Dissertations / Theses on the topic 'Acyrthosiphon pisum'

Morphologie et ultrastructure de la spore infectante (conidie ou zoospore) des 2 entomopathogenes. Production des tubes germinatifs de c. Obscurus stimulee par lipides epicuticulaires et miellat du puceron. Suivi des differentes etapes d'infection de l'hote par les pathogenes (germination spores, penetration tegument, developpement dans hemococle, reactions de defense); mise en evidence des differences, en particulier au niveau de la realisation et de l'encapsulation. Dans le couple l. Giganteum - a. Aegypti,des cellules sanguines vivantes sont impliques dans l'encapsulation tumorale. Modalites de la reproduction sexuee de l. Giganteum (differenciation morphologique des cellules reproductrices, "copulation" entre gametes)

L'objectif de cette thèse est l'étude par la technologie des puces à ADN, du transcriptome de la bactérie Buchnera aphidicola, qui vit en symbiose avec le puceron du pois Acyrthosiphon pisum. Le génome extrêmement réduit de Buchnera a perdu l'essentiel de ses gènes de régulation, mais conserve les voies de biosynthèse permettant la production des acides aminés essentiels pour son hôte. La première partie de cette thèse concerne le développement du logiciel ROSO, qui permet de déterminer les sondes oligonucléotidiques destinées aux puces. Une interface a été conçue pour son utilisation en ligne (http://pbil.univ-lyon1.fr/roso). Dans une seconde partie, la conception et l'utilisation d'une puce dédiée à Buchnera ont permis d'étudier le transcriptome de la bactérie, lorsque son hôte subit un stress nutritionnel et osmotique. Cette analyse montre que Buchnera est capable de réguler son expression génique et de réorienter son métabolisme, pour répondre à la demande changeante de son hôte.

Arthropod species that have the potential to damage crops are food resources for communities of predators and parasitoids. From an agronomic perspective these species are pests and biocontrol agents respectively, and the relationships between them can be important determinants of crop yield and quality. The impact of biocontrol agents on pest populations may depend on the availability of other food resources in the agroecosystem. A scarcity of such resources may limit biological control and altering agroecosystem management to alleviate this limitation could contribute to pest management. This is a tactic of ‘conservation biological control’ and includes the provision of flowers for species that consume prey as larvae but require floral resources in their adult stage. The use of flowers for pest management requires an understanding of the interactions between the flowers, pests, biocontrol agents and non-target species. Without this, attempts to enhance biological control might be ineffective or detrimental. This thesis develops our understanding in two areas which have received relatively little attention: the role of flowers in biological control by true omnivores, and the implications of flower use by fourth-trophic-level life-history omnivores. The species studied were the lacewing Micromus tasmaniae and its parasitoid Anacharis zealandica. Buckwheat flowers Fagopyrum esculentum provided floral resources and aphids Acyrthosiphon pisum served as prey. Laboratory experiments with M. tasmaniae demonstrated that although prey were required for reproduction, providing flowers increased survival and oviposition when prey abundance was low. Flowers also decreased prey consumption by the adult lacewings. These experiments therefore revealed the potential for flowers to either enhance or disrupt biological control by M. tasmaniae. Adult M. tasmaniae were collected from a crop containing a strip of flowers. Analyses to determine the presence of prey and pollen in their digestive tracts suggested that predation was more frequent than foraging in flowers. It was concluded that the flower strip probably did not affect biological control by lacewings in that field, but flowers could be significant in other situations. The lifetime fecundity of A. zealandica was greatly increased by the presence of flowers in the laboratory. Providing flowers therefore has the potential to increase parasitism of M. tasmaniae and so disrupt biological control. A. zealandica was also studied in a crop containing a flower strip. Rubidium-marking was used to investigate nectar-feeding and dispersal from the flowers. In addition, the parasitoids’ sugar compositions were determined by HPLC and used to infer feeding histories. Although further work is required to develop the use of these techniques in this system, the results suggested that A. zealandica did not exploit the flower strip. The sugar profiles suggested that honeydew had been consumed by many of the parasitoids. A simulation model was developed to explore the dynamics of aphid, lacewing and parasitoid populations with and without flowers. This suggested that if M. tasmaniae and A. zealandica responded to flowers as in the laboratory, flowers would only have a small effect on biological control within a single period of a lucerne cutting cycle. When parasitoids were present, the direct beneficial effect of flowers on the lacewing population was outweighed by increased parasitism, reducing the potential for biological control in future crops. The results presented in this thesis exemplify the complex interactions that may occur as a consequence of providing floral resources in agroecosystems and re-affirm the need for agroecology to inform the development of sustainable pest management techniques.

