A comparison of the reproduction of Brevicoryne brassicae and Myzus persicae in relation to soluble nitrogen concentration and leaf age (leaf position) in the brussels sprout plant

Wide variations in total soluble nitrogen occurred in different leaves of Brussels sprout plants. These variations were partly the result of leaf age (leaf position) and partly the result of different fertiliser application to the plants. The fecundity of Brevicoryne brassicae and Myzus persicae caged on such leaves also varied greatly and was correlated with total soluble nitrogen within leaves of the same age, but not between leaves of different ages. The value of total soluble nitrogen concentrations, based on analysis of leaf tissue, for indicating plant suitability for aphids is discussed as well as the difference in response of the two aphid species to experimental conditions favouring proteolysis in the leaf.

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Ein vergleich der vermehrung von Brevicoryne brassicae und Myzus persicae in beziehung zum gehalt löslichen stickstoffs und dem blattalter von rosenkohlpflanzen

Zusammenfassung Brevicoryne brassicae (L.) und Myzus persicae (Sulz.) wurden an Kohlblättern gekäfigt, die infolge verschiedener physiologischer Ursachen sehr unterschiedliche Mengen löslichen Stickstoffs enthielten. Den Pflanzen wurden zwei Düngerstoffe ((NH₄)₂SO₄ und KCL) verabreicht und die Blattläuse auf jungen, mittelalten und alten Blättern gekäfigt. Dadurch wurde der Gehalt löslichen Stickstoffs in den Blättern zwischen 0,543% und 1,286% variiert. Die Nachkommenzahl der Blattläuse bei diesen Düngungen und auf verschiedenaltrigen Blättern war sehr unterschiedlich (zwischen 7,3 und 30,2 bei B. brassicae; 17,6 und 59,4 bei M. persicae) und konnte in jedem Blattalter mit dem Stickstoffgehalt korreliert werden. Der Befund, daß die Korrelationen zwischen Blattlausnachkommenzahl und Stickstoffgehalt nicht unabhängig vom Blattalter waren, deutet darauf hin, daß der Stickstoffgehalt in physiologisch aktiven Blattgeweben nicht relativ mit dem der Siebröhren übereinstimmt. M. persicae vermochte in höherem Maße als B. brassicae Blätter auszunützen, in denen der Eiweißabbau durch Düngung oder Alter begünstigt war. Dieser Unterschied zwischen den beiden Arten steht möglicherweise mit ihren verschiedenen Nährstoffbedürfnissen in Zusammenhang.

     

The production of different morphs by alate viviparae of the aphid Myzus persicae temporarily exposed to long scotophases

The development of alatae of the green peach aphid, Myzus persicae, as gynoparae rather than as virginoparae was investigated with regard to the number of exposures to a long-night (LN) regime of 15 h darkness per diem which the aphids experienced before and/or after their birth. The minimum number of exposures to LN that resulted in all of the alatae developing into gynoparae was two prenatal plus one postnatal or one prenatal plus two postnatal, provided the scotophases in these treatments were at least 12 h long. A cumulative effect of several successive exposures to LN was also evident when the presumptive alatae were exposed to LN either from birth or not until several days after birth. Fewer exposures to LN were needed in the former case.

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Zusammenfassung Die Entwicklung von Alatae der grünen Pfirsichblattlaus, Myzus persicae, hauptsächlich zu Gynoparae, eher als zu Virginoparae, wurde im Hinblick auf den Einfluss der Anzahl an Langnächten (LN: 15 Studen Dunkelheit pro Tag), denen die Aphiden vor und/oder nach der Geburt ausgesetzt waren, untersucht. Zur ausschliesslichen Entwicklung aller Alatae zu Gynoparae waren mindestens 2 prenatale und eine postnatale LN-Exposition oder eine prenatale und 2 postnatale LN-Expositionen notwendig, vorausgesetzt die Dunkelphasen betrugen mindestens 12 Stunden. Ausserdem zeigte sich ein kumulativer Effect durch mehrere, aufeinanderfolgende LN-Expositionen, wenn die Alatae diesen von Geburt an, oder einige Tage nach der Geburt, ausgesetzt waren. Im ersten Fall waren weniger LN-Expositionen notwendig.

     

Taste perception of Myzus persicae in relation to food uptake and developmental processes

A number of essential processes in the development of Myzus persicae are initiated in early larval life. During this period the food quality often affects further development. This paper deals with the question whether amino acids, known to be necessary for developmental processes, play a specific rôle in diet acceptance. The amino acid methionine appeared to stimulate food uptake to a great extent. Experiments with diets containing ³²P showed that food uptake within 1 hr by first-instar larvae on diets of unequal nutritive value was markedly different.

