Distribution Of Aphids Research Articles

Predatory activity and spatial pattern: the response of generalist carabids to their aphid prey

Summary The spatial distribution of cereal aphids infesting a field of winter wheat during the population establishment, development and decline phases were studied using a field‐scale grid of sampling locations. The distribution of two generalist predators, Pterostichus melanarius and P. madidus, were sampled contemporaneously. Using spatial analysis by distance indices (SADIE), spatial pattern in the aphid population, predator activity–density, predator hunger and aphid predation was detected and mapped. We tested the hypothesis that carabids and aphids were spatially associated with one another through predation. Aphid predation by individual beetles was detected using enzyme‐linked immunosorbent assays (ELISA) and hunger was assessed by measurement of foregut weights. Initially, there was a strong spatial dissociation between aphids and P. melanarius activity–density. While the aphid population was increasing there was a strong spatial association between aphids and both P. melanarius and P. madidus activity–density. During aphid population decline there was no measurable association between aphids and predatory activity–density. Predation of aphids was strongly locally associated with predator activity–density on all sample dates for both predator species, regardless of the association with aphid spatial pattern. Areas within the field most isolated from P. melanarius predation had the highest rates of aphid population increase. Although the proportion of P. melanarius individuals consuming aphids was much lower compared to P. madidus, it was concluded that it was a more effective biological control agent due to its comparative abundance.

Geographical location, climate and land use influences on the phenology and numbers of the aphid, Myzus persicae, in Europe

AbstractAim The purpose of this study was to improve understanding of the relationship between the spatial patterns of an important insect pest, the aphid Myzus persicae, and aspects of its environment. The main objectives were to determine the predominant geographical, climatic and land use factors that are linked with the aphid's distribution, to quantify their role in determining that distribution, including their interacting effects and to explore the ability of artificial neural networks (ANNs) to provide predictive models.Location The study focused on four spatial scales to account for the aphid data base characteristics and available land use data sets: Europe; a broad zone over Europe covering Belgium, Denmark, France, Ireland, Italy, The Netherlands, Scotland, Sweden and Wales (Regio data base coverage); North‐West Europe (i.e. Belgium, France and the United Kingdom); and England with Wales.Methods Multiple linear regression (MLR) was used to identify the variables in the Geographic location, Climate and Land use groups, that explained significant proportions of the variance in M. persicae total annual numbers and Julian date of first capture. A variance partitioning procedure was used to measure the fraction of the variation that can be explained by each environmental factor and of shared variation between the different factors. Finally, ANNs were employed as an alternative modelling approach for the two largest study areas, i.e. Europe and the Regio data base coverage, to determine whether the relationship between aphid and environmental variables was better described by more complex functions as well as their ability to generalize to new data.Results Land use variables are shown to play a significant role in explaining aphid numbers. The area of agricultural crops, in particular oilseed rape, is positively correlated with M. persicae annual numbers. Among the climatic variables, rainfall is negatively correlated with aphid numbers and temperature is positively correlated. The geographical components also explain a significant part of aphid annual numbers. However, the variance partitioning procedure indicates that while each group has an effect, none is dominant. Aphid first capture is mainly explained by climate where rainfall tends to delay migration and warmer conditions tend to advance it. Climate accounts for the greatest part of the variance when considered separately from the other factors. The geographical and land use components also have a significant effect on first capture at each scale, but their direct contribution is negligible. The ability of the ANN models to generalize to new total numbers and phenological data compared with MLR models was less for Europe (9 and 6% increase in the variance accounted for, respectively) than for the Regio data coverage where an increase of 44% in the variance accounted for was observed.Main conclusions This research supports the hypothesis that climate, land use and geographical location play a role in determining patterns of aphid annual numbers and phenology. The ability of ANN models to predict aphid distribution is improved by the inclusion of temporal land use data. However, identification of the processes involved in such relationships is difficult due to numerous interactions between the environmental factors.

