Explaining the abundance of ants in lowland tropical rainforest canopies

The extraordinary abundance of ants in tropical rainforest canopies has led to speculation that numerous arboreal ant taxa feed principally as "herbivores" of plant and insect exudates. Based on nitrogen (N) isotope ratios of plants, known herbivores, arthropod predators, and ants from Amazonia and Borneo, we find that many arboreal ant species obtain little N through predation and scavenging. Microsymbionts of ants and their hemipteran trophobionts might play key roles in the nutrition of taxa specializing on N-poor exudates. For plants, the combined costs of biotic defenses and herbivory by ants and tended Hemiptera are substantial, and forest losses to insect herbivores vastly exceed current estimates.     

Ecological effects of salicin at three trophic levels: new problems from old adaptations

Salicin, a toxic phenol glycoside, is used by larvae of the beetle Chrysomela aenicollis as a substrate for producing defensive secretions. In the east-central Sierra Nevada mountains of California, salicin concentrations ranged from 0.05 percent to over 5 percent of dry weight in leaves of different plants of Salix orestera, the Sierra willow. Beetles produced more secretion and suffered less predation on willows containing more salicin. In addition, leaf damage due to herbivory among 16 willow clones ranged from 0 to 20 percent of leaf area and was linearly related to salicin content. These results illustrate how a plant secondary chemical can become a problem for the plant when herbivores are adapted to use the chemical for their own benefit. The results also show the effect of a plant chemical on three trophic levels-the producer, a herbivore, and the predators of the herbivore.     

Plant defense guilds

Optimal plant defense should incorporate any mechanisms that influence the feeding behavior of potential pests. From a diverse collection of examples suggesting that the defense of a plant may be improved in the company of specific neighbors, we discuss a framework of operational mechanisms that begin to clarify some aspects of the recognized influence of species diversity on herbivory. Neighbors serve as insectary plants for herbivore predators and parasites, and influence herbivore feeding behavior by repelling, masking, attracting, and decoying. Insectary plants lower the numerical response of herbivores by increasing the efficiency of their predators and parasites. Repellent plants primarily lower functional response by causing the predator to fail to locate or reject its normal prey. Attractant-decoy plants dilute herbivore impact by drawing off herbivores, either increasing or decreasing their numerical and functional response (or either). The concept of gene conservation guilds adds diversionary and delaying tactics to the adaptation-counteradaptation view of plant-herbivore coevolution. The useful life of a given gene for resistance may best be extended by mechanisms that disrupt genetic tracking (specialization) by herbivores. Some plants may remain inedible not because their chemistry or morphology represents an evolutionary impasse, but because they live in an environment that provides acceptable options of variable quality. Feeding environments that provide little or no choice promote specialization by forcing physiological adaptation. Conversely, the evolutionary momentum of specializing herbivores may be lowered by enhancing their susceptibility, either by selection against virulent individuals, or by decreasing the exposure frequency of susceptible genotypes. The latter mechanism of conserving susceptible individuals takes advantage of herbivore behavioral sensitivity to variable plant quality. Direct selection against virulent genotypes requires temporal cycling of the herbivore population between resistant and nonresistant hosts. Both events may occur within defense guilds that provide acceptable feeding options of similar but distinctive quality.     

寄主植物-害虫-天敌三营养层系统相互作用的上行控制

寄主植物-害虫-天敌三营养层相互作用的重要性、害虫数量被其天敌所调节(下行控制)、寄主植物的物理和化学特性直接和间接影响害虫和其天敌的多度及分布(上行控制)已是生态学界活跃的研究主题。在不同的陆地生态系统中,作为害虫种群数量控制因子,寄主植物资源的上行控制可能比天敌的下行控制更普遍。寄主植物的基础营养物质、诱导产生的次生代谢物质和形态特征影响害虫的生理和行为,依次决定害虫的生殖、寿命和存活,直接控制害虫种群数量动态;影响天敌的行为和适合度,间接控制害虫种群数量动态。     

