Characterization of resistance to multiple aphid species (Hemiptera: Aphididae) in Medicago truncatula

Aphids are phloem-feeding insects that damage many important crops throughout the world yet, compared to plant-pathogen interactions, little is known about the mechanisms by which plants become resistant to aphids. Medicago truncatula (barrel medic) is widely considered as the pre-eminent model legume for genetic and biological research and in Australia is an important pasture species. Six cultivars of M. truncatula with varying levels of resistance to two pests of pasture and forage legumes, the bluegreen aphid Acyrthosiphon kondoi Shinji and the spotted alfalfa aphid Therioaphis trifolii f. maculata. (Buckton) are investigated. Two resistance phenotypes against T. trifolii f. maculata are described, one of which is particularly effective, killing most aphids within 24 h of infestation. Each resistance phenotype provided a similar but somewhat less effective degree of resistance to the closely-related spotted clover aphid Therioaphis trifolii (Monell). In the case of A. kondoi only one resistance phenotype was observed, which did not vary among different genetic backgrounds. None of the observed resistance against A. kondoi or T. trifolii f. maculata significantly affected the performance of green peach aphid Myzus persicae (Sulzer) or cowpea aphid Aphis craccivora Koch. The existence of multiple aphid resistance mechanisms in similar genetic backgrounds of this model plant provides a unique opportunity to characterize the fundamental basis of plant defence to these serious agricultural pests.     

Mobility of salivary components as a possible reason for differences in the responses of alfalfa to the spotted alfalfa aphid and pea aphid

The spotted alfalfa aphid (SAA), Therioaphis trifolii maculata (Buckton), causes a characteristic veinal chlorosis and necrosis in the growing tips of susceptible cultivars of alfalfa. The pea aphid, Acyrthosiphon pisum (Harris), causes general degenerative changes in alfalfa but no specific, local symptoms. Biochemical and electrophoretic analyses detected similar enzymes in the ejected saliva of either species: pectin methylesterase, endopolygalacturonase and at least three isozymes of a copper dependent oxido-reductase that showed both catechol oxidase and peroxidase activity. Pectinase and catechol oxidase activities per unit of soluble protein were much greater in the saliva of pea aphid compared with that of SAA. The isozymes of the oxidase from SAA were roughly half the molecular weights of the corresponding isozymes from pea aphid, however, and radiotracer studies showed that soluble secretions injected into alfalfa by SAA travelled to growing tips considerably faster than the secretions of pea aphid. It is suggested that differences in the lesions caused by these aphids may be due to reaction kinetics rather than specific salivary toxins; that the rate of arrival of salivary components, possibly the oxidases, at phloem unloading sites may determine whether the plant's local defensive system is able to repress the immediate challenge or undergoes a run-away reaction leading to necrosis.     

Independent action and contrasting phenotypes of resistance genes against spotted alfalfa aphid and bluegreen aphid in Medicago truncatula

Host resistance to aphids is poorly understood. Medicago truncatula, a model legume and cultivated pasture species, was used to elucidate defense against two aphid species, Therioaphis trifolii f. maculata (spotted alfalfa aphid, SAA) and Acyrthosiphon kondoi (bluegreen aphid, BGA). Aphid performance and plant damage were compared between near-isogenic cultivars, Mogul and Borung, that differ in resistance to both aphids. Analyses of aphid resistance in Mogul x Borung F2 plants and their progeny revealed modes of action and chromosome locations of resistance genes. Separate genes were identified for SAA resistance (TTR) and BGA resistance (AKR); both mapped to chromosome 3 but were found to act independently to reduce survival and growth of their target aphid species. The TTR locus controls distinct, and contrasting, local and systemic plant responses between the near-isogenic cultivars. TTR-mediated plant responses imply interaction between a resistance factor(s) in vascular tissue and a bioactive component(s) of SAA saliva. Features of both resistance traits suggest homology to aphid resistance in other legumes; elucidation of their molecular mechanisms will likely apply to other aphid-plant interactions.     

