Apterous Virginoparae Research Articles

THE NUTRITIONAL ECOLOGY OF A PARASITOID WASP, EPHEDRUS CALIFORNICUS BAKER (HYMENOPTERA: APHIDIIDAE)

AbstractWe tested the hypothesis that the pattern of development and growth of a generalist parasitoid wasp varies in different hosts. We reared Ephedras californicus Baker (Hymenoptera: Aphidiidae), a solitary parasitoid of aphids, under controlled laboratory conditions on five kinds of hosts: nymphal instar 1 (24 h old), 2 (42 h), 3 (96 h), and 4 (144 h) of apterous virginoparae of Acyrthosiphon pisum (Harris), and nymphal instar 1 (24 h) of Macrosiphum creelii Davis (Homoptera: Aphididae). Parasitoid dry mass increased with the host instar at parasitization. Females were larger than males although the degree of sexual size dimorphism declined with increased host size. Development time from oviposition to adult eclosion varied non-linearly with the host instar at parasitization, and was shortest in first and fourth nymphal instars. Parasitoids developing in M. creelii gained more mass in less time than their counterparts developing in A. pisum of the same initial size. In low-quality hosts, parasitoids apparently trade off increased development time for a gain in adult mass. A possible explanation of sexual size dimorphism in E. californicus is that large females may be able to overcome aphid defensive behaviours better than small ones.

INFLUENCE OF STARVATION ON DEVELOPMENT AND REPRODUCTION IN APTEROUS VIRGINOPARAE OF THE PEA APHID, ACYRTHOSIPHON PISUM (HARRIS) (HOMOPTERA: APHIDIDAE)

AbstractThe influence of nutrient stress on growth, development, and reproduction in apterous virginoparae of the pea aphid, Acyrthosiphon pisum (Harris), was investigated in the laboratory. We tested the hypothesis that species with a high reproductive investment have low resistance to starvation. Aphids in two groups were starved daily from birth for 4 h and 6 h, respectively, and compared with feeding counterparts reared on leaves of broad beans, Vicia faba L. Aphid wet weight increased as an exponential function of age in all groups. Starved aphids had lower adult weight and required longer from birth to parturition than feeding aphids. These effects increased with the length of daily starvation. The number of offspring produced was correlated with adult dry weight. Aphids were unable to compensate, or to compensate completely, for water and nutrient loss resulting from starvation. It is suggested that pea aphids allocate resources first to maintenance and then to reproduction when deprived of food.

Covariance of adult size and development time in the parasitoid waspAphidius ervi in relation to the size of its host,Acyrthosiphon pisum

Adult size (in terms of dry weight; DW) and development time (Tp) of the solitary parasitoidAphidius ervi varied when reared in different nymphal instars of its host, apterous virginoparae of the pea aphid (Acyrthosiphon pisum). Parasitoid DW increased with an increase in the DW of the host at parasitization, from the first to the third aphid instar. Female wasps gained 1.1 times more in DW than their male counterparts in all four host classes, butTp did not significantly differ between the sexes. Parasitoid DW was consistently more variable thanTp. The two traits covaried positively with an increase in host size from the first to the third instar, but they varied independently in parasitoids from fourth-instar hosts. The host size (and stage) at the time of parasitization imposes constraints on the growth and development of immatureA. ervi that are reflected in the pattern of covariation between DW andTp. When growing in aphids below a certain size threshold, parasitoids can maximize fitness by a trade-off between DW andTp. Consequently, the assumption implicit in host-size models of parasitoid oviposition decisions — that females incur a relatively greater reduction in size (used as an index of fecundity) than males when developing in poor quality hosts — can be falsified.

Bionomics and population growth statistics of apterous virginoparae of woolly apple aphid, Eriosoma lanigerum, at constant temperatures

AbstractDevelopment, survival, reproduction and population growth statistics of apterous virginoparae of woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) at constant temperatures of 10, 13, 15, 20, 25, 30 and 32 °C are reported. The developmental times of all life stages were inversely related to temperature ranging from 10 to 30 °C. Span of total development (time from birth to adulthood) decreased from 57.8 days at 10 °C to 11.7 days at 30 °C and increased to 16.8 days at 32 °C. A good linear model fit (R2 > 0.96) between developmental rate and temperature in the range 10–25 °C was observed for all life stages. The lower developmental threshold was estimated at 5.8 °C for instar I, 4.8 °C for instar II, 4.9° for instar III and 4.4 °C for instar IV. The lower temperature threshold for total development was estimated at 5.2 °C. The upper developmental limit was found to be 32 °C. Mean degree‐day accumulations required for completion of instars I, II, III, IV and total development were: 125.6, 51.0, 47.7, 50.7 and 267.6, respectively. Fecundity, larviposition period and adult longevity were reduced with increasing temperature. Net reproductive rate was greatest at 15 °C whereas intrinsic rate of increase peaked at 25 °C. Optimal performance, as measured by fecundity, survival and intrinsic rate of increase, ocurred in the range 13–25 °C.

