Systemic antifeedant effects of azadirachtin on the peach-potato aphidMyzus persicae

The electrical penetration graph (EPG) method was used to analyse the feeding behaviour of apterous, adultMyzus persicae (Sulzer) (Homoptera: Aphididae) onNicotiana clevelandii (Gray) seedlings, treated systemically with azadirachtin. A preliminary experiment showed that the effects of tethering aphids for EPG recording were minimal. The percentage of the 9 h recording period devoted to non-penetration activities, and to stylet pathway patterns increased as the azadirachtin concentration in the root treatment increased. The number of probes initiated, and the numbers of sieve tube penetrations also increased with increased azadirachtin concentration. The mean time elapsing between the initiation of the first probe to reach a sieve element and contact with this tissue was not significantly altered by azadirachtin treatment. However, azadirachtin treatment significantly reduced the percentage of probes that reached sieve elements and increased non-penetration activity before and after the first perid of ingestion from the sieve elements. The percentage of the recording period spent in the EPG pattern associated with sieve tube penetration was significantly reduced by an azadirachtin concentration of 300 ppm, and the duration of each individual penetration was significantly reduced by an azadirachtin concentration of 100 ppm. When the total EPG was split into 3 h periods, significant interactions were seen between time period and azadirachtin concentration for the duration of non-penetration, pathway, and sieve tube penetration patterns.     

Gustatory discrimination between plants by larvae of the scarabaeid, Sericesthis geminata (Coleoptera)

Third-instar larvae of the scarabaeid Sericesthis geminata, given choices between soil containing no root material and soil containing root material of one of the pasture plants Lolium perenne, Phalaris tuberosa or Trifolium repens, accumulated in the soil containing the root material. In addition the larvae responded to differences between plant species and within a plant species.Alcohol and ethyl ether soluble components of plant root extracts generally stimulated feeding. Tests with alcohol, ethyl ether and non-lipid free ethyl ether extracts of roots of the above three plant species and of Dactylis glomerata showed that all except the ethyl ether extract of T. repens were stimulating. There were no other significant interspecific differences between extracts when plants were grown during the summer under the same conditions.

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Zusammenfassung Die Reaktion von Larven des 3. Stadiums des Scarabaeiden Sericesthis geminata auf die Wurzeln von vier Weidegrasarten wurde in einer Reihe von Wahlexperimenten untersucht. Die Larven sammelten sich vorzugsweise in Böden an, welche wachsende oder lyophilisierte Wurzeln von Lolium perenne, Phalaris tuberosa oder Trifolium repens enthielten, im Gegensatz zu Böden ohne jegliches Wurzelmaterial. Wurde unter gleichen Wachstumsbedingungen eine Auswahl von Wurzelmaterial geboten, so zeigten die Larven eine Vorliebe für L. perenne bwz. T. repens. Unterschiede im Alter und den Wachstumsbedingungen der Pflanzen beeinflußten die Wahl einer bestimmten Art. Äthanol-, Äthyläther- und von Nichtlipoiden befreite Äthylätherextrakte der drei Graswurzeln, die im Treibhaus in Töpfen gezogen wurden, stimulierten die Nahrungsaufnahme der Larven. Äthylätherextrakte von T. repens hatten keinen bedeutenden Einfluß auf die Nahrungsaufnahme, obwohl der von Nichtlipoiden befreite Alkohol- und Äthylätherextrakt die Nahrungsaufnahme erhöhte. Ätherextrakt von P. tuberosa aus dem Freiland wirkte erheblich abschreckend auf die Nahrungsaufnahme der Larven.