五种不同苜蓿品种对苜蓿斑蚜实验种群存活率和生殖力的影响及抗性分析

苜蓿斑蚜Therioaphis trifolii(Monell)是危害苜蓿最为严重的害虫之一。通过室内饲养,选用5个不同的苜蓿品种,测定了不同苜蓿品种上苜蓿斑蚜存活率及生殖力的影响。结果表明:苜蓿斑蚜在不同苜蓿品种的世代平均存活率以固原紫花最高,达97.83%,阿尔冈金最低,为72.73%。以存活率和内禀增长率作为测定抗性的指标,供试品种对苜蓿斑蚜抗性的大小依次为德国大叶﹥阿尔冈金﹥宁苜1号﹥固原紫花﹥金皇后,与田间抗性鉴定结果基本相近。     

Biology and trophic interactions of lucerne aphids

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刈割对苜蓿主要害虫种群数量动态的影响

在甘肃省定西市九华沟系统研究了刈割对苜蓿主要害虫种群数量动态的影响.结果表明,刈割对害虫种群数量的影响在不同害虫种类之间存在明显差异.刈割对苜蓿斑蚜、豌豆蚜和蓟马的控制效果非常明显.6月初第1次刈割能极显著降低其季节平均数量,并使其保持较低的种群密度水平,7月中旬第2次刈割对其季节平均数量的影响小于第1次刈割.刈割对盲蝽种群的影响有所不同,虽然第1次刈割初期盲蝽的种群数量显著低于未刈割田,但刈割后盲蝽的种群数量回升较快,到8月上旬其种群数量显著高于未刈割田.第2次刈割对其季节平均数量的影响大于第1次刈割.     

An association between phlebotomine sandflies and aphids in the Peruvian Andes

Abstract. As the composition of natural sugars in the diet of adult sandflies (Diptera: Psychodidae: Phlebotominae) may affect the development of Leishmania (Kinetoplastida: Trypanosomatidae) in sandfly guts, and so play an important role in the epidemiology of leishmaniasis, there is increasing interest in the sources of sugars for wild sandflies. Advanced chromatography techniques have provided indirect evidence that wild sandflies feed on honeydew, a substance released by aphids (Hemiptera: Aphididae) when feeding. Our objective was to determine whether sandfly density can be influenced directly by the local density of aphids. Aphid density was determined by counting absolute numbers of aphids on alfalfa stems in Purisima Valley, Peru, where sandflies transmit Leishmania peruviana causing Andean cutaneous leishmaniasis (uta). Sandfly relative abundance was measured using sticky trap sampling repeatedly in alfalfa fields. Lutzomyia verrucarum accounted for 92% of the total sandflies collected. As there was a female bias in sandflies collected close to houses, only the numbers of male sandflies were used in analysis. Most of the adult aphids found feeding on alfalfa were either Therioaphis trifolii forma maculata (97%) or Acyrthosiphon pisum (3%). By regression analysis, a significant relationship was found between the density of Lu. verrucarum males and the density of adults of both aphid species. This is the first ecological study to support the hypothesis that aphid honeydew may be a source of sugar for sandflies.     

The use of visual cues in host evaluation by aphidiid wasps I. Comparison between threeAphidius parasitoids of the pea aphid

Host evaluation behaviour was examined in three species of aphid parasitoids,Aphidius ervi haliday,A. pisivorus Smith, andA. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae). Parasitoids were provided under laboratory conditions with three kinds of hosts representing two aphid species: (green) pea aphid,Acyrthosiphon pisum (Harris), and green and pink colour morphs of the alfalfa aphid,Macrosiphum creelii Davis. Females of all threeAphidius species distinguished between aphids on the basis of colour, movement, and host species. Patterns of host acceptance by parasitoids were species-specific. InA. ervi, host preference was the same in light and dark conditions: pea aphid>green alfalfa aphid≫pink alfalfa aphid. In contrast,A. pisivorus attacked and accepted pea aphid and green alfalfa aphid equally in the light and preferred both of these over pink alfalfa aphid; however, it made no distinction between pea aphid and pink alfalfa aphid in the dark. Females ofA. smithi attacked all three kinds of hosts (pea aphid>green alfalfa aphid≫pink alfalfa aphid) but apparently laid eggs only in pea aphid. The frequencies of attack and oviposition by all wasps were higher on ‘normal’ pea aphids than on those anaesthetized with CO₂. Host recognition is confirmed by chemical cues in the aphid cuticle that are detected during antennation, and host acceptance is dependent on an assessment of host quality during ovipositor probing.     