Behavioral and electrophysiological responses of Aphids to host and nonhost plant volatiles

Alate and apterous virginoparae ofAphis fabae Scop, and alate virginoparae ofBrevicoryne brassicae (L.), walking in a linear track olfactometer, were attracted by odor from leaves of their host plants.A. fabae responded to odor from undamaged but not damaged bean leaves. Gynoparae (autumn migrants) ofA. fabae, however, did not respond to their host plant (spindle,Euonymus europaeus) odor. Odors of certain nonhost plants masked the attractiveness of the host plant leaves, but tansy (Tanacetum vulgare) and summer savory (Satureja hortensis) volatiles repelledB. brassicae andA. fabae, respectively. 3-Butenyl isothiocyanate attractedB. brassicae andLipaphis erysimi (Kalt.), the latter species being more sensitive in both behavioral and electrophysiological studies. Isothiocyanate receptors were found on the antennae ofA. fabae, which was repelled by these compounds, 4-pentenyl isothiocyanate being the most active.

Performance ofAphis Fabae on Chocolate Spot Disease-Infected Faba Bean Plants

The effect of chocolate spot disease (incited byBotrytis fabae) on the host plant quality of two cultivars of faba beans (Vicia faba) for the black bean aphid (Aphis fabae), was investigated under greenhouse conditions. Faba bean cultivar Bolero is resistant to the aphid, whereas cv. Diana is susceptible. On healthy leaves of cv. Bolero, aphids completed their development one day later than the aphids reared on infected leaves of this cultivar and those which matured on healthy or infected leaves of cv. Diana. Mean weight of apterous virginoparae, mean relative growth rate, and intrinsic rate of natural increase were enhanced if the aphids were reared on infected leaves of either cultivar. Mean total progeny per female increased only on infected leaves of cv. Bolero, but not on cv. Diana.

The effects of starvation on development and reproductive potential of apterous virginoparae of vetch aphid, Megoura viciae

AbstractApterous virginoparae of Megoura viciae Buckton starved during the fourth instar lost weight but nevertheless completed their development, showing that growth and development could proceed independently. Their weight at the end of starvation was a function of initial weight. Aphids used considerable amounts of lipid during starvation, and if allowed to feed on becoming adult showed a delayed onset to reproduction. Starvation in the fourth instar arrested embryogenesis, and in small aphids resulted in degeneration of gonadal and somatic tissues.RésuméEffets du jeûne sur le développement et le potentiel reproducteur des virginipares de Megoura viciae Des virginipares de M. viciae Buckton, privées de nourriture à partir de la mue au quatrième stade, achèvent leur développement et muent en adulte en perdant du poids; elles montrent que croissance et développement peuvent être indépendants. Le jeûne pendant le quatrième stade provoque en moyenne la perte de 84% des réserves lipidiques. Le poids à la mue imaginale dépend significativement du poids lors de la mue du quatrième stade: de petits pucerons achèvent leur développement plus lentement que les gros. Le jeûne pendant le 4ème stade interrompt l'ovulation et le développement des gonades; lorsque les adultes peuvent se réalimenter après ce jeûne, la période précédant la ponte est plus longue. L'examen histologique montre que les pucerons les plus petits subissent une régression somatique et gonadale plus importante que les plus lourds: la dégenérescence des gonades apparaît chez les petits pucerons après le jeûne au 4ème stade, tandis que les plus gros voient leur potentiel reproductif réduit par un arrét de l'embryogenèse.

Odour‐conditioned anemotaxis of apterous aphids (Cryptomyzus korschelti) in response to host plants

ABSTRACT. Orientation responses of adult apterous virginoparae of Cryptomyzus korschelti Börner were recorded using a locomotion‐compensator in front of a wind tunnel. Individual aphids were tested under four consecutive treatments: without wind; clean wind; and wind carrying odour of the host plant Stachys sylvatica or odour of a non‐host plant Solanum tuberosum. The walking tracks were tortuous in all treatments except when the odour of host plants was used. Host plant odour induced upwind orientation of aphids (odour‐conditioned positive anemotaxis). Track variables such as vector length, straightness, upwind time and upwind length, increased when the aphids moved upwind. Walking speeds were not affected. The simultaneous stimulation by wind and host plant odour caused aphids to walk upwind for more than 1 m in 10 min. These findings suggest that olfactory attraction of aphids is involved in host plant selection.

