Provenance, experience and plant utilisation by the polyphagous aphid, Aphis fabae

Twenty-nine clones of Aphis fabae Scopoli (Aphididae: Homoptera) were isolated into laboratory culture from the primary host plants Euonymus europaeus and Viburnum opulus and the secondary host plants Arctium lappus, Impatiens glandulifera, Tropaeolum majus and Vicia faba. All clones performed well on either T. majus or V. faba, with mean intrinsic rates of increase (r_m) in the range 0.35–0.41 aphids aphid^{– 1} day^{– 1}, but none performed well on both plant species. Each clone could, therefore, be described as affiliated to either V. faba or T. majus. All of the 13 T. majus-affiliated clones and 15 of the 16 V. faba-affiliated clones could not be maintained beyond two parthenogenetic generations on the contrary plant. These results confirm that the performance of A. fabae on T. majus and V. faba is negatively correlated. Exceptionally, one V. faba-affiliated clone (clone AED95/119) persisted indefinitely on T. majus, exhibiting a progressive improvement in performance across four parthenogenetic generations: larval mortality dropped from 80% to <20%, mean adult weight almost doubled from 0.28 to 0.53 mg, and mean number of embryos per adult aphid increased threefold from 8.6 to 24.4 embryos. The mean r_m of clone AED95/119 that had been reared on T. majus for more than 4 generations was 0.17 aphids aphid^{– 1} day^{– 1}, significantly lower than the value of 0.34 aphids aphid^{– 1} day^{– 1} on V. faba. It was also shown that the r_m on V. faba did not differ significantly between aphids of clone AED95/119 that had been derived from long-term cultures on V. faba and T. majus. It is concluded that the negative correlation between performance on V. faba and T. majus is not genetically fixed, but may diminish with exposure to T. majus. The implication is that this clone may have a capacity to utilise T. majus that is independent of its capacity to utilise V. faba, and is expressed only on sustained exposure to T. majus. It is suggested that, although the latent capacity to utilise T. majus is probably not exhibited widely under natural conditions, aphids possessing it may be at a selective advantage when more suitable host plants are temporarily unavailable.     

Juvenile Hormone and host-plant colonization by the black bean aphid, Aphis fabae

Abstract Host-plant colonization by winged, summer forms of Aphis fabae Scop, involves the resumption of embryogenesis and larviposition, leading eventually to flight muscle degeneration. Topical application of Juvenile Hormone I to young adults which (a) had access to the host plant, (b) were starved, (c) were starved and treated with precocene III, or (d) were decapitated shortly after the final ecdysis suggests that embryogenesis and flight muscle histolysis may be stimulated by an increase in Juvenile Hormone titres after settling. The duration of the pre-reproductive period and the initial reproductive rate were not significantly affected, possibly because other neuroendocrine factors are involved in parturition.     

'Bistability' experiments and photoperiodic morph determination in the aphid Aphis fabae

Abstract. Newly born larvae (presumptive gynoparae) of the aphid Aphis fabae were exposed to 'symmetrical skeleton' photoperiods, consisting of two equal pulses of light per 24 h. The general form of the photoperiods tested was LDLD 1:10:1:12 h. This regime is open to two 'interpretations', LDLD 1:10:1:12 h (PP_s12) and LDLD 1:12:1:10 h (PP_s14). As both light pulses are close to 12 h apart, it is expected that the interpretations result in two distinct steady state phase relationships, i.e. this regime would show bistability. If this is true and both interpretations could be adopted, PP_s12 is expected to result in a low and PP_s14 in a high percentage of 'apterized' insects.
Experiments undertaken with the aphid showed that bistability did not occur either at 15C or 20C, and the results could be entirely explained on the basis of an 'instantly' damping circadian oscillator clock.     

