Juvenile hormone effects on polymorphism in the pea aphid, Acyrthosiphon pisum

When reared in short days (LD 12:12) at 15°C, apterous Acyrthosiphon pisum gave birth to sexual females (oviparae) exclusively for the first eight days of larviposition. After this time they switched to the production of parthenogenetic females (viviparae). Topical application of juvenile hormones I, II and III to fourth instar or adult ovipara-producers induced the precocious appearance of parthenogenetic females in the progeny sequence. Various forms intermediate between oviparae and viviparae were also produced and repetitive JH-I treatments resulted in a few alatiform progeny. However, many of the JH induced apterous, parthenogenetic females appeared to be normal viviparae and were capble of reproduction. Thus, prenatal treatment of oviparous embryos with JH diverts development towards the viviparous form. JH-I treatment of long-day reared A. pisum had no effect on the type of progeny produced.

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Effets de l'hormone juvénile sur le polymorphisme d'Acythosiphon pisum

Résumé Quand il est élevé sous jours courts (LN 12/12) à 15°C, le type anglais vert d'Acyrthosiphon pisum ne donne naissance qu'à des femelles sexuées (ovipares) pendant la première partie de sa période de reproduction. Ensuite quelques types intermédiaires ovipares/vivipares peuvent apparaitre avant que les pucerons ne bifurquent spontanément vers la production de femelles parthénogénétiques (vivipares). L'application cutanée d'hormones juvéniles (JH I, II, et III) aux larves de quatrième stade ou à des adultes producteurs d'ovipares provoque l'apparition prématurée d'intermédiaires et de vivipares dans la descendance. Les différentes formes intermédiaires produites par des applications répétées de J.H. comprenaient des types ailés ou partiellement ailés. Cependant, les vivipares aptères induits par J.H. étaient morphologiquement normaux et beaucoup étaient capables de se reproduire. Des traitements semblables aux J.H. de vivipares élevées en jours longs (LN 16/8) n'ont pas eu d'effets sur le type de la descendance.On ne sait pas si l'action de JH exogène sur l'induction des vivipares est direct ou indirect. La reprogrammation des embryons, autrement destinés à se développer comme ovipares, est examinée en relation avec notre connaissance du contrôle endocrine du polymorphisme des pucerons.

     

The significance of gut sucrase activity for osmoregulation in the pea aphid, Acyrthosiphon pisum

The osmotic pressure of the body fluids of aphids is lower than in their diet of plant phloem sap. It is hypothesised that aphids reduce the osmotic pressure of ingested food by sucrase-mediated hydrolysis of dietary sucrose to glucose and fructose, and the polymerisation of glucose into oligosaccharides of low osmotic pressure per hexose unit. To test this hypothesis, the impact of the alpha-glucosidase inhibitor acarbose on the sugar relations and osmoregulation of aphids was explored. Acarbose inhibited sucrase activity in gut homogenates and the production of monosaccharides and oligosaccharides in the honeydew of live aphids. Acarbose caused an increase in the haemolymph osmotic pressure for aphids reared on a diet (containing 0.75 M sucrose) hyperosmotic to the haemolymph and not on the isoosmotic diet containing 0.2 M sucrose. It did not affect aphid feeding rate over 2 days, except at high concentrations on 0.75 M sucrose diet, and this may have been a secondary consequence of osmotic dysfunction. Acarbose-treated aphids died prematurely. With 5 microM dietary acarbose, mean survivorship on 0.2 M sucrose diet was 4.2 days, not significantly different from starved aphids, indicating that, although these aphids fed, they were deprived of utilisable carbon; and on 0.75 M sucrose diet, mean survivorship was just 2.8 days, probably as a consequence of osmotic failure. It is concluded that the aphid gut sucrase activity is essential for osmoregulation of aphids ingesting food hyperosmotic to their body fluids.     