Separation of Myzus (Nectarosiphon) antirrhinii (Macchiati) from Myzus (N.) persicae (Sulzer) and related species in Europe (Homoptera: Aphididae)

Abstract. Multivariate morphometric analysis (canonical variates) was used to discriminate between closely related taxa within the Myzus persicae group. It is demonstrated that dark green, anholocyclic populations with a 2n=13 or 2n=14 karyotype in Europe, hitherto treated as a form or biotype of M.persicae, all conform to a discrete morphometric grouping and should therefore be treated as a separate taxonomic entity, permanently isolated from the M.persicae gene pool. It is suggested that this taxon was first described as Siphonophora antirrhinii by Macchiati in 1883. A discriminant function is provided to separate most individual apterae of antirrhinii from those of persicae. Myzus icelandicus Blackman sp.n., on Caryophyllaceae and other plants in Iceland, is distinguished from M.polaris H.R.L. and M.certus (Walker), and a key is given to apterous virginoparae of the species of the M.persicae group in Europe.

Biology of Morphs of Brachycolus asparagi Mordvilko (Homoptera: Aphididae)1

A generalized life cycle and biology of the morphs are described for Brachycolus asparagi Mordvilko. Oviparae laid overwintering eggs on the asparagus ferns, Asparagus officinalis L., beginning in September. The eggs hatched in late March and developed into fundatrices that established themselves on the emerging asparagus spears. A fundatrix gives birth to about 18 nymphs, as compared with 54 nymphs for an apterous virginopara. In summer, the apterous morph had a 33.5% higher intrinsic rate of increase than the alate morph. Crowding of nymphal asparagus aphids increased wing production. The fecundity curve for the apterous virginoparae peaked once, early in their reproductive phase, whereas the curve for the alate virginoparae peaked a number of times and showed that their reproductive phase spanned most of their adult life. A single sexupara could give birth to oviparae, as well as to male and virginoparous morphs. The oviparae produced an average of 10.5 eggs. Males were capable of multiple matings.

Precocene II-induced alate production in isolated and crowded alate and apterous virginoparae of the aphid, Macrosiphum euphorbiae

Precocene II was applied at doses ranging from 0.05 to 0.70 μg per individual to newly moulted adult alate and apterous virginoparae of Macrosiphum euphorbiae kept isolated or in groups of 10 per plant, under an 18L:6D photoperiodic regime. While isolated controls of both morphs produced exclusively apterous progeny, alatae virginoparae were produced in generally dose-dependent proportions by precocene-treated individuals. Grouped controls of both morphs produced alatiform progeny as expected, but in precocene—treated groups, the proportions of alate progeny generally increased as a function of dose. The overall proportions of alate offspring produced, and numbers of days after treatment when morph production was affected, were generally greater for alatae than for apterae, indicating a greater sensitivity to precocene in alatae. However during the first few days after treatment, the alatizing effect of precocene was stronger for apterae, suggesting that the first embryos produced by alatae were irreversibly determined as apterae. In an experiment where isolated alatae and apterae received 0.5 μg of precocene II at different ages ranging from 1 to 13 days after the adult moult, the alatizing effect of the compound, measured by the persistence of alate production, varied with age and morph. While in alatae, the persistence decreased more or less regularly with age, in apterae it initially increased to a maximum in the middle of reproductive life, and subsequently decreased. The results provide support for the hypothesis that juvenile hormone is involved in regulating alary dimorphism in M. euphorbiae.

Embryogenesis and oögenesis in alate virginoparae, gynoparae, and oviparae of the aphid Myzus persicae, in relation to photoperiod