Isopod and insect root borers may benefit Florida mangroves

Far from threatening the persistence and geographic extent of red mangrove (Rhizophora mangle) in Florida, wood-boring marine isopods may aid the plant to survive wave action by initiating branching of aerial prop roots. Evidence for a recent, sudden increase in density or range of one such isopod, Sphaeroma terebrans, is anecdotal and weak. Insect damage to mangrove aerial roots even before they descend to the water is at least as great as that wrought by isopods and also causes root branching. Aerial and submarine damage combine to stimulate root initiation so that, for every root produced aerially by the tree, at least 1.4 roots reach the substrate. Similar responses to herbivory, which have been reported for other plants, suggest that herbivores may both benefit and harm plants, and that their impact may be more difficult to assess in specific instances than has been realized.     

Chronic herbivory: impacts on architecture and sex expression of pinyon pine

Pinyon pine, Pinus edulis (Engelm.), in Northern Arizona is exposed to recurring high levels of herbivory by the moth Dioryctria albovitella (Hust.). During a 3-year period, infested trees experienced on average a 30 percent reduction in annual shoot production. This herbivory affects tree architecture, growth rate, reproductive output, and sexual expression. Less infested trees produce 47 percent more trunk wood, 43 percent more branch wood, and are monoecious. Architectural changes in infested trees can result infunctionally male plants due to a complete loss of normal female cone-bearing ability. When herbivores are experimentally removed, normal growth and reproduction patterns resume. These strong herbivore impacts should represent a potent selection pressure in the evolution of host traits.     

Herbivore-plant interactions: mixed-function oxidases and secondary plant substances

The mixed-function oxidases of a polyphagous insect larva (the southern armyworm, Spodoptera eridania) were found to be induced by a diversity of secondary plant substances. The induction proceeds rapidly and in response to a small quantity of secondary substance. Following induction, the larva is less susceptible to dietary poisoning. It is argued that mixed-function oxidases play a major role in protecting herbivores against chemical stress from secondary plant substances.     

Wolves, moose, and tree rings on isle royale

Investigation of tree growth in Isle Royale National Park in Michigan revealed the influence of herbivores and carnivores on plants in an intimately linked food chain. Plant growth rates were regulated by cycles in animal density and responded to annual changes in primary productivity only when released from herbivory by wolf predation. Isle Royale's dendrochronology complements a rich literature on food chain control in aquatic systems, which often supports a trophic cascade model. This study provides evidence of top-down control in a forested ecosystem.     

茶树对茶尺蠖取食危害的补偿光合生理反应研究

利用叶绿素荧光仪和光合测定系统研究了茶树受到害虫茶尺蠖危害后的补偿光合生理变化.结果表明,茶树在受到茶尺蠖危害后的21 d之内,受害叶片和同株未受害叶片的光系统Ⅱ的光化学效率(Fv/Fm)、光合电子传递速率(ETR)和净光合速率(Pn)的值均高于对照,NPQ明显低于对照,且这种差异在危害后第7 d最大,随后逐渐减小.说明茶树对茶尺蠖危害后,诱导产生了补偿光合作用,且补偿能力随时间的推移而变小.此外,茶树在茶尺蠖取食后,气孔导度和蒸腾速率增加.     

重金属积累影响植物和植食性昆虫互作的研究进展

旨在为害虫的综合防控提供理论指导,本文归纳了重金属积累对植物抗虫性的影响,总结了重金属积累影响植物抗虫性的作用机理,分析了植食性昆虫取食对植物重金属积累的影响.认为重金属影响植物抗虫性的作用机理仍不清楚,并提出开展自然环境下植物重金属积累对植食性昆虫影响研究的重要性和必要性.     

