Effect of entomopathogenic Aspergillus strains against the pea aphid,Acyrthosiphon pisum (Hemiptera: Aphididae)

Aphids (Homoptera: Aphididae) are sap-sucking insect pests that feed on several plants of agronomical importance. Entomopathogenic fungi are valuable tools for potential aphid control. As part of a selection process, laboratory bioassays were carried with five different concentrations of Aspergillus clavatus (Desmazières), Aspergillus flavus (Link) and Metarhizium anisopliae ((Metschnikoff) Sorokin) spores against the pea aphid, Acyrthosiphon pisum (Harris). Aspergillus isolates induced higher mortalities than M. anisopliae, which is a well-known entomopathogen in the literature. Lethal concentrations (LC₅₀ and LC₉₀) were 1.23 × 10³ and 1.34 × 10⁷ spores/ml for A. flavus, 4.95 × 10² and 5.65 × 10⁷ spores/ml for A. clavatus, and 3.67 × 10³ and 9.71 × 10⁷ spores/ml for M. anisopliae 5 days after treatment. Mycelia development and sporulation on adult cadavers were observed 48 h after incubation. The intrinsic growth rate of A. pisum decreased with increased spore concentration for all fungal strains, suggesting an increase in pathogen fitness related to a consumption of host resources. In conclusion, Aspergillus species could be useful in aphid control as pest control agents despite their saprophytic lifestyle. This is also to our knowledge the first report of A. clavatus and A. flavus strains pathogenic to aphids.     

Effect of temperature and cultivar on pea aphid, Acyrthosiphon pisum (Hemiptera: Aphididae) life history

Life history parameters of the pea aphid, Acyrthosiphon pisum were studied at five constant temperatures on two cultivars of peas, Scout and Sancho. The development and mortality of juveniles and the life-span, age-specific fecundity and survivorship of adult aphids were recorded and used to construct life tables. The juvenile development period (from birth to adulthood) was longest at 11.9 degrees C (16.8 days on cv. Scout and 16.2 days on cv. Sancho) and shortest at 26.7 degrees C (8.5 days on cv. Scout and 8.8 days on cv. Sancho). At all temperatures, except 26.7 degrees C, juveniles developed faster on cv. Sancho than on cv. Scout. On both pea varieties juvenile mortality was highest at temperatures above 19.6 degrees C and lowest at 19.6 degrees C. Highest cumulative juvenile mortality was recorded on cv. Scout at 26.7 degrees C when only 9% of aphids survived from birth to reproductively mature adults. Fecundity rates were unaffected by temperature in the range tested on cv. Sancho but increased with increasing temperatures between 11.9 and 19.6 degrees C on cv. Scout. These differences in life history parameters were reflected in the population growth (rm) of aphids on both pea cultivars which increased with increasing temperatures between 11.9 and 23.1 degrees C on cv. Sancho and 11.9 and 19.6 degrees C on cv. Scout, declining thereafter. Population growth was consistently greater at all temperatures for aphids reared on cv. Sancho than those reared on cv. Scout.     

Influence of temperature on pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) resistance to natural enemy attack

The ability to resist or avoid natural enemy attack is a critically important insect life history trait, yet little is understood of how these traits may be affected by temperature. This study investigated how different genotypes of the pea aphid Acyrthosiphon pisum Harris, a pest of leguminous crops, varied in resistance to three different natural enemies (a fungal pathogen, two species of parasitoid wasp and a coccinellid beetle), and whether expression of resistance was influenced by temperature. Substantial clonal variation in resistance to the three natural enemies was found. Temperature influenced the number of aphids succumbing to the fungal pathogen Erynia neoaphidis Remaudière & Hennebert, with resistance increasing at higher temperatures (18 vs. 28 degrees C). A temperature difference of 5 degrees C (18 vs. 23 degrees C) did not affect the ability of A. pisum to resist attack by the parasitoids Aphidius ervi Haliday and A. eadyi Stary, González & Hall. Escape behaviour from foraging coccinellid beetles (Hippodamia convergens Guerin-Meneville) was not directly influenced by aphid clone or temperature (16 vs. 21 degrees C). However, there were significant interactions between clone and temperature (while most clones did not respond to temperature, one was less likely to escape at 16 degrees C), and between aphid clone and ladybird presence (some clones showed greater changes in escape behaviour in response to the presence of foraging coccinellids than others). Therefore, while larger temperature differences may alter interactions between Acyrthosiphon pisum and an entomopathogen, there is little evidence to suggest that smaller changes in temperature will alter pea aphid-natural enemy interactions.     