Extraordinary proliferation of microorganisms in aposymbiotic pea aphids,Acyrthosiphon pisum

Aposymbiotic pea aphids, which were deprived of their intracellular symbiotic bacterium, Buchnera, exhibit growth retardation and no fecundity. High performance liquid chromatographic (HPLC) analysis revealed that these aposymbiotic aphids, when reared on broad bean plants, accumulated a large amount of histamine. To assess the possibility of extraordinary proliferation of microorganisms other than Buchnera, we enumerated eubacteria and fungi in aphids using the real-time quantitative PCR method that targets genes encoding small-subunit rRNAs. The result showed that these microorganisms were extremely abundant in the aposymbiotic aphids reared on plants. Microbial communities in aposymbiotic aphids were further profiled by phylogenetic analysis of small-subunit rDNAs. Of 172 nonchimeric sequences of fungal 18S rDNAs, 138 (80.2%) belonged to the phylum Ascomycota. Among them, 21 clustered within a monophyletic group consisting of insect-pathogenic fungi and yeast-like symbionts of homopteran insects. Thirty-one (18.0%), two (1.2%), and one (0.6%) clones were clustered within the Basidiomycota, Zygomycota, and Oomycota, respectively. Of 167 nonchimeric sequences of eubacterial 16S rDNAs, 84 (50.3%) belonged to the gamma-subdivision of Proteobacteria to which most primary endosymbionts of insects and prolific histamine producers belong. Forty (24.0%), 25 (15.0%), 10 (6.0%), and five (3.0%) clones were clustered within alpha-Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB) group, Actinobacteria, and beta-Proteobacteria, respectively. Three had no phylogenetic association with known taxonomic divisions. None of the sequences studied in this study coincided exactly with those deposited in GenBank.     

Body colour and genetic variation in winged morph production in the pea aphid

Aphids (Homoptera: Aphidoidea) produce a number of different phenotypes in their life-cycle, among which are winged (alate) and wingless (apterous) morphs. Lowe & Taylor (1964) and Sutherland (1969a, b) were the first to suggest that aphid clones differ in their propensity to produce the winged morph and that in the pea aphid (Acyrthosiphon pisum Harris), this propensity is linked to the colour of the phenotype. We tested for the occurrence of genetic variation in winged morph production by rearing individuals from red and green clones of pea aphid under wing-inducing (crowding) and control conditions, and scored the phenotypes of their offspring. Clones differed significantly in alate production and red clones produced on average a higher proportion of winged morphs than green clones. Importantly, however, there was considerable variation between clones of the same colour. Broad-sense heritabilities of winged morph production were 0.69 (crowding treatment) and 0.63 (control). Clones also differed in the number of offspring they produced. When exposed to the crowding stimulus, aphids deferred offspring production, resulting in a higher number of offspring produced in the crowding treatment than in the control.     

Cannibalism in the pea aphid,Acyrthosiphon pisum

Previous observations of cannibalism have been made in the aphid Acyrthosiphon pisum （L.）： this article seeks to quantify factors contributing to such be- haviors. We observed and quantified the responses of a number of clones and life stages to varying levels of starvation, in the form of increasingly desiccated Vicafaba L. plants （receiving 50, 25, or 10 mL every second day） or a complete absence of host plant. We found that, while the longest incidences of cannibalism are carried out by juveniles （F = 3.45, P = 0.019, df = 3） and targeted at adults, the starvation treatments had the most significant effect on the prevalence of cannibalism in mature A. pisum （F ---- 2.24, P = 0.025, df = 9）. Furthermore, there was no difference between the prevalence or dura- tion of cannibalistic activities within and between different clones （P 〉 0.05 in all cases）, though juveniles were more likely to target unrelated aphids （V = 6 112, P = 0.011）, and spent more time feeding on aphids from the same culture （V = 6 062, P = 0.018）.     

Effects of parasitism by Praon pequodorum on age-specific fecundity and population growth of the pea aphid, Acyrthosiphon pisum

The effects of parasitism by Praon pequodorum Viereck (Hymenoptera: Aphidiidae) on the survival, development and reproduction of apterous pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), were studied in the laboratory. Ten cohorts of aphids differing in age from 0.5 h to 9 days were tested. At 20°C, pea aphids survived an average of 7 days after parasitization. Parasitized first and second instars died before reaching the adult stage. Third instars died as adults but without producing any offspring. Parasitized fourth instars and adult aphids produced a variable number of offspring; their mean total fecundity increased as an exponential function of the age at parasitization. Host age did not significantly affect the period from the beginning of parasitism to the end of reproduction. Equations are provided to estimate the length of the reproductive period, the total fecundity, the intrinsic rate of increase, and the doubling time as functions of aphid age at parasitization. The data are discussed with regard to host population growth. It is shown that a parasite's potential impact on an aphid population is critically dependent on its preference for and successful oviposition in early host instars.

