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.     

Preceding crop affects soybean aphid abundance and predator–prey dynamics in soybean

Crop rotations alter the soil environment and physiology of the subsequent crop in ways that may affect the abundance of herbivores and their natural enemies. Soybean aphids are a consistent pest of soybean throughout North America, but little work has focused on how preceding crops may affect pest–predator dynamics. In a replicated experiment over three years, we examined how two preceding crops (spring wheat or an oat/pea mixture) affected seasonal soybean aphid pressure and the ratio of aphids to their predator community. Peak aphid populations were reduced by 40% and 75% in years 1 and 2 by planting spring wheat before soybeans (relative to the oat–pea mixture). Aphid densities were unaffected by preceding crop in the third year of study (aphids were at threshold in this year). Predators responded positively to aphid population increases and were unaffected by preceding crops. Additional research on how crop rotations can be used as a tool to manage soybean aphids warrants further attention.     

Causes of regional and yearly variation in pea aphid numbers in eastern England

Regional variation in the number of pea aphids caught in the suction traps of the Rothamsted Insect Survey (RIS) was associated with the proportion of each region under pea crops. The degree of infestation of crops was similar in areas of high and low pea production as the mean annual abundance of aphids per hectare of crop remained constant. Yearly variation in abundance was loosely associated with temperature from January to July. Cold weather in January and February resulted in large numbers of aphids. Warm weather in February led to early colonization, and emigration from, pea crops as well as making early sowing of the crop more likely. A forecast of the time of first appearance of Acyrthosiphon pisum in the aerial plankton can be made, based on February temperature. Populations of A. pisum on peas appear to be regulated by alata production. High densities of aphids resulted in almost all the nymphs developing into alatae which, on reaching maturity, emigrated, causing populations on the crop to decline. This explains population crashes of the pea aphid observed at early growth stages of the crop, on vining and combining peas. Late sowing of peas, a probable effect of cold winters, results in higher aphid densities at flowering. The probable explanation for this is that late-sown crops are colonized at an earlier growth stage, so that the aphid population has a longer period of time in which to develop.     

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

The 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.     

Seasonal activity and distribution of cereal aphid parasitoids in Belgium

Activity of antagonists in winter and early spring as well as in late summer and autumn plays an important role in the control of cereal aphid populations. Indeed, parasitoids active early in the year are important to avoid high aphid densities. Late summer and autumn correspond to the transition period between two wheat cultures, and parasitoid activity would thus reduce aphid infestation. During these critical periods, other crops like rye-grass and red clover containing alternative hosts could play the role of parasitoid reservoirs. During 1996, parasitoid activity was measured by trap planting in wheat, rye-grass, red clover and fallow grassland. In each plot, early spring was characterized by an important parasitoid activity, while aphids remained at a low level. Later in spring, activity decreased, and aphid development began even during this period. During the summer, when aphids reached their population peak, parasitoid activity rose again. Percentage of parasitism of aphids sampled was only important during summer in red clover and rye-grass. In wheat and fallow grassland, percentage of parasitism remained at a low level. The role of synchronization between parasitoid activity and aphid development is discussed.     

Suction‐trap catches partially predict infestations of the grain aphid Sitobion avenae in winter wheat fields

Effective pest monitoring programmes are needed for providing reliable advice on when pest populations require active management. We studied whether suction‐trap catches of the grain aphid Sitobion avenae during the period 1989–2009 can be used to predict field infestations of this aphid in Swedish winter wheat fields. We found that suction‐trap catches of S. avenae until the time of crop heading (GS51) were significantly related to both number of aphids per tiller (R² = 0.69 at GS 59 and R² = 0.27 at GS 69) and proportion of fields with infestations above economic threshold (R² = 0.49 at GS 59 and R² = 0.40 at GS 69). This effect was consistent across Swedish regions and years. This information could be used by advisory services and farmers to decide whether field inspection to estimate the profitability of insecticide treatment at heading is needed. To improve the predictive ability further, suction‐trap catches could be combined with weather data and information about biological control potential in different landscapes.     

