Cereal Aphid Populations Research Articles

The use of incidence counts for estimation of aphid populations. 2. Confidence intervals from fixed sample sizes

Two approaches have been used in the monitoring of local populations of cereal aphids: direct counting of aphids on a number of tillers, and the less time-consuming assessment of incidence levels (the proportion of tillers infested). This paper compares the accuracy of these two methods, using a fixed sample size, as is desirable in a practical monitoring system. It is shown that the two methods are equally reliable over a range of incidence levels, but that the confidence intervals for the population density are very broad. Reduction of these sampling error requires a considerable increase in sample size, so they should instead be taken into account in the management decision-making process.

The use of incidence counts for estimation of aphid populations. 1. Minimum sample size for required accuracy

In attempts to reduce the time required for monitoring cereal aphid populations, it has been suggested that direct counting be replaced by the use of incidence counts: estimation of aphid density from the proportion of wheat tillers infested. It is important, however, that the use of this simpler and more rapid method does not result in a loss of accuracy. This paper calculates the minimum sample size (number of tillers to be inspected) required to yield a given accuracy, using the two alternative sampling methods. Over the range of aphid densities close to the economic thresholds for pesticide application, the use of incidence counts does not require a much greater sample size than that needed for direct counting.

The effect of the grain aphid, Sitobion avenae (F.), on winter wheat in England: an analysis of the economics of control practice and forecasting systems

In 1975, 1976 and 1977 counts were made of cereal aphid populations in winter wheat fields in West Sussex and Norfolk. Data were also obtained on the area of cereals treated with insecticides to control aphids in different years, dates of application and the types of insecticide used. Most crops were treated when aphid populations were at their peak or had already started to decline. A model which simulates the damage done by Sitobion avenae (F.) to winter wheat was used to analyse the survey data and revealed a large difference between potential and achieved profits. It also showed how the value of insecticide treatment varies throughout the course of an infestation and how the value of a forecasting system depends on its timing and accuracy, the size of the aphid outbreak and its probability of occurrence.

The role of ground beetles (Carabidae) as predators on early populations of cereal aphids in spring barley

AbstractCarabid beetles of the species Bembidion lampros, Agonum dorsale, Pterostichus melanarius and Loricera pilicornis were caught in spring barley fields in 1982 and 1983.The percentages of beetles containing aphid remains were related to aphid density. A. dorsale was the most efficient predator at low aphid densities but B. lampros was more numerous and therefore most important. The other species were not significant at low aphid densities.The retention time for chitinous aphid remains in guts of B. lampros was investigated in the laboratory. Specimens of B. lampros were dissected at different intervals following ingestion of Rhopalosiphum padi. The percentage of beetles containing aphid remains declined exponentially with time (mean retention time = 27 h).B. lampros in the laboratory consumed 3 R. padi per day at 16 °C and 5 R. padi per day at 21 °C.Methods for estimation of carabid population densities (soil samples, direct quadrate counts, removal trapping) were compared. Removal trapping proved to be the most applicable method. The density of B. lampros was estimated at 60 specimens per m2.ZusammenfassungÜber die Rolle von Laufküfern (Carabidae) als Prädatoren früher Populationen von Blattläusen auf FrühgersteLaufkäfer der Arten Bembidion lampros, Agonum dorsale, Pterostichus melanarius und Loricera pilicornis wurden 1982 und 1983 in Frühgerstenfeldern in Nord‐Seeland gefangen. Die Käfer wurden seziert, und ihr Anteil mit Blattlausresten im Darm wurde mit der Blattlausdichte verglichen. A. dorsale war der effektivste Prädator bei niedrigen Blattlausdichten, doch war B. lampros zahlreicher und deshalb von größerer Bedeutung. Die anderen Arten waren bei niedriger Blattlausdichte nicht signifikant.Die Aufenthaltsperiode der chitinösen Blattlausreste im Darm von B. lampros wurde im Laboratorium untersucht. Individuen von B. lampros wurden in verschiedenen Intervallen nach dem Verzehr von Rhopalosiphum padi seziert. Das Prozent von Käfern mit Blattlausresten sank exponential mit der Zeit (mittlere Aufenthaltsperiode = 27 h).B. lampros verzehrte im Laboratorium bei 16° 3 R. padi und bei 21°C 5 R. padi per Tag.Die Methoden zur Bestimmung der Dichte von Laufkäferpopulationen (Bodenproben, direkte Quadratzählung, Beseitigungsfang) wurden verglichen. Der Beseitigungsfang stellte sich als die geeignetste Methode heraus. Die Dichte von B. lampros wurde auf 60 Individuen pro m2 veranschlagt.

