Effects of natural enemies on the rate of herbivore adaptation to resistant host plants

The potential of natural enemies to influence the rate of herbivore adaptation to resistance factors in plants is examined using conceptual and mathematical models. Results indicate that natural enemies could increase or decrease the rate of herbivore adaptation. The specific behavioral and physiological effects of a resistance factor on the herbivore, as well as the behavior of the natural enemy, and the population dynamics of the natural enemy/herbivore system are important in assessing the extent to which the natural enemies will affect the rate of herbivore adaptation to a resistance factor. Herbivore adaptation to partial resistance in a host-plant is generally expected to be slower than adaptation to high levels of resistance, even in the presence of natural enemies, if genetic variance is not limiting.

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Résumé Des modèles conceptuels et mathématiques ont servi à examiner l'influence du potentiel d'ennemis naturels sur le taux d'adaptation d'herbivores à des facteurs de résistance des plantes. Les résultats montrent que les ennemis naturels peuvent augmenter ou réduire le taux d'adaptation des herbivores. Les effets spécifiques (comportementaux et physiologiques) d'un facteur de résistance sur l'herbivore, aussi bien que le comportement de l'ennemi naturel et la dynamique de population du système ennemi naturel/herbivore permettent de déterminer le niveau de l'effet des ennemis naturels sur le taux d'adaptation de l'herbivore au facteur de résistance. Une adaptation de l'herbivore à une résistance partielle à une plante est généralement envisagée comme plus lente qu'une adaptation à des hauts niveaux de résistance, même en présence d'ennemis naturels, mais il peut y avoir des exceptions.

     

自然植物种群中病原菌与寄主植物相互作用的遗传学

在农业种群中,作物和菌病相互作用的遗传学已为人们所广泛研究,但对自然植物种群中病原菌与其寄主相互作用体系的某些重要现象却缺乏足够的重视。本文主要论述寄主与病原菌相互作用的遗传学本质;寄主抗性基因和病原菌毒性基因的获得代价及对各自适应力的影响;简单介绍了寄主-病原菌作用体系在种群水平上的遗传学内容及共进化的意义。     

Effect of crop rotations involving host and non-host plants on vesicular-arbuscular mycorrhizal infection of host plants

Summary The effects of crop rotations involving two host (lettuce and lavender) and two non-host (cabbage and radish) plants on the development of mycorrhizal infection in host plants were studied in unsterile soil and in sterilized soil with or without rock phosphate and inoculated withGlomus mosseae. As in previous experiments, pre-cropping with non-host plants did not decrease VA infection in the host plants. On the other hand, pre-cropping with a host plant increased VA infection in the same or another host plant grown afterwards. These effects were noted irrespectively of rock phosphate additions and of soil sterilization.     

不同离体寄主及其成熟度对亚洲柑桔木虱存活的影响

【目的】亚洲柑桔木虱Diaphorina citri Kuwayama的虫口密度及活动与柑桔黄龙病的田间传播、流行有十分密切的关系,寻找合适的室内饲养条件能够便于观察和研究其生物学特性和传病机制。【方法】本文以九里香Murraya exotica(L.)Mant.、酸桔Citrus sunki Hort.ex Tanaka和马水桔Citrus reticulata Blanco.cv.Mashuiju 3种寄主植物不同成熟度离体梢为研究材料,(1)比较亚洲柑桔木虱卵分别在3种寄主植株和离体嫩梢上的孵化率;(2)比较3种寄主不同成熟度离体梢对各龄若虫存活率和蜕皮的影响;(3)比较3种寄主不同成熟度离体梢对成虫存活率的影响。【结果】(1)亚洲柑桔木虱在植株嫩梢上卵的孵化率高于离体嫩梢,九里香表现最明显;(2)低龄若虫在叶片未完全展开的离体嫩梢上存活率最高,而高龄若虫在完全展开的嫩梢上最高;(3)用离体成熟梢饲养柑桔木虱成虫存活率高于离体嫩梢,酸桔和马水桔离体梢饲养的存活率较九里香高。【结论】用寄主植物离体梢饲养的亚洲柑桔木虱卵孵化率和若虫、成虫存活率都较高而且较稳定,该方法可用于这种木虱的室内繁殖中。     

Peruvian natural dye plants

The use of natural dyes to color textiles and other objects has a long history in Andean South America, but has for the most part become a lost technology with the introduction of synthetic dyes. A literature and field survey to recover information about the traditional use of dye plants in Peru, from pre-Hispanic to recent times, was accompanied by taxonomic identification of collected dye plant materials. Fiftysix dye plants from Peruvian sources are listed.     