     

Induced resistance by Myzus persicae in the peach cultivar `Rubira'

The effect of a previous infestation by the green peach aphid Myzus persicae (Sulzer) on the settling behaviour and reproduction of the same aphid species was investigated in the resistant peach cultivar Rubira, and compared with that observed in the susceptible control cultivar GF305. A previous infestation of 48 h triggered induced resistance in Rubira. There were significantly fewer aphids settling on preinfested than on uninfested plants, indicating an increased rejection of Rubira as a host plant. The level of induced resistance in preinfested plants was positively related to the duration of the first infestation. In GF305, previous infestation had no detrimental effect on aphid settlement and even slightly enhanced larviposition by adult females. The aphid probing behaviour after a 48-h preinfestation was also monitored for 8 h with the electrical peneration graph (EPG) technique. On preinfested GF305, most EPG parameters indicated an enhanced host plant acceptance. On preinfested GF305, aphids produced less sieve element salivation and more continuous sap ingestion than on uninfested GF305, indicating that the previous aphids provoked changes in plant properties beneficial to the test aphids. In Rubira, a major induced factor of resistance was thought to be expressed in the sieve element as phloem sap ingestion was 4-fold shorter on preinfested than on uninfested plants. The time taken by the aphid stylets to reach a sieve element was also significantly increased on preinfested Rubira, suggesting the induction of resistance factors outside the phloem. The originality of the Rubira/M. persicae interaction is discussed in the perspective of a better understanding of plant induced responses to aphids.     

Host discrimination by Hyposoter exiguae (Hymenoptera: Ichneumonidae)

Host discrimination byHyposoter exiguae (Viereck) was investigated, usingTrichoplusia ni (Hübner) as a host in the presence and absence of host food. Forty-six percent of the parasite females tested exhibited ovipositional patterns significantly different from a random distribution. Of these, 82% showed patterns ranging from near perfect to slight discrimination.     

Suitability of Aphis fabae, Myzus persicae (Homoptera: Aphididae) and Aleyrodes proletella (Homoptera: Aleyrodidae) as prey for Coccinella undecimpunctata (Coleoptera: Coccinellidae)

The suitability of Aphis fabae Scopoli, Myzus persicae Sulzer and Aleyrodes proletella L. as food sources for Coccinella undecimpunctata L. was evaluated by studying the impact of prey consumption on the predator’s population growth parameters and feeding parameters. Unlike A. proletella, A. fabae and M. persicae supported the development and reproduction of C. undecimpunctata. A. fabae and M. persicae were considered to be essential prey, whereas A. proletella was considered to be an alternative prey. Aphid species showed different degrees of suitability: M. persicae significantly decreased the pre-oviposition period and increased adult longevity, fecundity and fertility compared with A. fabae. Moreover, A. fabae represents a suitable diet for larval development, but is not a suitable food source for adult reproduction. The predator’s population growth parameters, R₀, r_m and λ were increased with M. persicae, whereas T decreased. We found that the 4th instar larvae were the most voracious, particularly when fed on M. persicae; nevertheless, with this prey daily weight gain and feeding efficiency of 4th instar larvae were similar to that of individuals fed with A. fabae.     

Control of Myzus persicae and Lipaphis erysimi (Hemiptera: Aphididae) by adults and larvae of a flightless strain of Harmonia axyridis (Coleoptera: Coccinellidae) on non-heading Brassica cultivars in the greenhouse

The green peach aphid [Myzus persicae (Sulzer)] and turnip aphid [Lipaphis erysimi (Kaltenbach)] are economically important pests with a worldwide distribution. We have evaluated the efficacy of releasing adults and larvae of a flightless strain of the multicolored Asian lady beetle (Harmonia axyridis Pallas) as a control measure against these aphids on plants of non-heading Brassica cultivars. Both adults and larvae of H. axyridis were observed to be effective biocontrol agents, markedly decreasing the numbers of aphids. The residence duration of adults was longer than that of larvae. The proportion of non-marketable plants damaged by aphids was lower in plots into which either adults or adults and larvae of H. axyridis had been released. These results suggest that both adults and larvae of this flightless strain of H. axyridis are effective in controlling aphids on plants of non-heading Brassica cultivars.     