Effects of surrounding landscape on parasitism of alfalfa aphids in an IPM crop system in northern Catalonia

The parasitism (Hymenoptera, Braconidae, Aphidiinae) of alfalfa aphids (Hemiptera, Aphididae) was determined during three crop growing seasons. The highest rates of parasitism of Acyrthosiphon pisum Harris and of Therioaphis trifolii Monell occurred during the first-second and the fourth alfalfa intercuts, respectively. The landscape surrounding the fields affected only parasitism rates of A. pisum. During the second intercut the forest area had a negative influence on parasitism rates, whereas the bordering surfaces of alfalfa and winter cereals had a positive influence. Positive correlations were found between the rates of parasitism of A. pisum and the rate of aphid population increase in the first intercut. By contrast, negative correlations were found in the second intercut, when the aphid population peaked, suggesting that parasitoids contribute to the regulation of the aphid. This study stresses that regulation of alfalfa aphids cannot be explained solely on the basis of one functional group of natural enemies.     

Resistance and susceptibility of alfalfa （Medicago sativa L.） cultivars to the aphid Therioaphis maculata （Homoptera： Aphididae）： insect biology and cultivar evaluation

Biology of the aphid Therioaphis maculata was studied on alfalfa （Medicago sativa L.）, including four resistant （Mesa-Sirsa, CUF101, Baker and Lahontan） and two susceptible （ARC and Caliverde） alfalfa cultivars, and one of the most cropped Brazilian cultivars, Crioula. Under controlled conditions, antibiosis （i.e., reduced longevity, fecundity and increased mortality of the aphid） was observed mainly on the resistant alfalfa cultivars, except on Lahontan. Crioula seemed to be tolerant to aphids. Present data support geographic limitation usage of cultivars, and we suggest Baker and Mesa-Sirsa as sources of antibiosis, and provide biological information of a tropical T. maculata biotype on alfalfa.     

The role of vision and color in the close proximity foraging behavior of four coccinellid species

The role of vision and color in close-proximity foraging behavior was investigated for four species of lady beetles: Coccinella septempunctata, Hippodamia convergens, Harmonia axyridis, and Coleomegilla maculata. The effect of light level and color cues on consumption rates varied among the four predator species. The consumption rates of these predators on the pea aphid Acyrthosiphon pisum (Harris) was measured under light and dark conditions. C. septempunctata,H. convergens, and Ha. axyridis consumed significantly more aphids in the light than in the dark, while the consumption rate of Col. maculata was not affected by light level. Foraging ability was also measured on red and green color morphs of the pea aphid on red, green, and white backgrounds. C. septempunctata consumed significantly more of the aphid morph that contrasted with the background color, and showed no difference between morphs on the white background. H. axyridis consumed significantly more red morph aphids regardless of background. The remaining two species showed no difference in consumption rates on the two color morphs. The variation in the use of visual cues demonstrates how different species of predators can exhibit different foraging behaviors when searching for the same prey. Received: 4 August 1997 / Accepted: 3 February 1998     

小十三星瓢虫对苜蓿斑蚜的捕食功能反应

对小十三星瓢虫Adonia variegata(Goeze)捕食苜蓿斑蚜Therioaphis trifolii(Monell)的研究表明,其功能反应为Holling-Ⅱ型模型,方程为Na=0.967N/(1+0.0095N),捕食苜蓿斑蚜的数量随斑蚜密度增加而增大,日最大捕食量为102头。在10~25℃下,小十三星瓢虫捕食率y与温度x的关系为y=3.4x-7.9375;在25~35℃间的捕食率y与温度x的关系为y=137.08-2.25x。25℃下小十三星瓢虫捕食率最高,捕食率达79.4%。在种内干扰条件下,其捕食作用率E随天敌密度P的增加而减少,干扰反应数学模型为E=0.6063P-0.6743。随着叶片数的增多,小十三星瓢虫和斑蚜之间的距离相对增大,造成捕食率的下降。     