博士
國立臺灣大學
生化科學研究所
99
Patterning insect embryos is controlled by a spectrum of well-conserved genes. Anteroposterior axis formation is well understood in Drosophila in which bicoid and caudal encode proteins that form morphogenetic gradients from both poles of the embryo and both of them play a key role in anterior and posterior patterning of the fruit fly embryo. However, recent studies suggest bicoid is an invention of new regulatory protein during the evolution. In some non-dipteran insects such as wasp (Nasonia vitripennis) and beetle (Tribolium castaneum), the anterior specification relies on a synergistic interaction between hunchback and orthodenticle. Evidence shown here indicates it is the asymmetric localization of Aphb rather than the synergistic interaction between Aphb and Apotd, which regulate the anterior development in the asexual pea aphid. Furthermore, unlike Drosophila caudal which forms a linear concentration gradient in early embryogenesis, Apcad does not show a gradient expression in early developmental stages. But, Apcad transcript is expressed in the posteriormost of the germ band in mid- and late- embryogenesis, and might involve in the germ cell formation in the pea aphid. In conclusion, Aphb, Apotd and Apcad exhibit some conserved features in later embryogenesis in the pea aphid as well as in other insects; however, they diverse in early oogenesis and embryogenesis. Compared to Drosophila which patterns most of its segments in syncytial blastoderm stage, most arthropods generate its segments from a celluarized environment. Here, three conserved segment polarity genes, engrailed-1, engrailed-2 and wingless have been cloned and illustrated the expression of their transcripts. It is shown that the first appearing segment is the third segment of thorax (T3), and then remaining segments add from head to abdomen sequentially. The expression of Apwg is also shown periodically and co-localized with Apcad transcript in the posterior of the germ band. It suggests that the segmentation mechanism in pea aphid might be conserved, similar to other short germ band insects. However, the possible regulation between genes which involve in axis formation (Aphb, Apotd, and Apcad) and genes which involve in segment formation (Apen-1, Apen-2, and Apwg) remains unclear and worthy of further investigation.

pisum Harris, 1776) and syrphids (Diptera: Syrphidae; aphid´s predators) and their spatio-temporal associations in pea (Pisum sativum L.) monocrops and pea/spring barley intercrops were assessed (2014 – 2016). The second part of the dissertation thesis was based on the comparisons of abundances of pea aphid (A. pisum) and their natural enemies found on field pea plants, grown either as a monoculture or intercropped with spring cereals in small plot trials vs. large plot trials (2013 - 2015). In the third part of the dissertation thesis (2015 – 2017) the abundances and the distributions of B. pisorum eggs and the seeds infested by the insect pest were assessed in four differently structured field pea crops.

The rotation of the earth leads to a cyclic change of night and day. Numerous strategies evolved to cope with diurnal change, as it is generally advantageous to be synchronous to the cyclic change in abiotic conditions. Diurnal rhythms are regulated by the circadian clock, a molecular feedback loop of RNA and protein levels with a period of circa 24 hours. Despite its importance for individuals as well as for species interactions, our knowledge of circadian clocks is mostly confined to few model organisms. While the structuring of activity is generally adaptive, a rigid temporal organization also has its drawbacks. For example, the specialization to a diurnal pattern limits the breadth of the temporal niche. Organisms that are adapted to a diurnal life style are often poor predators or foragers during night time, constraining the time budget to only diurnal parts of the day/night cycle. Climate change causes shifts in phenology (seasonal timing) and northward range expansions, and changes in season or in latitude are associated with novel day length – temperature correlations. Thus, seasonal organisms will have some life history stages exposed to novel day lengths, and I hypothesized that the diurnal niche determines whether the day length changes are beneficial or harmful for the organism. I thus studied the effects of day length on life-history traits in a multi-trophic system consisting of the pea aphid Acyrthosiphon pisum and predatory larvae of Chrysoperla carnea (common green lacewing) and Episyrphus balteatus (marmalade hoverfly). In order to identify the mechanisms for phenological constraints I then focused on diurnal rhythms