Oral activity of FMRFamide-related peptides on the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) and degradation by enzymes from the aphid gut

Insect myosuppressins and myosuppressin analogues were tested for oral toxicity against the pea aphid Acyrthosiphon pisum (Harris) by incorporation into an artificial diet. Acyrthosiphon pisum myosuppressin (Acypi-MS) and leucomyosuppressin (LMS) had significant dose-dependent effects (0.1-0.5μg peptide/μl diet) on feeding suppression, mortality, reduced growth and fecundity compared with control insects, but Acypi-MS was more potent than LMS. One hundred percent of aphids had died after 10days of feeding on 0.5μg Acypi-MS/μl diet whereas 40% of aphids feeding on 0.5μg LMS/μl diet were still alive after 13days. Myosuppressins were degraded by aphid gut enzymes; degradation was most likely due to a carboxypeptidase-like protease, an aminopeptidase and a cathepsin L cysteine protease. The estimated half-life of Acypi-MS in a gut extract was 30min, whereas LMS was degraded more slowly (t?=54min). No toxicity was observed when the analogues δR(9) LMS and citrolline(9) Acypi-MS or FMRFamide were fed to the pea aphid. These findings not only help to better understand the biological effects of myosuppressins in aphids but also demonstrate the potential use of myosuppressins in a strategy to control aphid pests.     

Rapid response to intraclonal selection in the pea aphid (Acyrthosiphon pisum)

Summary Pea aphids show intraclonal variability in antipredator behaviour. Among the offspring of a single parthenogenetically reproducing female, some individuals drop from the plant in response to alarm pheromone while others remain on the plant. We demonstrate that this intraclonal behavioural variability can be altered by selection. The proportion of aphids dropping in response to alarm pheromone was significantly greater in lines in which this behaviour was selected than in clonally identical lines in which the opposite phenotype was favoured. This change occurred within one generation and could not be attributed to grand-maternal effects, nor to environmental effects. These results demonstrate the ability of clonal aphids to adapt to changes in the environment within a single generation.     

Application of DL-beta-aminobutyric acid (BABA) as a root drench to legumes inhibits the growth and reproduction of the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae)

DL-beta-aminobutyric acid (BABA) is a non-protein amino acid that is an effective inducer of resistance against a variety of plant pathogens. However, examples of BABA-induced resistance against insect herbivores have not been reported. We applied BABA as a soil drench to legumes and monitored its effects on the pea aphid Acyrthosiphon pisum (Harris). On tic bean (Vicia faba var. minor), BABA increased aphid mortality, caused a reduction in the mean relative growth rate of individual insects and lessened the intrinsic rate of population increase (rm). BABA also caused significant reductions in the growth rate of A. pisum on pea (Pisum sativa), broad bean (Vicia faba var. major), runner bean (Phaseolus coccineus), red clover (Trifolium pratense) and alfalfa (Medicago sativa). No direct toxic effects of BABA against A. pisum were found, and no phytotoxic effects that may have caused a reduction in aphid performance were detected. Possible mechanisms behind this BABA-induced inhibition of aphid performance are discussed.     

Transmission of symbiotic bacteria Buchnera to parthenogenetic embryos in the aphid Acyrthosiphon pisum (Hemiptera: Aphidoidea)

All phloem-feeding aphids have an absolute requirement for their primary bacterial symbionts Buchnera sp. The bacteria are transmitted vertically to either embryos in the viviparous morph or to eggs in the oviparous morph, with the implication that the symbiont population regularly passes through a genetic 'bottleneck', i.e. only a small proportion of the maternal symbiont population is transmitted to offspring. In this paper, we visualise this process in viviparous aphids using a specific immunolabelling technique for Buchnera. The images show a stream of bacteria originating from a single mycetocyte and entering the embryo, possibly via a membranous conduit, and individual bacterial cells free in the haemocoel of the aphid. Staining within the embryo blastoderm suggests over expression of antigen, perhaps indicative of rapid bacterial division immediately following infection.     