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Résumé Les effets du parasitisme par P. pequodorum Viereck (Hym.: Aphidiidae), sur la survie, le développement et la reproduction des aptères de A. pisum, ont été examinés au laboratoire. L'étude a porté sur 10 cohortes de pucerons dont les âges différaient de 0,5 heure à 9 jours. A 20°C, les pucerons parasités ont survécu en moyenne pendant 7 jours après avoir été parasités. Leur évolution ultérieure dépend au stade auquel ils ont été parasités: au premier et second stades, ils sont morts avant de devenir adultes; au troisième stade, ils sont morts adultes avant de se reproduire; au quatrième stade et adultes, ils ont donné un nombre variable de descendants. La fécondité totale moyenne a crû comme une fonction exponentielle de l'âge au moment où ils avaient été parasités. L'âge de l'hôte n'a pas modifié significativement la durée de la période entre le moment où ils ont été parasités et la fin de la phase de reproduction. Des équations ont été établies en fonction de l'âge des pucerons au moment où ils ont été parasités, pour estimer la longueur de la période de reproduction, la fécondité totale, le taux intrinsèque d'accroissement et le temps de doublement des cohortes de pucerons. Les résultats sont discutés sous l'angle de la dynamique de la population. On en déduit que l'impact potentiel d'un parasite sur une population de pucerons dépend d'abord de ses préférences pour les premiers stades de l'hôte et du succès de sa ponte sur ces stades.

     

Resistance of different lucerne cultivars to the pea aphid Acyrthosiphon pisum: influence of phloem composition on aphid fecundity

Sugars and amino acids were analysed in the phloem sap (sampling by the exudation method) of four clones of lucerne (Medicago sativa L.) characterized by their resistance to the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae). Differences in the qualitative amino acid balance are shown and a negative correlation between the reproductive rate of the aphid and the sugars/amino acids ratio is underlined. To demonstrate any causal relationship between these two variables, the reproduction of A. pisum on artificial diets copying the sap of the two extreme clones (resistant and susceptible) was measured. The results show that the resistance is not a simple nutritional effect; however, the amino acid balance contributes to the resistance exhibited by some cultivars.

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Résumé L'analyse (sucres et acides aminés) de la sève de 4 cultivars de luzerne (Medicago sativa) caractérisés pour leur résistance au puceron du pois (Acyrthosiphon pisum (Harris)) (Homoptera: Aphididae), est réalisée sur des exsudats de phloème. La teneur en sucres (exprimée en équivalent saccharose) montre d'importantes différences: rapport de 1 à 3 respectivement entre les clones sensible et résistant. La teneur globale en acides aminés exsudés varie en sens inverse, entraînant une corrélation négative pour les 4 clones étudiés entre le rapport sucre/acides aminés (0,6 à 3,6) et la résistance mesurée par le taux net de reproduction à 14 jours (78,5 à 11,2 larves/femelle). L'analyse des acidses aminés révèle de plus des différences qualitatives entre cultivars, notamment pour certains acides aminés essentiels méthionine, histidine, lysine, aromatiques.Le rôle de l'équilibre en acides aminés et en sacharose dans la résistance de certains cultivars au puceron du pois est apprécié par des mesures de la reproduction de A. pisum sur des milieux artificiels reproduisant le rapport sucre/acides aminés et/ou le spectre des acides aminés des 2 clones extrêmes (sensible et résistant). La résistance n'apparaît pas être le résultat d'une simple différence de la qualité nutritionnelle de la sève; la balance en acides aminés doit cependant participer pour une part à la résistance au puceron.

     

Temporal changes in host adaptation in the pea aphid, Acyrthosiphon pisum

Abstract.