and the circadian clock of the pea aphid. Aphids reacted to shorter days with a reduced fecundity and shorter reproductive period. Short days did however not impact population growth, because the fitness constraints only became apparent late in the individual’s life. In contrast, E. balteatus grew 13% faster in the shorter day treatment and preyed on significantly more aphids, whereas C. carnea grew 13% faster under longer days and the elevation of predation rates was marginally significant. These results show that day length affects vital life-history traits, but that the direction and effect size depends on species. I hypothesized that the constraints or fitness benefits are caused by a constricted or expanded time budget, and hence depend on the temporal niche. E. balteatus is indeed night-active and C. carnea appears to be crepuscular, but very little data exists for A. pisum. Hence, I reared the pea aphid on an artificial diet and recorded survival, moulting and honeydew excretion. The activity patterns were clearly rhythmic and molting and honeydew excretion were elevated during day-time. Thus, the diurnal niche could explain the observed, but weak, day length constraints of aphids. The diurnal niche of some organisms is remarkably flexible, and a flexible diurnal niche may explain why the day length constrains were relatively low in A. pisum. I thus studied its circadian clock, the mechanism that regulates diurnal rhythms. First, I improved an artificial diet for A. pisum, and added the food colorant Brilliant Blue FCF. This food colorant stained gut and honeydew in low concentration without causing mortalities, and thus made honeydew excretion visible under dim red light. I then used the blue diet to raise individual aphids in 16:08 LD and constant darkness (DD), and recorded honeydew excretion and molting under red light every three hours. In addition, we used a novel monitoring setup to track locomotor activity continuously in LD and DD. Both the locomotor rhythm and honeydew excretion of A. pisum appeared to be bimodal, peaking in early morning and in the afternoon in LD. Both metabolic and locomotor rhythm persisted also for some time under constant darkness, indicating that the rhythms are driven by a functional circadian clock. However, the metabolic rhythm damped within three to four days, whereas locomotor rhythmicity persisted with a complex distribution of several free-running periods. These results fit to a damped circadian clock that is driven by multiple oscillator populations, a model that has been proposed to link circadian clocks and photoperiodism, but never empirically tested. Overall, my studies integrate constraints in phenological adaptation with a mechanistic explanation. I showed that a shorter day length can constrain some species of a trophic network while being beneficial for others, and linked the differences to the diurnal niche of the species. I further demonstrated that a flexible circadian clock may alleviate the constraints, potentially by increasing the plasticity of the diurnal niche
Die Rotation der Erde bedingt den zyklischen Wechsel von Tag und Nacht. Verschiedene Anpassungen an den täglichen Wechsel evolvierten, da es generell von Vorteil ist, mit der abiotischen Umwelt synchron zu sein. Die Tagesrhythmik wird von der circadianen Uhr reguliert, einem molekularen Rückkopplungsmechanismus auf RNA- und Protein- Ebene mit einer Periode von etwa 24 Stunden. Trotz der Bedeutung der circadianen Uhr, sowohl für Individuen als auch für Wechselwirkungen mit anderen Arten, ist unser Wissen auf wenige Modellorganismen beschränkt. Während die Strukturierung von Aktivitätsmustern im Wesentlichen adaptiv ist, kann eine strenge zeitliche Organisation auch Nachteile mit sich bringen. Zum Beispiel limitiert die Spezialisierung auf ein Aktivitätsmuster die Breite der zeitlichen Nische. So können tagaktive Organismen häufig nur schlecht in Dunkelheit Nahrung finden, so dass das Zeitbudget von der Tageszeit begrenzt wird. Der Klimawandel führt zu Veränderungen der Phänologie (saisonales Timing) und zur Ausbreitung der Arten Richtung Norden, und Veränderungen in der Phänologie oder im Breitengrad sind mit neuen Korrelationen von Tageslänge und Temperatur verknüpft. Daher werden einige Stadien im Lebenszyklus saisonaler Organismen neuen Tageslängen ausgesetzt. Ich habe die Hypothese aufgestellt, dass die zeitliche Nische bestimmt, ob Veränderungen in der Tageslänge für den Organismus von Vorteil oder von Nachteil sind. Daher untersuchte ich die Effekte von Tageslängen auf den Lebenszyklus von Arten in einem multi-trophischen System, bestehend aus der Erbsenblattlaus, Acyrthosiphon pisum und räuberisch lebenden Larven von