Genetic variation in an introduced aphid pest (Metopolophium dirhodum) in New Zealand and relation to individuals from europe

RAPD-PCR was used to determine the genetic variation of Metopolophium dirhodum collected in a winter wheat field and in a nearby 2.5-m-high suction trap at Lincoln, New Zealand. Over three collection dates, five distinct genotypes were identified, using two primers (OPK16 and OPC09) independently. There was a significant temporal effect on the ratio of genotypes in populations collected in the field. There was no significant spatial aggregation or association of these genotypes in the field. Two of the genotypes present in the field were also detected in the suction trap sample. Using a higher resolution method of RAPD-PCR (with the Stoffel fragment of Taq polymerase), a total of 124 genotypes were distinguished from 142 individuals collected from Scotland and New Zealand. The Jaccard similarity index ( S ) was used to measure similarity between individual aphids within and between populations from both hemispheres. All populations were very diverse ( S < 0.33). However, at similar crop growth stages, M. dirhodum was significantly more diverse in Scotland than in New Zealand. The results are discussed in relation to the value of monitoring aphid flights for pest forecasting, and in terms of the most appropriate RAPD-PCR techniques.     

Responses of summer cereal aphid populations to reduced rate aphicide applications in field plots of winter wheat

Abstract 1 Recommended and reduced rate applications of pirimicarb and alpha‐cypermethrin were applied to winter wheat crops to control summer infestations of grain aphid (Sitobion avenae) and rose‐grain aphid (Metopolophium dirhodum). 2 Aphid numbers were assessed weekly and the yield response to treatment application was compared with accumulated aphid days on the crop. 3 Responses to aphicide treatment varied between sites according to variations in the subsequent development of aphid populations under varying weather conditions and differential pressures from aphid natural enemies. 4 Alpha‐cypermethrin treatment reduced spider density at most sites, and also resulted in a resurgence of aphid populations at three sites.     

Relative importance of long‐term changes in climate and land‐use on the phenology and abundance of legume crop specialist and generalist aphids

Abstract Insect populations are prone to respond to global changes through shifts in phenology, distribution and abundance. However, global changes cover several factors such as climate and land-use, the relative importance of these being largely unknown. Here, we aim at disentangling the effects of climate, land-use, and geographical drivers on aphid abundance and phenology in France, at a regional scale and over the last 40 years. We used aerial data obtained from suction traps between 1978 and 2015 on five aphid species varying in their degree of specialization to legumes, along with climate, legume crop area and geographical data. Effects of environmental and geographical variables on aphid annual abundance and spring migration dates were analyzed using generalized linear mixed models. We found that within the last four decades, aphids have advanced their spring migration by a month, mostly due to the increase in temperature early in the year, and their abundance decreased by half on average, presumably in response to a combination of factors. The influence of legume crop area decreased with the degree of specialization of the aphid species to such crops. The effect of geographical variation was high even when controlling for environmental variables, suggesting that many other spatially structured processes act on aphid population characteristics. Multifactorial analyses helped to partition the effects of different global change drivers. Climate and land-use changes have strong effects on aphid populations, with important implications for future agriculture. Additionally, trait-based response variation could have major consequences at the community scale.     

Grain aphid population structure: no effect of fungal infections in a 2-year field study in Denmark

1 Sitobion avenae (F.) is a serious pest in Danish cereal crops. To understand the population genetic structure, aphids were sampled in seven different winter wheat (Triticum sativum Lamarck) fields throughout Denmark. The aphids were genotyped with seven microsatellite markers. In total, 2075 aphids were collected and 1203 of these were genotyped. 2 The Danish S. avenae populations displayed very high genotypic diversity, high percentages of unique genotypes and low linkage disequilibria; this is likely to be a result of genetic recombination encompassed by their holocyclic lifestyle. The populations showed very limited differentiation and no sign of isolation by distance. Almost all the genetic variation was ascribed within the populations rather than between populations, probably due to a high migration rate at approximate 10% per generation. 3 Seasonal changes in clonal diversity and distribution of asexual summer generations of S. avenae within the infestation period in a single winter wheat field were followed over two consecutive years by weekly sampling from 60 plots each of 20 × 20 m. Clonal diversity was high in all samples with no dominant clonal lineages and no significant difference in the genotypic diversity between weeks or between years. However, a temporal genetic differentiation effect, throughout the infestation, suggests that selective factors or high temporal migration play an important role in shaping the genetic structure S. avenae. 4 Analyses of fungal infected and uninfected aphids were performed to test whether some clonal linage were more often infected by fungi from the Entomophthorales under field conditions. In total, 54 progeny from aphids with Entomophthorales were genotyped and compared with 422 uninfected aphid genotypes. The Entomophthorales‐infected aphid genotypes did not cluster out together, suggesting that these fungal pathogens did not affect the population differentiation or clonal distribution of S. avenae in a Danish agroecosystem. 5 Our findings indicate that S. avenae populations can be controlled using conservation biological control     