• 1 Temporal changes in host adaptation were followed in a local population of the pea aphid, Acyrthosiphon pisum. Aphid clones were collected in one alfalfa and one clover field at three different times. In the spring, first-generation females were collected. Later, in the autumn, females belonging to the last parthenogenetic generation were collected. Lastly, sexual females were collected after mating in autumn and allowed to produce eggs which were hatched. The performance was evaluated on alfalfa and clover. The spring-collected individuals were also assessed on peas.
• 2 On the overwintering hosts clover and alfalfa, the clones performed best on the plant of origin, i.e. negative correlations in performance. Correlations between performance on the temporary summer host, pea, and that on clover/alfalfa were weak or nonsignificant.
• 3 Significant variation in host performance was found within both host fields at spring, which is a prerequisite for changes in clone composition due to selection/migration.
• 4 The clones from alfalfa showed an increase in mean performance on alfalfa between spring and autumn, whereas no changes among the clones from the clover field were observed. This difference in seasonal response between the two fields could have been the result of larger variation in performance among the alfalfa clones and/or a differential tendency to migrate among clones in both fields.
• 5 After sexual recombination in the autumn, mean performance in the alfalfa field returned to the spring level, probably as a result of emergence of new genetic combinations. In the clover field, mean performance did not change significantly over time.

     

The effects of two species of hymenopterous parasitoid on the reproductive system of the pea aphid, Acyrthosiphon pisum

Two cultures of first instar pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), were subjected to parasitization by Ephedrus plagiator (Nees) and Aphidius ervi Haliday (Hymenoptera: Braconidae) respectively, and a third culture, of fourth instar pea aphids, was subjected to parasitization by E. plagiator. Significant parasitogenic effects on the reproductive system occurred within 24 h of exposure to parasitoids in the form of reductions in both embryo number and the size of the largest embryo, and degenerative changes in the embryos themselves. No evidence was found of direct feeding by the larvae on the host's tissues, until just before larval pupation. The largest embryos of some fourth instar aphids escaped the effects of parasitization probably because they had developed a resistant cuticle by the time of oviposition by the parasitoid. Results suggested that embryonic degeneration was an indirect effect of parasitization due to starvation, interference with the aphid's hormone levels, or both.

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Résumé Trois élevages de 100 à 200 premiers stades d'A. pisum, nés à 24 heures les uns des autres, ont été divisés chacun en un lot témoin et un lot expérimental. Deux des élevages expérimentaux ont alors été soumis au parasitisme d'Ephedrus plagiator ou de Aphidius ervi, le troisième élevage a pu se développer jusqu'au 4è stade avant d'être exposé à E. plagiator. Des échantillons de 10 pucerons ont été retirés de chaque lot après 24 heures et ensuite toutes les 48 heures pour être disséqués dans du liquide physiologique. Les nombres d'ovarioles et d'embryons et la taille du plus gros embryon ont été notés. Des cellules développées, issue de la séreuse de l'oeuf de l'hyménoptère se sont disséminées dans l'hémolymphe de l'hôte et ont servi d'aliment aux larves en développement. Seul le dernier stade larvaire des parasitoïdes s'est alimenté sur les tissus de l'hôte et ceci avait lieu juste avant la nymphose. Des effets significatifs se sont traduits après 24 heures par la réduction du nombre des embryons, par la diminution de la taille du plus grand de ceux-ci et par des altérations dans les embryons eux-mêmes.

     

Facultative 'secondary' bacterial symbionts and the nutrition of the pea aphid, Acyrthosiphon pisum

Abstract.  Facultative 'secondary' bacterial symbionts influence various traits of aphids, including plant utilization patterns and resistance to parasitoids. The present study is designed to test the hypothesis that these multiple effects are underlain by symbiont-mediated changes to the aphid requirement for the dominant dietary nutrients, sucrose and amino acids. The performance of pea aphids ( Acyrthosiphon pisum ) on chemically defined diets of systematically altered sucrose and amino acid content varies among eight parthenogenetic clones, with a pattern that does not match the aphid complements of secondary symbionts, Hamiltonella defensa , Regiella insecticola and Serratia symbiotica . Aphid performance is reduced, increased and unaffected by elimination of S. symbiotica , R. insecticola and H. defensa , respectively, but with no significant effect on the range of diets on which aphids performed well. It is concluded that the impact of secondary symbionts on aphid traits is most unlikely to have a purely nutritional basis.     