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Résumé La qualité de la nourriture que reçoit Myzus persicae pendant le début de sa vie larvaire détermine souvent les modalités de son développement ultérieur (production de formes aptères où ailées par exemple). On a charché à déterminer si les acides aminés, reconnus comme étant nécessaires au développement, jouent seulement un rôle spécifique dans le métabolisme des Aphides ou si ils interviennent comme facteurs stimulant la prise de nourriture. La méthionine en particulier se révèle avoir un rôle important comme phago-stimulant; en l'absence de méthionine la quantité de nourriture absorbée est diminuée. Par contre sur des aliments dépourvus d'histidine et d'isoleucine, le taux de nourriture absorbée ne change pas.Des expériences de choix alimentaire, entre deux substrats placés côte à côte, ou disposés en couches superposées, montrent que dans le ler cas les Aphides peuvent se localiser sur le milieu le mieux équilibré en ces acides aminés, et dans le second cas peuvent enfoncer leurs stylets jusqu'au milieu le plus favorable. L'adjonction de ³²P à l'un des milieux permet d'apprécier la quantité de nourriture prélevée.

     

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.

     

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.     

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.

     

Inhibition by kinoprene of photoperiod-induced male production by apterous and alate viviparae of the aphid Myzus persicae

Photoperiod-induced male production by apterous and alate viviparae of the green peach aphid. Myzus persicae, was reduced or prevented by treating the aphids with the JH analog kinoprene (Zoecon's insect growth regulator ZR 777). Concomitant with this reduction in the number of males was an increase in the production of females. This was most clearly demonstrated for apterous viviparae that had been raised from birth under weak long-night regimes of 10–10.5 hr dark day, and exposed to 0.1% kinoprene-treated radish seedlings for 2–3 days on reaching the fourth larval instar or adulthood.Male production by alate viviparae, whose apterous mothers were born and raised for 5 days under a long-night regime of 15 hr dark day and then maintained under a short-night regime of 8 hr dark day, was completely inhibited by exposing them to kinoprene-treated plants for 2–3 days when they had reached the fourth instar.It is concluded that the kinoprene treatment affects sex chromosome replication in the oögonia of an aphid so that these germ cells develop parthenogenetically into females (2n = 12 with two X chromosomes) rather than males (2n = 11 with one X chromosome). This may result either from a direct action of absorbed kinoprene on the oögonia or from an indirect action whereby the kinoprene stimulates the insect's hormonal system to produce a hormone that stimulates development of the oögonia into females.     

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.

     

Transgenic potato plants with enhanced resistance to the peach-potato aphid Myzus persicae

Potato plants (Solanum tuberosum) cv. Desireé were transformed with the genes encoding the proteins bean chitinase (BCH), snowdrop lectin (GNA) and wheat -amylase inhibitor (WAI) under the control of the constitutive CaMV 35S promoter. Transgenic plants with detectable levels of foreign RNA were then selected for further characterisation with respect to protein expression levels by immunodot blot analysis using polyclonal antibodies raised against the respective protein. With the exception of WAI, plants expressing high levels of RNA, expressed correspondingly high levels of the foreign protein (1.5–2.0% of the total soluble protein). Although high levels of WAI mRNA were detected in some of the transformants, the protein could not be detected. On the bases of expression levels, two lines, designated PWG6#85 (transformed with the double construct WAI/GNA) and PBG6#47 (transformed with the double construct BCH/GNA), were selected for testing in aphid trials for enhanced levels of resistance.Both transgenic lines had a marked and significant effect on fecundity. The number of nymphs produced per female per day peaked at 4.1 and 4.2 for lines PBG6#47 and PWG6#85 respectively, compared to a value of 5.4 on control plants. Total nymphal production was also significantly lower on either of the transgenic lines compared to control plants (P<0.001) with the differences between the lines being only just significant (P=0.058). On line PBG6#47 there was a delay in nymphal production of 1.6 days, representing a delay of 15%, and on line PWG6#85 this was 3.2 days, representing a delay of ca. 30%. The intrinsic rates of increase (r _m ) were also significantly lower on both of the transgenic lines in comparison to that on control plants (P<0.001), however the differences between the lines were not significant. The potential of using such genes as part of an over all strategy for the control of aphid populations is discussed.     