Electrophysiological characterisation of olfactory sensilla in the black bean aphid, Aphis fabae

Electrophysiological responses of three different olfactory sensilla (proximal primary rhinaria (PPR), distal primary rhinaria (DPR) and secondary rhinaria (SR)) to the sex pheromone components, nepetalactol, nepetalactone, and a plant volatile, (E)-2-hexenal, were investigated in four different morphs of the black bean aphid, Aphis fabae Scopoli. The DC responses recorded directly from the antennal sensilla and termed electrosensillograms (ESGs) were generally much larger (up to 14 mV) than electroantennogram (EAG) responses (up to 2.5 mV). Characteristic morph-specific response profiles to these compounds were observed in each type of rhinarium and response waveforms were different between (E)-2-hexenal and the sex pheromone components. (E)-2-Hexenal elicited the largest responses at PPR, while nepetalactol and nepetalactone elicited the largest responses at SR in gynoparae and males. Nepetalactol and nepetalactone also showed significant activities on DPR and PPR in all morphs. In contrast, (E)-2-hexenal had almost no activity on SR. However, almost all of the SR investigated in males and gynoparae were sensitive to both nepetalactol and nepetalactone. A small sub-set of male SR responded mainly to nepetalactol. SR of winged virginoparae did not respond to the sex pheromone compounds. Paraffin oil (the solvent control) also elicited significant responses at PPR in virginoparae but not in other morphs. In a further experiment, SR of winged virginoparae showed no response to 30 other plant volatile compounds or the alarm pheromone component, (E)-beta-farnesene. Nepetalactol and nepetalactone had similar dose-response profiles in the SR of gynoparae. The results indicate that SR in males and gynoparae are highly specialised to detect sex pheromone compounds, while the DPR and PPR are relatively broadly tuned to both plant volatiles and sex pheromone components. The presence of SR in winged virginoparae that are not responsive to sex pheromone components, alarm pheromone, or any of the plant volatile compounds tested may indicate a possible role of these sensilla to detect, as yet, unknown compound(s) with a high specificity. The present study also suggests that PPR may play a role in detecting paraffin-related compounds such as cuticular hydrocarbons of plants.     

How symbiotic bacteria influence plant utilisation by the polyphagous aphid, Aphis fabae

To explore the effect of rearing-plant species on the contribution of the symbiotic bacterium, Buchnera, to aphid performance, larvae of Aphis fabae that contained the bacteria (symbiotic aphids) and larvae experimentally deprived of the bacteria (aposymbiotic aphids) were reared on 16 plant species. Mortality of aphids was low on most plant species. The relative growth rate (RGR) of the larvae varied with plant species, and was generally depressed by elimination of the bacteria; the mean values of RGR varied between 0 and 0.29 μg μg⁻¹ day⁻¹ for symbiotic aphids and 0 and 0.17 μg μg⁻¹ day⁻¹ for aposymbiotic aphids. The extent to which RGR was depressed by aposymbiosis varied significantly between plant species, suggesting that aphid host plant may influence the contribution of the bacteria to plant utilisation. It is proposed that the bacteria may be particularly important on plants with phloem sap of high amino acid content of low quality, i.e. low concentrations of essential amino acids. Received: 18 August 1996 / Accepted: 13 January 1997     

Photoperiodic regulation of the development of winged gynoparae in the aphid, Aphis fabae

ABSTRACT. In uncrowded rearing conditions, determination of the winged gynopara of the Aphis fabae Scopoli is dependent upon both pre- and postnatal short days (LD 12:12). Extension of the photophase to produce longday (LD 16:8) conditions localized on the head or abdominal region, showed that during the early larval instars of the parent generation (G1) there is a maternally-controlled induction of gynoparae. However, during later stages of embryonic development the presumptive gynoparae respond directly to photoperiod through the mother's abdominal wall. During early postnatal development, presumptive gynoparae (G2) remain sensitive to photoperiodic conditions; the photoperiodic receptors lie in the head. These results are discussed with respect to possible endocrine mediators of this photoperiodically controlled polymorphism.     