Chrysoperla carnea (Gemeine Florfliege) und Episyrphus balteatus (Hainschwebfliege). Um die Mechanismen der Einschränkungen in der Phänologie zu verstehen, untersuchte ich anschließend die Tagesrhythmik und die circadiane Uhr der Erbsenblattlaus. Die Blattläuse haben auf Kurztagbedingungen mit einer niedrigeren Fruchtbarkeit und kürzerer Reproduktionsspanne reagiert. Kurze Tage haben jedoch nicht das Populationswachstum beeinflusst, da die Leistungseinbußen erst spät im Leben des Individuums in Erscheinung traten. Im Gegensatz zur Erbsenblattlaus entwickelte sich E. balteatus 13 % schneller unter Kurztagbedingungen und erbeutete signifikant mehr Blattläuse, während C. carnea sich 13% schneller unter Langtagbedingungen entwickelte und marginal höhere Prädationsraten erreichte. Diese Ergebnisse verdeutlichen, dass die Tageslänge wichtige Aspekte der Biologie von Organismen beeinflusst, aber dass die Richtung und Bedeutung von Art zu Art unterschiedlich ist. Ich nahm an, dass die Einschränkungen oder Vorteile durch ein verkleinertes oder vergrößertes Zeitbudget bestimmt werden und daher von der zeitlichen Nische abhängen. E. balteatus ist tatsächlich nachtaktiv, während C. carnea dämmerungsaktiv zu sein scheint. Für A. pisum existieren hingegen nur unzureichende Daten. Daher züchtete ich A. pisum auf künstlichem Futter und nahm Überlebensraten, Häutung und Honigtau-Exkretion auf. Die Aktivitätsmuster waren deutlich rhythmisch, und Häutung und Honigtau-Exkretion waren tagsüber erhöht. Daher kann die Einnischung auf Tagaktivität die beobachteten (aber schwachen) Nachteile kurzer Tage erklären. Die zeitliche Nische einiger Organismen ist überraschend flexibel, und eine flexible zeitliche Nische könnte erklären warum der Effekt der Tageslänge relativ niedrig in A. pisum war. Daher untersuchte ich die circadiane Uhr der Erbsenblattlaus, da dieser Mechanismus die Aktivitätsmuster reguliert. Zunächst verbesserte ich das künstliche Futter von A. pisum, und fügte den Lebensmittelfarbstoff Brilliant Blue FCF hinzu. Dieser Farbstoff färbte sowohl Magen als auch Honigtau in niedriger Konzentration ohne die Mortalität zu erhöhen, und machte dadurch die Exkretion von Honigtau unter schwachem Rotlicht sichtbar. Ich nutzte anschließend das blaue Futter, um Blattläuse einzeln in 16:08 LD und konstanter Dunkelheit (DD) aufzuziehen und dabei Honigtau-Exkretion und Häutungen alle drei Stunden zu notieren. Zusätzlichen nutzten wir ein neues Überwachungssystem um Aktivitätsmuster in Lokomotion kontinuierlich in LD und DD aufzuzeichnen. Sowohl Lokomotionsrhythmik als auch Honigtau-Exkretion von A. pisum schienen bimodal zu sein und erreichten früh morgens und nachmittags ihre Maximalwerte in LD. Beide Rhythmen bestanden auch unter konstanter Dunkelheit einige Zeit fort, was aufzeigt, dass die Rhythmen von einer funktionierenden inneren Uhr gesteuert werden. Die Rhythmik im Metabolismus dämpfte jedoch innerhalb von drei bis vier Tagen aus, während die Lokomotionsrhythmik mit einer komplexen Verteilung verschiedener free-running-Perioden fortbestand. Diese Ergebnisse passen zu einer gedämpften circadianen Uhr, die aus mehreren Oszillatorgruppen besteht. Ein solches Modell wurde vorgeschlagen, um circadiane Uhren mit Messungen der Photoperiode zu verknüpfen, aber nie empirisch überprüft. Insgesamt verbinden meine Versuche die Einschränkungen phänologischer Anpassung mit einer mechanistischen Erklärung. Ich zeigte, dass kürzere Tage einigen Arten eines trophischen Netzwerks Vorteile, anderen jedoch Nachteile verschafften, und habe diese Unterschiede auf die zeitliche Nische der Arten zurückgeführt. Ich habe weiterhin gezeigt, dass eine flexible circadiane Uhr die Nachteile lindern kann, möglicherweise weil sie die Plastizität der zeitlichen Nische erhöht

Thesis (Ph. D.)--University of Wisconsin--Madison, 1972.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

博士
國立臺灣大學
生物科技研究所
106
Introduction. Aphids are hemipteran sap-sucking insects that can vector plant viruses. They propagate rapidly via parthenogenetic (asexual) and viviparous reproduction from generation to generation yet they enrich genetic diversity, once every life cycle, through sexual oviparous reproduction. In both asexual and sexual morphs, the primary endosymbiotic bacteria (endosymbionts) are critical to the synthesis of essential amino acids. With such special reproductive and endosymbiotic features described above, the pea aphid Acyrthosiphon pisum became a rising model insect after its whole genome sequence was published in 2010. Here in my study, I aimed to study two developmental events during early embryogenesis of the parthenogenetic and viviparous pea aphid: (1) the formation of anteroposterior (AP) and dorsoventral (DV) axes; and (2) the regulation of germline development by endosymbiosis. Results (I) AP Axis Formation. Transcripts of Aphb, an ortholog of the Drosophila hunchback in the pea aphid, are known to be localized to the anterior poles of the oocytes and syncytia. This implies that anterior localization of Aphb mRNA may specify the anterior axis in the asexual viviparous pea aphid. In order to understand whether ApHb protein also participates in anterior formation via asymmetric localization as Aphb mRNA, dissected ovarioles were stained using an affinity-purified antibody against ApHb. I found that ApHb, unlike anteriorly-localized Aphb, was uniformly distributed in oocytes and syncytia. This suggests that ApHb is not involved in anterior formation. Both Aphb and ApHb, like their insect orthologs, were identified in the embryonic neuroblasts, indicating that the Aphb gene remained a conserved role in neurogenesis. Nevertheless, expression of Aphb and ApHb was unexpectedly detected in the germ cells throughout all developmental stages. Such germline expression pattern of hb has not been reported in other insect models, suggesting that Aphb may obtain a new role in germline development in asexual aphids. Transcripts of Apcad, an ortholog of the conserved posterior gene cad in the pea aphid, were not identified in the posterior region until blastoderm formation. The absence of posterior localization of Apcad mRNA in oocytes and syncytia suggests that Apcad, though remains conserved in posterior development, is not involved in posterior determination. Results (II) DV Axis Formation. For studying how the DV axis was established, I detected expressions of orthologous mRNAs known to participate in the establishment of the DV axis in Drosophila, assuming that asymmetric localization of the target mRNAs was also conserved in the specification of DV axis in the asexual pea aphid. Transcripts of the four decapentaplegic paralogs (Apdpp1–4), however, unlike dorsal expression of dpp mRNA in Drosophila, was not particularly restricted to any regions within the egg chambers. I did not make antibodies against ApDpp1–4 proteins to detect their distributions. Nonetheless, signals of the phosphorylated Mothers Against Dpp (pMad) protein—a conserved indicator of Dpp activity—and those of Apzen (aphid zerknüllt (zen) ortholog) mRNA—a conserved marker for the insect extraembryonic membrane that forms from the dorsal region—were asymmetrically localized to one side within the egg chambers. Coincidentally, localization of Apsog mRNA, an orthologous mRNA of the ventral gene short gastrulation (sog) in Drosophila, was identified at the opposite side of pMad and zen expressions. The asymmetric localization of pMad/zen and Apsog was not detected until cellularization of the blastoderm, suggesting that formation of the DV axis stars from blastulation or it occurs earlier in the syncytia but does not rely on these conserved DV determinants. Results (III) germline development and endosymbiosis. The primary endosymbiont Buchnera aphidicola invades into the egg chamber prior to gastrulation and ever since then it is associated with the embryonic germ cells throughout embryogenesis. Based upon the fact that the B. aphidicola and germ cells are closely associated, we aimed to understand whether B. aphidicola was essential to the development of germ cells. In the aposymbiotic pea aphids, where B. aphidicola was eliminated by antibiotics, the number of germ cells was largely reduced before katatrepsis (embryo flip), suggesting that B. aphidicola provides nutrients required for the proliferation of germ cells. Expression of Caspase-3 was identified in the germ cells of the aposymbiotic morphs, further suggesting that the reduction of germ cells is caused by apoptosis. The migratory path of germ cells, nevertheless, remained almost the same as that in aphids without the treatment of antibiotics. This implies that the delivery of the guiding signals for germline migration toward the gonads is independent from endosymbiosis. Conclusion. In this study, the aphid orthologs of the developmental toolkit genes for the axis formation and body patterning, including Aphb, Apcad, ApDl, Aphh, Apcact, Apdpp1–4, Apsog, mad, and Apzen, were analyzed that allows to reveal how asexual viviparous aphid established body plan. After the formation of axes, Buchnera cells invade into the embryos that were required for regulating host germ-cell survival. Taken together, these results may shed light on how parthenogenetically viviparous insects established their body axes and how obligate symbionts of insects may play a non-nutritional role for host embryogenesis and organogenesis.

