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 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.     

Antixenosis resistance to Aphis fabae Scopoli (Hemiptera:Aphididae) in bean cultivars

Aphis fabae Scopoli (Hemiptera: Aphididae) is heteroecious and polyphagous that is harmful on secondary hosts such as many important agricultural products like beet, common bean, faba bean, potato and other products. This aphid is the cause of more than 33 viral transition. One of the mechanisms of plant resistance is antixenosis. This mechanism influences on placement and nutrition of pests that result in less damage. In this study, antixenosis resistance mechanism of 12 varieties of bean was tested. Experiment was on completely randomised design with 12 treatments and 6 replications. Bean varieties include of white bean, kidney bean and wax bean, and each replication includes one pot, and then, pots were placed under the isolated room that were filled with winged adult aphids in circular form. After 24 and 48?h, aphids and level of nymph production were counted. The lowest number of adult aphids was observed on Sayad variety among 12 varieties (during 24?h). The least number of produced nymphs was in Daneshkade variety. In Sayad variety, the frequency of matured insects and produced nymphs was minimum.     

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.     

The effect of 6-benzylaminopurine (benzyladenine) on senescence and chocolate spot (Botrytis fabae) of winter beans (Viciafaba)

In laboratory trials on detached bean leaves, benzyladenine delayed both senescence and aggressive attack of chocolate spot disease. In field plots, over 80% of the aggressive spots were on senescent leaves and the distribution of aggressively attacked leaves was predictable from the distribution of senescent leaves. The total frequency of aggressively attacked leaves per shoot was apparently related to the frequency of senescent spotted leaves. Although benzyladenine significantly reduced leaf senescence in field plots sprayed in May, the senescent leaves were more frequently attacked aggressively. Wider plant spacing (14 in instead of 8 in) similarly increased the ratio of aggressive attack to senescence, and the individual fields retained until June the differences in infection earlier established by frost damage.     

Yield components and cultivar, sowing date and density in field beans (Viciafaba)

Delay in sowing the cultivars Ostlers (Viciafaba var. equina) and Herz Freya (V.faba var. minor) beyond late February depressed yield. Densities of at least sixty plants per m² were required to ensure that yield was not limited by sowing rate. Differences in yield in response to changes in density were reflected particularly in changes in numbers of pod-bearing nodes per plant, but also to a lesser extent in numbers of pods per pod-bearing node. The inherently larger seed weight of cv. Ostlers compared with cv. Herz Freya did not confer any yield advantage, differences in number of beans per pod and number of pods per pod-bearing node tending to equalize the yield of the two cultivars. The most stable component of yield throughout was number of beans per pod, and the least stable was number of pod-bearing nodes per plant.     

Pre-flowering and post-flowering insecticide applications to control Aphis fabae on field beans: their biological and economic effectiveness

Most spring-sown field beans are treated with insecticides to control Aphis fabae, but there is usually a risk of toxicity to pollinating honeybees if insecticides are applied during flowering. An experiment was repeated at Rothamsted for 6 consecutive years, comparing treatments before and after flowering. It is concluded that (1) pre-flowering treatments (demeton-S-methyl spray at 0–25 kg a.i. ha^-1 or phorate granules at 1–12 kg a.i. ha^-1) were more effective and profitable than post-flowering treatments, (2) application of phorate granules before flowering gave the greatest economic return, and minimised the danger to foraging bees and (3) aphid populations varied considerably from year to year, as did the relationship between aphid infestation and yield, but our evidence supports the suggestion that insecticide spray treatments are profitable if 5% or more of the plant stems are infested at the end of primary aphid migration.     

Seed transmission of broad bean stain virus and Echtes Ackerbohnenmosaik-Virus in field beans (Viciafaba)

When grown in a glasshouse during spring or autumn field bean (Vicia faba minor) seedlings infected with seed-borne broad bean stain virus (BBSV) or Echtes Ackerbohnenmosaik-Virus (EAMV) usually showed symptoms on some leaves within 4 wk of emergence. Symptoms caused by each virus were indistinguishable. The viruses were transmitted as often through unblemished seeds as through seeds with necrotic patches or stains on the seed coat, and sometimes as often through large as through small seeds. Soaking seeds for 24 h in solutions of 8-azaguanine or polyacrylic acid did not decrease transmission. Both viruses were detected in nearly mature seeds by inoculation to Phaseolus vulgaris but neither virus was detected in fully ripened seeds by inoculation or serological tests. The percentage of seeds from field plots that produced infected seedlings when sown in a glasshouse was closely related to the percentage of parent plants that showed symptoms of BBSV and/or EAMV at the end of flowering. The relationship seemed similar in different cultivars. On average EAMV was transmitted through more seeds than BBSV, probably because more parent plants were infected with EAMV. Inspection of seed crops for symptoms of BBSV and EAMV at the seedling stage and again at the end of flowering is probably the most practicable way of identifying progeny seed lots with little or no infection.     

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 field behaviour of seed-borne Ascochyta fabae and disease control in field beans

In field sowings at Cambridge 2–15% of field bean seeds carrying Ascochyta fabae produced seedlings with leaf lesions. The fungus spread for distances up to 10 m in an average season and usually infected the new crop of seed. The amount of such infection arising from a single lot varied widely when samples were grown at different centres, presumably because of differences in local weather conditions. Seed lots with approximately 1% infected seeds seem suitable for ware crop production but little or no A. fabae can be tolerated in seed intended for multiplication. Infection in British-grown commercial seed has been greatly reduced by the selection of clean seed. Health standards adopted in the Field Bean Seed Scheme may have eliminated A. fabae from one cultivar.     

