Cereal Aphid Populations Research Articles

Characterisation of aphid antixenosis in aphid-resistant ancestor wheat, Triticum monococcum.

Due to the increasing presence of insecticide resistance across cereal aphid populations, new aphid management strategies, including the engineering of host resistance to aphids into commercial wheat varieties, are required. Previous studies have identified ancestor wheat, Triticum monococcum accessions MDR045 and MDR049, with resistance against the grain aphid, Sitobion avenae. To test the hypothesis that resistance can be accounted for by antixenosis (reduced attractiveness of host plants) via the release of repellent volatile organic compounds (VOCs), we explored the response of S. avenae to MDR045 and MDR049 following S. avenae herbivory, using behaviour and electrophysiology experiments. In four-arm olfactometry assays, alate S. avenae showed aphid density-dependent reduced preference to VOC extracts from T. monococcum MDR045 and MDR049. By contrast, alate S. avenae showed aphid density-dependent increased preference to extracts from aphid-susceptible hexaploid wheat, Triticum aestivum var. Solstice and T. monococcum MDR037. Coupled gas chromatography-electroantennography (GC-EAG), using the antennae of alate S. avenae, located 24 electrophysiologically active compounds across all tested accessions. Synthetic blends created from 21 identified EAG-active compounds confirmed bioactivity of corresponding VOC extracts in four-arm olfactometry assays against alate S. avenae. Our data suggest that resistance of T. monococcum MDR045 and MDR049 to S. avenae can be at least partially accounted for by antixenosis through antennal perception of specific repellent VOC blends induced by S. avenae feeding behaviour. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Seasonal dynamics of cereal aphid population

Goal. To compare the seasonal dynamics of cereal aphid abundance in the Steppe and Forest-Steppe zones during 2023 and to determine the factors that influenced it. Methods. To assess the state of the cereal aphid population on cereal crops, we used the results of personally conducted entomological phytosanitary monitoring of crops (according to generally accepted methods) in the farms of the Steppe and Forest-Steppe zones; information from current reports from the places where field experiments were conducted directly by the forecasting laboratory, as well as other laboratories of the IPP of NAAS, which is also confirmed by the materials of decadal reports of regional plant protection stations and signalization and forecasting points of the State Inspection of Plant Protection, confirmed by information on the phytosanitary status of regional state research stations. Cereal aphid adults and larvae were counted in populations of populations (in the crop phase, the end of the tube emergence is earing). Results. The state of cereal aphid populations on crops of cereal spiked crops in 2023 was studied, both in general in Ukraine and separately in the Steppe and Forest-Steppe zones. The dynamics of their number in farms of different natural and climatic zones was investigated, and an analysis of its peculiarities in the conditions of the year was carried out. Conclusions. In 2023, the harmfulness of cereal aphids on cereal crops remained at the level of long-term averages. The expansion of their harmful zone and an increase in their number was noted during the earing period (milk ripeness). On winter cereal crops, phytophages prevailed in the Steppe zone. In the Forest-Steppe zone, the phytophage was more damaging to winter cereals than to spring cereals. The results of entomological monitoring in Mykolaiv region (State Enterprise «Experimental Farming «Zori nad Bugom») showed that during the accounting period the bulk of aphids were concentrated on winter wheat crops, and winter barley was damaged in small numbers. On the contrary, the surveys conducted in Kyiv region (State Enterprise «Experimental Farming «Salyvonkivske») showed that in the second half of June — the first decade of July, the number of aphids on spring barley crops was approximately twice as high as on spring wheat. As a result of the study, it was practically confirmed that the optimal temperature regime for the development of cereal aphids is 16—20°C, and the relative humidity is 60—80%.

Aphid parasitism in winter wheat fields in a heterogeneous agricultural landscape.