Forecasting migration of cereal aphids (Hemiptera: Aphididae) in autumn and spring

The migration of cereal aphids and the time of their arrival on winter cereal crops in autumn and spring are of particular importance for plant disease (e.g. barley yellow dwarf virus infection) and related yield losses. In order to identify days with migration potentials in autumn and spring, suction trap data from 29 and 45 case studies (locations and years), respectively, were set‐off against meteorological parameters, focusing on the early immigration periods in autumn (22 September to 1 November) and spring (1 May to 9 June). The number of cereal aphids caught in a suction trap increased with increasing temperature, global radiation and duration of sunshine and decreased with increasing precipitation, relative humidity and wind speed. According to linear regression analyses, the temperature, global radiation and wind speed were most frequently and significantly associated with migration, suggesting that they have a major impact on flight activity. For subsequent model development, suction trap catches from different case studies were pooled and binarily classified as days with or without migration as defined by a certain number of migrating cereal aphids. Linear discriminant analyses of several predictor variables (assessed during light hours of a given day) were then performed based on the binary response variables. Three models were used to predict days with suction trap catches ≥1, ≥4 or ≥10 migrating cereal aphids in autumn. Due to the predominance of Rhopalosiphum padi individuals (99.3% of total cereal aphid catch), no distinction between species (R. padi and Sitobion avenae) was made in autumn. As the suction trap catches were lower and species dominance changed in spring, three further models were developed for analysis of all cereal aphid species, R. padi only, and Metopolophium dirhodum and S. avenae combined in spring. The empirical, cross‐classification and receiver operating characteristic analyses performed for model validation showed different levels of prediction accuracy. Additional datasets selected at random before model construction and parameterization showed that predictions by the six migration models were 33–81% correct. The models are useful for determining when to start field evaluations. Furthermore, they provide information on the size of the migrating aphid population and, thus, on the importance of immigration for early aphid population development in cereal crops in a given season.     

Evidence for gene flow and local clonal selection in field populations of the grain aphid (Sitobion avenae) in Britain revealed using microsatellites

Samples of the grain aphid, Sitobion avenae (F.), a major European pest of cereals, were collected in June and July 1997 from fields sown with winter wheat in a rough transect south-west of Rothamsted, UK. These aphids were genotyped at four microsatellite loci known from previous studies to be highly polymorphic. Allelic frequencies were similar between samples collected in the fields and in the 12.2 m high suction trap at Rothamsted, and there were many widespread genotypes (clones), providing evidence that the species is highly migratory. However, field samples were found to display a high level of genotypic heterogeneity (= variable clonal composition), most probably the result of clonal selection. The suction trap genotypes sample were slightly different from the field samples, indicative of the inclusion of genotypes from plant hosts (cereals and grasses, Poaceae) other than winter wheat and/or genotype-biased emigration from the field. The relevance of these data to modelling of aphid outbreaks is briefly discussed.     

小麦蚜虫田间调查及监测技术

小麦蚜虫是世界范围内小麦生产中一类重要害虫。针对麦蚜世代历期短、繁殖力强,具有趋光、趋化及迁飞等生物学及行为习性;在田间多呈聚集分布,且麦蚜易受寄主植物抗性、天敌、气象因素及农田生态条件等生物与非生物因素影响等发生为害特点,本文阐述了我国小麦蚜虫田间调查、监测技术及防治策略,以期为我国小麦蚜虫综合防控提供基础科学支撑。     

Quantifying the impact of polyphagous invertebrate predators in controlling cereal aphids and in preventing wheat yield and quality reductions

Exclusion barriers were used to manipulate numbers of polyphagous invertebrate predators so that their impact on cereal aphids and consequently wheat yield and quality could be examined. Experiments were conducted within the framework of the LINK Integrated Farming Systems Project which allowed comparisons to be made between the integrated and conventional farming systems under examination on a study farm in Hampshire, UK. Only in 1995 were the numbers of aphids per tiller, the aphid peak and rate of increase to the peak significantly greater in the exclusion areas where the density of polyphagous predators had been reduced. The maximum increase in aphids as a result of excluding polyphagous predators was 31%, which was equivalent to 130 aphid days. However, the polyphagous predators did not reduce the number of tillers infested. The relatively low impact of polyphagous predators was attributed to the aphid population phenology and greater effects may have been found had aphids infested the crops earlier in their development. Sowing date was shown to govern the time over which a crop may be susceptible to yield loss from aphids, with later-drilled crops being more susceptible to late-summer aphid infestations. Aphid numbers rarely affected grain yield but were found to be related to some grain quality parameters, but reducing polyphagous predators had no direct impact on grain yield or quality even where the aphid burden increased. The peak period of activity and density differed between the species of Carabidae, Staphylinidae and Araneae consequently influencing their relationship with the aphids. Some negative correlations were found between these groups of polyphagous predators and aphids. Species composition and abundance differed between fields thereby influencing the level of aphid predation. The exclusion barriers were most effective at reducing numbers of Carabidae although numbers of Staphylinidae and Araneae were also reduced. The consequences for Integrated Crop Management are discussed.     