Identification and functional characterization of an odorant receptor in pea aphid,Acyrthosiphon pisum

The sensitive olfactory system is necessary for survival of insects.Odorant receptors (ORs)are located on the dendrites of olfactory receptor neurons and play a critical role in odor detection.Insect ORs are functionally analyzed via heterologous expression in a Xenopus oocyte system using a two-electrode voltage-clamp (TEVC)electrophysiological recording.Here,we have identified a novel OR in the pea aphid,Acyrthosiphon pisum,then we cloned and named it ApisOR4.We analyzed the ApisOR4 tissue expression patterns and found expression only in antennae tissues.Further functional analysis using TEVC revealed that ApisOR4 is broadly tuned to eight volatiles,which elicit electrophysiological response in pea aphid antennae.This study provides an initial functional analysis of aphid ORs and identifies candidate volatiles to be used in developing new strategies for aphid control.     

Instar-specific defense of the pea aphid,Acyrthosiphon pisum: Influence on oviposition success of the parasiteAphelinus asychis (Hymenoptera: Aphelmidae)

The parasite Aphelinus asychisWalker (Hymenoptera: Aphelinidae) oviposits in all four instars of the pea aphid, Acyrthosiphon pisum(Harris) (Homoptera: Aphididae). Searching females display a highly stereotyped sequence of behaviors when encountering a host. Once recognized, an aphid is examined and probed by the wasp with the everted ovipositor prior to oviposition. Oviposition success is influenced by aphid behavior that is related to aphid size and expressed through instarspecific escape and defense reactions. Being smaller and less able to defend themselves, first and early-second instars of pea aphid are more susceptible to successful parasitism than third and fourth instars, in that order. Observed patterns of preference by Aphelinus females for particular aphid species and instars reflect the outcome of behavioral interactions between the hosts and the parasites, rather than preference in the strict sense.     

Pandora neoaphidis transmission and aphid foraging behaviour

Pandora neoaphidis is an aphid-specific entomopathogen that produces infective conidia. As aphid movement increases, so does the likelihood of contact with conidia. Volatile distress signals released in response to aphid infestation as an indirect defence against herbivory may affect aphid foraging and, therefore, the fungus-aphid interaction. In this study, two different methods were used to investigate the effect of plant volatiles and P. neoaphidis-sporulating cadavers on (1) the colonisation of Vicia faba plants by Acyrthosiphon pisum and (2) P. neoaphidis transmission. This study indicates that A. pisum does not avoid bean plants containing P. neoaphidis and that transmission of conidia occurs during plant colonisation and, to a lesser extent, during in situ feeding. Although significantly more aphids were recovered from damaged plants compared to undamaged plants, the likelihood of infection was not affected by previous infestation by aphids.     

The photoperiodic responses and phenology of an English strain of the pea aphid Acyrthosiphon pisum

Abstract. 1. The response curves for the photoperiodic induction of the sexual forms (oviparae and males) differ significantly in an English clone of the pea aphid Acyrthosiphon pisum Harris. Male production is sharply peaked. The late summer scotophases (dark periods) that initiate male production are 1.0–1.5 h shorter than those that initiate ovipara production; the induction of males, but not oviparae, virtually ceases at scotophases longer than 12 h. This disparity suggests that there are two photoperiodic clocks.
2. All ovipara-producing aphids switch spontaneously to virginopara production part-way through the progeny sequence, irrespective of photoperiod. This may confer the ability to overwinter partheno-genetically under favourable climatic conditions. Since males are always born last in the progeny sequence this possibility would be pre-empted unless the terminal male sequences were suppressed by long winter scotophases.
3. The role of the photoperiodic response in determining the seasonal phenology was tested in the field by exposing a succession of laboratory-reared aphids to natural photoperiods, in late summer and autumn. Adult males and oviparae developed synchronously in early October, the difference in critical scotophase compensating for the late appearance of males in the progeny sequence. A large part of the 'civil twilight' is photoperiodically active.
4. Clones propagated outdoors by isolating aphids in each generation from the terminal sequence of virginoparae did not survive the whole winter of 1985/86. The chances of survival were reduced by severe weather and by the inability of the photoperiodic system to 'turn off' the production of early born oviparae which are, therefore, 'wasted'.     