Phloem amino acids and the host plant range of the polyphagous aphid, Aphis fabae

This study investigated the relationship between the essential amino acid requirement of the aphid Aphis fabae Scop. and the phloem sap amino acid composition of its host plants. The dietary amino acid requirement of A. fabae varied between clones. One or more of the eight clones of A. fabae tested displayed depressed larval survival, larval growth rate, or r_m on diets lacking histidine, methionine, threonine, and valine, but none of the other five essential amino acids. The required amino acids corresponded closely to the essential amino acids that varied in relative concentrations among 16 plant species tested: histidine, threonine, tryptophan, and valine. It is suggested that the interclonal variation in the dietary requirements of an aphid species may contribute to the intraspecific variation in plant utilisation patterns. The phloem sap amino acid composition and sucrose : amino acid ratio did not differ consistently between host plant species of A. fabae and non‐host species, indicating that phloem amino acid composition is not an important factor in determining the host plant range of this aphid species.     

The photoperiodic control of wing development in the black bean aphid,Aphis fabae

Newly born presumptive gynoparae of Aphis fabae were transferred from their prenatal short-day rearing conditions (light-dark 12:12, 15°C) to a variety of postnatal photoperiodic regimes. Long days prevented wing formation and the majority of aphids developed into apterous or alate-apterous intermediate adults. Continued short days resulted, almost exclusively, in winged adults. The photoperiodic-response curve (T = 24) revealed a critical photoperiod of light-dark 13.5:10.5 and further investigations showed that morphogenesis depended more upon night- than day-length. Maximal apterization occurred with 8 or 9 h dark regardless of the length of the photophase but at photophases of 12 h or less the critical night length was reduced to 8.5 h. Night-interruption experiments revealed two peaks of photosensitivity when the scotophase was 12–14 h long but only a single peak was seen with longer dark periods. A series of experiments using early night interruptions followed by extended dark revealed apparent critical night lengths which decreased as the interruption was placed later in the scotophase. Resonance experiments involving 12 or 16 h photophases and extended scotophases at 15°C revealed long-day effects with scotophases shorter than critical and short-day effects with longer dark periods. However, similar regimes at 20°C produced three peaks of apterization 24 and 20 h apart indicating the possibility of a circadian element involved in the photoperiodic response. The results are compared with the photoperiodic responses of other insects.     

Lipid composition in long-day and short-day forms of the black bean aphid,Aphis fabae

Long-day reared winged (alate) virginoparae from laboratory stock cultures which had been reared throughout larval development on bean stipules were significantly smaller (0.46+/-0.02 mg; mean+/-SEM) than short-day-reared gynoparae (0.69+/-0.04 mg; the winged autumn migrant) which completed development on intact beans. When winged virginoparae were raised from the third stadium on bean seedlings they grew larger (0.86+/-0.02 mg) but the gynoparae contained proportionally more total lipid (12.1+/-0.4%, gynoparae; 7.4+/-0.6%, stipule-reared virginoparae; 9.2+/-0.8%, seedling-reared virginoparae). Wingless aphids (apterae) were heavier, whether reared in short (0.99+/-0.03 mg) or long days (0.95+/-0.04 mg) but the lipid content was low (4.5+/-0.7% and 4.9+/-0.6%, respectively). The triacyl-, diacylglycerol and the phospholipid contents followed this trend but analysis of the fatty acid moieties of the triacylglycerides showed phenotypic differences. The ratios of myristic acid:palmitic acid were significantly higher in the winged forms than the wingless forms and were much higher in the gynoparae than the winged virginoparae. Short-day-reared wingless females also had a higher myristic acid:palmitic acid ratio than long-day-reared apterae, possibly reflecting the embryonic gynoparae maturing in their ovaries.     

Migratory and targeted flight in seasonal forms of the black bean aphid, Aphis fabae

ABSTRACT. Adult winged forms of Aphis fabae Scop., the spring migrants (fundatrigeniae; alate virginoparae), the summer migrants (alate virginoparae) and the autumn migrants (gynoparae), were flown in an automated vertical wind tunnel, with a small green target presented every 60 s. On average, targeted flight developed in the spring and summer migrants after 19 and 15 min, respectively. However, in autumn migrants targeted flight occurred after 184 min of flight. No evidence of target approach was found up to 30 min prior to this time, although some movement towards the target was observed in the 30 min before the first response of autumn migrants, suggesting that a gradual change from migratory to targeted flight occurred. No correlation was found between aphid weight and the time to first response for spring or summer migrants, but a positive correlation was found for autumn migrants. Flight patterns of autumn migrants, in the absence of a target, are described and compared with flight patterns previously reported for summer migrants.     

