Cowpea aphid performance and behaviour on two resistant cowpea lines

In a series of laboratory and climate chamber tests we compared the growth and behaviour of Aphis craccivora on one susceptible (ICV-1) and two aphid-resistant (ICV-11 and ICV-12) cowpea lines. The aphids' growth rates were much lower on the resistant cowpea lines than on the susceptible one, indicating strong antibiosis. In addition, the aphids invariably settled in higher numbers on the susceptible line than on either of the resistant. Compared to ICV-1, damaged leaves of the resistant line ICV-12 were settled upon to a higher degree than undamaged leaves, and leaf discs from the same line were even less resistant.On resistant lines individual aphids waited a significantly longer time before making their first test probe. Total probing time as well as the time preceding a decision to stay or leave was also longer.These results are discussed in relation to the possible mechanisms involved, and we also consider the effects of previous leaf feeding on the expression of resistance in the field.

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Résumé Au cours d'expériences au laboratoire et en chambres climatisées nous avons comparé la croissance et le comportement de A. craccivora sur une lignée sensible (ICV-1) et deux lignées résistantes (ICV-11 et ICV-12) de V. unguiculata. Les vitesses de croissance des pucerons ont été beaucoup plus lentes sur les lignées résistantes que sur la lignée sensible, ce qui révèle une forte antibiose. De plus, les pucerons atterrissent invariablement en plus grand nombre sur la variété sensible. Par comparaison avec ICV-1, les atterrissages sur lignée résistante ICV-12 étaient plus nombreux sur les feuilles endommagées que sur les feuilles intactes; les disques de feuilles de cette même lignée étaient encore moins résistants.Les pucerons ont séjourné individuellement un temps plus long sur les lignées résistantes avant de faire leur premier sondage. Le temps consacré aux sondages ainsi que le temps précédant de choix entre départ ou maintien sur la feuille étaient plus longs avec les lignées résistantes.Ces résultats ont été discutés en fonction des mécanismes impliqués. Nous avons aussi examiné les effets de la consommation antérieure sur les manifestations de la résistance dans la nature.

     

Stylet activity of cowpea aphid (Homoptera: Aphididae) on leaf extracts of resistant and susceptible cowpea cultivars

Electrical penetration graph recordings using direct current (DC-EPGs) were used to analyze aspects of the probing behavior of cowpea aphid,Aphis craccivora Koch, on intact plants and on hexane, ethyl acetate, and methanol extracts of leaves of aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cultivars of cowpeaVigna unguiculata (L.) Walp. In one set of experiments, recordings were done on plants with or without parafilm wrapping, or on plants painted with raw leaf juice and extracts of the two cultivars. In another study, recordings were done on leaf extracts homogenized in water or in 0.5M sucrose solution and then placed in parafilm membrane sachets. Electrodes were inserted into soil mix for the experiments on potted plants or into extract fractions and raw juice for the membrane feeding experiments on leaf extracts in parafilm sachets. Waveform signals were recorded from resistance fluctuations from interactions between aphids and substrates, and electromotive forces generated within each preparation. ICV-12 plants with or without parafilm wrapping, and ethyl acetate extracts and raw juice of that cultivar significantly (P≤0.05) reduced stylet penetration behavior. Thus, antixenosis as manifested by disruption of aphid stylet activity on host substrates, appeared to be a governing modality of aphid resistance in ICV-12.     

Activation of ethylene‐related genes in response to aphid feeding on resistant and susceptible melon and tomato plants

The simple gaseous compound ethylene (ET) has long been recognized as a common component of plant responses to insect feeding and pathogen attack. However, it is presently uncertain whether it plays a role in host–plant resistance to piercing–sucking insects such as aphids. In these experiments, we investigated the expression of key ET‐associated genes in resistant and susceptible interactions in two model systems: the tomato‐Mi‐Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae: Macrosiphini) system and the melon‐virus aphid transmission gene (Vat)‐Aphis gossypii Glover (Hemiptera: Aphididiae: Aphidini) system. We examined expression patterns of genes associated with ET synthesis, perception, signal transduction, and downstream response. When compared with control plants, plants infested with aphids showed marked differences in gene expression. In particular, ET signaling pathway genes and downstream response genes were highly upregulated in the resistant interaction between A. gossypii and Vat⁺, indicating ET may play a role in Vat‐mediated host–plant resistance. A key integrator between the ET and jasmonic acid pathways (Cm‐ERF1) showed the strongest response.     