Effect of the parasitoid Diaeretiella rapae on the feeding rate of its host Brevicoryne brassicae

The food uptake by Brevicoryne brassicae, as measured by accumulation of radiophosphorus, is influenced by the presence of developing larvae of the parasitoid Diaeretiella rapae. Though the egg and embryonic stages of the parasitoid have no effect on host feeding the presence of a first-instar larva lowers the food uptake. Feeding returns to a level similar to that of non-parasitised aphids when a second-instar parasitoid is present within a host, but drops again when the third instar is reached. Host death occurs during the fourth-larval instar.

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Zusammenfassung Der Einfluss der Parasitierung durch den Parasitoiden Diaeretiella rapae auf die Futteraufnahme von Brevicoryne brassicae wurde mit Hilfe ausgeschnittener, mit Radiophosphor behandelter Blätter studiert. Während der ersten Phase, wenn das Ei und die Embryonalstadien des Parasitoiden vorhanden sind, bleibt die Futteraufnahme unverändert. Dagegen fällt sie auf ein gesicher niedrigeres Niveau als bei nichtparasitierten Blattläusen während des ersten Larvenstadiums des Parasitoiden (48 h). Dies ist eine Folge der aktiven Futteraufnahme des Parasitoiden. Während des zweiten Larvenstadiums des Parasitoiden steigt die Futteraufnahme des Wirts wieder an und zwar auf das Niveau nichtparasitierter Blattläuse. Das zweite Larvenstadium des Parasitoiden ist ein Ruhestadium und ernährt sich von flüssigen und halbflüssigen Nährstoffen. Während des dritten Larvenstadiums des Parasitoiden fällt die Futteraufnahme des Wirts und der Tod tritt während des vierten Larvenstadiums des Parasitoiden ein.

     

Male production by apterous viviparae of the aphid Myzus persicae temporarily exposed to different scotoperiods

Male production by apterous viviparae of a holocyclic biotype of the green peach aphid, Myzus persicae, was induced by pre-natal and/or post-natal exposures to a long-night regime of 15 h dark per diem. When the apterae were exposed to three or more long nights immediately after birth and they subsequently developed under a short-night regime of 8 h dark per diem, they produced females (mostly alate viviparae) during the first 8–10 days of reproduction and a high proportion of males thereafter. When the apterae were exposed to two long nights immediately before their birth and to short nights thereafter, they produced relatively few females (mostly alate viviparae), and males were deposited already after 4–6 days of reproduction, i.e. 16–18 days after the first exposure to the long nights. The proportion of males among the progeny of these apterae was highest when the two prenatal exposures comprised scotophases of 11–15 h; under such long-night regimes many aphids switched to producing males exclusively. To achieve this effect, the two long scotophases had to be separated by a photophase of more than 1–2 h. Fewer males were produced and most of the apterae reverted to the production of females (apterous viviparae) when the duration of the two prenatal scotophases was 9 h 45 min-10 h 30 min, or 18 h and longer.One long night of 15–39 h could also induce temporary male production if the aphids were exposed to it late in the 4th larval instar or as teneral adults.     

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.     

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.     

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.

     

植物提取物和药剂对蔬菜蚜虫种群的联合控制作用

研究白蝴蝶(Syngonium podophyllum)乙醇提取物、苍耳(Xanthium sibiricum)乙醇提取物、机油乳剂和0.3%印楝素乳油对桃蚜(Myzus persicae)和萝卜蚜(Lipaphis erysimi)的控制效果.室内四因子(1/2实施)二次正交回归旋转组合设计测试对有翅蚜的忌避作用,结果表明,对有翅桃蚜的主要忌避作用物为苍耳乙醇提取物,当苍耳提取物与白蝴蝶乙醇提取物混用,以及机油乳剂和印楝素混用时,对桃蚜有翅蚜的忌避效果提高;而对萝卜蚜有翅蚜的忌避作用主要受苍耳提取物和白蝴蝶提取物的影响.这些干扰作用均是非线性的.田间试验结果,单独使用白蝴蝶提取物对有翅成蚜有较强的驱避作用;对萝卜蚜自然种群的干扰控制作用以4种植物提取物和药剂混配效果最好,达95.7%;对桃蚜自然种群干扰控制效果最好的则是白蝴蝶提取物,控制效果达87%;同时,白蝴蝶提取物与印楝素乳油混配以及苍耳提取物与印楝素乳油混配,对两种蚜虫的控制效果均达80%以上.     