Abortive feeding behaviour in a black aphid of the Aphis fabae group

A black Aphis sp. on Tropaeolum can be separated, morphologically, from A. fabae Scop. In controlled experiments this aphid, both winged and wingless forms, actively selects Vicia faba as a host plant, settles to feed and reproduce, but always dies prematurely. Offspring also soon die. The aphid is unable to take up plant sap from beans. The behaviour associated with host plant selection is not adjusted to its feeding requirements.

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Zusammenfassung Eine Aphis-Art der A. fabae-Gruppe, die in Südengland häufig an Tropaeolum majus zu finden ist, kann von A. fabae und ihren nächsten Verwandten durch das lange Endsegment des Rüssels unterschieden werden.Junge ungeflügelte Imagines von A. fabae, die noch nicht zur Fortpflanzung geschritten sind, verhalten sich, wie die Geflügelten, sehr kritisch bei der Wahl der Wirtspflanzen. Auf ungeeigneten Wirten siedeln sie sich weder zur Nahrungsaufnahme noch zum Absetzen von Junglarven an.Die Lebensabläufe von Blattläusen, die freie Wahl zur Annahme oder Verweigerung ihrer Wirte hatten, wurden verglichen bei A. fabae an Ackerbohnen und der Tropaeolum-Laus and Kapuzinerkresse und Ackerbohnen.Es wird gezeigt, daß die Tropaeolum-Laus Ackerbohnen leicht annimmt und an ihnen Junge absetzt. Auch Geflügelte versuchen diese Bohnen zu besiedeln. Sowohl Geflügelte wie Larven sterben jedoch an Bohnen ab. Ihr Wirtswahlverhalten ist ihren Nahrungsanforderungen nicht angepaßt.Bei einem Übertragungsversuch auf Bohnen und zurück auf Kapuzinerkresse zeigen die Exkretionsraten, daß die Blattläuse auf Bohnen keinen Pflanzensaft aufnehmen, obwohl ihre Stechborsten ins Pflanzengewebe eingesenkt bleiben.

     

Reproductive stragegies of the alate and apterous morphs of the grain aphid, Sitobion avenae

Differences were observed in the total fecundity and patterns of reproduction of four morphs of Sitobion avenae (F.). The reproductive rates of apterous and alate exules declined gradually with time but decreased rapidly in gynoparae and oviparae. Under short daylengths apterous exules gave birth in three phases; the first consisting mainly of gynoparae, the second of males and the third of non-gynoparous viviparae. The strategic importance of the sequence of morphs and the reproductive behaviour of each is discussed in relation to the maximization of overwintering population size.

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Stratégies reproductives des types ailés et aptères de Sitobion avenae F.

Résumé Des différences ont été observées entre les fécondités totales et les modes de reproduction de quatre types de Sitobion avenae. Les taux de reproduction diminuent graduellement dans le temps chez les aptères et ailés virginopares et rapidement chez les gynopares et ovipares. En photophases courtes, les virginopares aptères donnent naissance à trois types: le premier composé essentiellement de gynopares, le second de mâles et le troisième de vivipares. L'importance stratégique de la succession des types et du comportement reproducteur de chacun est discutée en relation avec l'accroissement maximum de la taille de la population hivernante.

     

Contrasting effects of necrotrophic and biotrophic plant pathogens on the aphid Aphis fabae