Inheritance of resistance to the cowpea aphid in cowpea

Summary Inheritance of resistance to cowpea aphid, Aphis craccivora Koch, in three resistant cultivars of cowpea, Vigna unguiculata (L.) Walp, was studied. The parents, F₁ and F₂ population were grown in an insect-proof screenhouse. Each 3-day-old seedling was infested with 10 apterous adult aphids. Seedling reaction was recorded when the susceptible check was killed. The segregation data revealed that the resistance of ICV11 and TVU310 is governed by single dominant genes. All the F₂ seedlings of the cross ICV10xTVU310 were resistant, indicating that they have the same gene for resistance. However, the F₂ populations from the crosses ICV10xICV11 and ICV11xTVU310 segregated in a ratio of 151, indicating that the dominant genes in ICV11 and TVU310 are non-allelic and independent of each other. The resistance gene of ICV10 and TVU310 is designated as Ac₁ and that of ICV11 as Ac₂.     

Components of resistance to Aphis craccivora in some cowpea cultivars

Experiments were conducted to determine in six cowpea cultivars the modalities of resistance to the cowpea aphid. The resistance modality in IT82D-812 is mainly due to antixenosis, even though reproduction was minimal on this cultivar. Both antixenosis and antibiosis were found to operate in ICV 12, with antibiosis operating in the area of high nymphal mortality and low reproduction. It is suggested that when studying the modality of resistance among crop cultivars, studies of both antixenosis and antibiosis be made in order to determine where the resistance modality lies.

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Résumé Les expériences avaient pour but de découvrir les causes de la résistance de 6 cultivars de niébé à A. craccivora. La résistance du cultivar IT82D-812 est due principalement à une antixénose, bien que la reproduction du puceron ait été minimale sur ce cultivar. Antixénose et antibiose interviennent toutes deux chez le cultivar ICV 12, l'antibiose provoquant une trés forte mortalité larvaire et une reproduction faible. On en déduit que l'étude des modalités de résistance de différents cultivars, doit comprendre l'examen de l'antixénose et de l'antibiose, de façon à déterminer où se situent les causes de la résistance.

     

Aphis craccivora settling behaviour and acquisition of cowpea aphid-borne mosaic virus in aphid-resistant cowpea lines

The settling behaviour of Aphis craccivora Koch, the vector of cowpea aphid-borne mosaic virus (CAMV) in cowpea, Vigna unguiculata (L.) Walp., on aphid-resistant, aphid-tolerant and aphid-susceptible cowpea lines was investigated. It was found that although apterae counts on the aphid-susceptible and aphid-tolerant lines were higher than on the aphid-resistant ones, apterae were more widely dispersed among the latter. Whereas there was a positive significant correlation between alatae numbers and incidence of CAMV in the aphid-susceptible and aphid-tolerant lines, this correlation was negative in the aphid-resistant ones. However, the incidence of CAMV was not significantly different from each other in all the lines. This indicated that aphid activity (e.g. wide dispersal) was more important in the spread of CAMV than the absolute number of viruliferous alatae, an effect which was manifested on the aphid-resistant lines.Aphids acquire CAMV more readily from aphid-susceptible and aphid-tolerant source plants than from aphid-resistant ones. The significance of this in relation to secondary spread of CAMV and the effect of noncolonising aphids are discussed.