The spatial dynamics of crop and ground active predatory arthropods and their aphid prey in winter wheat.

The distribution of aphid predators within arable fields has been previously examined using pitfall traps. With this technique predominantly larger invertebrate species are captured, especially Carabidae, but the technique provides no estimate of density unless mark-recapture is used. However, many other numerically important aphid predators occur in arable fields and relatively little is known about their distribution patterns nor whether they exhibit a density-dependent response to patches of cereal aphids. Identification of the most effective predators can allow management practices to be developed accordingly. In this study, the distribution of cereal aphids and their predators was examined by suction sampling within a field of winter wheat in Devon, UK, along with visual estimates of weed patchiness. Sampling was conducted on four occasions in 1999 across a grid of 128 sample locations. The distribution of 11 predatory taxa from the Carabidae, Staphylinidae and Linyphiidae was examined. Additionally, the total number of aphid predators and a predation index were used in these analyses. Carabid adults and larvae, along with staphylinid larvae showed the strongest aggregation into patches and the most temporal stability in their distribution. Other taxa had more ephemeral distributions as did the cereal aphids. The distribution of carabid larvae was disassociated from the distribution of cereal aphids for the first two sampling occasions indicating biocontrol was occurring. Other predatory groups showed both association and disassociation. Carabid larvae, Bathyphantes and total numbers of Linyphiidae showed a strong correlation with weed cover for two of the sample dates. Cereal aphids were disassociated from weed cover on three sampling occasions.

Spatio-temporal distribution of corn leaf Aphids (Homoptera: Aphididae) and lady beetles (Coleoptera: Coccinellidae) in Iowa cornfields

Abstract Prey–predator interactions are spatially and temporally dynamic and influenced by environmental factors. Field studies were conducted to investigate the dynamics of spatio-temporal interactions among corn leaf aphids, lady beetles, and environmental factors in cornfields by mapping and comparing their distributions. Lady beetle species in this study included Harmonia axyridis Pallas, Coleomegilla maculata (DeGeer), and Coccinella septempunctata L. A global positioning system, geostatistics, and a geographic information system (GIS) were used to locate sample points, characterize distribution patterns, and map the distributions of corn leaf aphids, lady beetles, and environmental factors. Geostatistical analysis showed that both corn leaf aphid and lady beetle populations were aggregated during the peak population period and randomly distributed early and late in the season. Map-correlation analysis, however, showed that the distribution of lady beetles did not always coincide with that of corn leaf aphids. The results also showed that none of the environmental factors we sampled were significantly correlated with corn leaf aphid and lady beetle distributions. This study documents the dynamic relationships in time and space between lady beetles and corn leaf aphids.

Fertility Affects Susceptibility of Chrysanthemum to Cotton Aphids: Influence on Plant Growth, Photosynthesis, Ethylene Evolution, and Herbivore Abundance

This research details the influence of fertility on plant growth, photosynthesis, ethylene evolution and herbivore abundance of chrysanthemum (Dendranthema grandiflora Tzvelev `Charm') inoculated with cotton aphids (Aphis gossypii Glover). We tested five fertility levels that consisted of 0%, 5%, 10%, 20%, and 100% (375 ppm N) of recommended nitrogen levels. Aphid abundance was greatest at high fertility. Fertility affected the vertical distribution of aphids. A higher population of aphids were observed in physiologically mature and older leaves at low fertility, whereas at high fertility young leaves had 33% more aphids than older, basal leaves. Aphids depressed plant vegetative and reproductive growth, and altered carbohydrate partitioning at high fertility. Aphid-inoculated (AI) plants at high fertility had increased specific leaf area [(SLA), i.e., thinner leaves] and greater leaf area than aphid-free (NonAI) plants. Aphids caused greater ethylene production in reproductive buds and young leaves of high fertility plants, but had no effect on ethylene evolution in physiologically mature or older, basal leaves. Plant growth, leaf nitrogen (N), phosphorus (P), iron (Fe) and manganese (Mn) increased at higher fertility, as did chlorophyll and photosynthetic rates. Leaf N was highest in young and physiologically mature leaves compared to basal leaves. Aphids decreased leaf N and P. Aphids reduced photosynthesis in young leaves of high fertility plants, whereas physiologically mature and older leaves were unaffected.