The artificial feeding of phosphamidon to Myzus persicae

Three strains of Myzus persicae have been fed on liquid media through parafilm membranes and compared on the basis of their survival and fecundity. The uptake of one strain (the Dutch) is limited by the fact that this aphid adapts very badly to artificial membranes, whereas one of the important limiting factors on uptake by the other two strains appears to be the composition of the diet. These two strains (light and dark) show no significant difference in their LC₅₀ values for phosphamidon in artificial diet, in contrast to results previously obtained on sugar solutions. The presence of phosphamidon caused an immediate reduction in the uptake of the light strain, but this effect was delayed in the dark strain, becoming evident 48 hours after these aphids were transferred to non-toxic diets. Some evidence is given which suggests an increased rate of reproduction for aphids which imbibe sub-lethal doses of phosphamidon.

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Zusammenfassung Drei Stämme von Myzus persicae wurden durch Parafilm-Membranen mit Nährlösungen gefüttert und auf Grund ihrer Überlebensrate und Fruchtbarkeit verglichen. Die Nahrungsaufnahme des einen Stammes (des holländischen) ist dadurch beschränkt, daß sich diese Blattläuse sehr schlecht an künstliche Membranen gewöhnen, während einer der wichtigsten begrenzenden Faktoren für die Nahrungsaufnahme bei den beiden anderen Stämmen die Zusammensetzung der künstlicher Diät zu sein scheint. Diese zwei Stämme (der helle und der dunkle) zeigen bei künstlicher Diät keinen signifikanten Unterschied in ihren LD₅₀-Werten, im Gegensatz zu früher mit Zuckerlösungen erhaltenen Ergebnissen. Wenn die Blattläuse nach Fütterung an Phosphamidon-haltigen Lösungen auf nichtgiftige Diäten übertragen wurden, war ihre Nahrungsaufnahme signifikant niedriger als bei Läusen, die ununterbrochen auf nichtgiftiger Diät gehalten wurden. Es ergaben sich einige Hinweise, die vermuten lassen, daß die Reproduktionsrate bei Läusen, welche subletale Dosen von Phosphamidon aufnehmen, erhöht ist.

     

Neighbour-stranger song discrimination in the Chaffinch(Fringilla coelebs)

Zusammenfassung In 3 Versuchsreihen (playback-Experimente) wurde an 40 territorialen Buchfinken- (Vokales Repertoire, 2–3 Strophentypen) die Reaktion auf die Gesänge von Nachbarn und Fremden gemessen. Es ergaben sich schwache Hinweise auf eine stärkere Reaktion gegenüber Fremdgesang, allerdings waren die Resultate hier weniger klar als von anderen Arten berichtet wird. Wir nehmen an, daß die individuelle Erkennung von Artgenossen bei Arten, deren Gesangsmuster mehrere Strophentypen umfaßt, weniger stark entwickelt ist als bei solchen Arten, deren Repertoire nur einen Strophentyp pro aufweist.     

Probing behaviour of the green peach aphid Myzus persicae on resistant Prunus genotypes

Electrical penetration graphs of Myzus persicae (Sulzer) (Homoptera: Aphididae) feeding behaviour on four resistant and two susceptible genotypes of peach (Prunus persica L. Batsch) and related species showed that resistance was mainly linked to (i) reduced duration of phloem sap uptake, (ii) reduced percentage of pattern E1 (salivary secretion into sieve elements) followed by pattern E2 (sap ingestion) and (iii) increased number of shifts from E1 to E2 and back. These results suggest the unsuitability of phloem sap, and thus repetitive failures to initiate sustained ingestion. Extensive comparisons of the EPGs also revealed more specific trends. Aphids on the most susceptible cultivar GF305 produced significantly longer potential drops than on other peach genotypes. On the resistant Rubira, aphids generated more penetrations before the first E occurred, indicating the possible presence of a resistance factor before the phloem was reached. The clone P1908 of the wild species Prunus davidiana displayed traits of both susceptibility (less but longer probes) and resistance. In particular, aphids produced more E1, suggesting difficulties in preparing sieve elements before feeding. The aphid probing process could be correlated with aphid settling behaviour and bionomics, as previously reported, and gave evidence for the existence of different mechanisms underlying resistance in the tested genotypes against M. persicae.     