Assessment of cotton aphids, Aphis gossypii, and their natural enemies on aphid-resistant and aphid-susceptible wheat varieties in a wheat–cotton relay intercropping system

The cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), is an important cotton pest in northern China, especially in the seedling stage of cotton. After large scale commercial use of transgenic Bt cotton, cotton aphids became one of the most important cotton pests. A 2‐year study was conducted to evaluate the role of four winter wheat varieties that were resistant or susceptible to wheat aphid, Sitobion avenae Fabricius (Homoptera: Aphididae), in conserving arthropod natural enemies and suppressing cotton aphids in a wheat–cotton relay intercropping system in northern China. The results indicated that wheat–cotton intercropping preserved and augmented natural enemies more than a monoculture of cotton. The density of natural enemies in cotton was significantly different among relay‐intercropping fields with different wheat varieties. The highest density of natural enemies and low cotton aphid populations were found in the treatment of cotton in relay intercropped with the wheat variety Lovrin10, which is susceptible to wheat aphid. The lowest density of predators and parasitoids associated with high cotton aphid populations were found with the wheat variety KOK1679, which is resistant to wheat aphid. The results showed that wheat varieties that are susceptible or moderately resistant to wheat aphid might reduce cotton aphids more effectively than an aphid‐resistant variety in the intercropping system by enhancing predators to suppress cotton aphids during the cotton seedling stage.     

Timing of dispersal: effect of ants on aphids

Mutualists can affect many life history traits of their partners, but it is unclear how this translates into population dynamics of the latter. Ant–aphid associations are ideal for studying this question, as ants affect aphids, both positively (e.g., protection against natural enemies) and negatively (e.g., reduction of potential growth rates). The unresolved question is whether these effects, which have been observed at the level of individuals and under controlled environmental conditions, have consequences at the population level. On estimating aerial aphid populations by using weekly suction trap data spanning up to 22 years from different locations in France, we show that in ant-attended aphid species long-distance dispersal occurs significantly later, but that the year-to-year changes in the peak number of migrants are not significantly lower than for non-attended aphids. Host alternation had the same retarding effect on dispersal as ant attendance. We discuss the delay in the timing of dispersal in ant-attended aphids, and potential costs that arise in mutualistic systems.     

EVOLUTION OF AN APHID-PARASITOID INTERACTION: VARIATION IN RESISTANCE TO PARASITISM AMONG APHID POPULATIONS SPECIALIZED ON DIFFERENT PLANTS

The evolution of associations between herbivorous insects and their parasitoids is likely to be influenced by the relationship between the herbivore and its host plants. If populations of specialized herbivorous insects are structured by their host plants such that populations on different hosts are genetically differentiated, then the traits affecting insect-parasitoid interactions may exhibit an associated structure. The pea aphid (Acyrthosiphon pisum) is a herbivorous insect species comprised of genetically distinct groups that are specialized on different host plants (Via 1991a, 1994). Here, we examine how the genetic differentiation of pea aphid populations on different host plants affects their interaction with a parasitoid wasp, Aphidius ervi. We performed four experiments. (1) By exposing pea aphids from both alfalfa and clover to parasitoids from both crops, we demonstrate that pea aphid populations that are specialized on alfalfa are successfully parasitized less often than are populations specialized on clover. This difference in parasitism rate does not depend upon whether the wasps were collected from alfalfa or clover fields. (2) When we controlled for potential differences in aphid and parasitoid behavior between the two host plants and ensured that aphids were attacked, we found that pea aphids from alfalfa were still parasitized less often than pea aphids from clover. Thus, the difference in parasitism rates is not due to behavior of either aphids or wasps, but appears to be a physiologically based difference in resistance to parasitism. (3) Replicates of pea aphid clones reared on their own host plant and on a common host plant, fava bean, exhibited the same pattern of resistance as above. Thus, there do not appear to be nutritional or secondary chemical effects on the level of physiological resistance in the aphids due to feeding on clover or alfalfa, and therefore the difference in resistance on the two crops appears to be genetically based. (4) We assayed for genetic variation in resistance among individual pea aphid clones collected from clover fields and found no detectable genetic variation for resistance to parasitism within two populations sampled from clover. This is in contrast to Henter and Via's (1995) report of abundant genetic variation in resistance to this parasitoid within a pea aphid population on alfalfa. Low levels of genetic variation may be one factor that constrains the evolution of resistance to parasitism in the populations of pea aphids from clover, leading them to remain more susceptible than populations of the same species from alfalfa.     

