Entomophthora infecting the cereal aphids Metapolophium dirhodum and Sitobion avenae

Entomophthora aphidis, E. planchoniana, and E. thaxteriana killed many Metapalophium dirhodum and Sitobion avenae in barley during 1970. E. planchoniana first infected M. dirhodum late in June, after rain ended a long dry period, but few aphids were infected until after July 7, when heavy rain killed 65–80% of aphids. E. planchoniana was the most frequent of the 3 species until July 27, when E. aphidis and E. thaxteriana each became more abundant. S. avenae was more often infected by E. thaxteriana than the other species of Entomophthora. During the second half of July, 40–76% of adult M. dirhodum and 34–80% of S. avenae were infected. The 3 fungus species were equally common in M. dirhodum in sheltered fields, but E. thaxteriana was less common in an exposed field. In a sheltered field, E. thaxteriana was less frequent than the other species along the perimeter, and E. planchoniana was most common and E. aphidis the least common about 37 m into the crop.     

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 value of three cereal aphid species as food for a generalist predator

The value of the cereal aphid species Metopolophium dirhodum (Wlk.), Sitobion avenae (F.) and Rhopalosiphum padi (L.) as prey for the linyphiid spider Erigone atra (Bl.) was assessed. Fecundity of females was determined for spiders fed on eight experimental diets: three single‐species aphid diets, a mixed diet of all three aphid species, three mixed diets with each aphid species in combination with fruit flies Drosophila melanogaster (Meig.), and pure D. melanogaster as a high quality comparison diet. The development and survival of first‐instar juveniles fed on three diets of single aphid species, and on a diet of Collembola were compared with those subjected to starvation. Prey value for adult females was assessed by egg production, hatching success and offspring size. In pure diets all three aphid species were of low value to the spiders, causing a rapid decline in egg production and supporting no growth of significance of first‐instar juveniles. No difference in value of aphid species of single‐species aphid diets was found in the fecundity experiment, while a ranking of aphid species of M. dirhodum > R. padi > S. avenae was revealed in the survivorship experiment. A mixed‐aphid diet was not found to be advantageous compared with single‐species aphid diets, and no advantage of including aphids in mixed diets with fruit flies was found. Metopolophium dirhodum and R. padi were neutral in mixed diets, while a diet of S. avenae and fruit flies caused reduced egg production compared with the pure diet of fruit flies, revealing a toxic effect of S. avenae on the spider. The value‐ranking of aphid species in mixed diets was similar to that of single‐species diets. A similar ranking of aphid species was found for different fitness parameters (fecundity of adult females and development of juveniles). A ranking of aphids by offspring size of mothers on aphid‐only diets was S. avenae > M. dirhodum > R. padi. All aphid‐fruit fly diets resulted in larger offspring than a diet of only D. melanogaster, with the overall largest offspring being produced on the diet of M. dirhodum and fruit flies.     

The influence of nitrogen fertiliser on the population development of the cereal aphids Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.) on field grown winter wheat

The effect of nitrogen fertiliser on populations of the cereal aphids Sitobion avenae and Metopolophium dirhodum on winter wheat was investigated in a three year field experiment. Naturally occurring aphid populations were monitored on three nitrogen treatments; none, nitrogen application using Canopy Management guidelines (130–210 kg ha^-1) and conventional practice (190 kg ha^-1). Inoculations of laboratory reared S. avenae were used to enhance field populations on half the plots. Natural populations of M. dirhodum remained below the current UK spray threshold level of two-thirds of shoots infested at the start of flowering, or five aphids per shoot in all years, whilst populations of S. avenae exceeded the threshold in all years. The response of the two species to nitrogen differed. Significantly higher populations of M. dirhodum were recorded in both treatments which received nitrogen in all years, whilst the response of S. avenae varied between years. In 1994 and 1995 when environmental conditions favoured aphid development, higher populations were recorded in the two treatments which received nitrogen. In 1993 when high rainfall created unfavourable conditions, higher populations were recorded in the plots receiving no nitrogen. Differences in peak density and cumulative aphid index of S. avenae resulted from differences in the rate of population increase between ear emergence and peak density on the different treatments. Populations prior to ear emergence were higher in the plots which received nitrogen but the differences were not statistically significant. There was no evidence of a difference in the timing of population decline in the different treatments. In 1993 higher levels of infection by entomopathogenic fungi were observed in all treatments. Significantly higher levels of infection were recorded in the treatments receiving nitrogen, which may have accounted for the lower S. avenae populations recorded. It is possible that the larger canopies recorded in these treatments produced conditions which favoured infection by fungi, thereby limiting aphid population growth. The results indicate that application of nitrogen increases natural populations of M. dirhodum, and under favourable conditions, populations of S. avenae. However, in suboptimal climatic conditions, the application of nitrogen fertiliser can lead to lower populations of 5. avenae. The data also suggest that there is no consistent difference between a conventional and Canopy Managed approach to nitrogen fertiliser use in terms of the risk of infestation by cereal aphids.     