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Le comportement d'atterissage d'Aphis craccivora et l'acquisition du virus de la mosaïque transmis par puceron chez les variétés de niébe résistantes au puceron

Résumé Le comportement d'atterissage d'Aphis craccivora, vecteur du virus de la mosaique transmis par puceron (CAMV) sur Vigna unguiculata, a été examiné sur des variétés résistantes, sensibles ou tolérantes aux pucerons. On a observé que bien que les dénombrements d'aptères sur variétés sensibles ou tolérantes aient été plus élevés que sur variétés résistantes, les aptères étaient plus largement dispersés sur ces dernières. Tandis qu'il y avait une corrélation positive significative entre les nombres d'ailés et la présence de CAMV sur les variétés sensibles et tolérantes aux pucerons, cette corrélation était négative sur les variétés résistantes. Cependant, la fréquence de CAMV n'était pas significativement différente parmi toutes ces variétés. Ceci a montré l'activité des pucerons (c'est à dire leur dispersion) étail plus importante dans la diffusion du CAMV que le nombre absolu d'ailés virosés, effet qui était manifeste sur les variétés résistantes aux pucerons.Les pucerons contaminés au CAMV le sont plus par des plantes sensibles ou tolérantes aux pucerons que par des plantes résistantes. La discussion porte sur la signification de ceci en relation avec la diffusion secondaire de CAMV, et de l'effet des pucerons non colonisateurs.

     

Interactions of Russian wheat aphid, a hymenopterous parasitoid and resistant and susceptible slender wheatgrasses

Interactions among three trophic levels of resistant and susceptible slenderwheat grasses, Elymus trachycaulum (Link) Goule ex Shinners ex. H.F. Lewis, Russian wheat aphid, Diuraphis noxia (Mordvilko), and a hymenopterous parasitoid were studied in the laboratory and greenhouse. These relationships were compared with a commercial susceptible wheat Triticum aestivum L. variety. Aphids reared on the resistant entries showed significantly lower weights and numbers. Significant reduction of parasitoid mummy weight and adult size was positively correlated with the effects on the aphids. Resistant entries also induced a longer prereproductive period for both the aphids and parasitoids. Numbers of aphids and aphid damage were significantly modified by the addition of parasitoids. Parasitism was higher on plants that did not have leaf rolling. These findings may indicate that antibiosis resistance studied here is not the most desirable because it decreases natural enemy vitality.     

Feeding behaviour of Aphis craccivora (Koch) on cowpea cultivars with different levels of aphid resistance

The feeding activity of Aphis craccivora (Koch) was monitored on cowpea plants of aphid-susceptible (Vita 7) and aphid-resistant (TVu 801) cultivars, using an AC electronic feeding monitoring system. Waveforms corresponding to salivation, phloem ingestion and non-phloem ingestion were observed. Aphids probing on the resistant cultivar showed a significantly reduced ingestion of phloem sap compared with those aphids which fed on the susceptible cultivar. The insect also made more brief and repeated probes on TVu 801. In addition, the duration of non-probing activities and non-phloem ingestion was shorter on the susceptible than on the resistant cultivar.     

Electrical penetration graphs of the damson-hop aphid, Phorodon humuli on resistant and susceptible hops (Humulus lupulus)

Electrical penetration graphs (EPG's) were used to locate resistance to Phorodon humuli (Schrank) (Homoptera, Aphididae) in hops (Humulus lupulus, Cannabinaceae). Aphids on those hops showing resistance had a much reduced E2 pattern (uptake of phloem). In addition, many aphids on the resistant plants spent time non-probing within two minutes of withdrawing from the phloem. This was not observed with aphids on susceptible hops. The results suggest that resistance is located in the phloem. The involvement of a mechanical factor such as the blocking of aphid stylets, the presence of antinutritional factors, or simply an inadequate supply of nutrients, are discussed as possible resistance mechanisms.     

Variation in feeding behaviour of Nilaparvata lugens on resistant and susceptible rice varieties

The feeding behaviour of Nilaparavata lugens was monitored on three rice varieties showing different levels of resistance in the Philippines, using a video-assisted observation method. N. lugens made more frequent, shorter probes on the moderately resistant IR46 and resistant IR62 rice varieties than on the susceptible IR22. Honeydew production was significantly lower on the resistant varieties though insect weight gains in 24 h were similar on IR46 and IR22, both being significantly greater than on the highly resistant variety.Population development, growth index and damage ratings were low on IR62 indicating antibiosis and/or non preference. When IR46 plants were infested as seedlings population increase, growth index and damage ratings were similar to those on the susceptible IR22. When infested at a later stage of plant growth the damage rating showed a moderate level of resistance though some population development was maintained, indicating antibiosis and tolerance. N. lugens started probing less frequently after surface exploration on both resistant varieties than on IR22 suggesting the presence of a resistance factor associated with the surface waxes of these varieties.