Opposing effects of native and exotic herbivores on plant invasions

Exotic species are widely assumed to thrive because they lack natural enemies in their new ranges. However, a meta-analysis of 63 manipulative field studies including more than 100 exotic plant species revealed that native herbivores suppressed exotic plants, whereas exotic herbivores facilitated both the abundance and species richness of exotic plants. Both outcomes suggest that plants are especially susceptible to novel, generalist herbivores that they have not been selected to resist. Thus, native herbivores provide biotic resistance to plant invasions, but the widespread replacement of native with exotic herbivores eliminates this ecosystem service, facilitates plant invasions, and triggers an invasional "meltdown."     

植物与其它有机体的化学作用—潜在的有害生物控制途径

植物与其它有机体种间存在着通过次生物质为媒介的化学作用，这些化学作用在农业生态系统中则表现为植物对有害生物的化学防御。面对动物取食、微生物侵染和其它植物竞争，植物能合成释放特定的次生物质抵御侵害。而且，植物这种对有害生物的化学防御机制常常是在侵害条件下诱导产生的。当前的研究显示，作物/害虫/天敌三营养食物链也有自然的种间化学作用关系操纵，作物和杂草种间除了有相互抑制的化感作用外，还存在着通过次生物质进行的信息传递关系。揭示并充分利用植物这种内在的化学防御机制不仅能拓宽认识植物与其它有机体种间关系的视野，而且能开拓植物保护的新途径。     

玉米虫害诱导基因启动子在拟南芥中的活性分析

植物在感知到虫害信号后会经过复杂的转录调控,开启防御基因的表达。这一过程大多受到茉莉酸信号途径的调控,现有的相关研究主要集中在双子叶模式植物拟南芥中,在单子叶植物玉米中是否具有相似的转录调控模式目前尚不清楚。为了探索这一问题,从被玉米螟咬食和150 μmol/L JA处理12 h的RNAseq玉米文库中获得两个同时受诱导的基因,Zm281和ZmPal,重点对其启动子的诱导活性进行了分析。结果表明,这两个玉米启动子在未受JA处理的拟南芥中不能启动GUS报告基因的表达,但是在茉莉酸诱导后GUS报告基因受到强烈诱导,且在各组织器官中均有表达。该结果表明受虫咬后诱导表达的基因同时受JA的诱导,可为研究JA诱导虫害应答的分子机理奠定基础。     

Herbivory in rocks and the weathering of a desert

Two species of snail, Euchondrus albulus and Euchondrus desertorum, eat endolithic lichens growing under the surface of limestone rocks in the Negev Desert, Israel. This unusual type of herbivory has the unexpected and major impact of weathering this rocky desert at a rate of 0.7 to 1.1 metric tons per hectare per year. The biotic weathering contributes to the process of soil formation at a rate that is similar to wind-borne dust deposition. These findings demonstrate that herbivores can have a significant regulatory impact on ecosystem processes, even in cases where the total amount of primary production consumed is small.     

虫害诱导的植物挥发物

综述了植物挥发性物质的特性,挥发物与韧皮部取食的昆虫,茉莉酮酸(JA)与挥发物的释放,C6挥发物与植食性昆虫的作用,挥发物的诱导物及挥发物的生态学功能,为以后研究植物挥发物、植物-植食性昆虫-植食性昆虫天敌间的相互关系等方面提供了依据。     

Leaf herbivores decrease fitness of a tropical plant

Damage by insect herbivores to neighboring individuals of the shrub Piper arieianum in a neotropical wet forest varies greatly. This differential damage has a genetic basis and results in a 2-year decrease in growth, seed production, and seed viability, with larger plants recovering before smaller plants. The results provide evidence that leaf herbivores represent a potentially strong selective force for the evolution of plant defenses.     