Electrophoretic study of enzymes from cereal aphid populations. I. Electrophoretic techniques and staining systems for characterising isoenzymes from six species of cereal aphids (Hemiptera: Aphididae)

AbstractOne–dimensional slab polyacrylamide gel electrophoretic techniques, staining systems and isoenzyme banding patterns for 14 soluble enzymes separated from crude homogenates of individuals of six species of cereal aphids (Sitobion avenae (F.), S. fragariae (Wlk.), Metopolophium dirhodum (Wlk.), M. festucae (Theo.), Rhopalosiphum padi (L.) and R. maidis (Fitch)) are described. The value of the techniques and banding patterns to taxonomic and population genetic studies of these and other aphid species are briefly discussed. With the six species, it was possible to separate the different genera as well as individual species within genera. The enzymes found to be most useful for inter–generic and/or -specific separations were adenylate kinase (AK), esterase (EST), glucose-6-phosphate dehydrogenase (G-6-PDH), hexokinase (HK), malate dehydrogenase (MDH), peptidase (PEP), phosphatase (PHOS), phosphoglucomutase (PMG), 6-phosphogluconate dehydrogenase (6-PGD) and sorbitol dehydrogenase (SORDH), whilst glutamate oxaloacetate transaminase (GOT), α-glycerophosphate dehydrogenase (α-GPD), malic enzyme (ME) and peroxidase (POD) were of relatively little taxonomic use. There were no banding pattern differences between the various morphs of S. avenae (first to fourth-instar nymphs, apterous and alate adults using the 14 enzymes.

Weather and Modelling Cereal Aphid Populations in Norfolk (UK)1

The role of weather in determining an outbreak of the grain aphid Sitobion avenae is discussed in relation to its life cycle. Attention is centred on overwintering survival, and the weather during the spring migration into cereal crops and its effect on subsequent population development. The relationships between the aphid, crop, and weather are investigated using a simulation model.Conditions météorologiques et modélisation des populations de pucerons des céréales dans le Comté de Norfolk (Grande‐Bretagne)L'incidence des conditions météorologiques sur le développement de Sitoblon avenae est étudiée par référence aux différents stades évolutifs de l'espèce. Une attention particulière est accordée au taux de survivance durant la période d'hibernation et aux conditions prévalant durant la phase de migration printannière vers les cultures céréalières. La relation entre le puceron, la plante et les conditions météorologiques est exprimée à l'aide de modèles.

Duration of cereal aphid populations and the effects on wheat yield and breadmaking quality

SUMMARYField‐caged and open‐plot populations of the aphid Sitobion avenae on winter wheat (cv. Maris Widgeon) were sampled approximately twice‐weekly in the summer of 1978. Cage populations began at growth stage 10.2 (Feekes scale) (Zadoks, G. S. 52); they were removed by spraying with pirimicarb at growth stages 10.54 (71), 11.1–11.2 (77) and 11.2–11.3 (85) respectively. All cage populations reduced mean weight per grain but the effect per aphid unit was lowest in the population of longest duration. Although the aphid index in the open plots was higher than that in the early cage treatment, yield was unaffected. Cage infestations affected the breadmaking quality of the grain: percentage flour extraction was reduced and there was an increase in colour, nicotinic acid content and thiamine (vitamin B1) content of the flour; percentage nitrogen in the flour was unaffected but there was a reduction in baking value and in the high molecular weight glutenin content; infestation also reduced α‐amylase activity. Different aspects of grain quality did not change in parallel with one another or with yield changes and thus damage thresholds will vary according to the yield/quality measure under consideration.

The `Natural Enemy Ravine' in Cereal Aphid Population Dynamics: A Consequence of Predator Activity or Aphid Biology?

The `Natural Enemy Ravine' in Cereal Aphid Population Dynamics: A Consequence of Predator Activity or Aphid Biology?