The number, timing, and fitness of colonizing parasitoids in fields of ephemeral crops often depend on factors external to the fields. We investigated cereal aphid parasitism in 23 winter wheat fields using sentinel plants infested with bird cherry-oat aphids, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), and we investigated the effect of parasitoids on cereal aphid population growth using exclusion and parasitoid-accessible cages infested with bird cherry-oat aphids. Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae), Aphelinus nigritus (Howard) (Hymenoptera: Aphelinidae),and Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae), in decreasing order of abundance, parasitized R. padi on sentinel plants. The mean percent parasitism in parasitoid-accessible cages was 5.2% in autumn and 35.0% in spring. Aphid population intensity was greater in complete exclusion than in parasitoid-accessible cages. Measures of landscape composition and configuration were quantified, and aphid parasitism in autumn by L. testaceipes and A. nigritus was positively associated with % landcover by summer crops and patch density. Parasitism by both species was negatively associated with contagion and % woodlands. Parasitism during spring was positively associated with % grassland and fractal dimension and negatively associated with % canola. The number of braconid mummies per sentinel plant was positively correlated to the number of braconid mummies on wheat stems from parasitoid-accessible cages. Results indicate that cereal aphid mortality caused by parasitoids and their ability to exert effective biological control is related to landscape structure. Comparing this study to an earlier study in the same agroecosystem demonstrated temporal stability of the landscape influence on aphid parasitism by L. testaceipes in winter wheat.

Spatio-temporal Influences on Cereal Aphid (Hemiptera: Aphididae) Population Dynamics and the Incidence of Barley Yellow Dwarf Virus.

Problems with aphids in small grain cereals, either direct by feeding, or indirect by transmission of Barley Yellow Dwarf Virus, are expected to increase due to climate change and a recent ban on neonicotinoid seed treatments by the European Union. Moreover, insecticide resistance against pyrethroid insecticides is reported at multiple locations throughout the world. Therefore, a better understanding of cereal aphid population dynamics and increased attention towards an integrated pest management is needed. In this study, cereal aphids were monitored on 193 maize and small grain cereal fields throughout Flanders, Belgium. The population dynamics and species distribution were observed throughout the year and the effects of spatio-temporal variables were explored. A significant negative effect was found of grassland in a 1,000 m radius and a positive effect of grain maize in a 3,000 m radius around a small grain cereals field on the maximum infestation rate with aphids in autumn within this field. In a 3,000 m and 5,000 m radius, a significant positive effect of grain maize and a significant negative effect of other small grain cereals was found on the maximum infestation rate during the whole growing season within this field. The mean daily average temperature from 118 to 19 d before sowing had a significant positive effect on the maximum infestation rate in autumn. Mean precipitation, wind speed, and humidity from 52 to 26, 46 to 23, and 107 to 13 d before sowing respectively, had a significant negative effect on the maximum infestation rate in autumn.

Genetic Diversity and Gene Flow Observed in Two Cereal Aphid (Hemiptera: Aphididae) Species and Populations in the Chinese Corn Belt Region

Abstract The cereal aphids, Rhopalosiphum maidis (Fitch) and Rhopalosiphum padi (L.) (Hemiptera: Aphididae), are serious pests of maize, Zea mays L., globally. Basic information about the genetic structure of these aphids is unknown. We, therefore, estimated the genetic diversity and genetic flow from partial fragments of the mitochondrial cytochrome oxidase I gene collected from different geographic populations of aphids throughout the Songliao Plain of northeastern China. Our analysis of a 425-bp sequence on 297 R. maidis and 287 R. padi individuals revealed 17 and 3 variable sites, respectively. Fifteen haplotypes were obtained among the R. maidis populations, and only haplotype RM1 was shared. Three shared haplotypes were obtained among the R. padi populations. No obvious geographical trends were detected based on the haplotype network and neighbor-joining tree. Relatively low haplotype diversity indices were observed in the R. maidis populations (haplotype diversity [Hd] = 0.14207, average number of nucleotide differences [K] = 0.17340, and nucleotide diversity [Pi] = 0.00041), whereas relatively high haplotype diversity indices were observed in the R. padi populations (Hd = 0.53249, K = 1.46614, and Pi = 0.00345). There was moderate gene flow (number of migrants [Nm] = 2.33) among R. maidis populations, but there was low gene flow (Nm = 0.82) among R. padi populations. Analysis of molecular variance showed high genetic differentiation within populations. Genetic distance and geographic distance were not significantly associated according to the Mantel test. The results suggest that the difference in the aphids' existence strategies has resulted in a different mitochondrial evolution pattern in the Songliao Plain region, and they provide a foundation for accurately forecasting systems against this pest.