Multivariate discrimination between East African cape hares (Lepus capensis) and savanna hares (L. victoriae) based on occipital bone shape

In East Africa, cape hares (Lepus capensis) and savanna hares (L. victoriae) look much alike where their ranges overlap. Earlier studies suggested discrimination between the two species by several skull traits, but did not present morphometric statisitics. Our present discriminant analysis based on seven metric variables of the occipital bone related to skull length (condylobasal length) resulted in a high (95.1%) overall probability of correct separation of the two species. While all cape hares were classified correctly, correct classification was a bit lower in savanna hares (88.2%). A principal components analysis of the same variables confirmed the shape difference for the two species. Both region and sex-specific variation in the shape of the studied occipital bone complex was found in savanna hares but not in cape hares. The somewhat reduced level of correct identification of savanna hares might be due to a tendency for higher shape variation. Application of our discriminant analysis to other regions in East Africa is discussed.     

Behavioural and developmental components of the teneral stage in Myzus persicae

The duration of the teneral stage in M. persicae was closely related to temperature, but experiments involving the reciprocal transfer of newly moulted alatae reared on bean or chinese cabbage to leaves of the other host plant, or to dry filter paper, showed that it was also influenced both by the environmental conditions in which the aphids were reared and by the surface on which they were placed at the final moult.

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Verhaltens- und entwicklungskomponenten des ausreifungs-stadiums bei Myzus persiace

Zusammenfassung Die Dauer des Ausreifungsstadiums von Myzus persicae erwies sich in ähnlicher Weise von der Temperatur abhängig wie die von A. fabae. Es konnte jedoch gezeigt werden, daß die Ausreifungsperiode nicht nur einfach einen Abschnitt der Entwicklung darstellt. Die bis zum ersten Flug verstreichende Zeit hing nämlich nicht nur von der vollständigen Entwicklung des Flugapparates, sodern auch von dem Grade der Flugerregbarkeit ab. In Versuchen bei einer konstanten Temperatur von 23° wurden junge Geflügelte, die auf Ackerbohnen oder Chinakohl herangezogen worden waren, kurz nach der Imaginalhäutung auf Blätter der jeweils anderen der beiden Wirtspflanzen oder auf trockenes Fließpapier übertragen. Sie zeigten, daß die Dauer der Ausreifungsperiode sowohl von den Aufzuchtbedingungen der Läuse (als Larven) wie von der Substratoberfläche beeinflußt werden, auf die sie bei der Imaginalhäutung gesetzt wurden.

     

Effects of sub-lethal imidacloprid levels on potato leafroll virus transmission by Myzus persicae

The effects of sub-lethal imidacloprid concentrations on acquisition and inoculation of potato leafroll virus (PLRV) by Myzus persicae (Sulzer) (Hemiptera: Aphididae) were investigated. In experiments using two aphid clones to acquire PLRV from infected potatoes, virus transmission declined significantly with increasing concentrations of imidacloprid. The same was true in experiments using imidacloprid-treated Physalis floridana Rydb. as acquisition sources. When viruliferous M. persicae were placed on uninfected, imidacloprid-treated P. floridana, there were significant declines in PLRV transmission. Sub-lethal concentrations of imidacloprid clearly inhibited both acquisition and inoculation of PLRV by M. persicae, either through poisoning, temporary intoxication, and/or antifeedant effects.     

Host discrimination by Elasmus schmitti (Hymenoptera, Eulophidae) and Latibulus argiolus (Hymenoptera, Ichneumonidae), parasitoids of colonies of Polistes wasps (Hymenoptera, Vespidae)

The ability to discriminate parasitized and non-parasitized hosts allows the parasitoids to avoid intraspecific and often interspecific competition. In 2005–2009, the incidence of mixed infestation of Polistes nimpha (Christ) colonies by parasitoids Elasmus schmitti Ruschka (Hymenoptera, Eulophidae) and Latibulus argiolus (Rossi) (Hymenoptera, Ichneumonidae) was analyzed. In settlements of different types, the frequencies of mixed infestation deviated from the values expected in case of random distribution. The presence or absence of discrimination ability cannot be confirmed unequivocally based on our material. The data obtained are discussed in relation to the biological features of parasitoids.     