Impacts of global warming on the interaction between host plants,insect pests and their natural enemies

全球气候变化是近来人类关注的焦点问题,其最显著的特征是气候变暖.因为昆虫具有生活周期短、繁殖率高等特点,所以,气候变暖对昆虫的发育、繁殖和存活会产生强烈的直接影响.气候变暖促使一些昆虫提前春天的物候现象,向高纬度或高海拔地区迁移.然而,昆虫在自然界并非孤立地存在,它们与寄主植物和自然天敌相互联系、相互作用,并在长期的进化过程中逐渐适应特定区域的气候条件.因此,全球气候变暖对“植物-害虫-天敌”的种间关系必然产生直接或间接的影响,导致不同昆虫之间以及昆虫与其相关营养层的物种之间的相互关系在气候变化下呈现出时间上的异步性和空间上的错位,从而影响植物的适应性和抗虫性、害虫的发生规律和危害程度以及天敌的种群消长和控害效能.昆虫除了可以通过休眠或滞育的方式在时间上避开高温的影响外,还可以通过迁飞或移动的方式在空间上避开高温的影响,在这种迁移和扩散不同步的情况下可能使害虫食性和取食植物的害虫及其天敌的种类发生变化,从而改变生物群落的组成与结构,影响生态系统的服务和功能.     

全球气候变暖对“植物-害虫-天敌”互作系统的影响

全球气候变化是近来人类关注的焦点问题,其最显著的特征是气候变暖。因为昆虫具有生活周期短、繁殖率高等特点,所以,气候变暖对昆虫的发育、繁殖和存活会产生强烈的直接影响。气候变暖促使一些昆虫提前春天的物候现象,向高纬度或高海拔地区迁移。然而,昆虫在自然界并非孤立地存在,它们与寄主植物和自然天敌相互联系、相互作用,并在长期的进化过程中逐渐适应特定区域的气候条件。因此,全球气候变暖对"植物-害虫-天敌"的种间关系必然产生直接或间接的影响,导致不同昆虫之间以及昆虫与其相关营养层的物种之间的相互关系在气候变化下呈现出时间上的异步性和空间上的错位,从而影响植物的适应性和抗虫性、害虫的发生规律和危害程度以及天敌的种群消长和控害效能。昆虫除了可以通过休眠或滞育的方式在时间上避开高温的影响外,还可以通过迁飞或移动的方式在空间上避开高温的影响,在这种迁移和扩散不同步的情况下可能使害虫食性和取食植物的害虫及其天敌的种类发生变化,从而改变生物群落的组成与结构,影响生态系统的服务和功能。     

Vitrification in plants as a natural form of cryoprotection

A small group of woody plants from the far northern hemisphere can, while in the dormant state, tolerate freezing and thawing to and from any subzero temperature at rates less than 30 degrees C/hr. In addition, the hardiest of them can tolerate cooling and warming between -20 degrees C and any colder temperature at virtually any combination of rates subsequent to cooling to -20 degrees C at rates less than 5 degrees C/hr. We term this latter capability "quench hardiness." I and my colleagues have shown that the limits of this quench hardiness can be closely correlated to the stability of intracellular glasses formed during the slow cooling of hardy tissues in the presence of extracellular ice. In this paper, I briefly review the evidence for intracellular glass formation and present data indicating that major components of the glass forming solutions are raffinose and stachyose. Evidence from differential scanning calorimetry that sugar-binding soluble proteins are also important is presented. Finally, I correlate data from our work with that of other workers to make the case that, even when most of a cytoplasmic solution is vitrified, fluid microdomains remain which can lead to long-term biodegradation during storage at high subzero temperatures.     