Phenotypic mechanisms of host resistance against greenbug (Homoptera: Aphididae) revealed by near isogenic lines of wheat.

Interactions between biotype E greenbug, Schizaphis graminum (Rondani), and wheat, Triticum aestivum L., were investigated using resistant and susceptible near isogenic lines of the greenbug resistance gene Gb3. In an antixenosis test, the greenbugs preferred susceptible plants to resistant ones when free choice of hosts was allowed. Aphid feeding resulted in quick and severe damage to susceptible plants, which seemed to follow a general pattern spatially and was affected by the position where the greenbugs were initially placed. Symptom of damage in resistant plants resembled senescence. Within-plant distribution of aphids after infestation was clearly different between the two genotypes. Significantly more greenbugs fed on the first (oldest) leaf than on the stem in resistant plants, but this preference was reversed in the susceptible one. After reaching its peak, aphid population on the susceptible plants dropped quickly. All susceptible plants were dead in 10-14 d after infestation due to greenbug feeding. Aphid population dynamics on resistant plants exhibited a multipeak curve. After the first peak, the greenbug population declined slowly. More than 70% of resistant plants were killed 47 d after infestation. Performance of both biotype E and I greenbugs on several Gb3-related wheat germplasm lines were also examined. It seems that the preference-on-stem that was characteristic of biotype E greenbugs on the susceptible plants was aphid biotype- and host genotype-dependent. Results from this study suggested that antixenosis, antibiosis, and tolerance in the resistant plants of wheat might all contribute to resistance against greenbug feeding.

Phenotypic Mechanisms of Host Resistance Against Greenbug (Homoptera: Aphididae) Revealed by Near Isogenic Lines of Wheat

Interactions between biotype E greenbug, Schizaphis graminum (Rondani), and wheat, Triticum aestivum L., were investigated using resistant and susceptible near isogenic lines of the greenbug resistance gene Gb3. In an antixenosis test, the greenbugs preferred susceptible plants to resistant ones when free choice of hosts was allowed. Aphid feeding resulted in quick and severe damage to susceptible plants, which seemed to follow a general pattern spatially and was affected by the position where the greenbugs were initially placed. Symptom of damage in resistant plants resembled senescence. Within-plant distribution of aphids after infestation was clearly different between the two genotypes. Significantly more greenbugs fed on the first (oldest) leaf than on the stem in resistant plants, but this preference was reversed in the susceptible one. After reaching its peak, aphid population on the susceptible plants dropped quickly. All susceptible plants were dead in 10–14 d after infestation due to greenbug feeding. Aphid population dynamics on resistant plants exhibited a multipeak curve. After the first peak, the greenbug population declined slowly. More than 70% of resistant plants were killed 47 d after infestation. Performance of both biotype E and I greenbugs on several Gb3-related wheat germplasm lines were also examined. It seems that the preference-on-stem that was characteristic of biotype E greenbugs on the susceptible plants was aphid biotype- and host genotype-dependent. Results from this study suggested that antixenosis, antibiosis, and tolerance in the resistant plants of wheat might all contribute to resistance against greenbug feeding.

Centaur database: an information system for aphid surveys and pest control

Abstract:The development and the use of an information system (Centaur) including aphid trapping data from suction and yellow traps are described. Centaur is a client‐server database on an NT server and the interface is in Windows. The system allows users to enter and retrieve data of aphid captures and to produce summaries of data at various time levels (daily, weekly, yearly) for specific sites. The data can be illustrated graphically and they can be exported or printed. In addition, the system allows the incorporation of biological data and morphological images, and maps which estimate the spatial distribution of aphids. The information retrieval is fast and user‐friendly. The system can be of considerable value for research, community ecology, plant protection, public and private authorities, plant protection specialists, agronomists, agrochemical companies, farmers and the agricultural industry as it can be used for decision support. The data can be used to make forecasts for risk and/or to give advice for timely interventions. The system is currently operated in Greece and includes data from 1993 but it can be applied to other European countries and can be used for other insect pests.

