Effects of population density on alienicolae of Aphis fabae Scop.

A technique for rearing aphids in dense populations is described. Apterae were reared in high (‘C’) and low (‘U’) population densities and the proportions of alatae among their progenies were compared. Proportions of alatae were larger among progenies of ‘C’ apterae, and the proportions also increased as the density of the population in which the progenies were reared increased. Progenies of alatae never became alatae.     

Effects of population density on alienicolae of Aphis fabae Scop.: V. Variations in size, relative wing length and numbers of antennal sensorla of field alatae

Size, relative wing length and numbers of antennal sensoria of alate Aphis fabae caught in a suction trap 12.2 m above ground and of migrants, flyers and non-flyers among alate A. fabae from field infestations on beans and beet are compared. The size of aphids in successive samples decreased throughout the period of colonization but, on average, beet aphids were bigger and broad bean aphids were smaller than field bean aphids. There were very few migrant alatae among the very large or the very small aphids from any of the crops, neither were aphids of these extreme sizes caught in the suction trap. Non-flyers and beet aphids generally had relatively shorter wings than migrants and bean aphids respectively. The numbers of antennal sensoria differed more between aphids from the three crops than between classes of alatae from the same crop, although trap aphids, presumed to be migrating from field beans had more sensoria than alatae taken from that crop. The mean dry mass of flyers was usually less than that of migrants of a similar size, although if the mass of nymphs deposited before flight is added, it is apparent that a flyer would be heavier than a migrant of the same size at maturity. This additional mass is thought to be due to increased development of the embryos in the ovarioles of flyers at this time and indicative of their greater adaptation for reproduction.     

Factors influencing the infestation of a bean field by Aphis fabae Scop

The infestation pattern in a bean field is related to the effects of shelter on the activity of the migrants and developing apterous colonies.

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Zusammemfassung Frühlingsmigranten von Aphis fabae, die ein Bohnenfeld befielen, waren hauptsächlich auf die Bestandsränder beschränkt, wo die von ihnen begründeten Kolonien Randbefall bildeten. Der Initialbefall nahm in der auf die primäre Migration folgenden Zeit an Dichte und Ausmaß zu, wobei die Befallsverteilung im wesentlichen die gleiche blieb wie die von den primären Zufliegern erzeugte. Der Innenteil des Feldes wurde allgemeiner befallen, als ein kleiner Teil der im Felde herangewachsenen Geflügelten in den Bestand eindrang und diesen Teil des Feldes besiedelte; jedoch faßte der Befall nicht Fuß.Auf der geschützten Leeseite des Feldes entwickelte sich ein viel schwererer Befall, obwohl die Anzahl der hier festgestellten Migranten nicht größer war als an jeder anderen Seite des Feldes. Es wird daraus geschlossen, daß die verhältnismäßig ruhigen Bedingungen auf dieser geschützten Seite eine größere Flugaktivität der einfallenden Frühjahrszuwanderer gestattete und daher jeder von ihnen eine größere Anzahl von Pflanzen infizierte als die Migranten in anderen Teilen des Feldes. Es wird angenommen, daß physikalische Wirkungen des Windschutzes, z.B. höhere Temperaturen, Ursache dafür waren, daß an dieser Seite größere Kolonien beobachtet wurden.

     

The control of Aphis fabae Scop, on spring-sown field beans (Vicia faba L.)

Disulfoton or phorate granules or demeton-S-methyl, menazon and vamidothion sprays, applied once in early June as preventive treatments before heavy aphid colonies developed, gave good control of Aphis fabae Scop, on field beans. Phosalone gave relatively poor results and DDT was ineffective. Applications in June to crops sown in February and early March were made with minimal wheel damage to the crop and are known to be less harmful to bees than sprays at flowering time. Eradicant treatments with demeton-S-methyl and dimethoate sprays or with disulfoton or phorate granules on heavily infested plants during flowering were also effective, but menazon was less satisfactory. These eradicant sprays are likely to be harmful to bees, and wheel damage in late June reduced yield by 1–2 cwt/acre (125–250 kg/ha). Peak populations of 3000 aphids/plant in early July reduced yield by 6 cwt/acre (750 kg/ha) in one trial.     

The feeding and excretion rates of Aphis fabae Scop. on Vicia faba L.

The feeding and excretion rates of nymphs of Aphis fabae, feeding on young leaves of Vicia faba, were studied, using host plants grown in water culture and made radioactive with 32P. The amounts of sap ingested at first were small but the rate of ingestion increased rapidly between 12 and 16 hr. The maximum rate of feeding was estimated at 0.2 mg sap/hr, an uptake of 59 per cent of the mean body weight of the insects per hour. The results are discussed in relation to other recent work on aphid feeding and excretion.