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Résumé Le comportement alimentaire de Nilaparvata lugens sur variétés de riz, sensible (IR22), partiellement résistante (IR46) et fortement résistante (IR62), a été contrôlé avec une méthode associant la vidéo à l'observation. N. lugens faisait des piqûres plus fréquentes et plus brèves sur IR46 et IR62, que sur la variété sensible. La production de miellat était significativement plus faible sur les variétés résistantes, bien que les gains de poids des insectes aient été les mêmes en 24 h sur IR46 et IR22, les deux étant significativement supérieurs à celui sur IR62.La croissance de la population, l'indice de croissance et le taux de dégâts étaient tous plus faibles sur IR62, ce qui révèle une antibiose et/ou une absence de préférence. Quand la contamination des IR46 a au lieu au stade semis, la croissance de population, l'indice de croissance et le taux de dégâts étaient semblables à ceux de la variété sensible IR22. Quand la contamination avait lieu à un stade ultérieur, le laux de dégâts révélait un niveau modéré de résistance bien qu'une certaine croissance de population se soit maintenue, ce qui révèle antibiose et tolérance.Après exploration de la surface des feuilles des deux variétés résistantes, N. lugens sondait moins fréquemment que sur IR22, ce qui laisse présumer un facteur de résistance associé aux cires superficielles de ces variétés.

     

Larval feeding behavior of Dipel-resistant and susceptible Ostrinia nubilalis on diet containing Bacillus thuringiensis (Dipel ESTM)

Diet choice tests were conducted to examine the effects of Bacillus thuringiensis Berliner on larval feeding behavior of Dipel-resistant and susceptible strains of European corn borer, Ostrinia nubilalis (Hübner). Larvae (first through fourth instars) were presented an untreated standard diet and three diets incorporating different concentrations of a commercial formulation of B. thuringiensis, Dipel ES^TM. Significantly higher proportions of susceptible and resistant larvae were found on the control diet compared to the proportions recorded on any of the Dipel-treated diets. Soon after release (0.5 to 3 h), the occurrence of larvae on each of the diets was similar across different instars. The number of first and second instars on the control diet increased steadily over 72 h after release, when 43 to 75% of larvae were found on the control diet. The proportion of third and fourth instars on the control diet also increased initially, with an equilibrium occurring 12 to 24 h later when 30 to 40% of larvae were found on the control diet. Both strains appeared to avoid the Dipel-treated diets and their responses were similar over different Dipel concentrations. The Dipel-resistant strain showed higher ability to avoid the treated diets than the susceptible strain.     

取食不同寄主植物对棉蚜后代抗药性的影响

测定了5种药剂对棉蚜Aphis gossypii抗氰戊菊酯、吡虫啉品系和敏感品系取食棉花、黄瓜和石榴的后代的毒力,并对它们的后代体内乙酰胆碱酯酶和羧酸酯酶的比活力做了初步探索。结果表明,氰戊菊酯抗性品系取食棉花比取食黄瓜的后代对氰戊菊酯的抗性大76.4倍,对灭多威、氧乐果、硫丹和吡虫啉的抗性也大0.5～4.6倍;取食石榴的后代对5种药剂的抗性介于取食棉花和黄瓜的之间。吡虫啉抗性品系的测定结果与氰戊菊酯抗性品系基本一致。敏感品系取食黄瓜比取食棉花的后代对5种药剂的敏感性更高。3个品系取食不同植物的后代相比,其体内乙酰胆碱酯酶的比活力,取食棉花的为取食黄瓜的2.4～2.8倍;羧酸酯酶的比活力,取食棉花的为取食黄瓜的1.8～2.4倍。证明棉蚜的抗性和敏感品系取食的寄主植物不同,可引起对药剂敏感性的变化。乙酰胆碱酯酶和羧酸酯酶活力的变化均是引起这种变化的重要因素。     