Influence of host plant heterogeneity on the distribution of a birch aphid

Abstract. 1. The spatial and temporal abundance of the aphid Euceraphis betulae was investigated in relation to heterogeneity in host plant (Betula pendula) vigour and pathogenic stress. The performance of aphids feeding on vigorous and stressed foliage was also examined.2. The plant stress and plant vigour hypotheses have been suggested as opposing ways in which foliage quality influences herbivore abundance. In many plants, however, vigorous growing foliage co‐exists with stressed or damaged foliage.3. There was a negative correlation between branch growth (vigour) and branch stress (leaf chlorosis), with the most vigorous branches displaying little or no stress, and the most stressed branches achieving poor growth. There was a similar negative correlation between vigour and stress at the level of individual trees, which themselves represented a continuum in quality.4. At the beginning of the season, E. betulae were intermittently more abundant on vigorous branches than on branches destined to become stressed, but aphids became significantly more abundant on stressed branches later in the season, when symptoms of stress became apparent. Similar patterns of aphid abundance were seen on vigorous and stressed trees in the following year.5. Euceraphis betulae performance was generally enhanced when feeding on naturally stressed B. pendula leaves, but there was some evidence for elevated potential reproduction when feeding on vigorous leaves too.6. Overall, plant stress probably influences E. betulae distribution more than plant vigour, but the temporal and spatial variability in plant quality suggests that plant vigour could play a role in aphid distribution early in the season.

Aphids of sub-Antarctic Îles Crozet and Kerguelen: species diversity, host range and spatial distribution

The native terrestrial food web of sub-Antarctic islands is dominated by decomposers with rare herbivores and almost no predators. As a consequence of increasing human activities, the number of alien plants and invertebrates species, including phytophagous species, has been dramatically rising on these islands. These repeated introductions seem likely to have a great impact on the ecosystem functioning. This is the first detailed study on species diversity, host range and spatial distribution of aphids on French sub-Antarctic islands. Six cosmopolitan and polyphagous aphid species have been recorded on these islands. Five species have been found in the wild where they colonized native and introduced plants, and one species was confined to a glasshouse. Aphids colonized a littoral band and were limited to below 200 m a.s.l. Their spatial distribution is constrained by host plant distribution and temperature. The two dominant species, Myzus ascalonicus and Rhopalosiphum padi, are obligately parthenogenetic in these islands and have been observed to be active on plants during winter. The other species are also presumably obligate parthenogens because of the absence of host plants where sexual reproduction can occur. We suggest that polyphagy and parthenogenesis are major biological traits that influence colonization success by aphids in a sub-Antarctic environment.

Effects of the Presence of the Allegheny Mound Ant (Hymenoptera: Formicidae) in Providing Enemy-Free Space to Myrmecophilous Aphid and Soft Scale Populations

We tested whether ant-provided enemy-free space was a possible mechanism to explain the distribution of myrmecophilous aphids and soft scales in jack pine forests of north-central Michigan. Populations of the aphid Cinara banksiana Pepper and Tissot decreased significantly when the Allegheny mound ant, Formica exsectoides Forel, was excluded from their colonies. A combination of inclusion/exclusion experiments indicated that mound ants provided enemy-free space for aphids against mirid predators. In the absence of ants, mirids were a significant source of mortality to aphids. When ants were present, significantly more aphids survived in the presence of mirids than when ants were not present. Additional direct benefits to aphids provided by ant tending were not detected. In contrast, the soft scale, Toumeyella parvicornis (Cockerell), did not gain enemy-free space from the lady-beetle Hyperaspis binotata (Say) in the presence of ants during this study. Lady-beetle larvae increased in number over 2 yr, and consumed large numbers of scales, which resulted in similar decreases of scale populations between ant-absent and ant-present treatments. This study indicates that an ant species can show differential effectiveness in providing enemy-free space to myrmecophilous homopterans.