Neighbourhood of host plants influences oviposition decisions of a stem-boring weevil

The spatial arrangement of suitable host plants in the field may significantly constrain insects to find optimal hosts. Plant neighbours around a focal host plant can either lead to lower (associational resistance) or higher (associational susceptibility) herbivore loads. We tested whether the spatial arrangement of hosts of different suitability for the larval development of the shoot-base boring weevil Apion onopordi affects oviposition decisions in the field. Host plants in our study were healthy creeping thistles (Cirsium arvense; suboptimal hosts) and thistles infected by a rust pathogen (Puccinia punctiformis; optimal hosts). For analysis, we used nearest neighbour methods that disentangle the spatial distribution of organisms that are dependent on the position of other species (e.g. phytophagous insects and their host plants). Although theory predicts that the small-scale spatial infestation pattern can have major consequences for the population dynamics in insect–plant systems, field studies quantifying spatial pattern of phytophagous insects are rare.

The spatial arrangement of host plants clearly influenced oviposition pattern in A. onopordi. In contrast to previous studies, we demonstrated that not the rust infection itself determined if a plant was infested by weevils, but rather the density of rusted shoots within a certain neighbourhood. We found strong indications for associational susceptibility of healthy thistle shoots to weevil oviposition when growing in the neighbourhood of rusted thistles. Weevil-infested plants were spatially aggregated, indicating that A. onopordi is limited in its dispersal ability within patches. Other stem-boring insects on creeping thistle were affected in their oviposition decisions by other factors than A. onopordi. Thus, it may be difficult to find general rules for oviposition choice in phytophagous insects.

Our study showed that the spatial arrangement of host plants in the field critically determines oviposition choice and should thus be included as constraint in theories of optimal host selection.     

Myco-heterotrophy: when fungi host plants

Background

Myco-heterotrophic plants are partly or entirely non-photosynthetic plants that obtain energy and nutrients from fungi. These plants form a symbiosis with arbuscular mycorrhizal, ectomycorrhizal or saprotrophic fungi to meet their nutrient demands.

Scope

This Botanical Briefing summarizes current knowledge about myco-heterotrophy, discusses its controversial aspects and highlights future directions for research.

Conclusions

Considerable recent progress has been made in terms of understanding the evolutionary history, germination and nutrition of myco-heterotrophic plants. Myco-heterotrophic plants: (1) are diverse and often ancient lineages that have coevolved with fungi, (2) often demonstrate unusually high specificity towards fungi during germination and maturity, and (3) can either cheat common mycorrhizal networks supported by neighbouring photosynthetic plants to satisfy all or part of their energetic and nutritional needs, or recruit free-living saprotrophic fungi into novel mycorrhizal symbioses. However, several fundamental aspects of myco-heterotrophy remain controversial or unknown, such as symbiotic costs and physiology.Key words: Cheater, common mycorrhizal network, mutualism, myco-heterotrophy, non-photosynthetic, symbiosis     

Lepidopteran caterpillar fauna of cerrado host plants

The cerrado biome is rich in caterpillar species although the general biology and ecology of most tropical species remains unknown. Three host plant genera (Byrsonima, Erythroxylum and Qualea) were examined for caterpillars in four cerrado sensu stricto areas near Brasi´lia (DF, Brazil), from 1991 to 1995. Altogether, more than 16000 host plants were sampled and less than 20% of them possessed caterpillars. All the caterpillars found were reared under laboratory conditions. We successfully reared 137 species of 24 lepidopteran families. The average number of caterpillar species per host species was 28.3. The faunal similarity among plant genera, as well as among study sites, was low, and not related to the distances between them. The low proportion of host plants with caterpillars and the high incidence of rare species appears to be a general pattern for the cerrado. A large proportion (74%) of the caterpillar species occurred on only one host plant family. The most frequent species were either specialists (restricted to one host plant genus) or generalists. We provide a brief outline of some taxonomic problems, some observations on general biology, and temporal and local patterns of some specific caterpillars species. The methodology used, which included weekly data collection, in restricted study areas of the same habitat, with the same sampling method for recording the caterpillar species on the same host plant species, can be used as a tool to explore biodiversity and to discuss some aspects of the conservation of cerrado insects.     