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Zusammenfassung Unter Benutzung von Wirtspflanzen, die in Wasserkultur angezogen und mit 32P radioaktiv gemacht waren, wurden Nahrungsaufnahme- und Exkretionsraten der Larven von Aphis fabae untersucht, die an jungen Blättern von Vicia faba saugten. Die aufgenommenen Saftmengen wurden für Zeitabschnitte von 1–24 Stunden Dauer geprüft. Die maximale Nahrungsaufnahmerate wurde mit 0,2 mg/Stunden geschätzt. Die Exkretionsrate von 32P variierte beträchtlich, war aber bei kürzerer Nahrungsaufnahme von weniger als 12 Stunden Dauer höher, und bei längeren Nahrungsaufnahmezeiten niedriger und weniger variabel. Die Ergebnisse werden im Hinblick auf andere neuere Arbeiten über die Ernährung und Exkretion von Blattläusen diskutiert. Es wird vermutet, daß die maximale Rate der Nahrungsaufname, die für diese Insekten angegeben wird, unter den Bedingungen des Versuchs die normale war und daß die Mehrzahl der Aphiden offenbar 12 Stunden oder mehr brauchen, um mit ihren Stechborsten bis zum Phloem vorzudringen.

     

The nature and causes of annual fluctuations in numbers of Aphis fabae Scop. on field beans (Vicia faba)

Experiments for nine successive years showed that Aphis fabae Scop. populations on mid-March-sown field beans were either large with peak densities between late June and mid-July or very small with peak densities in early August. It is concluded that the largest populations develop when many plants have been colonized by primary migrants from Euonymus europaeus and temperature and radiation are above average during June and early July, as in the year 1957. Cold, dull weather slows multiplication and decreases the size of the peak population even when there is a large initial colonization, as in 1954. The peak population may also be less than predicted from the initial colonization when natural enemies are exceptionally abundant in early June, as in the year 1960. Yield losses of mid-March-sown crops in years of large A. fabae populations ranged from 53 % in 1954 (peak population of 1260 aphids per plant) to 100% in 1957 (6920 aphids per plant). Small summer populations with peak densities of about 0·2–85 aphids per plant developed on mid-March-sown plots in years when fewer than about 6% of the plants were colonized by primary migrants. Yield losses ranged from 6·3–13·6%. Three years' experiments indicated that crops sown in late April or May are relatively lightly infested in years when large populations develop on mid-March-sown crops. Conversely, they may be relatively heavily infested when the populations on these crops are small, as in 1955 when temperatures and sunshine during July and early August were above average. Small and large early summer populations tend to alternate in successive years. The alternation is upset by hot, sunny weather during July and August, and perhaps September and October, which compresses the population cycle Thus the large and small populations expected from this alternation in 1956 and 1960 developed instead during exceptionally fine weather in late summer 1955 and 1959, converting 1956 and 1960 to years of small and large populations respectively.     

Aggregation and the transformation of counts of Aphis fabae Scop, on beans

In several sets of counts of Aphis fabae colonies on bean stems, obtained with different sampling methods, variance was always proportional to the same power of the mean; s²=am^b where b= 1.72 and a differed by different sampling methods. The resulting standard transformation for A. fabae on beans, z=x^{0 2}, is marginally more effective than z= log (x+1).     

The effect of certain antibiotics on reproduction of the black bean aphid, Aphis fabae Scop.

The antibiotic terramycin at 0.2% concentration was consistently effective in greatly reducing the populations of Aphis fabae on Vicia faba when sprayed on larvae on and off the plant. The insects were not killed, but their fertility was decreased by over 97% in the first generation, leading to total sterility in the second generation. At 0.01% concentration, terramycin was not effective and only moderately so at 0.1% Larval development was invariably delayed by 1 day and the weight and size of the resulting adults were significantly reduced. After the most effective treatments, the adults were very inactive in their feeding and excretion, and sometimes became completely sterile. Even when the aphids reproduced, they ceased to do so after 6–10 days in different terramycin treatments and frequently the larvae were born dead. The affected insects could not, apparently, regain their reproductive capacity even after their transfer to untreated plants. When the insects were sprayed on the plants, terramycin in water was as effective as with surfactants: but when the insects were sprayed off the plants an oxyethyl phenol derivative (NP 10) greatly increased the efficiency of terramycin: surfactants alone had no effect on the insects. The other four antibiotics, namely tetracycline, aureomycin, chloramphenicol and reverin were not effective at the 0.2% concentration when the plants alone were sprayed before introducing the apids. The addition of glycerin to the antibiotics and keeping plants in a high humidity for 24 hr. after the treatment also had no effect.     