Effect of Erynia neoaphidis infection and coccinellid foraging on the spatial distribution of aphids on plants.

Effect of Erynia neoaphidis infection and coccinellid foraging on the spatial distribution of aphids on plants.

Influence of elevated CO2 on interspecific interactions at higher trophic levels

Abstract We report the results of a study investigating the influence of elevated CO2 on species interactions across three trophic levels: a plant (Brassica oleracea), two aphid herbivores (the generalist Myzus persicae and the specialist Brevicoryne brassicae), and two natural enemies (the coccinellid Hippodamia convergens (ladybird) and the parasitoid wasp Diaeretiella rapae). Brassica oleracea plants reared under elevated CO2 conditions (650 ppmv vs. 350 ppmv) were larger and had decreased water and nitrogen content. Brevicoryne brassicae reared on plants grown in elevated CO2 were larger and accumulated more fat, while there was no change in M. persicae traits. Fecundity of individual aphids appeared to be increased when reared on plants grown in elevated CO2. However, these differences were generally lost when aphids were reared in colonies, suggesting that such changes in plant quality will have subtle effects on aphid intraspecific interactions. Nevertheless, CO2 treatment did influence aphid distribution on plants, with significantly fewer M. persicae found on the shoots, and B. brassicae was only found on senescing leaves, when colonies were reared on plants grown in elevated CO2. We reared B. brassicae and M. persicae in competition on plants grown at both the CO2 concentration treatments. We found a significantly lower ratio of M. persicae: B. brassicae on plants grown under elevated CO2 conditions, strongly suggesting that increasing CO2 concentrations can alter the outcome of competition among insect herbivores. This was also reflected in the distribution of the aphids on the plants. While the CO2 treatment did not influence where B. brassicae were found, fewer M. persicae were present on senescing leaves under elevated CO2 conditions. Changes in plant quality resulting from the CO2 treatments did not appear to alter aphid quality as prey species, as the number consumed by the ladybird H. convergens, and the number parasitised by the parasitoid wasp D. rapae, did not change. To our knowledge, this study provides the first empirical evidence that changes in host plant quality mediated by increasing levels of CO2 can alter the outcome of interspecific competition among insect herbivores.