Assessment of herbivore performance on host plants

Two models for assessing the performance of herbivores on a variety of host plants are developed by combining knowledge of population genetics and population ecology, especially that of the fixation probability of mutant genes. The absolute host performance model precisely assesses host performance for one herbivore population based on parameters of fecundity, larval survivorship, and selection pressure. The relative host performance model compares host performance for one population among different host plant species and for several populations on the same host species. Two herbivore populations, Bemisia tabaci (Gennadius) and Tetranychus truncates Ehara, were used to validate the absolute and relative host performance models. Results indicated that the assessment systems of host performance were reasonable and reliable. These models could be applied to a wide range of herbivore species for assessing their performance on host plants.     

A review of host plants of Callipogon (Eoxenus) relictus Semenov (Coleoptera: Cerambycidae: Prioninae), a Korea natural monument,with a new host,Quercus aliena Blume

A comprehensive checklist identifying host plants of phytophagous insects are essential in protecting forest ecosystems from major insect pests. We investigated host plants of Callipogon (Eoxenus) relictus Semenov (Coleoptera: Cerambycidae: Prioninae), an insect categorized as a natural monument in South Korea. Field surveys in Gwangneung forest led us to newly recognize the oriental white oak, Quercus aliena Blume (Fagaceae), as a host plant of C. (E.) relictus. Based on this result and a literature search, we provide an updated list of host plants of C. (E.) relictus in the present study. In addition, we also discussed about microorganisms (mushrooms) and habitats in Gwangneung forest (South Korea) and Ussurisky Nature Reserve (Russia) that are relevant to C. (E.) relictus.     

Quality or quantity: the direct and indirect effects of host plants on herbivores and their natural enemies

Resource quality (plant nitrogen) and resource quantity (plant density) have often been argued to be among the most important factors influencing herbivore densities. A difficulty inherent in the studies that manipulate resource quality, by changing nutrient levels, is that resource quantity can be influenced simultaneously, i.e. fertilized plants grow more. In this study we disentangled the potentially confounding effects of plant quality and quantity on herbivore trophic dynamics by separately manipulating nutrients and plant density, while simultaneously reducing pressure from natural enemies (parasitoids) in a fully factorial design. Plant quality of the sea oxeye daisy, Borrichia frutescens, a common coastal species in Florida, was manipulated by adding nitrogen fertilizer to increase and sugar to decrease available nitrogen. Plant density was manipulated by pulling by hand 25 or 50% of Borrichia stems on each plot. Because our main focal herbivore was a gall making fly, Asphondylia borrichiae, which attacks only the apical meristems of plants, manipulating plant nitrogen levels was a convenient and reliable way to change plant quality without impacting quantity because fertilizer and sugar altered plant nitrogen content but not plant density. Our other focal herbivore was a sap-sucker, Pissonotus quadripustulatus, which taps the main veins of leaves. Parasitism of both herbivores was reduced via yellow sticky traps that caught hymenopteran parasitoids. Plant quality significantly affected the per stem density of both herbivores, with fertilization increasing, and sugar decreasing the densities of the two species but stem density manipulations had no significant effects. Parasitoid removal significantly increased the densities of both herbivores. Top-down manipulations resulted in a trophic cascade, as the density of Borrichia stems decreased significantly on parasitoid removal plots. This is because reduced parasitism increases gall density and galls can kill plant stems. In this system, plant quality and natural enemies impact per stem herbivore population densities but plant density does not.     

Effects of natural enemies on relative fitness of Heliothis virescens genotypes adapted and not adapted to resistant host plants