Distribution of aphids in cereal crops

Cereal crops were examined weekly for aphids during 1969. Plants in twenty samples of row 0.3 m long were examined in a sheltered perimeter of a crop and along a transect 36.6 m into the crop. Aphids were usually first found within 1–4 weeks of the first alatae caught in a suction trap operating 12.2 m above ground. When first alatae caught in a suction trap operating 12.2 m above ground. When the first found from 10 to 27% of the 0.3 m lengths sampled contained aphids. Rhopalosiphum padi, first found late in May, were scarce (< 0.53/0.3 m) throughout June and July. Sitobium spp. and Metapolophium dirhodum, which appeared in mid-June, were more numerous than R. padi; most occurred during the second half of July, and populations decreased just before harvest in early August. Sitobium avenae was more abundant (max. 19.3/sample) than either S. fragariae (0.91) or M. dirhodum (2.51). More aphids occurred in oats (max. 52/0.3 m) during July than in wheat (45), and barley had fewer (6.8). S. avanae was more abundant than M. dirhodum in sheltered areas of barley and wheat, and in exposed areas of the same crop M. dirhodum was commonest. Along sheltered perimeters, the ratio of S. avenae to M. dirhodum was largest in barley (11:1), intermediate in oats (6:1) and smallest in wheat (3.7:1). Sitobium spp. were most numerous on the ears, when most M. dirhodum were on the leaves. Regression analyses of log. S² on log. m suggested that S. avenae was more evenly distributed within (36.6 m) the field (b = 1.056 + 0.109) than along the sheltered perimeter (b = 1.432 + 0.132), though it seemed similarly distributed along perimeters of barley, oats and wheat. The distributions of M. dirhodum and Sitobium spp. along sheltered perimeters of all crops were apparently similar.     

The effect of barley yellow dwarf virus on honeydew production by the cereal aphids, Sitobion avenae and Metopolophium dirhodum

Individual S. avenae and M. dirhodum excreted significantly fewer droplets of honeydew on plants infected with BYDV than on healthy plants. S. avenae excreted less honeydew on the ears than on the leaves of wheat. M. dirhodum excreted less than S. avenae on the leaves. The size of honeydew droplets increased with the age of aphids but was not affected by BYDV infection. Possible reasons for the observed effects of BYDV on honeydew excretion are discussed.     

Geographic and microgeographic genetic differentiation in two aphid species over southern England using the multilocus (GATA)4 probe

Samples of the grain aphid Sitobion avenue (F.) and the rose-grain aphid Metopolophium dirhodum (Walker) were collected in late March from wheat fields and adjacent road-side grasses at a number of locations in southern England. Unparasitized aphids were DNA fingerprinted using the multilocus (GATA)₄ probe. Over all locations, the fingerprints of individual S. avenue caught in wheat had lower overall average distances of band migration (ADBM) and shared a higher proportion of bands, than fingerprints of individuals caught in adjacent road-side grasses. The ADBM of fingerprints of S. avenue collected on road-side grasses altered significantly with geographical location, while the ADBM of fingerprints of S. avenue caught on wheat did not. A comparison of the fingerprints of individual M. dirhodum caught in wheat and neighbouring road-side grasses did not reveal any genetic differentiation. Fingerprints of M. dirhodum that were caught in the same host type did however, show significant variation in ADBM between different locations. With both S. avenue and M. dirhodum, spatial autocorrelation revealed that locations that were close together were no more likely to have individuals with similar ADBM than locations mat were far apart Our results suggest that (i) particular clones of S. avenue prefer to colonize wheat; and/or that (ii) particular clones of S. avenae perform better on wheat man other clones. It is unclear why M. dirhodum did not show any genetic structuring according to host type, but this species appears to engage in sexual reproduction much more frequently than S. avenae in southern England. M. dirhodum is likely to have displayed genetic heterogeneity between locations either because of founder effects, or because of genetic drift.     