Infectivity of Pandora neoaphidis (Zygomycetes: Entomophthorales) to Acyrthosiphon pisum (Hom., Aphididae) in response to varying temperature and photoperiod regimes

The infectivity of the pea aphid, Acyrthosiphon pisum , by the aphid-specific entomophthoralean fungus, Pandora neoaphidis , was studied in environmental chambers using computer simulated late-season temperature and photoperiod patterns and an excised fava bean leaf system. A complementary log-log (CLL) time–dose–mortality model was used to model time–dose trends in infectivity of A. pisum by P. neoaphidis as a function of time and dose, and calculate the LC₅₀. The likelihood ratio test based on the CLL model was used to test for differences in levels of aphid infectivity by P. neoaphidis over different photoperiod regimes. Differences in the LC₅₀ values from CLL modelling over different time periods were found among the two regimes of 11- and 16-h photophases at a constant temperature of 20°C, and two regimes at daily fluctuating temperatures from 5.4 to 18.9°C (with half-hourly changes of 0.56°C the mean temperature was 12.12°C). The LC₅₀ for the same time period was lower under the higher temperature conditions than under lower fluctuating temperature conditions. The likelihood test ratio statistics showed no significant difference in the slope parameter for three out of four treatments (two from the constant temperature of 20°C, and one from 5.4 to 18.9°C, irrespective of photophase conditions). This suggests that different temperatures and photophases may change the temporal characteristics of P. neoaphidis , and result in higher or lower infectivity to the pea aphid at certain dosage levels. However, changes in the photoperiod appear to be less important for the infectivity of P. neoaphidis to pea aphid than changes in temperature.     

Bacteria from the alimentary canal of the pea aphid,Acyrthosiphon pisum (Harr.) (Homoptera,Aphididae)

Bacteria isolated from the alimentary canal of the pea aphid, Acyrthosiphon pisum, were identified mainly as species of the genera Sarcina, Micrococcus, Achromobacter, and Flavobacterium. Starch was rapidly hydrolysed by all species of Sarcina and Flavobacterium and by most species of Achromobacter and slowly by some species of Micrococcus. All of the types of bacteria found in the alimentary tract of the pea aphid were represented in the bacterial flora on the leaves of the pea plants on which the aphids were reared. It is suggested that these organisms become established in the gut after being picked up from the leaf surface while the aphid is probing for the phloem bundles.     

Molecular and morphological characterization of two aphid genera,Acyrthosiphon and Aulacorthum (Hemiptera: Aphididae)

The taxonomic histories of two genera, Acyrthosiphon and Aulacorthum, have been controversial because of the ambiguous morphology used as criteria to distinguish these genera. In this study, molecular and morphological characters were analyzed to determine whether the current classification of these genera is reasonable. Two phylogenetic trees based on five genes (COI, COII, srRNA, lrRNA, and EF1a) supported the distinctiveness of Acyrthosiphon and Aulacorthum, and a canonical discriminant analysis using 19 morphological characters showed that the two genera were separated by five morphological characters (HTB, C, Ant.III, HFM, and SIPH). Based on these results, we confirm that the current classification of Acyrthosiphon and Aulacorthum is supported by molecular and morphological characters.     

Male-specific flight apparatus development in Acyrthosiphon pisum (Aphididae, Hemiptera, Insecta): comparison with female wing polyphenism

Wing polymorphisms observed in many Insecta are important topics in developmental biology and ecology; these polymorphisms are a consequence of trade-offs between flight and other abilities. The pea aphid, Acyrthosiphon pisum, possesses 2 types of wing polymorphisms: One is a genetic wing polymorphism occurring in males, and the other is an environmental wing polyphenism seen in viviparous females. Although genetic and environmental cues for the 2 wing polymorphisms have been studied, differences in their developmental regulation have not been elucidated. In particular, there is little knowledge regarding the developmental processes in male wing polymorphism. Therefore, in this study, the development of flight apparatuses and external morphologies was compared among 3 male wing morphs (winged, wingless, and intermediate). These male developmental processes were subsequently compared with those of female wing morphs. Developmental differences between the male and female polymorphisms were identified in flight muscle development and degeneration but not in wing bud development. Furthermore, the nymphal periods of wingless and intermediate males were significantly shorter than that of winged males, indicating the adaptive significance of male winglessness. Overall, this study indicates that the male and female wing polymorphisms are based on different regulatory systems for flight apparatus development, which are probably the result of different adaptations under different selection pressures.     