THRESHOLD EFFECTS OF LANDSCAPE STRUCTURE ON BIOLOGICAL CONTROL IN AGROECOSYSTEMS

Habitat fragmentation may adversely affect the ability of natural enemies to control pest outbreaks in agricultural landscapes by interfering with their search behavior and ability to aggregate in response to prey. We determined how landscape structure affected the ability of two ladybird beetles (Coleoptera: Coccinellidae) to track aphid populations in experimental landscapes that differed in the abundance and degree of fragmentation of red clover (Trifolium pratense). One coccinellid was a native species (Coleomegilla maculata Pallas) and the other (Harmonia axyridis Timberlake) was introduced specifically for the biological control of crop pests such as pea aphids (Acyrthosiphon pisum Harris; Homoptera: Aphididae). Landscape structure exhibited a threshold in lacunarity (a measure of interpatch distances) below 20% habitat, at which point clover patches became significantly more isolated. This threshold in landscape structure was mirrored by a similar threshold in the distribution of pea aphid populations. The distribution of the biocontrol agent, H. axyridis, tracked this threshold in aphid distribution, but the native coccinellid, C. maculata, was unable to do so in fragmented clover landscapes. Although C. maculata was a more active forager within clover cells, overall it was less mobile and moved significantly less among clover cells and between landscapes than H. axyridis, which may have contributed to its inability to track aphid populations in fragmented landscapes. The two coccinellids did not differ in their search success within fragmented landscapes, however, and it was only in clumped landscapes that H. axyridis maximized search success and foraged within clover cells that had 2.5–3 times more aphids than those in which C. maculata occurred. Thus, the potential of predators to control pest populations in fragmented landscapes may ultimately reflect the extent to which thresholds in landscape structure interfere with the aggregative response of predators. In this system, the aggregative response of coccinellids was more closely tied to thresholds in the distribution of clover than aphids. With its greater mobility, H. axyridis was more effective than the indigenous C. maculata at tracking aphids when they occurred at low patch occupancy (below the threshold in landscape structure), which is a requisite for successful biocontrol. If native insect predators are generally more sensitive to habitat fragmentation, greater reliance may be placed on the introduction of exotic species for biocontrol, which is not without economic cost and potential ecological impacts to native insect communities. Our study demonstrates that, in addition to economic thresholds, there are also ecological thresholds that must be surmounted if biocontrol measures are to be successful. In addition to enhancing vegetational diversity within agroecosystems, conservation biological control should also strive to mitigate fragmentation effects on natural enemies, especially if thresholds in landscape structure disrupt predator–prey interactions and compromise the efficacy of biocontrol programs.

Distribution of bird cherry-oat aphids ( Rhopalosiphum padi (L.)) in relation to landscape and farming practices

Apterous aphids show varying degrees of aggregation in the field. Both alate and apterous Rhopalosiphum padi (L.) were compared in terms of degree of aggregation in relation to landscape features and farming management (conventional vs. organic). Alate R. padi were clearly aggregated, but no effect of landscape features or farming management was found on the degree of aggregation. Apterous R. padi were aggregated, and to a degree that varied according to field. Aggregation tended to be lower in landscapes with high perimeter-to-area ratios of the fields, but there was no significant difference between organically and conventionally managed fields. The fields with low aggregation had few alate, low R. padi population growth rate and therefore a low abundance.

Desenvolvimento do Pulgão Aphis gossypii Glover (Hemiptera: Aphididae) em Três Cultivares do Algodão Herbáceo Gossypium hirsutum L. r. latifolium Hutch.

Estudou-se o desenvolvimento do pulgão Aphis gossypii Glover (Hemiptera: Aphididae) em três cultivares do algodão hérbaceo, CNPA Precoce 1, CNPA Precoce 2 e CNPA 7 H. Plantas de algodão com cerca de 20 cm mantidas em vasos individuais telados foram infestadas com 20 pulgões adultos. Após 15, 30 e 45 dias, procedeu-se à contagem dos pulgões em cada planta das três cultivares. Observou-se diferença significativa do número médio total de pulgões entre a cultivar CNPA Precoce 2 e as outras cultivares testadas. Não foi registrada diferença na distribuição vertical dos pulgões na planta, exceto aos 45 dias, quando a cultivar CNPA Precoce 2 apresentou maior densidade de insetos na região mediana em relação à basal.

Competition in Cereal Aphids (Homoptera: Aphididae) on Wheat Plants

The cereal aphids Rhopalosiphum padi L. and Sitobion avenae (F.) coexist on the same host plant but occupy different ecological niches. R. padi arrives first in the season and reaches its population peak before S. avenae. In addition, R. padi prefers the stem and lower leaves, whereas S. avenae is found mostly on the ears and upper leaves of the plant. In greenhouse experiments, the likelihood of competition between R. padi and S. avenae on wheat seedlings and tillering plants was evaluated. The reproductive rate of S. avenae on tillering plants was negatively affected by previous infestation by R. padi, and this effect was larger when R. padi infestation started at an earlier plant growth stage. Likewise, previous infestation by R. padi decreased S. avenae reproduction on seed- lings. In contrast, previous infestation by S. avenae on the flag leaf of flowering plants did not affect R. padi on that plant part. When both aphid species co-occurred from the beginning, the presence of either aphid species negatively affected the reproductive rate of the other. R. padi consistently had a higher rate of population increase than S. avenae. The presence of the other aphid species did not affect within-plant aphid distribution or alate aphid production. Results were similar on wheat seedlings and tillering plants. Finally, alate S. avenae preferred uninfested seedlings over R. padi- infested ones, whereas no preference was observed when the experiment was performed with tillering plants.