Temporal variability of aphid biological control in contrasting landscape contexts

Landscape complexity may provide ecosystem services to agriculture through the provision of natural enemies of agricultural pests. Strong positive effect of adjacent semi-natural habitats on natural enemies in croplands has been evidenced, but the resulting impact on biological control remains unclear. Taking into account the temporal dynamics of pest and natural enemies in agricultural landscapes provides better resolution to the studies and better understanding of the biological control service.In this study, the population dynamics of aphids and two groups of predators (coccinellid and carabid beetles) were examined. Insects were sampled in 20 wheat fields, surrounded by structurally simple and complex landscapes in Chilean central valley. Considering the whole sampling period, the diversity of aphids and natural enemies were similar in wheat crops surrounded by both types of landscapes, and the abundance of ladybirds was higher in crops in the complex landscapes. The dynamics of predators was more advanced in complex landscapes than in the simple ones, whereas the dynamics of aphids were similar in both types of landscape. Negative correlation between abundance of predators and aphid population growth rate in both landscape contexts were observed suggesting a control of the pest population by the predators. Different temporal patterns were observed in these correlations in the two landscape contexts, which suggests differences in the biological control related to the landscape composition.The present study shows that colonization of crops by natural enemies occurs sooner in structurally complex landscapes and suggests that this early colonization may facilitate an early and efficient control of aphid populations, nevertheless the biological control efficiency seems to be higher in structurally simple landscapes later in the season.     

Measuring and modelling the effects of inoculation date and aphid flights on the secondary spread of Beet mosaic virus in sugar beet

The effect of the inoculation date on the spread of Beet mosaic virus (BtMV) in sugar beet field plots was studied. Two plants in the centre of each plot were inoculated with BtMV using Myzus persicae. The spread of the infection around these sources was monitored by inspecting the plants on two diagonal transects through the centre of the plot. Early inoculations resulted in a greater spread than late inoculations, but any inoculation before the onset of the aphid migration resulted in a similar‐sized spread. The spread was concentrated in patches around the inoculated plants, and its rate was explained by vector pressure, as shown by regression analysis and a mechanistic simulation model. This vector pressure was quantified using data obtained by catching aphids in a green water trap in the crop, catching aphids in a 12 m high suction trap at a distant location, and infection of bait plants from adjacent virus source plants. The daily total aphid catches obtained by a suction trap provided the best statistical explanation for the spread of this virus. The parameter r, describing the relationship between vector pressure and the rate of disease progress, was remarkably robust. This parameter varied less than 10% between treatments (infection date) within a single experiment, and less than a factor two between four experiments performed at different sites in two years. The robustness of this parameter suggests that the spread of a potyvirus may be predicted on the basis of the initial infection date and vector abundance.     

Genotypic diversity of the cotton-melon aphid Aphis gossypii (Glover) in Tunisia is structured by host plants

The study of intraspecific variation with respect to host plant utilization in polyphagous insects is crucial for understanding evolutionary patterns of insect-plant interactions. Aphis gossypii (Glover) is a cosmopolitan and extremely polyphagous aphid species. If host plant species or families constitute selective regimes to these aphids, genetic differentiation and host associated adaptation may occur. In this study, we describe the genetic structure of A. gossypii collected in six localities in Tunisia on different vegetable crops, on citrus trees and on Hibiscus. The aim was to determine if the aphid populations are structured in relation to the host plants and if such differentiation is consistent among localities. The genetic variability of A. gossypii samples was examined at eight microsatellite loci. We identified only 11 multilocus genotypes among 559 individuals. Significant deviations from Hardy-Weinberg equilibrium, linkage disequilibria and absence of recombinant genotypes, confirmed that A. gossypii reproduces by continuous apomictic parthenogenesis. Genetic differentiation between localities was not significant, whereas a strong differentiation was observed between host plant families (0.175相似文献