Phloem specific aphid resistance in Cucumis melo line AR 5: effects on feeding behaviour and performance of Aphis gossypii

The feeding behaviour, excretion rate, and life history traits of the cotton-melon aphid, Aphis gossypii (Glover) (Homoptera, Aphididae), were measured on a resistant melon, Cucumis melo L., breeding line, AR 5. The site of resistance detection by the aphids was determined using the electrical penetration graph (EPG) technique. EPG recordings showed that resistance is expressed within the host plant, rather than on its surface, because the time to first stylet penetration was not significantly different between AR 5 and the closely related susceptible breeding line, PMR 5. EPG patterns associated with stylet pathway activities of the aphids were not significantly different between the resistant and susceptible lines. Significant behavioural differences were observed only after stylets contacted phloem sieve elements. On AR 5, the duration of salivation after sieve element puncture (waveform E1) was significantly longer, and the number of aphids showing phloem sap ingestion (waveform E2) was significantly reduced. We conclude that the resistance mechanism producing the effects seen in this study acts within the phloem sieve elements. Monitoring of excretion rates on the two genotypes showed that aphid feeding was delayed and greatly reduced on the resistant genotype. Comparisons of aphid life history traits and population development between host plant genotypes showed that the effects of resistance act throughout aphid development and are highly effective at slowing down population increase.     

Species diversity, abundance, and phenology of aphid natural enemies on spring wheats resistant and susceptible to Russian wheat aphid

The species composition, relativeabundance, and seasonal dynamics of selectednatural enemies of cereal aphids were monitoredin spring wheat fields in Moscow, Idaho in 1997and 1998. Trials also examined the potentialimpact of resistance to Russian wheat aphid(RWA), Diuraphis noxia (Mordvilko)(Homoptera: Aphididae) in wheat, on aphidbiological control agents. Natural enemypopulations were monitored on two springwheats: D. noxia susceptible variety`Centennial' and resistant genotype `IDO488'. Field plots were artificially infested withadult D. noxia, and sampled for cerealaphids and parasitoids weekly. Coccinellidpredators were monitored once in 1997 and twicein 1998. The coccinellids Hippodamiaconvergens Guerin, Coccinellaseptempunctata L., C. transversoguttataBrown and C. trifasciata Mulsant weredetected. No significant differences in adultor immature coccinellid densities were observedbetween the D. noxia resistant andsusceptible genotypes. During both years, themost abundant primary hymenopteran parasitoidswere Diaeretiella rapae (M'Intosh), Aphidius ervi Haliday, A. avenaphis(Fitch), and Lysiphlebus testaceipes(Cresson), Aphelinus varipes (Foerster),Aphidius colemani Viereck, Aphidiuspicipes (Nees), Aphidius sp., Monoctonus washingtonensis Pike & Stary, Praon gallicum Stary, Praon occidentaleBaker, and Praon sp. were also detected. Numbers of both D. noxia and D.rapae were significantly greater on Centennialthan on IDO488 in both years. When all speciesof cereal aphids and parasitoids areconsidered, the total percentage parasitism wasnot significantly different between thegenotypes. There was no interaction betweenD. noxia resistance and the populationdensity of the predators or parasitoidsmonitored. These results suggest that the D. noxia resistant line had no adverse impacton natural enemies under the conditions ofthese field experiments.     