Competition in Cereal Aphids (Homoptera: Aphididae) on Wheat Plants

The cereal aphids Rhopalosiphum padi L. and Sitobion avenae (F.) coexist on the same host plant but occupy different ecological niches. R. padi arrives first in the season and reaches its population peak before S. avenae. In addition, R. padi prefers the stem and lower leaves, whereas S. avenae is found mostly on the ears and upper leaves of the plant. In greenhouse experiments, the likelihood of competition between R. padi and S. avenae on wheat seedlings and tillering plants was evaluated. The reproductive rate of S. avenae on tillering plants was negatively affected by previous infestation by R. padi, and this effect was larger when R. padi infestation started at an earlier plant growth stage. Likewise, previous infestation by R. padi decreased S. avenae reproduction on seedlings. In contrast, previous infestation by S. avenae on the flag leaf of flowering plants did not affect R. padi on that plant part. When both aphid species co-occurred from the beginning, the presence of either aphid species negatively affected the reproductive rate of the other. R. padi consistently had a higher rate of population increase than S. avenae. The presence of the other aphid species did not affect within-plant aphid distribution or alate aphid production. Results were similar on wheat seedlings and tillering plants. Finally, alate S. avenae preferred uninfested seedlings over R. padi-infested ones, whereas no preference was observed when the experiment was performed with tillering plants.

Distribution of the aphid Hyalopterus pruniGeoffr. within and between habitats of Common Reed Phragmites australis ( Cav.) Trin. ex Steudel as a result of migration and population growth

The aphid Hyalopterus pruni migrates to its secondary host Common Reed in late spring and early summer. Reed fields are known to be more heavily infested at the edges compared to the centre, as the migrants are attracted to the colour of the reed. There is also evidence that reeds growing at wet sites are more heavily infested than at dry sites. This paper shows that both proceses interact in determining the distribution of aphids in different habitats. The observations were carried out in the vast reed field of the Zuidelijk Flevoland polder (The Netherlands) during a number of years after its reclamation in 1968. In the period of migration flying aphids were caught with sticky traps situated in and around the reed field. The distribution of aphids on the reed was determined at different times during the season along transects through the centre of the polder. The existence early in the season (June) of a higher infestation at the edges than in the centre of the field was confirmed. The density of winged aphids in this early period was higher in wet than in dry habitats, which may have been a result of a preference of the settling migrants for reed standing in water. Later in the season (August) the dry habitat still had a relatively low infestation in the centre, but at the wet sites the infestation was high everywhere. This could be attributed to the much quicker population growth that was found in the wet habitat and subsequent short range movement of newly born winged aphids.

HOST-PLANT CHEMICALS AND DISTRIBUTION OF Neuquenaphis ON Nothofagus

Extractable metabolites from leaves (EM) and volatiles released from six Nothofagus species were analyzed by TLC and GC-MS, respectively. Aphids of the genus Neuquenaphis, closely associated to Nothofagus, were sampled on each Nathofagus species. Cluster analyses of Nothofagus species were performed based on the presence or absence of EM and volatiles. Dissimilarity distances, from the cluster analyses of EM and volatiles, were used to evaluate their association with the aphid distribution. A major component identified from EM and volatiles of three species of Nothofagus, A-agarofuran, was attractive to alates of the oligophagous Neuquenaphis sensoriata, which use them as hosts. These results suggest that chemicals play a significant role in the host-plant associations between Neuquenaphis and Nothofagus.