Wing production by grouped and isolated apterae of the aphid Myzus persicae on artificial diet

Single and groups of plant-reared adult apterous Myzus persicae were transferred to an artificial diet and the progeny produced on subsequent days raised in groups on the diet. An enhancement in alata-production in response to interactions between the adult aphids was recorded. This would not have occurred or have been as marked if seedling hostplants (radish or mustard) had been used as larviposition and larval rearing substrates.Crowding the adult aphids at different densities and for various periods showed that relatively few contacts between them promote an increase in alata-production. Such increases are maintained for several days after the period of crowding.Isolated adults did not produce exclusively apterous progeny and their alata-production moreover increased to 80–90% after about a week on the diet despite the fact they were isolated from their progeny on a daily basis.

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Zusammenfassung Entweder in Gruppen oder einzeln auf Rettichkeimlingen herangezogene adulte Aptere von Myzus persicae wurden für die Experimente an eine künstliche Diät gesetzt und ihre täglich entnommenen Nachkommen gruppenweise mit dieser Diãt aufgezogen.Als sofortige Reaktion auf die Vereinzelung war eine Steigerung der Apteren-Produktion festzustellen. Als Reaktion auf zeitweiser Gruppierung erhöhte sich mit der Dauer dieses Vorganges die Geflügeltenzahl. Die Erhöhung ließ sich über einige Tage nachweisen.Gruppierungsexperimente mit verschiedener Anzahl von Adulten oder für verschieden lange Perioden zeigten, daß schon relativ wenige Kontakte eine Alaten-Produktion förderten.Isolierte Adulte brachten nicht ausschließlich ungeflügelte Nachkommen hervor und ihre Geflügelten-Produktion stieg nach einer Woche Aufenthalt auf der künstlichen Diät darüber hinaus auf 80–90% an, auch wenn sie tãglich von ihrer Nachkommenschaft getrennt wurden.

     

Duplication of the Rdl GABA receptor subunit gene in an insecticide-resistant aphid, Myzus persicae

Resistance to cyclodiene insecticides is associated with replacements of a single amino acid (alanine 302) in a γ-aminobutyric acid (GABA) receptor subunit encoded by the single-copy gene Resistance to dieldrin (Rdl). Alanine 302 is predicted to reside within the second membrane-spanning region of the Rdl receptor, a region that is thought to line the integral chloride ion channel pore. In all cyclodiene-resistant insects studied to date, this same alanine residue is replaced either by a serine, or, in some resistant strains of Drosophila simulans, a glycine residue. Therefore, individuals can carry only two different Rdl alleles. In contrast, here we report the presence of up to four different Rdl-like alleles in individual clones of the green peach aphid, Myzus persicae. In addition to the wild-type copy of Rdl gene (encoding A302 or allele A), M. persicae carries three other alleles with the following amino acid replacements: A302 → Glycine (allele G), A302 → Serine^TCG (allele S) and A302 → Serine^AGT (allele S′). Evidence from direct nucleotide sequencing and Single Stranded Conformational Polymorphism (SSCP) analysis shows that at least three of these different Rdl alleles (i.e. A, G and S) are commonly present in individual aphids or aphid clones. Southern analysis using allele-specific probes and analysis of sequences downstream of the exon containing the resistance-associated mutation confirm the presence of two independent Rdl-like loci in M. persicae. One locus carries the susceptible alanine (A) and/or resistant glycine (G) allele while the other carries the two serine alleles (S or S′). Whereas resistance levels are correlated with the glycine replacement, the S allele was present in all aphid clones, regardless of their resistance status. These results suggest that target site insensitivity is associated with replacements at the first (A/G) but not the second (S/S′) locus. Phylogenetic analysis of nucleotide sequences indicates that both putative aphid Rdl loci are monophyletic with respect to other insect Rdl genes and may have arisen through a recent gene duplication event. The implications of this duplication with respect to insecticide resistance and insect GABA receptor subunit diversity are discussed. Received: 10 March 1998 / Accepted: 21 July 1998     