Moderately decreasing fertilizer in fields does not reduce populations of cereal aphids but maximizes fitness of parasitoids

Examination of the tradeoff between the extent of decreasing nitrogen input and pest suppression is crucial for maintaining the balance between essential yield and an efficient, sustainable pest control strategy. In this study, an experiment with four manipulated nitrogen fertilizer levels (70, 140, 210, and 280 kg N ha−1 = conventional level) was conducted to explore the effects of decreasing nitrogen on cereal aphids (Sitobion avenae and Rhopalosiphum padi) (Hemiptera: Aphididae), Aphidiinae parasitoids (Hymenoptera: Braconidae: Aphidiinae), and body sizes of parasitoids. The results indicated that nitrogen application, in the range of 70–280 kg N ha−1, has the potential to impact the populations of cereal aphids and their parasitoids. However, both differences between densities of cereal aphids and their parasitoids in moderate (140–210 kg N ha−1) and those in high nitrogen input (280 kg N ha−1) were not significant, and the parasitism rate was also unaffected. A higher parasitism rate reduced population growth of the cereal aphid (S. avenae). Additionally, a moderate decrease of nitrogen fertilizer from 280 to 140–210 kg N ha−1 maximized the body sizes of Aphidiinae parasitoids, indicating that a moderate decrease of nitrogen fertilizer could facilitate biocontrol of cereal aphid by parasitoids in the near future. We conclude that a moderate decrease in nitrogen application, from 280 to 140–210 kg N ha−1, does not quantitatively impact the densities of cereal aphids or the parasitism rate but can qualitatively maximize the fitness of the parasitoids.

Drought Stress and Nitrogen Fertilization Affect Cereal Aphid Populations in Wheat Fields

Water stress and nitrogen deficiency are two constraints that negatively affect growth and productivity of wheat plants. Moreover, the interaction between these two stresses could affect the susceptibility of wheat plants to insect attack. In order to examine the influence of drought stress and nitrogen fertilization on piercing-sucking insect pests, the population abundance of four cereal aphid species; English grain aphid Sitobion avenae, wheat aphid Schizaphis graminum, Bird cherry-oat aphid Rhopalosiphum padi, and corn leaf aphid Rhopalosiphum maidis has been monitored in two water treatments (water stress and well-watered) and two nitrogen levels (120 and 180 kg N ha-1). Results revealed that S. graminum was the most dominant specie in all treatments, followed by S. avenae. The population of all aphids tends to increase in the second half of the season coinciding with the emergence of wheat spikes. Stressed-wheat plants attracted more aphids, especially when water deficit synchronizes with an increase in N fertilization. Aphids vigorously thrive better on stressed plants amended with high nitrogen level. Contrary, the lower infestation rate was observed in well-watered plots with lower nitrogen rate. Plant characteristics, such as days to heading, plant height, and chlorophyll content were significantly decreased in drought-stressed plants, while higher N rates increased such parameters. Grain yield and its components were reduced with drought stress and reduced nitrogen fertilization. The current study advocates avoiding severe drought concurrently with an increasing in nutritional augmentation which it might contribute in an increase in insect pest infestation and decreasing in wheat plant traits.

A large-scale field study of bacterial communities in cereal aphid populations across Morocco.