Structure and determination of the ambiphasic ovary of Acyrthosiphon pisum (Homoptera: Aphididae)

In ambiphasic females of Acyrthosiphon pisum Harris the antero-posterior disposition of the amphigonic and parthenogenetic ovarioles varies in accordance with the conditions under which they were produced.In ambiphasic females born when the mother stops producing parthenogenetic daughters and starts producing amphigonic daughters, the parthenogenetic ovarioles are located anteriorly. On the other hand, in ambiphasic females born when the mother stops producing amphigonic daughters and starts producing parthenogenetic daughters, the parthenogenetic ovarioles are located nearer the posterior region. This shows that when differentiation of the ovarioles takes place contemporaneously with the switching of the maternal tendency affecting the daughter's reproductive category, the asynchrony in the development of the different ovarioles determines whether or not the ovary becomes ambiphasic.

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Résumé Chez Acyrthosiphon pisum l'apparition de femelles ambiphasiques dans la descendance d'une génitrice parthénogénétique ne peut avoir lieu que lorsque celle-ci cesse de produire des femelles de l'une catégorie génétique et commence à en produire de l'autre catégorie.L'examen de la gonade des femelles ambiphasiques a mis en évidence l'existence de deux types différents d'ovaires caractérisés par la disposition particulière des ovarioles amphigoniques et parthénogénétiques.Chez les femelles ambiphasiques qui naissent quand les génitrices cessent de donner des femelles parthénogénétiques et commencent à engendrer des femelles amphigoniques, les ovarioles du type parthénogénétique sont situés près de la région céphalique, tandis que ceux du type amphigonique se situent au voisinage de la région postérieure. Au contraire, chez les ambiphasiques qui naissent quand les génitrices cessent de produire des femelles amphigoniques et commencent à donner des femelles parthénogénétiques, les ovarioles de la région céphalique sont du type amphigonique, tandis que ceux de la région postérieure sont du type parthénogénétique.Cette donnée, ainsi que l'asynchronisme dans le développement des différents ovarioles qui a pu être vérifié par l'analyse cytologique des embryons femelles, indique que la détermination de l'ovaire ambiphasique est provoquée par le changement des conditions physiologiques de la génitrice. Celles-ci règlent la détermination des femelles ambiphasiques à condition que ce changement ait lieu en même temps que la différenciation de la gonade embryonnaire.

     

The host plant range of the pea aphid subspecies Acyrthosiphon pisum ssp. destructor (Johnson) (Hom., Aphididae)

Abstract:  In order to establish the host range of the pea aphid subspecies, Acyrthosiphon pisum ssp. destructor , and hence from which plant species pea crops are likely to become infested, the performance of this aphid on different leguminous plants was assessed. The plant species used were: Lotus uliginosus , Medicago sativa , Melilotus officinalis , Ononis repens , Sarothamnus scoparius , Trifolium hybridum , Trifolium pratense , Trifolium repens , Vicia cracca and Vicia faba . Vicia faba and Trifolium hybridum were the plants on which aphids reached the greatest size, took the least time to reach maturity, and experienced the lowest mortality. The time taken for the aphids to develop to maturity was negatively correlated with adult size, whereas survival to maturity was positively correlated with adult size. The host preference of the aphids was also assessed. The plant species selected as hosts by alatae were those on which their offspring performed best.     

Evaluation of four co-occurring ladybirds for use as biocontrol agents of the pea aphid,Acyrthosiphon pisum (Homoptera: Aphididae)

The potential of four co-occurring ladybirds, Coccinella septempunctata (L.), Coccinella transversalis (F.), Cheilomenes sexmaculata (F.), and Propylea dissecta (Mulsant), as predators of the pea aphid, Acyrthosiphon pisum (Harris) was investigated. Larger ladybirds were more voracious while smaller ones had higher consumption indices and were more efficient converters of food.     

Spiroplasma symbiont of the pea aphid, Acyrthosiphon pisum (Insecta: Homoptera)

From a laboratory strain of the pea aphid, Acyrthosiphon pisum, we discovered a previously unknown facultative endosymbiotic bacterium. Molecular phylogenetic analysis based on 16S ribosomal DNA revealed that the bacterium is a member of the genus Spiroplasma. The Spiroplasma organism showed stable vertical transmission through successive generations of the host. Injection of hemolymph from infected insects into uninfected insects established a stable infection in the recipients. The Spiroplasma symbiont exhibited negative effects on growth, reproduction, and longevity of the host, particularly in older adults. Of 58 clonal strains of A. pisum established from natural populations in central Japan, 4 strains possessed the Spiroplasma organism.