Pale coloration in Aphis fabae reared on beans treated with the plant growth regulator,ethylene-bis-nitrourethane

Aphis fabae reared on broad bean plants treated with the experimental growth stimulator ethylene-bis-nitrourethane were extremely pale in colour and this persisted for the life of the individual, even when first instar nymphs were transferred from treated to untreated plants. Pale aphids had less than half the amounts of the pigments protoaphin and aphinin that were present in normal aphids. It is concluded that the aphids probably received a compound which inhibited pigment formation from the treated plants; the chelating properties of the metabolite of the compound in plants are consistent with this conclusion.     

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.     

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.     

Effects of Botrytis fabae infection and mechanical defoliation on seed yield of field beans (Vicia faba)

Effects on seed yield of mechanical defoliation and inoculation with Botrytis fabae were compared using pot-grown plants of Vicia faba (cv. Maris Beagle). Treatments, which were made at the end of flowering, were applied singly and in all combinations to leaves (a) below, (b) at, and (c) above the flowering nodes (i.e. 2³ factorial). Yield was unaffected by treatments applied to leaves below the flowering nodes. Removal of leaves at flowering nodes did not reduce the number of pods but yield was reduced because there were fewer and smaller seeds. Inoculation of this zone also reduced yield; pods were lost at some nodes but it could also be shown that, irrespective of pod loss, yield at individual nodes was reduced in proportion to the severity of infection on leaves at the same nodes. Removal of leaves above flowering nodes reduced yield almost to the same extent as removal of leaves at flowering nodes but inoculation resulted in only a small amount of infection and yield was not reduced significantly. These results, taken in conjunction with recent studies on the physiology of the host plant, show that beans are exceptionally vulnerable to attack by B. fabae at the stage of flowering and early pod development. At later stages of development infection is unlikely to have a substantial effect on yield.     

The effect of introducing aphid-pathogenic Entomophthoraceae into field populations of Aphis fabae

During two warm, dry seasons (1975 and 1976) aphid-pathogenic species of Entomophthoraceae introduced into Aphis fabae populations on field beans established briefly but failed to spread. In cool moist seasons (1977 and 1978), the fungi, principally Erynia neoaphidis and Neozygites fresenii, spread more rapidly in treated than untreated plots. In 1977, the maximum aphid population in plots treated with fungi reached a mean of 9000/plant on 19 July compared with 16 000/plant 1 wk later in untreated plots. The corresponding yield of beans in treated plots was twice that in untreated plots though only half that in plots kept free of aphids with pirimicarb. In two experiments in 1978, the maximum aphid population in treated areas was 700/plant, half that in untreated areas and 1 to 2 wk earlier. Yields from treated plots, however, were not significantly different from those from untreated plots. In nature, the fungi attack A. fabae populations in England only after they have become damaging, partly because fungal inoculum is sparse when the aphid population is small.     

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.

     

Walking and take-off in Aphis fabae.

ABSTRACT. A walking aphid ready to emigrate is directed by light, gravity and mechanical stimuli to the upper and outer parts of the plant. There, the new conditions enhance the probability of take-off, as a kinetic response, but the precise moment at which the aphid stops walking and takes flight does not depend on any new external ('releasing') stimulus. The probability of take-off, then, appears to depend partly on substrate stimuli received during walking. Aphids were tested either when suspended by the thorax (and carrying and walking on spheres or paper bands) or when walking on a treadmill with a variable surface structure and aspect relative to gravity. A variety of situations that stimulated faster walking (e.g. a 'cat-walk'), also delayed take-off. Other situations that retarded walking (e.g. being upside-down), similarly delayed taking off, and tended as well to induce probing of the surface. A common feature of these latter situations appeared to be that they elicited traction movements of the legs on the surface: a flexor reflex opposed to the leg extension that regularly precedes a take-off.     

Some effects of benomyl and carbendazim on Aphis fabae and Acyrthosiphon pisum on field bean (Vicia faba)

Field bean plants were treated with benomyl in a glasshouse, then nymphs of Aphis fabae and Acyrthosiphon pisum were caged on the second pinnate leaf. Soil drenches at concentrations of 150 and 75 μg benomyl/ml or above increased mortality of A. fabae and A. pisum respectively; 250 μg a.i./ml increased mortality and decreased progeny production of alate A. fabae. The effect on mortality persisted for at least 16 days after treatment. Foliar sprays increased mortality at concentrations of 75 μg a.i./ml and above (A. fabae). Field populations of A. pisum were reduced when bean plants were drenched or sprayed at a concentration of 250 μg a.i./ml and A. fabae populations were reduced by drenches but not by foliar sprays. A commercial formulation of carbendazim (Bavistin) increased aphid mortality whereas the formulation medium did not. Under the experimental conditions, benomyl affected the distribution of both species on young bean plants but did not induce a repellent effect; aphids preferred untreated leaves. Mortality and preference tests, and a field experiment, indicated that A. pisum was affected more than A. fabae.