Insects are frequently associated with bacteria that can have significant ecological and evolutionary impacts on their hosts. To date, few studies have examined the influence of environmental factors to microbiome composition of aphids. The current work assessed the diversity of bacterial communities of five cereal aphid species (Sitobion avenae, Rhopalosiphum padi, R. maidis, Sipha maydis and Diuraphis noxia) collected across Morocco, covering a wide range of environmental conditions. We aimed to test whether symbiont combinations are host or environment specific. Deep 16S rRNA sequencing enabled us to identify 17 bacterial operational taxonomic units (OTUs). The obligate symbiont Buchnera aphidicola was represented by five OTUs with multiple haplotypes in many single samples. Facultative endosymbionts were presented by a high prevalence of Regiella insecticola and Serratia symbiotica in S. avenae and Si. maydis, respectively. In addition to these symbiotic partners, Pseudomonas, Acinetobacter, Pantoea, Erwinia and Staphyloccocus were also identified in aphids, suggesting that the aphid microbiome is not limited to the presence of endosymbiotic bacteria. Beside a significant association between host species and bacterial communities, an inverse correlation was also found between altitude and α-diversity. Overall, our results support that symbiont combinations are mainly host specific.

Багаторічна динаміка щільності стану розвитку міжвидових популяцій злакових попелиць (Homoptera, Aphididae) упродовж вегетації пшениці озимої в умовах Лісостепу України

Багаторічна динаміка щільності стану розвитку міжвидових популяцій злакових попелиць (Homoptera, Aphididae) упродовж вегетації пшениці озимої в умовах Лісостепу України

Do natural enemies really make a difference? Field scale impacts of parasitoid wasps and hoverfly larvae on cereal aphid populations

Naturally occurring predators and parasitoids are known to reduce the abundance of pest invertebrates in arable crops, yet current treatment thresholds do not account for such a contribution to pest management. In the present study, we provide evidence for the presence of natural enemies correlating with a subsequent reduction in pest population growth. The abundance of cereal aphid pests and two key aphidophagous natural enemies, parasitoid wasps (Aphidiinae) and hoverfly larvae (Syrphinae), was assessed at field boundaries and interiors in southeast England. The highest rate of aphid population growth was associated with locations where no natural enemies were found. The presence of either Aphidiinae wasps or predatory Syrphinae larvae was associated with a reduction in the rate of aphid population growth, irrespective of location within the field, and overall aphid population growth was negatively correlated with increasing natural enemy abundance. The results of the present study indicate that natural enemies contribute significantly to pest control, and provide further evidence supporting the use of management strategies for promoting natural enemies in agro-ecosystems. Aphid predators and parasitoids make an important contribution to aphid pest control within cereal fields, and thresholds for insecticide application should account for this to avoid unnecessary treatments.

Shifts in natural enemy assemblages resulting from landscape simplification account for biocontrol loss in wheat fields

AbstractIn recent decades, landscape simplification due to agricultural intensification has resulted in biocontrol loss within agroecosystems leading to an increase in pest outbreaks. Empirical experiments have focused on the relationship between landscape pattern and the abundance of specific species. However, fewer studies have examined the varied responses of multiple natural enemy modules to landscape simplification. In the present study, 23 landscapes were examined to determine the effects of landscape simplification on cereal aphids and their natural enemies. Results showed that landscape simplification can increase cereal aphid populations with no significant effects on the total abundance of natural enemies. For each natural enemy module, it was found that the abundance of parasitic wasps was greatly increased by landscape simplification while the abundance of ground‐dwelling predators was significantly reduced. In contrast, the abundance of leaf‐dwelling predators was not significantly altered by landscape simplification. Therefore, the varied response of the three natural enemy modules to landscape simplification can result in major fluctuations in natural enemy–pest ratios and ultimately disrupt the top‐down control of natural predators and biocontrol services within agroecosystems. In conclusion, quantitative food‐web analysis could be a promising technique in clarifying the varied response of the three natural enemy modules to landscape pattern changes and species‐specific abundance, a field of biological pest control that requires further study.

The role of natural enemy foraging guilds in controlling cereal aphids in Michigan wheat.