Seasonal life history, abundance and biology of the parasitoids of the pea aphid, Acyrthosiphon pisum (Harris) in Manitoba. A survey of the parasitoids of the pea aphid was conducted in alfalfa and field peas in the Red River Valley area of Manitoba during 1981-85. Five primary parasitoids and twelve secondary parasitoids were collected. The five primary parasitoids, all aphidiids, were: Praon occidentale Baker, Praon pequodorum Viereck, Aphidius ervi Haliday, Aphidius pisivorus Smith and Aphidius smithi sharma and Subba Rao. P. pequodorum and A. ervi comprised most of the primary parasitoids each year. A. smithi was not found prior to the introduction of this parasitoid in Manitoba in 1983. The twelve secondary parasitoids, including 8 identified to the species level, were: five pteromalids, Asaphes lucens (Provancher), Coruna clavata Walker, Pachycrepoideus vindemiae (Rondani), Pachyneuron siphonophorae (Ashmead), Pachyneuron sp.; three alloxystids, Alloxysta victrix (Westwood), Alloxysta megourae complex, Phaenoglyphis ambrosiae (Ashmead); three megapilids, Dendrocerus carpenteri (Curtis), Dendrocerus sp. a. Dendrocerus sp. and one encyrtid, Aphidencyrtus aphidivorus (Mayr). A. lucens was the most abundant secondary parasitoid collected each year. The percentage parasitism of the pea aphid by the primaries was determined for 1983-85 by both rearing and dissecting aphids collected from stem samples in the field. The relative abundance of the adult primary parasitoids for 1981-85 was determined from D-Vac collections, and for both the primary and secondary species from emergence from field-collected mummies. Seasonal changes in the abundance of the parasitoids are discussed.

The research for this project was undertaken from 1984 to 1987. Natural infestations of pea aphids, Acyrthosiphon pisum (Harris), were measured throughout the summer on five (1984) or six (1985, 1986) cultivars of field peas in small field plots near Glenlea, Manitoba. sarting from equal numbers of pea aphids per cage, in 1986 pea aphid populations were also monitored in 1 m3 field cages which contained plants of one of these six field pea cultivars. Throughout the summers of 1985 and 1986 pea aphids were also sampled in a total of nine Century, four Trapper and two Triumph commercial pea fields in several regions across the province. In all of these tests, pea aphid population growth patterns were similar among cultivars. Aphid numbers rose from low levels during the vegetative to blooming stages of plant growth in mid-July, peaked in late July or early August as pods developed and matured, and declined rapidly by mid- to late August as pea plants senesced. However, numbers of pea aphids at the time of population peak differed consistently and significantly with the cultivar upon which they grew. Peak numbers of pea aphids were larger on Triumph or Trapper plants than they were on Century or Tipu plants. In commercial fields, populations of pea aphids rose more rapidly on Trapper than they did on Century or Triumph plants. In field plots seed weight was the yield component most sensitive to aphid feeding. Triumph had significantly lower seed yields in infested than in control subplots in two out of three years. Seed weight was significantly reduced in infested subplots of Tara peas in one year. Because aphid numbers were low and generally occurred later than at flowering or pod initiation in Century peas, no yield losses due to pea aphids occurred in this cultivar in any of the tests. However, linear regression of seed weight over aphid density indicated that, of the cultivars tested, Century is most susceptible to increasing aphid numbers. Trapper seed weight was least related to aphid density despite the relatively high numbers of pea aphids occurring on this cultivar. In laboratory studies pea aphids had the greatest intrinsic rates of natural increase rm, on the cultivar Trapper and the smallest on the cultivars Tipu and Century. Ten days after infestation, the most antixenosis resistance was expressed by the cultivar Tipu, and the least by Triumph. After 20 days, Triumph still was most preferred by the aphid. Trapper appeared somewhat tolerant of the effects of pea aphid feeding.