Response dynamics of three defense related enzymes in cotton leaves to the interactive stress of Helicoverpa armigera (Hübner) herbivory and omethoate application

In order to explore the response dynamics of the activities of defense related enzymes in cotton leaves towards the interactive stress of Helicoverpa armigera herbivory and omethoate application, the activities of phenylalanine ammonia-lyase (PAL), lipoxygenase (LOX), and polyphenol oxidase (PPO) were examined from 6 to 126 h after cotton leaves were treated 12 h of H. armigera herbivory, and then sprayed with 800 mg L–1 omethoate. The results showed that the changes in the activities of PAL, LOX and PPO that occured under the interactive stress of H. armigera herbivory and omethoate application reflected the interactive effects of the two stresses on cotton defense. The similarity between the response dynamics of PAL, LOX, and PPO activities in cotton leaves under the interactive stress and that under H. armigera herbivory treatment alone showed that the induction of H. armigera herbivory on the activities of PAL, LOX and PPO in cotton leaves played a leading role in the interactive effects, and the effect of omethoate application played only a minor role. A joint factor analysis was performed according to a method which has been used to analyze the joint toxicity of pesticides; this analysis sought to clarify if there was a synergistic, antagonistic, or additive effect on PAL, LOX, and PPO activity in cotton leaves resulting from the interactive H. armigera herbivory and omethoate treatment. In the interactive effect on the response of PAL activity in cotton leaves, antagonistic effects of the omethoate application towards H. armigera herbivory were observed at 6 and 12 h. Synergistic effects were then observed at 18 and 30 h. Antagonistic effects were observed from 54 to 78 h and synergistic effects were finally observed at 126 h. The correlation between H. armigera herbivory and omethoate application in the interactive effect on cotton defense responses of LOX activity also fluctuated from synergism to antagonism during the time course. In the interactive effect on PPO activity, only antagonism was observed between H. armigera herbivory and omethoate application. In the interactive stress of H. armigera herbivory and omethoate application on cotton defense responses, omethoate affected the defense responses of cotton to H. armigera herbivory by producing antagonistic and synergistic effects. These results will be useful to understand the relationship between host plant and herbivorous pest.     

Serengeti ungulates: feeding selectivity influences the effectiveness of plant defense guilds

Association of Themeda triandra, a palatable grass species, with less palatable plants protected it from grazing by two comparatively unselective herbivores, wildebeest and African buffalo. Grazing on T. triandra by two more selective herbivores, Thomson's gazelle and zebra, was not related to the relative abundance of less palatable plants. The differential effectiveness of plant defense guilds against different ungulates may contribute to the high species diversity of the East African grazer fauna.     

Responses of Detoxifying,Antioxidant and Digestive Enzyme Activities to Host Shift of Bemisia tabaci (Hemiptera: Aleyrodidae)

The polyphagous B-biotype of Bemisia tabaci (Gennadius) has demonstrated a high capacity to adapt to numerous hosts from diverse plant families. To illustrate induced responses by the host plant, biochemical research on eight plant-insect interaction correlative enzymes, representing detoxifying, antioxidant and digestive pathways, were investigated. Transferring whitefly adults to Zhongmian 23 from the pre-adapted host Zhongmian 41 induced activities of carboxylesterase (by 1.80-fold), glutathione S-transferase (by 3.79-fold), proteinase (by 1.62-fold) and amylase (by 2.41-fold) activities, but decreased polyphenol oxidase (by 1.89-fold) and peroxidase (by 1.88-fold). However, transferring whitefly adults to the favorite host abutilon from Zhongmian 41 was associated with increased activities of cytochrome P450 monooxygenase (by 1.61-fold) and amylase (by 1.42-fold), and decreased activities of polyphenol oxidase (by 2.96-fold) and peroxidase (by 2.07-fold). Our results, together with previous studies, proved that multiple pathways are involved in coping with host shifts by polyphagous herbivores, and the taxonomic status and preference of the host transferred would affect which pathway would be induced. These results would represent a key challenge in developing long-term sustainable insect control strategies.     

Butterfly-Plant Coevolution: Has Passiflora adenopoda Won the Selectional Race with Heliconiine Butterflies?

Hooklike trichomes of Passiflora adenopoda provide a specific, effectively absolute defense against heliconiine butterfly larvae, a major class of Passiflora herbivores. It is suggested that since mechanical defenses are usually more selective in their action against herbivores, they usually are evolved by a plant only after it has accumulated a series of chemical defenses.