3种寄主上桃蚜的选择性及形态分化

桃蚜是一种重要的农业害虫,寄主广泛,种下分化复杂。以采自黄土高原旱作区桃树、烟草、甘蓝上的桃蚜为研究对象,通过叶片选择法、传统比较形态测定法研究了3种寄主上桃蚜的选择性及形态分化。结果表明:在3种寄主同时存在的情况下,烟草上的桃蚜嗜食烟草,表现为63.5%的桃蚜选择烟草叶,13.8%选择甘蓝叶,8.2%选择桃叶,而甘蓝和桃树上的桃蚜对原寄主没有表现出明显的嗜好性;从形态指标来看,3种寄主上的桃蚜在体长、触角末节长度、后足腿节长度、触角与体长的比例方面存在显著差异(P0.05),说明这几个特征可以作为区分这3种寄主上桃蚜的依据。综合分析可以初步认为黄土高原旱作区烟草上的桃蚜可能形成了寄主专化型-烟草型。     

Interactions among the entomopathogenic fungus, Beauveria bassiana (Ascomycota: Hypocreales), the parasitoid, Aphidius matricariae (Hymenoptera: Braconidae), and its host, Myzus persicae (Homoptera: Aphididae)

The effect of the entomopathogenic fungus Beauveria bassiana on the biological characteristics and life table of Aphidius matricariae, a parasitoid of the green peach aphid, Myzus persicae, was studied under laboratory conditions. Aphids were first infected with twice the LC₉₅ of B. bassiana for third-instar M. persicae (2 × 10⁸ conidia/ml). Subsequently, at different intervals they were exposed to 1-day-old mated parasitoid females for 24 h. The number of mummies produced per female and the percentage emergence of the F1 generation differed significantly as a function of the time interval between application of the fungus and exposure to the parasitoid. The interference of B. bassiana on parasitoid development was also studied by first exposing the aphid hosts to the parasitoid for 24 h and subsequently applying B. bassiana. The number of mummies produced by a female A. matricariae varied from 11.8 to 24.8 and was significantly different when the aphids were first exposed to the parasitoids and then treated with B. bassiana 24, 48, 72, and 96 h after exposure. There were no significantly different effects of B. bassiana on net reproductive rate (R₀), mean generation time (T), intrinsic rate (r_m) and the finite rate of increase (λ) of A. matricariae as a result of development in hosts exposed to low or high conidial concentrations (1 × 10², 2 × 10⁸ conidia/ml). The parasitoids developed in infected hosts had lower r_m, λ, T and DT (doubling time) values compared with those that developed in uninfected hosts but no differences were observed in R₀ values. With proper timing, A. matricariae and B. bassiana can be used in combination in the successful biological control of M. persicae.     

Non-stable resistance to demeton-methyl in a strain of Myzus persicae

The progeny of one viviparous aptera from a strain of Myzus persicae which appeared to have become resistant to organophosphorus insecticides, were bred asexually in an environment free from these materials. At approximately the 7th generation, the clone when compared with a susceptible strain had a 25-fold resistance to demeton-methyl. With subsequent generations the resistance gradually declined and within 30 generations from its establishment the clone was no longer resistant.

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Zusammenfassung Die Nachkommen einer viviparen Aptera von Myzus persicae, die offenbar resistent gegen organische Phosphorverbindungen geworden waren, wurden in einer insektizidfreien Umwelt geschlechtslos vermehrt. Ungefähr in der siebenten Generation, wenn der Klon mit einem normalen Stamm verglichen wurde, hatte er eine 25-fache Resistenz gegen Demeton-methyl. Mit weiteren Generationen nahm die Resistenz allmählich ab und 30 Generationen nach seiner Gründung war der Klon überhaupt nicht mehr resistent.