The study reports on the effects of prenatal and/or postnatal exposures to short-night or long-night conditions, and of crowding, on embryogenesis and oögenesis in alate virginoparae, gynoparae, and oviparae of a holocyclic strain of the green peach aphid, Myzus persicae, from Yakima, Washington State. In alate virginoparae raised at a density of 10–20 per radish seedling in a short-night regime (8 hr darkness per diem), 3–4 embryos occurred in each of their 10 ovarioles, when the aphids attained adulthood. More than 30 larvae were deposited by most of these alatae. However, in young adult gynoparae, raised at these densities in a long-night regime (15 hr darkness per diem), only one viable embryo (a presumptive ovipara) occurred per ovariole. The follicle containing this embryo was followed by 1–2 abnormal follicles in each ovariole, and the number of larvae deposited by a gynopara was generally less than 10. In young adult oviparae similarly raised under a long-night regime, only one egg typically occurred in each of their 10 ovarioles, and the eggs deposited by an ovipara (only after it had mated) generally numbered less than 10. Alate virginoparae and gynoparae contained an additional embryo in some of their ovarioles when these morphs were raised at a lower density (1–5 per plant). Presumptive gynoparae partially developed the reproductive features of alate virginoparae when transferred to a short-night regime at birth; the converse was true when presumptive alate virginoparae were transferred to a long-night regime early in larval life. Oviparae maintained in short nights from before birth developed the appearance of apterous virginoparae but still produced eggs rather than embryos. However, their oögenesis was enhanced and eggs (10–20) were deposited by them without prior mating. Under all regimes tested, oviparae were always deposited early in the larviposition sequence of their alate mothers, and the number of oviparae deposited never exceeded 15. The possible involvement of juvenile hormone in the regulation of these events and the ecological significance of the results are discussed.

Precocious metamorphosis of the aphid Myzus persicae induced by the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene

For up to three days after being treated with the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene, adult green peach aphids ( Myzus persicae) gave birth to offspring (alate and apterous virginoparae, males) which underwent precocious metamorphosis. Only a few precocious gynoparae and no precocious oviparae were recorded. The precocious aphids became adultoid in the third or fourth-instar as a result of corpus allatum destruction. They were able to develop mature embryos, but could not deposit them because of incomplete differentiation of the reproductive tract. The treatment did not induce the production of alate virginoparae in the experimental clone of Myzus persicae. However, a few males were born late in the reproductive sequence of treated apterae. The corpora allata of the treated adults appeared on histological examination to be unaffected by precocene.

Observations on the morphs of Macrosiphum avenae and Metopolophium dirhodum on cereals during the summer and autumn

SUMMARYFrom June to early August 1970, populations of Macrosiphum avenae and Metopolophium dirhodum on marked tillers of field barley were compared with the numbers of alatae trapped at crop height and at 12.2 m. There were always more M. dirhodum than M. avenae on the tillers. Only apterae were produced until mid‐June when both alatae and apterae occurred; after mid‐July only alate M. avenae were found. Until mid‐June most of the flying alatae were caught at 12.2 m as they migrated from spring hosts to cereals. Thereafter, more alate M. avenae were trapped at 12.2 m than at crop level, whereas numbers of alate M. dirhodum were usually comparable at both heights. Although crop and flying populations occasionally showed temporal similarities, insufficient is known about their field distribution and the factors affecting their alate production and flight activity to interpret this relationship.In the autumn, two consecutive reproductive phases of M. dirhodum occurred on winter wheat grown in pots outdoors. Initially, apterous virginoparae and alatae, probably sexuparae, were produced, whereas only alate males appeared during the second phase. In contrast, M. avenae deposited mainly apterous virginoparae although some oviparae developed in October to lay scattered, probably infertile eggs on the tillers.

Morphological and cytological separation ofAmphorophoraBuckton (Homoptera: Aphididae) feeding on European raspberry and blackberry (Rubusspp.)

AbstractAphids of the genusAmphorophoracollected from European raspberry,Rubus idaeus, have a chromosome complement of 2n(♀)=18, whereasAmphorophorafromR. fruticosusagg. (blackberry, brambles) have a basic chromosome complement of 2n(♀)=20. Canonical variates analysis based on eight characters measured on numerous samples of apterous virginoparae showed thatAmphorophoraon EuropeanRubuscan be separated morphologically into two groups consistent with the differences in host plant and karyotype, and these two groups are concluded to be separate species. The correct name for the aphid on raspberry that is a vector of European raspberry viruses isAmphorophora idaei(Börn.), and the species on blackberry isA. rubi(Kalt.). Simple biometric methods of discriminating betweenA. idaeiandA. rubibased on pairs of variables are suggested, and their reliability is discussed. Taxonomic problems in the European and North AmericanRubus-feeding species ofAmphorophoraare considered with particular reference to their importance in applied entomology.