Preference of cereal aphids for different varieties of winter wheat

This paper reports on the development of a simple and robust preference meter (developed in-house) to score the host choice behavior of apterous aphids. With this tool, the preferences of two important cereal aphids Sitobion avenae (Fab.) and Metopolophium dirhodum (Walker) were investigated against four different varieties of winter wheat (Triticum aestivum L.) with a different susceptibility for Fusarium head blight (FHB). Differences in the choice behavior of both aphid species were observed for different wheat varieties. The preferred wheat variety of S. avenae and M. dirhodum was not the same. Also, both aphid species clearly had a differential preference for seedlings and ears. Using seedlings, M. dirhodum was about 1.8 times more rapid in making its choice than S. avenae. In separate experiments with ears, S. avenae was 4.5 times faster than in the experiments with seedlings. In the present study, we aim to highlight differences in preference behavior in relation to potential mechanisms for host selection.     

Aphid colonization of spring cereals

In 1970-1, Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae were the commonest alatae trapped from April/May to August, with most in July and early August. The first alatae appeared in the Rothamsted survey suction trap 0–34 days before aphids were found on the cereals, but during May and June no relationship was found between the numbers trapped and the number on the crop. Most species occurred first near the sheltered edge of the crop, but M. dirhodum was widespread over the field. Most infestations were quickly dispersed by the movements of older morphs; adults only stayed in one place for about 2 days. Alate M. dirhodum moved more often than apterae, but both morphs of S. avenae moved equally often and more frequently between larvipositions than did those of M. dirhodum. Apterae deposited more nymphs in a ‘group’ than alatae, and M. dirhodum deposited more than S. avenae. Few ‘groups’ persisted for more than a week. Although M. dirhodum occupied the crop area faster than S. avenae, all 0–3 m lengths of row sampled being infested within 2–5 wk of their first appearance, most or all of the tillers were colonized only in late July 1970.     

Entomophthora species infecting pea aphis

• 1 Three species of Entomophthora infected the pea aphis, Acyrthosiphon pisum, on lucerne at Rothamsted Experimental Station, Harpenden, Hertfordshire, between 1967 and 1972 and caused a maximum mortality of 83% in July 1968.
• 2 E.thaxteriana, the commonest species, occurred each year and frequently infected aphids during cool weather in spring and autumn. E.aphidis and E.planchoniana were absent in some years and were most common during warm weather in midsummer.
• 3 The incidence of infection by the three species was correlated with the density of conidia in the air above the crop, host density and rainfall, but not with any other weather factor considered.
• 4 Infection at any time was much more closely related to environmental factors during the preceding 12 than 3 days. The regressions, however, were weak and the relative importance of different environmental factors for the spread of infection can probably only be determined under controlled conditions in the laboratory.

     

New records of aphid hosts of Entomophthora aphidis and E. planchoniana in New Zealand

Examination of diseased aphids from the Christchurch area of New Zealand during summer 1974 established new records of Entomophthora aphidis and E. planchoniana attacking Macrosiphum hellebori and E. planchoniana parasitising Aulacorthum solani, plus the first record for New Zealand of E. aphidis infecting Myzus persicae.     

Consumption by carabid beetles of three cereal aphid species relative to other prey types

The cereal aphidRhopalosiphum padi has previously been found to be a low quality prey for a range of generalist arthropod predators. The aim of this study was to reveal, using food consumption experiments whether this applies to other cereal aphids. The question of whether predator feeding capacity increased when several aphid species were offered relative to a single aphid species was also addressed by measuring food consumption on a mixed aphid diet relative to single aphid diets. Food consumption by five carabid beetles of the three cereal aphid speciesRhopalosiphum padi, Sitobion avenae andMetopolophium dirhodum was determined relative to fruit fliesDrosophila melanogaster and the collembolanIsotoma anglicana. Feeding rate was measured as food consumption over 24 hour both for previously satiated and beetles starved for 7 days. Generally the largest aphid consumption was ofM. dirhodum and the lowest ofR. padi, withS. avenae in between. The mixed aphid consumption experiments did not reveal a higher feeding rate on mixed aphid diets relative to single aphid diets. The results indicate low preference forR. padi andS. avenae.     