Phytophagous insects have to contend with a wide variation in food quality brought about by a variety of factors intrinsic and extrinsic to the plant. One of the most important factors is infection by plant pathogenic fungi. Necrotrophic and biotrophic plant pathogenic fungi may have contrasting effects on insect herbivores due to their different infection mechanisms and induction of different resistance pathways, although this has been little studied and there has been no study of their combined effect. We studied the effect of the biotrophic rust fungus Uromyces viciae‐fabae (Pers.) Schroet (Basidiomycota: Uredinales: Pucciniaceae) and the necrotrophic fungus Botrytis cinerea Pers. (Ascomycota: Helotiales: Sclerotiniaceae) singly and together on the performance of the aphid Aphis fabae Scopoli (Hemiptera: Aphididae) on Vicia faba (L.) (Fabaceae). Alone, botrytis had an inhibitory effect on individual A. fabae development, survival, and fecundity, whereas rust infection consistently enhanced individual aphids' performance. These effects varied in linear relation to lesion or pustule density. However, whole‐plant infection by either pathogen resulted in a smaller aphid population of smaller aphids than on uninfected plants, indicating a lowering of aphid carrying capacity with infection. When both fungi were applied simultaneously to a leaf they generally cancelled the effect of each other out, resulting in most performance parameters being similar to the controls, although fecundity was reduced. However, sequential plant infection (pathogens applied 5 days apart) led to a 70% decrease in fecundity and 50% reduction in intrinsic rate of increase. The application of rust before botrytis had a greater inhibitory effect on aphids than applying botrytis before rust. Rust infection increased leaf total nitrogen concentration by 30%, whereas infection by botrytis with or without rust led to a 38% decrease. The aphids' responses to the two plant pathogens individually is consistent with the alteration in plant nutrient content by infection and also the induction of different plant defence pathways and the possible cross‐talk between them. This is the first demonstration of the complex effects of the dual infection of a plant by contrasting pathogens on insect herbivores.     

Maternal reproductive decisions are independent of feeding in the black bean aphid,Aphis fabae

Aphids are phloem feeders and an important assumption has been that reproduction is initiated only after phloem ingestion. Here we investigate the plant tissue location of parturition cues in winged and wingless, summer virginoparae and autumn migrants (gynoparae) of the black bean aphid, Aphis fabae. These seasonal forms have different host preferences. Using electrical penetration graph (EPG: to observe activity of the mouthparts) and video-monitoring procedures we demonstrate that the time to first parturition after host-plant contact is significantly shorter than the time to first registered phloem contact in the summer winged form. In gynoparae, the time to first parturition does not significantly differ from time to first phloem contact but is shorter than time to first phloem ingestion. Times to first parturition, first registered phloem contact and first phloem ingestion do not differ significantly in the summer wingless form. Simultaneous EPG and video recording procedures show that a high proportion of individuals of all morphs (45-70%) initiate reproduction before sustained phloem activities (salivation/ingestion). The only behaviours that all individuals demonstrate before first parturition are ‘non-penetration’ (aphid on plant surface with mouthparts outside plant) and stylet ‘pathway activity’, including secretion of gelling saliva and penetration of the non-vascular (epidermis and mesophyll) cells. A short period of penetration of the peripheral plant tissues (five cell punctures per individual) by aphids tethered and monitored by EPG decreases the time to first parturition of the winged summer form when subsequently placed on a Parafilm sachet containing 15% sucrose solution. This treatment also significantly increases the incidence of reproduction and individual reproductive output of gynoparae over a 24-h period. No detectable effects of tissue penetration on subsequent reproductive output are observed in the wingless summer form. Additionally, EPGs reveal that a number of aphids of all morphs display xylem ingestion, which occurs predominantly before initiation of phloem feeding but is not necessary to initiate parturition. It is concluded that aphids are likely to detect parturition cues during stylet punctures of cells within peripheral tissue layers, before reaching the phloem vessels.     

Life history and morphological plasticity of the soybean aphid,Aphis glycines

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a pest of soybean, Glycine max (L.) Merr. (Fabaceae), from eastern Asia that was first reported in North America in 2000. The influence of temperature on plasticity of life history and morphological traits of the soybean aphid has not been tested despite observable differences in population growth and morphology among isolates in laboratory colonies. Therefore, we used three isolates of the aphid to test whether lifespan, growth rate, fecundity, and morphology were plastic at 16, 24, and 28 °C. Population size of the aphid was influenced by temperature, probably because two reproductive traits, maximum number of offspring in 1 day and total fecundity, were plastic and increased in successive generations at 24 °C. All morphological traits were plastic, including lengths of body parts, number of antennal segments and caudal hairs, and color of siphunculi and body, and they were differentially influenced by isolate and temperature. Knowledge about the life history and morphology of the soybean aphid may help identify its capacity for phenotypic plasticity in heterogeneous temperatures and identify how temperature influences its survival, population growth, and diversity.     