We investigated the potential of two natural enemies of Heliothis virescens (F.) (Noctuidae) to affect its rate of adaptation to tobacco containing Bacillus thuringiensis Berliner toxin. Larval fitness of two laboratory strains of H. virescens, one adapted to B. thuringiensis toxin and one not adapted, was compared on toxic and nontoxic plants, in the presence of the parasitoid Campoletis sonorensis (Cameron) (Ichneumonidae) or the entomopathogenic fungus Nomuraea rileyi (Farlow) Samson. By exposing larvae to plants and enemies for no more than 24 h, we focussed on the behavioral rather than physiological component of their interaction with toxic plants and natural enemies. Parasitism of H. virescens larvae by C. sonorensis during exposure periods of 1–4 h was lower on toxic plants than nontoxic plants and was lower for nonadapted larvae than for toxin-adapted larvae. Decreased larval feeding damage on toxic versus nontoxic plants, and by nonadapted versus adapted larvae, may explain differences in parasitism, because C. sonorensis locates host larvae using cues from damaged plants. Effects of plant toxicity and larval strain on H. virescens survival were numerically consistent with effects on parasitism, but they were not statistically significant. When mean larval survival is used to estimate fitness of the nonadapted genotype relative to the toxin-adapted genotype, we find that C. sonorensis is expected to delay adaptation to toxic plants. Percent infection by N. rileyi of H. virescens larvae exposed to fungus-treated plants for 24 h was greater when plants were toxic, and was greater for nonadapted larvae than toxin-adapted larvae. There were corresponding decreases in larval survival on toxic compared to nontoxic plants, and of nonadapted compared to adapted larvae. Interaction of effects of plant line and larval strain on survival was significant in the presence of fungus, but not in the absence of fungus, which indicates that the effect of toxic plants on the relative fitness of toxin-adapted and nonadapted larvae was mediated by fungus. As in the interaction with C. sonorensis, behavior of larvae on plants may explain differences in susceptibility to N. rileyi. Because nonadapted larvae moved more than toxin-adapted larvae on toxic plants, nonadapted larvae may have been more likely to encounter a lethal dose of conidia. In contrast with C. sonorensis, N. rileyi, which decreased the fitness of the nonadapted genotype relative to the adapted genotype, is expected to accelerate adaptation to toxic plants.     

Further studies of drought resistance in woody plants

This publication is an extension of the 1956 review of drought resistance in woody plants. The more important recently used terms are listed and defined. Summaries of reports of drought effects on forest trees are presented in tabular form. Frost-drought is discussed as an important factor in the limitation of woody plants’ geographical ranges. The role that droughts play in the initiation of tree diseases is considered, especially in the light of new evidence from studies of diebacks-declines of forest trees. Interactions between soil moisture and transpiration are discussed as well as ways to control transpiration in large stands. Also considered are drought experiments with tree seedlings and symptomatology of drought injury. The means by which woody plants survive drought (excluding ephemerals) are discussed.     

New host plants of Erwinia amylovora in Bulgaria

Nine strains of Erwinia amylovora were isolated from new host plants in Bulgaria--chokeberry and strawberry. The strains were characterized morphologically and biochemically using the API 20E and BIOLOG system. It was established that they showed three different API 20E metabolic profiles, not found by previous studies of E. amylovora. All strains were identified as E. amylovora due to their metabolic fingerprint patterns obtained by the BIOLOG system. The identification was confirmed by PCR amplification of a specific region of plasmid pEA29 and genome ams-region. This study is the first characterization and identification of E. amylovora strains isolated from chokeberry and strawberry by the API 20E and BIOLOG system and by polymerase chain reaction.     

Behavior of potato gametoclonal plants against the necrotic strain of potato Y potyvirus

A total of 59 Solanum tuberosum androgenetic plants have been obtained through anther culture, 47 of which derived from a tetraploid clone, seven from a diploid hybrid, and five from an anther-derived clone. About two thirds of the anther-derived plants were dihaploids, a few were monohaploids (5.08%) or aneuploids (6.78%), whereas the tetraploid genotype generated about a third of tetraploids. Seven hundred twenty seven R₁ plants arisen from tubers of the androgenetic potatoes were mechanically inoculated with the necrotic strain of the potato Y potyvirus (PVY^N) and grown in a glasshouse. Fifty days after inoculation, the presence of PVY^N in R₁ plants was detected by DAS-ELISA (Double Autibody Sandwich). Only three plants (0.4%) of genotype H2-258 exhibited local necrotic symptoms (hypersensitivity reaction) suggesting the presence of the N _y gene, and this extreme resistance is epistatic to hypersensitive resistance. The immunity (R _y-gene) to PVY^N was retained through anther culturing and present at all levels of ploidy. The pattern of segregation for immunity was differentiated according to the ploidy level of the anther-derived plants. This changed segregation pattern may be due to a loss of resistance during the culturing, when an endoreduplication has taken place or to the possible regeneration from Second-division restituted unreduced microspores. Anyway, this segregation pattern must be taken into account when gametoclones are used in genetic studies. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 4, pp. 572–578. The text was submitted by the authors in English.