Production of males and gynoparae by apterous viviparae of Myzus persicae continuously exposed to different scotoperiods

At 18–19°C, apterous viviparae of a holocyclic strain of Myzus persicae raised from birth under constant scotoperiods of 9 hr 26 min–15 hr darkness per diem deposited apterous viviparae, alate viviparae, and males, in that sequence. Under the shortest scotoperiod (9 hr 26 min) in which males were recorded, only a few were deposited at the end of reproduction. With increasing duration of the scotoperiods, the aphids switched to the exclusive deposition of males progressively earlier in their reproductive lives. Thus more males and fewer females were produced; however the proportion of wingless females increased. Similar trends were recorded when the number of prenatal exposures to each scotoperiod was increased from 0 to 7.Alatae developed into gynoparae at scotoperiods of 10 hr 29 min or longer, and into virginoparae at 9 hr 40 min or shorter scotoperiods. Gynoparae and alate virginoparae, as well as alates that produced both oviparae and viviparae were found at 10 hr and 10 hr 15 min.When apterous viviparae were transferred to scotoperiods of 10 hr 29 min or 15 hr only when they attained adulthood, they also deposited males but only toward the end of their reproductive lives.     

各型桃蚜触角感器的比较研究

该文对桃蚜Myzus persicae(Sulzer)各型触角感器进行了比较研究。扫描电镜观察结果表明桃蚜具有钟形感器、毛形感器、原生感觉圈和次生感觉圈4种类型的触角感器。桃蚜各型触角感器的最大差异主要表现在次生感觉圈上,雄蚜、雌性母和有翅孤雌蚜具有次生感觉圈,雌性蚜、干母和无翅孤雌蚜无;但雄蚜具有的次生感觉圈数目多于雌性母和有翅孤雌蚜,且不仅仅分布在触角第3节,第4、5节也有分布。本文探讨了桃蚜触角感器在化学生态学上的功能作用,各型触角感器的差异与桃蚜寄主选择、迁移及交配行为的关系,并进一步分析了桃蚜触角感器的性二型现象。     

Embryogenesis and the production of males by apterous viviparae of the green peach aphid Myzus persicae in relation to photoperiod

Apterous viviparae of a holocyclic strain of Myzus persicae were given various numbers of prenatal and postnatal exposures to male-inducing, long-night scotophases (15 hr darkness per diem). The sex of the embryos in various positions within their ovarioles was determined from chromosome preparations and correlated with the sequence with which female and male larvae were deposited. An abnormal follicle was found frequently between the female and male embryos in the ovarioles of aphids raised under long nights.Apterous viviparae exposed to long nights from birth or earlier usually produced several females and then switched over to exclusive male production. The more prenatal exposures to long nights given to the aphids, the fewer females were deposited by them and the earlier they started to produce males. When apterae were continuously exposed to long nights from 2 days or more before their birth, some, and occasionally all, their ovarioles were solely androparous. In general, male-producing apterae deposited considerably fewer larvae (female as well as male) than apterae that produced females exclusively. The 1–2 day pause in larviposition that typically occurs between the deposition of the female and male larvae was attributed to a slower rate of development of the male embryos. The results are discussed in relation to the hormonal changes that may be induced by the photoperiodic treatments.     

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     

Preference and consumption of Macrolophus pygmaeus preying on mixed instar assemblages of Myzus persicae

This study examines the effects of changes in the prey frequency and abundance on prey selection among the four instars of Myzus persicae by the predator Macrolophus pygmaeus under laboratory conditions. The central hypothesis was that M. pygmaeus will become more selective as prey density increases. It was also observed that M. pygmaeus can occasionally abandon a prey item that had already been killed (non-consumptive prey mortality). It was assumed that the frequency of this behavior would increase with the prey size and prey density. For these purposes prey selection was evaluated by simultaneously presenting all instars of M. persicae to the predator in equal proportions and at increasing densities. M. pygmaeus showed a higher predation rate and a higher preference for smaller prey instars at all prey densities. However, if the predation rate by the predator is expressed in terms of biomass consumed, then biomass gain was higher when feeding on the larger instars of M. persicae. The prey selectivity was indicated by the total prey mortality (consumptive plus non-consumptive prey mortality) as well as by the non-consumptive prey mortality, was associated with relatively high prey densities, depending on the prey instar. Therefore, we argued that the predatory impact of M. pygmaeus on the various instars of the aphid depends not only on prey traits but also on their relative abundance in a patch. Observed decreases in biomass gain from larger prey were likely the result of high prey availability at densities before saturation, which might have caused confusion in the predator’s prey selection.