The influence of mixed aphid diets on larval performance of Coccinella septempunctata (Col., Coccinellidae)

Abstract: Three questions regarding possible benefits of mixed diets for the specialist aphid predator, Coccinella septempunctata larvae were investigated. (1) Do aphids species from different host plants complement each other nutritionally? (2) Is a mixed diet of high‐quality aphids beneficial? (3) How does the quality of mixed diets depend on the quality of constituent species? All mix‐combinations of aphid species of high (Metopolophium dirhodum), intermediate (Myzus persicae), and poor food quality (Aphis sambuci), and the three single‐species diets were compared. A mixed diet of two high‐quality species (Sitobion avenae and M. dirhodum) was also compared with single‐species diets. Larvae that were given pure A. sambuci and a mixed diet of A. sambuci + M. persicae died within 18 days and none of the larvae developed to fourth instar. Metopolophium dirhodum was generally of higher quality as food than M. persicae, whereas the mixed diet of M. dirhodum + M. persicae was intermediate. Sitobion avenae and M. dirhodum were found to have approximately the same food value. Coccinella septempunctatam larvae that were offered a mixed diet of these two high‐quality aphids gained no extra advantage. Overall, no benefit from mixing of aphid species was found. The quality of mixed diets depended on the quality of the constituent species.     

The effect of barley yellow dwarf virus on field populations of the cereal aphids, Sitobion avenae and Metopolophium dirhodum

The numbers of cereal aphids, especially Metopolophium dirhodum in 1979, and Sitobion avenae in 1980, were significantly increased on BYDV infected wheat and oats in 1979, and wheat, barley and oats in 1980. The differences were probably caused by attraction of alates of each species to virus infected plants which had changed colour as a result of their infection. Significantly more alates of M. dirhodum were found on virus infected oats in 1979, and of S. avenae on oats and barley in 1980, although not on wheat in either year. probably because the colour contrast in wheat was less intense than in the other crops. Flight chamber experiments with alates of both species confirmed their visual attraction to virus-infected leaves. The interaction between virus, vector and host plants is discussed with reference to the ecology of virus spread.     

The spatial distribution of canopy-resident and ground-resident cereal aphids (Sitobion avenae and Metopolophium dirhodum) in winter wheat

We investigated, within two cereal fields in Southern England, the within-canopy spatial distribution of the aphids Sitobion avenae and Metopolophium dirhodum in relation to crop yield and plant nitrogen. We extended the study to investigate the spatial distribution of aphids that fell to, or returned from, the ground in order to estimate availability of the within-canopy aphid population to ground-active predators. We revealed that crop canopy aphid spatial pattern was associated with nitrogen or yield. Differences were evident between species: S. avenae was generally negatively associated with yield or plant nitrogen, whilst M. dirhodum exhibited positive association. For both aphid species, we observed strong spatial pattern for aphids falling to the ground and conclude that this could, in part, mediate the effectiveness of ground-active predators as pest control agents.     

Barley yellow dwarf virus in aphids caught in suction traps, 1969-73

Suction traps operating at low level (1 5 m) were used to catch live alate Rhopalosiphum padi, Macrosiphum (Sitobion) avenae and Metopolophium dirhodum which were tested for transmission of barley yellow dwarf virus (BYDV). The first species caught and infective was R. padi, followed by M. (S.) avenae infective some 2–3 wk later and M. dirhodum 3–4 wk later still. Never more than 11-5% of the annual catch of any species transmitted BYDV and the proportion fluctuated from week to week and between seasons in different years. The relative abundance of infective vectors of ths three species varied; annual numbers of infective M. (S.) avenae and M. dirhodum varied inversely with infective R. padi, the latter also usually transmitted severer virus. The results of the infectivity tests have been compared with the catches of these aphids by the Rothamsted Insect Survey and show that numbers of alate aphids do not necessarily indicate the likely incidence of BYDV.     