Insect natural enemies (predators and parasitoids) provide important ecosystem services by suppressing populations of insect pests in many agricultural crops. However, the role of natural enemies against cereal aphids in Michigan winter wheat (Triticum aestivum L.) is largely unknown. The objectives of this research were to characterize the natural enemy community in wheat fields and evaluate the role of different natural enemy foraging guilds (foliar-foraging versus ground-dwelling predators) in regulating cereal aphid population growth. We investigated these objectives during the spring and summer of 2012 and 2013 in four winter wheat fields on the Michigan State University campus farm in East Lansing, Michigan. We monitored and measured the impact of natural enemies by experimentally excluding or allowing their access to wheat plants infested with Rhopalosiphum padi (L.) and Sitobion avenae (F.) (Hemiptera: Aphidae). Our results indicate that the natural enemy community in the wheat fields consisted mostly of foliar-foraging and ground-dwelling predators with relatively few parasitoids. In combination, these natural enemy groups were very effective at reducing cereal aphid populations. We also investigated the role of each natural enemy foraging guild (foliar-foraging versus ground-dwelling predators) independently. Overall, our results suggest that, in combination, natural enemies can almost completely halt early-season aphid population increase. Independently, ground-dwelling predators were more effective at suppressing cereal aphid populations than foliar-foraging predators under the conditions we studied. Our results differ from studies in Europe and the US Great Plains where foliar foraging predators and parasitoids are frequently more important cereal aphid natural enemies.

Nitrogen supply in conventional versus organic farming systems: effects on the performance of cereal aphids

Cereal aphids (Homoptera: Aphididae) are a periodical threat to winter wheat (Triticum aestivum L.) production worldwide, and outbreaks have been mainly related to increasing inputs of mineral fertilizers. The hypothesis of lower aphid abundance under organic fertilizer treatments, however, has not been tested at the species-specific level. In a 4-year study, we examined cereal aphid populations and plant parameters (dry biomass and nitrogen content) in winter wheat fields under low (legume-based), intermediate (legume-based plus organic liquid manure), and high (mineral) nitrogen intensities; low and intermediate intensities are characteristic of organic fields, while high intensities are inherent in conventional farming systems. Aphid species differed markedly in their response to fertilizer treatment. Unexpectedly, legume-based organic fields were related to higher abundances of the ear-colonizing species Sitobion avenae (F.), whereas manure-fertilized organic fields and conventional fields had significantly higher abundances of Metopolophium dirhodum (Wlk.) and Rhopalosiphum padi (L.). Nitrogen concentration of winter wheat increased with fertilizer intensity, and total aphid abundance (all species) was positively correlated with nitrogen content of grains in manure-fertilized organic fields and conventional fields, but was not correlated in legume-based organic fields dominated by S. avenae (89–96 % of the aphid community). Collectively, we demonstrate strong bottom-up effects that result in an improved performance of S. avenae in low-input systems. As total aphid abundance (all species) simultaneously decreased in legume-based organic fields, crop managers risk to underestimate pest damage by ignoring the impact of a single species, S. avenae, which has the greatest potential to reduce crop yield.

Generalist predators disrupt parasitoid aphid control by direct and coincidental intraguild predation

Generalist predators and parasitoids are considered to be important regulators of aphids. The former not only feed on these pests, but might also consume parasitoids at all stages of development. This direct or coincidental interference affects the natural control of aphids, the scale of which is largely unknown, and it has rarely been examined under natural conditions. Here, molecular diagnostics were used to track trophic interactions in an aphid-parasitoid-generalist predator community during the build-up of a cereal aphid population. We found that generalist predators, principally carabid and staphylinid beetles as well as linyphiid spiders, had strong trophic links to both parasitoids and aphids. Remarkably, more than 50% of the parasitoid DNA detected in predators stems from direct predation on adult parasitoids. The data also suggest that coincidental intraguild predation is common too. Generalist predators, hence, disrupt parasitoid aphid control, although the levels at which the predators feed on pests and parasitoids seem to vary significantly between predator taxa. Our results suggest that taxon-specific trophic interactions between natural enemies need to be considered to obtain a more complete understanding of the route to effective conservation biological control.