Photoperiodic induction of winged females in the black bean aphid. Aphis fabae

Abstract. The Photoperiodic of winged females (alatae) in the black bean aphid, Aphis fabae Scop. (Homopetera: Aphididae), is investigated in detail with emphasis on the interaction of the maternal and embryonic/young larval photoperiodic clocks. Previous work had shown that in uncrowded conditions the induction of gynoparae (winged females that produce sexual females) requires both prenatal and postnatal exposure to long-night (12 h) Photoperidic cycles: present results show that sole postantal exposure to long nights of any lenght does not induce wing formation in early-born aphids.
When aphids were exposed to experimental light-dark cycles postanatally only, their daughters developed as alate in long nights and as apterae in short nights: the critical night lenght (CNL) was 11:1 h. Additional prenatal exposure to experimental regimes resulted in a significantly shorter CNL (10.6 h). This difference could be accounted for by the fact that more experimental light-dark cycles were experienced in the latter case.
Apterous aphids transferred from LD 16:8 h to LD 12:12 h as either third-or fourth-stadium larvae, or young adults, switched for aptera-production to alata-production. The transition form aptera- to alata-production was rather abrupt in third-stadium transfers but more gradual when transfers occurred as fourth-stadium larvae and adults. Moreover, s the number of days required for 50% of the aphids to become alata-producers increased from 7–8 in third-stadium transfers, to 9–10 and 11–12 in the later transfers.     

Phenology of the black bean aphid,Aphis fabae,on organic crops and effect of parasitoid communities

1. Parasitoids represent the third trophic level in plant-insect food webs. They develop in or on herbivorous insects at the second trophic level, which in turn feed on plants that constitute the first trophic level. This food web system might be affected by agricultural landscape and practices.
2. We studied the phenology and population density of Aphis fabae (Hemiptera: Aphididae) and determined the impact of parasitoids in organic fields of beans and beet plants.
3. Twenty leaves per field were collected weekly. For each leaf, the total number of aphids, apterous and alate morphs, the number of mummies, and mortality of aphids were recorded.
4. Our results showed that the phenology of A. fabae varied throughout the season with maximal numbers observed at the beginning of summer. In addition, the production of alate morphs and the proportion of parasitism were positively correlated to an increase in aphid densities.
5. Six parasitoid species were recorded attacking A. fabae in the field, with Lysiphlebus fabarum and Binodoxys angelicae (Hymenoptera: Aphidiinae) being the most abundant parasitoids.
6. Field characteristics and availability of host plants in the surroundings affected A. fabae density. Lysiphlebus fabarum and B. angelicae appeared to be good biocontrol candidates against A. fabae.

     

Levels of clonal mixing in the black bean aphid Aphis fabae, a facultative ant mutualist

Aphids are a worldwide pest and an important model in ecology and evolution. Little is known, however, about the genetic structure of their colonies at a microgeographic level. For example, it remains largely unknown whether most species form monoclonal or polyclonal colonies. Here, we present the first detailed study on levels of clonal mixing in a nonsocial facultative ant mutualist, the black bean aphid Aphis fabae. In contrast to the earlier suggestion that colonies of this species are generally monoclonal, we found that across two subspecies of the black bean aphid, A. fabae cirsiiacanthoidis and A. fabae fabae, 32% and 67% of the aphid colonies were in fact polyclonal, consisting of a mix of up to four different clones, which resulted in an overall average relatedness within colonies of 0.90 and 0.79 in the two subspecies. Data further show that the average relatedness in A. f. cirsiiacanthoidis remained relatively constant throughout the season, which means that clonal erosion due to clonal selection more or less balanced with the influx of new clones from elsewhere. Nevertheless, relatedness tended to decrease over the lifetime of a given colony, implying that clonal mixing primarily resulted from the joining of pre‐existing colonies as opposed to via simultaneous host colonisation by several foundresses. Widespread clonal mixing is argued to affect the ecology and evolution of the aphids in various important ways, for example with respect to the costs and benefits of group living, the evolution of dispersal and the interaction with predators as well as with the ant mutualists.