Studies on Polyphagous Predators of Cereal Aphids

1. Experiments were done in fields of winter wheat at North Farm, West Sussex, and at Rothamsted in 1978 to investigate the effect of predation by carabid beetles and other polyphagous preadtors on populations of cereal aphids. 2. Predator populations were manipulated by pitfall trapping within plot surrounded by polythene barriers and by applying an insecticide (fonofos) within such plots. Plots were set up in March, April, May and June and the development of aphid populations within them compared with aphid populations in unenclosed control areas. 3. The numbers of carabid beetles caught in the enclosed and fonofos-treated plots were much less than in 'control' plots. 4. Aphid populations were all much smaller in 'control' plots than in those with depleted predator populations both at North Farm, where beetle populations were large, and at Rothamsted where populations were small. Aphid populations were much larger in plots where numbers of polyphagous predators were decreased early in the season than where this was done later. 5. There was an inverse relationship between numbers of polyphagous predators and aphids for the North farm experiment. In contrast, there were positive relationships between aphids and aphid-specific predators and between aphids and aphid parasites. This together with the virtual absence of the pathogenic fungus Entomophtora spp, indicated that the differences in aphid density between plots were caused by polyphagous predators rather than by other natural enemies. 6. Comparison of results from the two sites suggested that amongst the carabid beetles Agonum dorsale (Pont.) was the most important aphid predator, but there was also evidence that polyphagous predators other than carabids decreased the cereal aphid populations.

Arthropods in Cereal Crops: Nocturnal Activity, Vertical Distribution and Aphid Predation

The daily rhythms of activity of arthropods have been studied both in the air (Williams 1935; Lewis & Taylor 1965) and on the ground (Williams 1959, 1962; Greenslade 1963); however, little is known about the nocturnal activity of arthropods in cereal crops. Some day-time observations suggest that predators such as Araneae and Staphylinidae are scarce on cereal plants (e.g. Dean 1974) but these can be misleading if such arthropods are only active and/or present on the vegetation at night. Similarly, predation by some species may be underestimated if feeding is nocturnal and sampling diurnal. The following is a preliminary study on the nocturnal activity and vertical distribution of some arthropods in cereal crops. In addition, the role of some species as aphid predators is considered. The work forms part of a wider study on the ecology of cereal crops which includes the role of predators and parasites in reducing populations of cereal aphids (Potts & Vickerman 1974).

Field Populations of Cereal Aphids in South Dakota Spring Grains12

Studies of field populations of cereal aphids in spring small grains in South Dakota (1963–72) showed that Schizaphis graminum (Rondani), Macrosiphum avenae (F.), and Rhopalosiphum padi (L.) commonly colonized wheat, barley, and oats; R. maidis (Fitch) was found only in barley and only while the developing leaf blades were still furled. S. graminum often was present during a greater proportion of the season than the other species. Populations of all species were predominantly nymphal throughout the season with substantial numbers of alatae (migrant) only present as founders of colonies early in spring. S. graminum was distributed nearly randomly within fields, but M. avenae and R. padi were distinctly aggregated.

Cereal aphids, their parasites and predators caught in cages over oat and winter wheat crops

SUMMARYThe trapping of alate aphids in emergence cages each 1 yd2 (0–83 m2) over cereal crops from mid‐June to the end of July, 1964 to 1971, always revealed colonies of cereal aphids within the crop.Four species, Sitobion avenae, S. fragariae, Metopolophium dirhodum and Rhopalosiphum padi occurred every year in different proportions. Alate aphids from winter wheat were most numerous in 1968 and fewest in 1967. Alatae developed slightly earlier in cages than in the field and peak catches were a few days earlier than in a nearby 12‐2 m suction trap.Cereal aphid colonies were adversely affected by bad weather in May, e.g. in 1969, and by predators. Coccinellidae (chiefly Propylea 14‐punctata) were the dominant predators in 1971 and 1968, Syrphidae in 1966, 1971 and 1968 and Chrysopidae in 1970. Parasites belonging mainly to the genus Aphidius were numerous every year. When hyperparasites such as Asaphes vulgaris, Lygocerus sp., Conostigmus sp. and Phaenoglyphis sp. were abundant as in 1967, they affected numbers of aphids in the current year and increased them in the following year (1968), possibly by hindering early, heavy parasitism. Hyperparasites could have an important influence in fluctuations of cereal aphid populations from year to year. Aphids of one species or another are always present in cereal crops in sufficient numbers during the summer months to provide copious quantities of honey dew, and this is unlikely to be a limiting factor in the biology of the wheat bulb fly, Leptohylemyia coarctata.