacteria and increased. At a high initial Ochromonas sp. concentration Microcystis was grazed down.     

Seasonal dependence and functional implications of macrophyte–phytoplankton allelopathic interactions

Invasive plant species such as Ludwigia hexapetala might have a competitive advantage if they produce allelopathically active compounds against primary producers. Both phytoplankton and plant community structure may be affected due to different, species‐specific sensitivity to allelochemicals. Moreover, such allelopathic interactions could vary over the year depending on (i) the plant's phenological stage and (ii) the abilities of the native macrophytes to suppress—or the non‐native macrophytes to stimulate—the non‐native macrophyte population. We tested the allelopathic effects of aqueous leaf extracts of L. hexapetala on the photosynthetic activity of three target phytoplankton strains (Scenedesmus communis, a toxic Microcystis aeruginosa strain and a non‐toxic Microcystis aeruginosa strain) over three seasons of development (spring, summer and autumn). We also tested seasonal allelopathic effects of aqueous leaf extracts of both L. hexapetala (i.e. the non‐native invasive species) and the native Mentha aquatica on L. hexapetala seed germination. Finally, we identified three main secondary compounds present in the aqueous leaf extracts of L. hexapetala and we tested each individual compound on the phytoplankton's photosynthetic activity and on L. hexapetala seed germination. We observed marked seasonal and species‐specific patterns of L. hexapetala allelopathy on phytoplankton. The photosynthetic activities of S. communis and the toxic M. aeruginosa strain were stimulated by L. hexapetala aqueous leaf extracts in autumn and spring, respectively, whereas the non‐toxic M. aeruginosa strain was strongly inhibited in these two seasons. In summer, photosynthesis of all phytoplankton strains was inhibited. The germination rate of L. hexapetala seeds was stimulated by both L. hexapetala and M. aquatica aqueous leaf extracts, especially in summer, concomitant with the strong negative effects observed on the three phytoplankton strains. Three flavonoid glycosides (myricitrin, prunin and quercitrin) were identified as the main secondary compounds present in the L. hexapetala aqueous leaf extracts. The photosynthetic activity of S. communis was slightly stimulated by the three compounds. The photosynthetic activity of the toxic M. aeruginosa strain was stimulated by myricitrin and quercitrin, whereas that of the non‐toxic M. aeruginosa strain was inhibited by prunin. Finally, the germination rate and the germination velocity of L. hexapetala seeds were stimulated by myricitrin and prunin. These findings suggest that L. hexapetala could favour the photosynthetic activity of toxic cyanobacteria in spring and reduce their photosynthetic activity in summer, potentially leading to drastic changes in the phytoplankton communities and therewith ecological functioning of invaded ponds. Moreover, the stimulation of its seed germination could give a strong competitive advantage to L. hexapetala, thus promoting its invasiveness.     

化感物质对枯草芽孢杆菌(Bacillus subtilis)在厌氧条件下的生长及反硝化作用的影响

研究由秸秆腐解产生的化感物质 :阿魏酸 ( t-FA)、对羟基苯甲酸 ( p-HA)和苯甲酸 ( BA)在不同浓度下对厌氧培养的枯草芽孢杆菌 ( Bacillussubtilis)的生长及其反硝化活性的影响。结果表明 ,3种浓度的阿魏酸 ( 5.1 5、2 .58、0 .2 6mmol/L)均表现出对枯草芽孢杆菌的生长有抑制作用。对羟基苯甲酸 ( 0 .3 6、3 .62、7.2 4 mmol/L )对生长影响不明显。 8.1 9mmol/L和 4 .0 9mmol/L的苯甲酸有一定的刺激作用 ,而 0 .4 1 mmol/L的苯甲酸与对照无差别。实验表明枯草芽孢秆菌不仅能转化 NO- 3生成 NO- 2 ,而且还能转化 NO- 2 生成 N2 O。 3种化感物质对 NO- 3的转化均表现抑制作用 ,其抑制作用强弱依次为阿魏酸 >对羟基苯甲酸 >苯甲酸。高浓度的抑制作用强于低浓度。阿魏酸在 5.1 5mmol/L和 2 .58mmol/L浓度下 ,其抑制作用的差异显著性分别为 P<0 .0 1 ,P<0 .0 5。 NO- 2 的生成与 NO- 3的减少相互有关联 ,第 3天测定时 ,各处理中NO- 3急剧减少 ,而 NO- 2 急剧增加。在阿魏酸、苯甲酸处理中的 NO- 2 积累高峰在第 3天、第 4天 ,然后下降。而在对羟基苯甲酸的处理中 NO- 2 的积累一直上升 ,在第 6天的观察中仍未出现下降趋势。 3种化感物质均能抑制 N2 O的生成 ,至于在田间的抑制效果尚需进一步试验     

Effect of soil type, salinity, and allelochemicals on germination and seedling growth of a medicinal plant Lepidium sativum L.

The present work was conducted to elucidate the effect of soil type, salinity stress and allelochemicals from alfalfa on the germination efficiency, seedling growth and photosynthetic pigments of Medicago sativa L. The highest germination rate (69.9%) was recorded for seeds cultivated in sandy soil followed by that of clay soil (42%) and then loamy soil (19%). The maximum germination rate was attained at 50 mM NaCl concentration level, after that the values were decreased as the salinity levels increased. The maximum lengths (cm) of plumule and radicle and their growth rates (cm/day) were obtained at control level and found to decline significantly as the salinity increased. Aqueous extracts of alfalfa reduced the germination rate, radicle and plumule growth and seedling dry weight of L. sativum. However, chlorophyll and carotenoid content was increased, their maxima were recorded at 50% concentration level. The chlorophyll a/b ratio attained its maximum at the full strength concentration level.     

Effects of chlorogenic acid-and tomatine-fed caterpillars on the behavior of an insect predator

If generalist insect predators are a selective force contributing to patterns of feeding specialization by insect herbivores, then predators should be deterred from eating allelochemical-fed prey. The attack and feeding behaviors of naive predators (Podisus maculiventris stinkbugs) reared on control caterpillars (Manduca sexta) fed plain diet were compared to experienced predators reared on caterpillars fed tomato allelochemicals. Tomatine-fed prey were found more quickly by both naive and tomatine-experienced predators, and chlorogenic acid-experienced predators were more stimulated to begin searching for prey. However, experienced predators were less likely to attack both chlorogenic acidfed and tomatine-fed caterpillars than were naive predators. These results indicate that allelochemical-fed prey were easier for predators to locate, but allelochemical-containing prey often deterred predation by experienced predtors.     

Citrus limonoid effects on Colorado potato beetle larval survival and development

The effects of citrus limonoids, applied topically to potato (Solanum tuberosum L. var. Katahdin) foliage, on Colorado potato beetle (Leptinotarsa decemlineata) (Say) (Chrysomelidae) larval development, growth, and survival were quantified in laboratory assays and a small-plot field test. In laboratory assays, survival, development rate, and body weight decreased with increasing limonoid concentration, however these measures of larval response did not significantly differ among varying periods of limonoid exposure (three, six, or nine days). Significant limonoid application concentration and frequency effects on survival, development rate, and defoliation were observed in the field test. These results indicate the potential utility of lethal and non-lethal effects of citrus limonoids for management of the Colorado potato beetle.