The inheritance of life-cycle differences in Myzus persicae (Sulz.) (Hem., Aphididae)

The response to short photoperiod (10 h) of the F1 and F2 sexual generations of Myzus persicae (Sulz.) resulting from a cross between oviparae from a holocyclic clone and males from an androcyclic clone were examined and compared in experiments done at Imperial College Field Station, England. F1 and F2 progeny segregated into three distinct phenotypes; holocyclic, androcyclic and intermediate. Intermediate clones reared at 10 h photoperiod produced alatae which were physiologically intermediate between gynoparae and virginoparae, because their progeny consisted of oviparae, apterous virginoparae and intermorphs. Intermediacy was not affected by temperature and seems to be genetically determined. Segregation ratios in the F1 and F2 indicate that the androcyclic condition is induced by a recessive ‘ switch-gene ’ which completely suppresses the production of sexual females, and partially suppresses male production. This gene could be present in the heterozygous condition in a large proportion of parthenogenetic lines of the aphid, and thus confer a latent potentiality for anholocycly on populations even where conditions will not regularly permit this method of overwintering. Conversely where anholocycly is strongly favoured many aphids would be homozygous for the recessive, androcyclic character, but the potential for gamic reproduction could remain widespread.

A new aphid genus from Central Africa

SYNOPSISA new aphid genus of the subfamily Callipterinae is established for a new species from the Central Province of Malawi, the alate and apterous virginoparae and nymphs of which are described. The taxonomic affinities of the genus are discussed.

The role of photoperiod and temperature in the determination of parthenogenetic and sexual forms in the aphid Megoura viciae Buckton—I : The influence of these factors on apterous virginoparae and their progeny

Apterous virginoparae from long-established parthenogenetic clones of Megoura are capable of producing three types of daughters (winged and wingless virginoparae and sexual oviparae) in addition to males. This polymorphism is regulated by the environment which, by acting through a series of maternal “switch” mechanisms, directs the growing oöcytes and embryos into different developmental pathways. Although there is little reason to doubt that sex is determined genetically (presumably at the oöcyte stage), the sex ratio of the progeny is also under physiological control. In certain environments, notably at high or low temperatures (although not in long photoperiods), male production is inhibited. But even under the most favourable conditions males are relatively scarce and are born predominantly in the middle of the reproductive life of the parent. The later differentiation of part-grown female embryos is also governed environmentally. Long photoperiods and high temperatures induce them to become virginoparae, the reverse conditions, oviparae. The action of photoperiods of intermediate or “critical” length is particularly instructive as providing evidence of the maternal, and perhaps humoral, control of these forms. Their differentiation begins when the parent is still in the early larval instars and is completed in the adult stage. The progression of determination can be explained in terms of the competence of embryos in different stages of growth to respond to alternative maternal stimuli.

The Effect of Photoperiod and Temperature on Reproduction in Acyrthosiphon pisum (Harris) and on the Forms produced

The effect of photoperiod and temperature on the production of the various forms of Acyrthosiphon pisum (Harris) has been studied. In this study apterous virginoparous females were exposed throughout their lifetime to two photoperiods (8 hr./24 hr. and 16 hr./24 hr.) and six different temperatures. At each of the temperatures the apterae (parent Aphids) received one of four treatments of photoperiod, i.e., (1) 8 hr./24 hr. photoperiod throughout their whole life; (2) 8 hr. /24 hr. photoperiod during the period from birth until the last (imaginal) moult (nymphal period), followed by 16 hr./24 hr. photoperiod from the last (imaginal) moult until death (the adult period); (3) 16 hr./24 hr. throughout life; (4) 16 hr./24 hr. during the nymphal period followed by 8 hr./24 hr. during the adult period. The offspring produced by the various parents were collected at successive intervals, and their form determined.Four main forms of offspring were produced: apterous and alate virginoparae, males and oviparae. In addition, a subsidiary form of the apterous virginoparae was obtained, which had sensoria on the hind tibiae.

HOST ALTERNATION IN APHIS FABAE SCOP.

Experiments on the feeding preferences and relative fecundity of Aphis fabae among leaves of different ages and kinds were extended to the comparison of different forms of the aphid: apterous and alate virginoparae and gynoparae.All three forms showed a preference for the primary host, Euonymus, over a secondary host, sugar beet, but this preference was strongest in the gynoparae, weaker in the alate virginoparae and weakest in the apterae. The relative fecundity of the aphids on the two kinds of leaf paralleled their feeding preferences most closely in the gynoparae, less so in the alate virginoparae and least in the apterae.All three forms also showed some preference for growing over mature leaves of the same kind, but this preference was strongest in the apterous virginoparae, weaker in the alate virginoparae and weakest in the gynoparae. The relative fecundity of the aphids on the two ages of leaf paralleled their feeding preferences most closely in the apterae, less so in the alate virginoparae and least in the gynoparae.The physiological, ecological and evolutionary significance of the results is discussed in the light of the dual discrimination theory of aphid host selection.