The use of visual cues in host evaluation by aphidiid wasps

We examined host evaluation behaviour in three species of aphid parasitoids, Ephedrus californicus Baker, Monoctonus paulensis (Ashmead), and Praon pequodorum Viereck (Hymenoptera: Aphidiidae). Mated females were provided with pairwise choices among three kinds of hosts in the laboratory: (green) pea aphid, Acyrthosiphon pisum (Harris), and a green and a pink colour morph of alfalfa aphid, Macrosiphum creelii Davis. Patterns of attack and host acceptance were species-specific. Females of E. californicus did not respond to the presence of aphids prior to making antennal contact. Variations in rates of parasitization (pea aphid>green alfalfa aphid>pink alfalfa aphid) were consistent with differences in aphid defensive behaviours; no ‘preference’ for any host type was evident when aphids were anaesthetized with carbon dioxide. In M. paulensis, the order of preference (pea aphid>green alfalfa aphid>pink alfalfa aphid) did not vary when aphids were immobilized, or presented in the dark, or both. Host movement did not influence the rate of attack by M. paulensis. In contrast, the ranked order of preference in P. pequodorum varied with circumstance. In the light, females attacked pea aphid and green alfalfa aphid with equal frequency, but parasitized significantly more of the former; both kinds of aphids were attacked and parasitized at higher rates than pink alfalfa aphid. In the dark, P. pequodorum females parasitized green and pink alfalfa aphids equally and at higher rates than pea aphids. Whereas E. californicus was more successful ovipositing in immobilized hosts, P. pequodorum females attacked and laid more eggs in normal than anaesthetized aphids. Patterns of host recognition and evaluation are compared across six species representing four genera in the family Aphidiidae.     

Interactions between an introduced and indigenous coccinellid species at different prey densities

Coccinella septempunctata L. (Coleoptera: Coccinellidae), a Palearctic coccinellid, has established and rapidly spread throughout the United States. This quantitative examination of larval interactions between C. septempunctata and Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), a Nearctic coccinellid, was conducted under controlled prey densities. Larvae of both coccinellid species are affected by a limited diet [one pea aphid per day Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)] compared with an excess diet (>20 aphids per day). Larval survival decreased from 86 to 63% in C. maculata and from 84 to 33% in C. septempunctata; mean preimaginal developmental time increased from 20.6 to 26.7 days in C. maculata, and from 18.1 to 32.0 days in C. septempunctata. Additionally, on one aphid per day, mean adult weight was reduced from 12.39 to 9.79 mg in C. maculata, and from 39.57 to 14.44 mg in C. septempunctata. Interspecific interactions, favoring C. septempunctata over C. maculata at a␣low prey density (one aphid per day), take the form of␣reduced survival of C. maculata compared with C.␣septempunctata (14 versus 66%). Reduced survival of␣C. maculata may be the result of competition for aphids or intraguild predation by C. septempunctata on C.␣maculata. No interspecific interactions (measured as effects on larval survival, preimaginal developmental time, and adult weight) were observed between larvae of these two species at a high prey density (>20 aphids per predator per day). Received: 15 September 1997 / Accepted: 20 May 1998     

Potential for intraguild predation and competition among predatory Coccinellidae and Chrysopidae

In a laboratory study two coccinellid species, Coleomegilla maculata (DeGeer) and Harmonia axyridis Pallas, completed preimaginal development on lacewing eggs, Chrysoperla carnea Stephens or pea aphids, Acyrthosiphon pisum (Harris) in similar times. Preimaginal survival on C. carnea eggs was similar to survival on A. pisum for all stages of C. maculata and H. axyridis. Coccinellid adults that developed on C. carnea eggs were smaller than adults reared on A. pisum. Coccinella septempunctata L. did not complete preimaginal development on C. carnea eggs. Chrysoperla carnea preimaginal developmental time was approximately 20 days when fed either C. maculata eggs or A. pisum. Chrysoperla carnea fed C. maculata eggs developed into smaller adults, compared to adults reared as larvae on A. pisum, Ostrinia nubilalis (Hübner) eggs, or A. pisum alternated daily with O. nubilalis eggs. C. carnea did not complete preimaginal development on H. axyridis eggs. Cannibalism occurred more frequently between C. carnea third instars than between C. maculata fourth instars. When a C. carnea third instar was paired with a C. maculata fourth instar, more C. maculata were preyed upon by C. carnea, regardless of the herbivorous prey density. In the field these two predator species may negatively affect each other and reduce their suppression of pest densities.     