Spatial distribution of flower vs. honeydew resources in cereal fields may affect aphid parasitism

The potential impact of nectar availability for biological pest control is of increasing relevance due to the disappearance of non-crop plants in intensified agricultural landscapes. However, little is known about how floral resources and their spatial distribution in and around crop fields influence cereal aphid parasitoid (Hymenoptera, Aphidiidae) survival and population dynamics. Cereal aphid parasitoids may be less dependent on flowers as they can use honeydew from their aphid hosts as an alternative food resource. However, honeydew appears to be less suitable as a food source for parasitoids when compared to nectar. Here the effects of flower distribution (nectar), aphid abundance (honeydew quantity) and honeydew quality on parasitoid life history parameters were explored using a spatially explicit, individual-based simulation model. In addition, effects of the availability of floral resources in field margins on parasitism levels in winter wheat were investigated in a field study. In the simulation study three flower distributions were compared: (i) flowers restricted to the field margin (most common in agricultural landscapes) or (ii) flowers in strips within the crop, and (iii) random flower distribution in the field. Simulations suggest that nectar feeding increases parasitoid longevity and parasitism at low aphid densities, but only in fields with randomly distributed flowers. In contrast, the spatial distribution of flowers did not affect the parasitoid longevity and parasitism rate at high aphid densities, where parasitoid feeding was restricted to the abundant honeydew resources. In simulations, parasitoid survival and the number of aphids parasitized were also affected by the nutritional quality of the honeydew, with low quality honeydew having a less positive effect on parasitoid longevity and parasitism rate. The field study did not indicate evidence of a significant relationship between flower cover in field margins and parasitism rates in wheat near the margins. This finding is compatible with results from simulations and suggests that honeydew feeding is more prevalent in cereal aphid parasitoids than nectar feeding. In conclusion, nectar may be an important factor for the potential biocontrol success of cereal aphid parasitoids, but most likely only at low aphid densities and especially when flowers are broadly distributed in the field.

Comparison and validation of population models for cereal aphids

Models used to simulate changes in populations of cereal aphids need to be compared and validated if they are ever to be improved sufficiently for wide-scale use in crop protection. With this in mind, simulation runs using the models SIMLAUS, LAUS, and GETLAUS01 were tested over several years using data collected in different regions of Germany. The numbers of cereal aphids and aphid antagonists were recorded in fields of winter wheat and winter barley, by the adapting number of samples to aphid density. Simulation runs with the model SIMLAUS predicted accurately (96% of case studies, e.g. location and years) the type of hibernation of Sitobion avenae and Rhopalosiphum padi in fields of both winter wheat and winter barley. In eight of 52 case studies, from different locations and different years, the model predicted anholocyclic hibernation, though overwintering aphids were not found in the field. The model SIMLAUS was not suitable for predicting the number of aphids found in cereal crops in the autumn. In 12 of 35 case studies, the model LAUS predicted accurately (R² > 0.44,P 0.44,P < 0.05) between the observed and predicted populations of cereal aphids found during the summer in crops of winter wheat. Although the slopes of regressions differed from one in 12 of the case studies, all of the intercepts passed through the origin (a = 0). Correction of systematic errors, standardization of case studies, and possible model extensions are discussed with a view to using the revised models as an integral part of pest management.

Comparison of techniques to survey populations of cereal aphids (Homoptera: Aphididae) in winter cereals during autumn and spring with special consideration of sample size

Cereal aphid populations (Homoptera: Aphididae) in winter wheat and winter barley were evaluated in the autumn and early spring of two subsequent vegetation periods (2004/ 2005 and 2005/2006) by D-VAC mobile suction sampler, visual counts, and plant sampling in order to compare the efficiency of different cereal aphid survey techniques. Plant sampling (i.e. collecting whole plants from fields for evaluation in laboratory) generally detected the highest numbers of instars per m2 and enabled the most accurate aphid classifications while additionally permitting further laboratory analysis (e.g. immunosorbent assays). Visual counts (in situ) were most effective for producing quick, rough estimates of overall population density. D-VAC, which detected the lowest numbers of aphids/m2, was the least effective technique and was determined to be unsuitable for cereal aphid monitoring in autumn crops. Coefficients of variation confirmed this trend for the three sampling techniques. The minimum sample sizes required for estimation of aphid populations at different levels of precision (50%, 30%, 20% and 5%) were determined using different calculation methods (FENG and NOWIERSKI 1992; GREENWOOD and ROBINSON 2006) based on visual count data. The results of this study have important implications for the selection of appropriate techniques for surveying cereal aphid populations in winter wheat and winter barely in autumn and early spring.