Injection of essential amino acids substitutes for bacterial supply in aposymbiotic pea aphids (Acyrthosiphon pisum)

The symbiotic bacteria Buchnera contribute to the nutrition of pea aphids, Acyrthosiphon pisum, through the provision of essential amino acids which are lacking in the diet. However, chemically defined diets, containing nutritionally adequate amounts of essential amino acids, fail to rescue aposymbiotic aphids, in which the bacteria have been disrupted with antibiotics. In this study the injection of a mixture of essential amino acids into the haemocoel of aposymbiotic aphids was shown to alleviate, at least partially, the impact of symbiont loss. Specifically, the total amino acid content in the tissues of aposymbiotic aphids was reduced by approximately 40% to levels comparable with symbiotic insects, and there was a 1.7-fold increase in the number of embryos, suggesting that the availability of essential amino acids promotes aphid protein synthesis by rejuvenating the free amino acid pool of aposymbiotic aphids. In addition, a similar effect on the total amino acid content was observed when phenylalanine alone, but not glutamine, lysine or tryptophan, was injected into the haemocoel of aposymbiotic aphids, and there was also a significant increase in the number of embryos following injection of phenylalanine or tryptophan alone. The impact of amino acid injection on the embryo complement of aposymbiotic aphids was limited to an increase in the number of embryos, with no increase in basal embryo size. It is proposed that older embryos may rely on their own complement of symbiotic bacteria for essential amino acid provisioning. Taken together, the data highlight the importance of bacterial provisioning of essential amino acids, particularly the aromatic amino acids, in the intact symbiosis.     

A new species ofAphidius [Hymenoptera] attacking the pea aphid,Acyrthosiphon pisum

Aphidius staryi Chen & Luhman n. sp. is described. The species was collected and introduced into California from Israel and Turkey byD. González. The new species is morphologically most similar toAphidius smithi, and keys toEady's urticae group.     

Diversity and geographic distribution of secondary endosymbiotic bacteria in natural populations of the pea aphid,Acyrthosiphon pisum

In addition to the essential intracellular symbiotic bacterium Buchnera, several facultative endosymbiotic bacteria called collectively secondary symbionts (S-symbionts) have been identified from the pea aphid Acyrthosiphon pisum. We conducted an extensive and systematic survey of S-symbionts in Japanese local populations of A. pisum using a specific PCR detection technique. Five S-symbionts of A. pisum, PASS, PAUS, PABS, Rickettsia and Spiroplasma, and two facultative endosymbionts universally found in various insects, Wolbachia and Arsenophonus, were targeted. Of 119 isofemale strains originating from 81 localities, 66.4% of the strains possessed either of four S-symbionts: PASS (38.7%); PAUS (16.0%); Rickettsia (8.4%); and Spiroplasma (3.4%), while 33.6% of the strains contained only Buchnera. PABS, Wolbachia and Arsenophonus were not detected from the Japanese strains of A. pisum. In order to understand intra- and interpopulational diversity of S-symbiont microbiota in detail, 858 insects collected from 43 localities were examined for infection with the four S-symbionts. It was demonstrated that different S-symbionts coexist commonly in the same local populations, but double infections with two S-symbionts were rarely detected. Notably, the S-symbionts exhibited characteristic geographical distribution patterns: PASS at high frequencies all over Japan; PAUS at high frequencies mainly in the northeastern part of Japan; and Rickettsia and Spiroplasma at low frequencies sporadically in the southwestern part of Japan. These results indicate that the geographical distribution and infection frequency of the S-symbionts, in particular PAUS, might be affected by environmental and/or historical factors. Statistical analyses suggested that the distribution of PAUS infection might be related to host plant species, temperature and precipitation.