高温对共存种棉蚜与棉长管蚜死亡及繁殖的影响

棉蚜和棉长管蚜是棉花上的共存种,为探索其年内及年际间优势地位的不同是否与两者对高温的不同响应有关,室内研究了高温胁迫(32、34、36和38℃)对棉蚜和棉长管蚜死亡及繁殖的影响.结果表明:随着温度的升高和高温持续天数的延长,棉蚜和棉长管蚜累计死亡率均升高,棉长管蚜累计死亡率高于棉蚜;两种蚜虫的每日死亡率可用互补重对数模型较好地拟合,模型估计的棉蚜和棉长管蚜半数致死温度值随高温持续天数的延长而降低,棉蚜半数致死温度高于棉长管蚜;在32 ～ 38℃范围内,两种蚜虫的繁殖率随温度的升高而降低,棉蚜繁殖率显著高于棉长管蚜,表明在32℃以上高温条件下,棉蚜比棉长管蚜更具有竞争力.随着全球气候变暖,由于棉蚜比棉长管蚜更耐高温,推测未来棉蚜比棉长管蚜竞争优势更加明显.     

Intraguild interactions of aphidophagous predators in fields: effect of Coccinella septempunctata and Episyrphus balteatus occurrence on aphid infested plants

Intraguild relations between beneficial insects have become a major research topic in biological pest control. In order to understand the intraguild competitions between aphidophagous populations in natural conditions, a field experiment was carried out in the experimental farm of the Gembloux Agricultural University. As biological control of pests involve a community of diverse natural enemies, this experiment firstly aimed to assess the aphidophagous predator diversity and abundance in green pea (Pisum sativum) field and secondly to investigate the impact of the large natural occurrence of C. septempunctata on the aphidophagous beneficial dispersion and efficiency as aphid biological control agents in pea field. Visual observations were weekly performed throughout the 2006 growing season. The pea aphids were attacked by several predatory groups, mainly ladybird beetles and hoverflies. Higher densities of ladybirds and hoverflies were recorded in the beginning of July, associated with an aphid occurrence peak. Using net cage system in the field, the particular intraguild relations between added C. septempunctata or E. balteatus and the natural beneficial arrivals and dispersion were observed. The E. batteatus (eggs and larvae) presence inhibited other aphidophagous predators presence on the aphid infested plants. Lower abundance of E. balteatus was observed on aphid infested plants already colonised by C. septempunctata. To explore more accurately the oviposition and predation behaviours of ladybirds and hoverflies and to determine the chemical factors that could influence these behaviours, current researches are performed in laboratory and will be discussed to promote efficient biological control of aphids by natural enemies.     

Occurrence and Transmission of Facultative Endosymbionts in Aphids

The occurrence of a secondary bacterial symbiont (PASS) of pea aphid, Acyrthosiphon pisum (Harris), was detected by polymerase chain reaction (PCR) with specific nucleotide primers based on PASS 16S rDNA nucleotide sequences from over 80% (50/57) of clones of pea aphid collected from widely separated locations in California. PASS was also detected by PCR in both red and green phenotypes of rose aphid, Macrosiphum rosae (L.), but not in six other species of aphids examined, including blue alfalfa aphid (A. kondoi Shinji). The nucleotide sequences of the PCR-amplified, partial 16S rDNAs (1060 bp) from pea aphid and rose aphid were identical and 99.9% similar to the published 16S rDNA of PASS. PASS and a recently described new rickettsia of pea aphid (PAR) were transmitted by needle injection of hemolymph from positive pea aphid clones into negative clones and into blue alfalfa aphids. Both PASS and PAR were maintained in the offspring of some of the injected mother aphids via high rate of maternal transmission. Received: 18 September 1996 / Accepted: 30 September 1996     