Diapause and overwintering of the hoverflyEpisyrphus balteatus

AbstractThe overwintering biology of the hoverflyEpisyrphus balteatus(DeGeer) (Diptera: Syrphidae) was studied and analysed. In Europe, females of this species can overwinter as adults in a facultative, reproductive diapause. The diapause phase is characterized by the ovaries ceasing to develop and by hypertrophy of the fat body. Diapause was induced during the second and third larval instars. The critical photoperiod for inducing diapause was between 11.8 and 11.9 h, corresponding to the day lengths that occur during mid‐ to late September in Hannover, Germany. When temperatures were lower, insects could be induced into diapause at longer day lengths, similar to those that occur in early September in Hannover. A semifield study was done during the winter of 1999/2000 to confirm the results obtained under laboratory conditions and to obtain additional information on the over‐wintering development and mortality ofE. balteatus. The results suggested that mortality was correlated with the duration of the experiment and with humidity, rainfall, and temperature. The importance of these results for the regulation of cereal aphid populations by this hoverfly is discussed.

Using the output from global circulation models to predict changes in the distribution and abundance of cereal aphids in Canada: a mechanistic modeling approach

AbstractClimate change will alter the abundance and distribution of species. Predicting these shifts is a challenge for ecologists and essential information for the formation of public policy. Here, I use a mechanistic mathematical model of the interaction between grass growth physiology and aphid population dynamics, coupled with the climate change projections from the UK's Hadley Centre HadCM3 global circulation model (GCM) and Canada's Center for Climate Modeling and Analysis CGCM2 GCM to predict the changes in the abundance and distribution of summer cereal aphid populations in wheat‐growing regions of Canada. When used with the HadCM3 projections, the model predicts a latitudinal shift northward in abundances but there is longitudinal variation as well. However, when used with the CGCM2 projections the model predicts that continental regions will see a decline while coastal regions will see an increase in summer cereal aphid populations. These effects are stronger under the higher emissions scenarios.

Comparing growth patterns among field populations of cereal aphids reveals factors limiting their maximum abundance

Cereal stands in central Europe are commonly infested with three species of aphids that may become serious pests. With increasing abundance, the proportion of a particular species in the total aphid population may remain constant, suggesting a density-independent exponential growth, or the proportion can change, suggesting density-dependent constraints on growth. The constraints that affect particular species, and thus their relative abundance, were studied. The proportionality between maximum abundances of the cereal aphids was studied using a 10-year census of the numbers of aphids infesting 268 winter wheat plots. For two species their abundance on leaves and ears was compared. With increasing aphid density the maximum abundance of Rhopalosiphum padi (Linnaeus) remained proportional, but not that of Sitobion avenae (Fabricius), which was constrained by the smaller surface area of ears compared to leaves. There was no evidence of inter-specific competition. Maximum abundance of R. padi and Metopolophium dirhodum (Walker) on leaves did not change proportionally as the proportion of M. dirhodum decreased with increasing overall aphid density. This decrease was probably caused by the restricted distribution of M. dirhodum, which is confined to leaves, where space is limiting. No change in proportion between populations was detected when the average densities were below 0.54 aphids per leaf or ear. Non-proportional relationships between aphid populations appeared to be due to spatial constraints, acting upon the more abundant population. Detecting the limitation of population growth can help with the assessment of when density-independent exponential growth is limited by density-dependent factors. This information may help in the development of models of cereal aphid population dynamics.