Bionomics of aphids reared on cereals and some Gramineae

In controlled temperature, light and relative humidity, Metopolophium dirhodum and Sitobion avenae multiplied more on young Proctor barley than on Blenda oats, and less on Cappelle wheat. Rhopalosiphum padi increased in number fastest on barley and slowest on oats. More survived, and generation lengths seemed shorter, on barley for M. dirhodum and S. avenae and on wheat for R. padi. Tests with young cereals outdoors generally agreed with those in controlled conditions. On mature plants, there were more M. dirhodum on barley, more R. padi on wheat and more S. avenae on oats than on the other cereals. Given a free choice in large cages outdoors, most aphids were found on barley. When allowed to choose between grasses, more M. dirhodum were on Dactylis glomerata, Poa pratensis and Festuca pratensis, more R. padi on Lolium perenne and F. pratensis, and more S. avenae on D. glomerata and L. perenne. Most aphids of all species combined were on F. pratensis, Lolium and Phleum, and fewest on Festuca rubra and Holcus mollis.     

The overwintering of cereal aphids on Gramineae in southern England, 1977–1980

Cereal aphids were sampled monthly on graminaceous host plants on farmland in Hampshire, UK from September 1977 to April 1980. Sitobion avenae overwintered anholocyclically on most types of Gramineae, particularly seedling grass crops and small-grain cereals. S. fragariae was probably mainly holocyclic on Rubus spp. Large summer populations of Metopolophium dirhodum were probably derived from holocyclic colonies on roses. M. festucae (subsp. cerealium) appeared to overwinter only anholocyclically, and was found mainly on mature grass crops and grasses in hedgerows. Rhopalosiphum padi was the most numerous species in autumn and overwintered anholocyclically in all three winters studied. R. insertum and R. maidis were rare and did not appear to survive the winter anholocyclically on graminaceous hosts.     

Aphid flight and change in abundance of winter wheat pests

Composition, dominance and change in population density of species flying over and feeding on winter wheat fields was studied between 1982 and 1998 at Mosonmagyaróvár. There were 29 aphid species among flying insects. The ones imposing risk to winter wheat were as follows: Diuraphis noxia Kurdj., Metopolophium dirhodum Walk., Rho‐palosiphum padi L., Schizaphis graminum Rond., Sitobion avenae Fabr. Number of flying individuals changed year by year, depending principally on climatic factors (temperature, relative humidity, and rainfall). Flight was continuous from late April to harvest. In the average of 17 years flight peak was observed in June.

Establishment of the firsts alate individuals of aphids with holocyclic development can be expected from the second decade of April. As a result of the continuous reproduction, the peak in number of individuals was observed in the second decade of June. During the six years between 1993 and 1998 this value was 17.18 aphids/ plant. Every year there were deviations from the average data, e.g., in 1994 aphid number per plant was 33.61. These pests appeared on the ears in the first decade of June, their number was continuously increasing due to drying of leaves.

During the six years when detailed data were recorded, Rh. padi L. was the dominant species three times (1994: 70.4%; 1995: 82.6%; 1996: 87.9%), M. dirhodum Walk. took this role two times (1993: 67.1%; 1997: 84.8%) and S. avenae Fabr. only once (1998: 53%).

Considering seventeen years’ data, it is necessary to produce resistant varieties and/or seed dressing, or insecticide treatment to control the first alates.     

The effect of temperature and wind on the flight activity of cereal aphids

The lower temperature threshold for take-off in Sitobion avenae obtained from an analysis of daily 12·2 m suction trap catches was 16°C. In the laboratory, the take-off threshold for S. avenae was 17·5°C in increasing temperatures, but 19°C when aphids were kept at constant temperatures for a short period of time. The equivalent thresholds were both 20·5°C for Metopolophium dirhodum. Over a period of 16 h no S. avenae took-off from plants at 10°C, 70% at 15°C and all within 16 h at 20°C. It was concluded that suction trap catches can be used to compare the temperature thresholds for take-off of both different species and morphs of a species of aphid. Emigrants of Rhopalosiphum padi, but not of M. dirhodum, took-off at a higher temperature than the alate exules. High winds were found to delay but not inhibit take-off both in the field, and in the laboratory, using both artificial and plant substrates. All aphids eventually flew, even from favourable hosts. It was concluded that adverse weather conditions will delay but not prevent cereal aphid migration in early summer.