Fine structure of aphid stylet pathways and its use in host plant resistance studies

Conclusion Although there have been reports, based on light microscope observations, of damage to mesophyll tissue as a result of stylet penetration, we saw no evidence of this in our wax sections. However, the use of the electron microscope revealed that such damage does occur, and has also shown that both inter- and intracellular penetration routes exist, often within the same track, whereas we had formerly believed the stylet pathways of these aphids to be almost entirely intercellular. The intramural-extracellular route of penetration, characterised by the presence of stylets and or saliva between the cell wall and plasmalemma, requires the greater resolution of electron microscopy and cannot be distinguished in light microscope preparations.Our results suggest that an accurate indication of the stylet pathway cannot be obtained from the use of light microscopy alone, and raise serious doubts about the value of previous studies describing the route of stylet penetration. Light microscopy shows the track only at the tissue level and not at the cellular level. We advocate that all future studies of aphid stylet penetration should utilise both light and electron microscope studies because only the higher resolution of the latter technique will indicate the true stylet pathway and the end points of the tracks. Only then can the feeding site be determined with any precision.     

The swimming and feeding behavior of Mesocyclops

The swimming and feeding behaviors of Mesocyclops are described from a review of the literature and personal observations. Mesocyclops exhibits considerable behavioral flexibility in response to environmental stimuli. Mesocyclops edax exhibits an increase in horizontal looping behavior at high prey densities, and performs a tight vertical looping behavior in response to the loss of captured prey. Ingestion rates by Mesocyclops are a complex function of prey density, morphology, and behavior in addition to prey size. Vertebrate predators induce a rapid escape response in Mesocyclops and may be responsible at least in part for their extensive diel vertical migrations. The complex behavioral patterns of Mesocyclops suggest that its distribution and abundance in nature will be distinctly nonrandom and influenced as much by its own behavioral responses as by other external physical factors such as water circulation patterns.     

Performance of the predator Delphastus pusillus on Bemisia resistant and susceptible tomato lines

Host plant resistance and biological control are often assumed to act additively to suppress populations of agricultural pests. Using tomato trichome based resistance to the whitefly Bemisia argentifolii, we tested this additivity assumption with Delphastus pusillus, a coccinelid predator of Bemisia. Various life history traits of D. pusillus were measured on the tomato cultivar Alta, which possessed foliage with 3-fold greater trichome densities than the second cultivar VF145B7879. Beetles housed on VF145B7879 exhibited significantly greater lifetime fecundities and walking speeds than beetles housed on Alta. No cultivar-specific differences were observed in D. pusillus longevities or handling times. Combining these observations with previously published reports of reduced B. argentifolii population growth rates on Alta compared to VF145B7879, we tested the hypothesis that increased levels of whitefly biological control could be obtained on VF145B7879 by comparison to Alta through releases of D. pusillus. Analyses of results obtained from replicated population trials detected significant reductions in whitefly populations due to D. pusillus releases, but they did not detect a significant influence of tomato cultivar on the ability of D. pusillus to suppress whitefly populations. Significantly longer beetle residence times on Alta than on VF145B7879 may have compensated for the significantly slower walking speeds and reduced lifetime fecundities observed on Alta and produced a neutral effect of foliar trichome densities on B. argentifolii biological control.     

Predation byCheilomenes vicina [Coleoptera: Coccinellidae] on the cowpea aphid,Aphis craccivora [Homoptera: Aphididae]: Effect of prey stage and density

Consumption of larvae and females ofAphis craccivora Koch by 1st and 4th larvae and adults ofCheilomenes vicina (Muls.) was studied under fluctuating temperature (24–30°C). The early aphid instars were consumed in significantly greater numbers than later instars and females. The feeding rates ofC. vicina were significantly positively correlated with the population density of prey. The number of prey consumed daily by each predator stage tested, increased more steeply at lower than at higher prey densities, exhibiting thus the type 2 functional response

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Résumé Consommation des larves et des ♀ d'Aphis craccivora par les11^e stades, les 4^e stades et les adultes deCheilomenes vicina a été étudiée à une température variant de 24 à 30°C. Les jeunes stades du puceron sont consommés en nombre plus grand significativement que les derniers stades et les ♂. Les taux d'alimentation deC. vicina manifestent une corrélation hautement significative avec la densité de population de la proie. Le nombre de proies consommées quotidiennement par chaque stade considéré du prédateur augmentait plus brusquement aux faibles qu'aux fortes densités de proies, manifestant ainsi chez le prédateur le type 2 de réponse fonctionnelle.