Interactions of crop density of field beans, abundance of Aphis fabae Scop., virus incidence and aphid control by chemicals

The number of Aphis fabae Scop. per plant and per acre developing on field beans (Vicia faba L.) was inversely related to seeding rate (i.e. plant density) except sometimes at very low rates; with equal numbers of plants per acre, fewer aphids developed on plants in rows 11 in. than 22 in. apart. Plots sown in mid-March with more than about 150,000 plants per acre were more attractive than less dense stands to colonizing alate A. fabae, but established colonies multiplied most on the sparsest and least on the densest plots. The number of plants per acre infected by pea leaf-roll virus was inversely related to planting density. There were more virus-infected plants on II in. than on 22 in. spaced rows-in contrast to the numbers of A. fabae. A single spray with demeton-methyl, timed to control A. fabae, did not significantly decrease virus incidence. Grain yields of sprayed plots were little altered by increasing the seed rate above a critical minimum, except in one year when the densest crops lodged. Increased yields from spraying were closely related to the numbers of A. fabae on unsprayed plots. Dense planting (more than 400,000 plants per acre) prevented or greatly decreased losses caused by A. fabae in unsprayed plots except in one year when the aphids were exceptionally abundant.     

Effect of the mutilation of wings on the reproduction of the Bean Aphid Aphis fabae Scop.

Mutilation of the wings by pinching and twisting them immediately after the aphid emerged hastened its reproduction. The hastening was more striking among individuals so treated which were kept in light than those kept in dark. Reproduction was also hastened, but to a slighter degree, among individuals with naturally deformed wings.It has been shown by earlier workers that bodily exercises hastened reproduction. The facts revealed in the present paper suggest that the nervous changes resulting from bodily exercise are more important than the actual exercises themselves.

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Zusammenfassung Verstümmelung der Flügel durch Zusammenpressen und-drehen gleich nach der Häutung beschleunigte die Fortpflanzung der Blattläuse. Diese Beschleunigung war unter im Licht gehaltenen Tieren auffallender als unter solchen, die in der Dunkelheit gehalten wurden. Die Fortpflanzung ging auch bei solchen Blattläusen — wenn auch im geringeren Grade — Schneller vor sich, die ohne künstlichen Eingriff schon mit verstümmelten Flügeln schlüpften.Von früheren Autoren ist gezeigt worden, daß auch körperliche Betätigung die Fortpflanzung beschleunigte. Die Befunde der vorliegenden Arbeit weisen nun darauf hin, daß die durch körperliche Bewegung verursachte Nerventätigkeit wichtiger ist als die Ausübung selbst.

     

Intra-specific mechanisms in relation to the natural regulation of numbers of Aphis fabae Scop

Parthenogenetic virginoparous apterae of Aphis fabae Scop. on field beans (Vicia faba) reproduced faster initially in populations of eight colonizing apterae than in those with 2–4 or 16–32 per plant. The aphids were at first mutually benefited but were quickly affected by competition as numbers rose above the critical density represented by about eight apterae and their first progeny. This is because the aphids remained densely aggregated and seemingly created a local shortage despite abundant food and space elsewhere on the plant. Such self-induced competition provides the basis for self-regulation of numbers of A. fabae in relation to (1) food and space provided by the growing plant and (2) mortality from natural enemies and from other causes including insecticides. As competition increased, the multiplication of A. fabae populations slowed, newly formed adult apterae emigrated and increasing numbers of alatae were formed. The mean weights of apterae decreased from about 1·8 mg. to 0·3 mg. and of alatae from 0·9 to 0·2 mg. Such decrease probably favours production of many adults that might otherwise fail to mature. Experiments in a glasshouse and in field cages indicated the success with which an A. fabae population adapts to and exploits a growing plant. Field bean plants sown in mid-March and infested as in the field produced an average of 15,000–17,000 A. fabae emigrants per plant of which 78–84% were adults (mostly alatae). This is equivalent to about 1600 million alate emigrants from 1 acre (0·4 hectare) of an infested field bean crop.     

Action of beta radiation on the black bean aphid Aphis fabae Scop. (Aphididae, Homoptera)

A study was made of the effect of direct single exposure to beta-radiation of 0.5, 5, 10, 20, 30, and 50 Gy on development and reproduction of Aphis fabae Scop. (Aphididae, Homoptera). The numbers of bean aphid are prognosticated with regard to the radiation dose applied.     

Effects of Aphis fabae Scop, and of its attendant ants and insect predators on yields of field beans (Vicia faba L.)