应用EPG技术分析不同品种苜蓿对苜蓿斑蚜的抗性

【目的】明确苜蓿斑蚜Therioaphis trifolii对不同品种苜蓿Medicago sativa的取食行为,探明抗蚜因子和抗虫位点,筛选抗蚜苜蓿品种。【方法】利用刺吸电位技术(electrical penetration graph, EPG)记录苜蓿斑蚜成蚜在10个苜蓿品种上的取食行为,并基于聚类分析方法筛选合适的EPG参数进行抗蚜性评价。【结果】苜蓿斑蚜成蚜在取食苜蓿过程中呈现np波、pd波、A波、B波、C波、E波、F波和G波8种波形,其中E波、F波和G波的总时间在不同品种间表现出显著差异。在5 h测试期间,E波持续时间在敖汉上最长,金皇后和中苜3号上次之,草原2号和阿尔冈金上最短;F波总时间以准格尔、阿尔冈金和金皇后上最长,敖汉、德宝和草原2号上最短,说明前者具有较强的机械抗性而后者机械抗性较弱。以第1次刺探持续时间、总刺探时间、F波总时间、C波总时间、E波总时间作为聚类分析的指标,10个苜蓿品种被聚成3类：阿尔冈金、草原2号、WL168HQ、德宝、中苜2号和新牧2号为第Ⅰ类,金皇后、中苜3号和准格尔为第Ⅱ类,敖汉为第Ⅲ类。【结论】苜蓿斑蚜成蚜在不同苜蓿品种上的取食行为存在差异,草原2号、阿尔冈金和WL168HQ在叶表皮、叶肉和韧皮部层次对苜蓿斑蚜成蚜存在抗性,金皇后在叶表皮和叶肉部位表现出抗性;苜蓿斑蚜成蚜在敖汉上能够长时间刺吸取食,因此敖汉抗性最弱。本研究为深入探讨苜蓿抗虫机理和蚜虫综合治理提供了理论参考。     

The significance of antioxidants in the aphid-plant interaction: The redox hypothesis

The hypothesis is advanced that a redox system controls oxidation rates during the responses of plants to attack by sucking insects, that soluble antioxidants, such as ascorbate and glutathione, enhance the effectiveness of the plant's defensive system, and that oxidising enzymes in the saliva of aphids (and other phytophagous sucking insects) serve to counter it. Plants typically respond to wounding, including that caused by sucking insects, by mobilising and oxidising phenolic compounds. The initial phenolic monomers, and especially the monomerico-quinones to which many give rise on oxidation, are generally deterrent to insects. Their final oxidation products, however, are polymers and phenol-protein conjugates, which are non-toxic, but serve to seal off damaged cells. It is suggested that effective defence by the plant requires oxidation of phenolics at a controlled rate that maintains a deterrent titre of the monomers, while allowing a well ordered deposition of sealants. It is also suggested that the salivary oxidases of the insects hasten oxidation in the affected tissues, thereby decreasing concentrations of monomeric phenols and quinones. It is further suggested that sedentary species may also thereby disorganise the sealing off of affected tissues. A kinetic model is developed to show that inclusion of a reductive cycle in the sequential oxidation of phenolics increases the steady state concentrations of monomeric phenols for a given throughput. Conversely, an increase in oxidation rates diminishes the titre of monomers for the same throughput. In initial biological tests of the hypothesis, infiltration of stems of lucerne cultivars with ascorbate or glutathione reduced the reproductive rate of spotted alfalfa aphid,Therioaphis trifolii maculata (Buckton), and of blue-green aphid,Acyrthosiphon kondo Shinji, feeding thereon. Intrinsically non-deterrent concentrations of ascorbate synergised the deterrence of the plant phenolics chlorogenic acid and catechin to the apple aphid,Aphis pomi (de Geer), and the spotted alfalfa aphid,T. t. maculata, respectively.