Predators (mainly coccinellid adults and larvae and syrphid larvae), although few, were important in decreasing numbers of Aphis fabae on a small plot of field beans during the early stages of infestation in a year favourable to the aphid. At the same time, ants (Lasius niger L.), attending aphids on other plants on the same plot, effectively protected the aphids from predators for about 2 weeks, enabling the attended aphids to multiply faster than the unattended. When all aphid populations started to decline, predators became more numerous and accelerated the decline on both sets of plants. Bean plants without aphids yielded fifty-six seeds per plant; those with aphids but free from ants gave seventeen; and those with ant-attended aphids, eight seeds per plant. The damage and loss of yield was caused by the large aphid populations that developed when the pods were maturing, and not by the fewer aphids present when the plants were in flower. It appears that small, temporary infestations during flowering might increase the yield of field beans.     

Studies on Entomophthora in populations of Aphis fabae on field beans

The population of Aphis fabae on field beans at a site in Highfield, Rothamsted in 1973 reached its peak 1 wk earlier than that at an equivalent site in Mill Dam Close, Woburn, 29 km NW of Rothamsted. Epizootics of Entomophthora caused weekly maximum mortalities of adult apterae of 71% at Highfield and 67% at Mill Dam Close. These epizootics and the periodicity of Entomophthora conidia in the air closely paralleled the development of the aphid population. There was little evidence of a consistent relationship between Entomophthora infection and any of the weather factors considered. At both sites most mortality was caused by E. planchoniana though many aphids were killed by E. aphidis and E. obscura. E. fresenii and E. virulenta killed very few aphids. Most conidia in the air were of the E. aphidis-type. Up to 44% of alatae emigrating from bean crops were infected with Entomophthora, confirming that aphid migration is an important means of distributing the fungi. Aphid numbers rose to more than 1600/plant at both sites, in spite of the action of Entomophthora, and would probably have been less had the fungi been more abundant earlier in the season.     

The significance of overlapping plant range to a putative adaptive trade-off in the black bean aphid Aphis fabae Scop

Abstract. 1. This study continues to explore the analysis of a putative adaptive trade‐off in the utilisation of host plants Vicia faba and Tropaeolum majus by the aphid, Aphis fabae. These plants are utilised exclusively by the subspecies Aphis fabae fabae and A. f. mordwilkoi respectively, and this plant‐use system has been studied previously as a potential source of disruptive selection. 2. Here the potential of these two host plants to generate disruptive selection is considered given common utilisation of the abundant host plant, Rumex obtusifolius, by both subspecies. 3. The life history of subspecific clones is quantified in the laboratory on V. faba, T. majus, and R. obtusifolius at various temperatures and used to parameterise a temperature‐driven simulation model of aphid population development. 4. Accuracy of the model is tested using a field experiment, and fitness of clones on specific and common host is simulated using temperature data from a number of English sites. 5. The model gives a close quantitative fit to field data and makes the following predictions: performance of A. f. fabae is higher on the specific host than the common host under all tested thermal regimes; and performance of A. f. mordwilkoi is superior on the specific host in warm years but inferior in cold years. 6. Given the great abundance of R. obtusifolius relative to T. majus, the model predicts that the plant utilisation system has little potential to consistently promote hybrid dysfunction. This adds further weight to the assertion that the plant utilisation system studied can offer little insight into the evolutionary processes involved in subspecific differentiation and probably contains a host plant/host plants acquired after the evolution of reproductive barriers.     

The influence of black bean aphid, Aphis fabae Scop., and its honeydew on the photosynthesis of sugar beet

The effect of black bean aphids on the photosynthesis of sugar beet plants was studied under glasshouse and field conditions. The presence of up to several hundred aphids per leaf had no significant effect on CO₂ exchange rates over a range of light intensities between complete darkness and light saturation. Artificially prepared honeydew, sprayed onto leaves in the same amounts and composition as was found on severely aphid-infested plants, covered 30% of the stomata on the upper epidermis but did not significantly alter the rate of photosynthesis of these leaves in the light or the rate of respiration in the dark. The stomata on the lower epidermis were uncovered and functional. High pressure liquid chromatography of aphid-produced honeydew detected 20 different amino-acids. Three amino-acids, aspartic acid, glutamic acid and gluta-mine, made up the bulk of the amino-acid weight in the honeydew produced on young plants, up till the 8 leaf-stage. In the 10 to 12 leaf-stage, several different amino-acids occurred in substantial amounts. The amino-acids to sugars ratio of the honeydew produced by the aphids decreased strongly as the sugar beet plants aged: from 1:6 in plants with 3 or 4 leaves to 1:25 in plants having 10 to 12 leaves.