Cereal Aphid Species Research Articles

Wide dispersal of aphid-pathogenic Entomophthorales among aphids relies upon migratory alates.

Entomophthoralean mycoses are of general importance in the natural control of aphids, but mechanisms involved in their dissemination are poorly understood. Despite several possible means of fungal survival, the dispersal of the mycoses in aphids has never been related to the flight of their migratory alates that are able to locate suitable host plants. In this study, aphid-pathogenic fungi proved to be widely disseminated among various aphids by their alates through migratory flight based on the following findings. First, up to 36.6% of the 7139 migratory alates (including nine species of vegetable or cereal aphids) trapped from air > 30 m above the ground in three provinces of China were found bearing eight species of fungal pathogens. Of those, six were aphid-specific Entomophthorales dominated in individual cases by Pandora neoaphidis, which occurs globally but has no resting spores discovered to date. Secondly, infected alates were confirmed to be able to fly for hours, to initiate colonies on plants after flight and to transmit fungal infection to their offspring in a laboratory experiment, in which 238 Sitobion avenae alates were individually flown in a computer-monitoring flight mill system after exposure to a spore shower of P. neoaphidis and then allowed to colonize host plants.

Effects of pattern and timing of high temperature exposure on reproduction of the rose grain aphid, Metopolophium dirhodum

Abstract Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) is one of the three most important cereal aphid species in Germany and central European countries. High temperature is known to play a detrimental role in the reproduction and survival of aphids. Detailed experiments were conducted to assess the effects of high temperatures (27, 29, 31, and 33 °C), exposure pattern (8 h day−1 for 1, 2, 4, and 6 days), and exposure development stage (2nd, 3rd, 4th instar larvae, and adult) on the reproduction and longevity of M. dirhodum. All three factors have a significant influence on the aphids. Increasing the temperature to over 29 °C significantly decreases their lifetime fecundity and longevity. Mature aphids are more sensitive to high temperatures than younger ones. A high temperature pulse to treat aphids older than 3rd instar larvae greatly shortened their longevity and lessened their lifetime fecundity. Lifetime fecundity and longevity was found to be inversely related to exposure pattern. A high temperature pulse lasting longer than 1 week greatly reduced the lifetime fecundity and longevity. The limitation of the data collected from experiments at constant temperatures for aphid forecasting is discussed.

Tillage impacts cereal-aphid (Homoptera: Aphididae) infestations in spring small grains.

We compared infestation levels of cereal aphids (Homoptera: Aphididae) in spring-seeded wheat and barley grown with and without preplant tillage for 8 site yr in eastern South Dakota. Crop residue covered approximately 25% of the soil surface with preplant tillage, whereas without preplant tillage 50% or more of surface residue was conserved. Rhopalosiphum padi (L.) comprised nearly 90% of all cereal aphids sampled, and R. maidis (Fitch), Schizaphis graminum (Rondani), and Sitobion avenae (F.) collectively comprised the remainder. R. padi routinely infested lower parts of tillers and were generally concealed by surface residue in plots with no preplant tillage. Across 7 site yr, R. padi were more abundant in plots with no preplant tillage than with preplant tillage (272.6 +/- 54.4 versus 170.1 +/- 37.2 aphid days per 25 tillers). However, in comparisons at individual site years, R. padi were greater in no-preplant tillage plots only once. For all cereal-aphid species combined, infestations were greater in plots with no preplant tillage for 1 of 8 site yr, but did not differ with tillage when compared across all site years. Cereal aphids were never more abundant in plots with preplant tillage. Our results show that conservation tillage leads to greater infestations of R. padi in spring small grains, as increased surface residue provides a favorable microhabitat for this aphid.

Comparison of field population growths of three cereal aphid species on winter wheat

Population growths of three aphid species colonising winter wheat stands, Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae, were analysed by regression method. The calculations were based on counts in 268 winter wheat plots at 3 or 7 day intervals over 10 (leaves) or 6 (ears) years. The population dynamics of a particular species differed widely between years. Density independent exponential growth of the population was most common, but its rate differed significantly between species, and for S. avenae also between populations on leaves and ears, on which the populations grew fastest. Field estimates of the intrinsic rate of increase derived from the exponential growths ranged between 0.010–0.026 in M. dirhodum, 0.0071–0.011 in R. padi, and between 0.00078–0.0061 and 0.0015–0.13 in S. avenae on leaves and ears, respectively. In the populations with the most vigorous population growth, S. avenae on ears and M. dirhodum on leaves, the rate of population increase significantly decreased with increasing aphid density.  

Comparison of Hindwing Hamuli from Five Species of Cereal Aphids (Hemiptera: Aphididae)

Wing-coupling apparatuses of five species of cereal aphids [western wheat aphid, Diuraphis tritici (Gillette); corn leaf aphid, Rhopalosiphum maidis (Fitch); bird cherry-oat aphid, Rhopalosiphum padi (L.); greenbug, Schizaphis graminum (Rondani); and the English grain aphid, Sitobion avenae (F.)] were examined under a scanning electron microscope. The scanning electron micrographs showed that the wing-coupling apparatuses of the five cereal aphid species were similar to the structure found in the Russian wheat aphid, Diuraphis noxia (Mordvilko). The wing-coupling apparatuses were composed of a forewing fold and a set of spiral-shaped (or twice-curved) hindwing hamuli. The hindwing hamuli were not fish hook-like (or once-curved) structures. Previous light-microscopy description of fish hook-like hamuli was the result of limited resolving power and field depth of light microscopy. The number of hamuli varied among and within the aphid species. An asymmetric number of the hamuli between the left and right hindwings were also found in all aphids. Rhopalosiphum padi and D. tritici had the least number of the hamuli, ranging from one to four, whereas S. avenae had the most hamuli, ranging from five to seven. Wing-coupling mechanisms and possible use of the hamuli as a taxonomic character are discussed.

Species diversity, abundance, and phenology of aphid natural enemies on spring wheats resistant and susceptible to Russian wheat aphid

The species composition, relativeabundance, and seasonal dynamics of selectednatural enemies of cereal aphids were monitoredin spring wheat fields in Moscow, Idaho in 1997and 1998. Trials also examined the potentialimpact of resistance to Russian wheat aphid(RWA), Diuraphis noxia (Mordvilko)(Homoptera: Aphididae) in wheat, on aphidbiological control agents. Natural enemypopulations were monitored on two springwheats: D. noxia susceptible variety`Centennial' and resistant genotype `IDO488'. Field plots were artificially infested withadult D. noxia, and sampled for cerealaphids and parasitoids weekly. Coccinellidpredators were monitored once in 1997 and twicein 1998. The coccinellids Hippodamiaconvergens Guerin, Coccinellaseptempunctata L., C. transversoguttataBrown and C. trifasciata Mulsant weredetected. No significant differences in adultor immature coccinellid densities were observedbetween the D. noxia resistant andsusceptible genotypes. During both years, themost abundant primary hymenopteran parasitoidswere Diaeretiella rapae (M'Intosh), Aphidius ervi Haliday, A. avenaphis(Fitch), and Lysiphlebus testaceipes(Cresson), Aphelinus varipes (Foerster),Aphidius colemani Viereck, Aphidiuspicipes (Nees), Aphidius sp., Monoctonus washingtonensis Pike & Stary, Praon gallicum Stary, Praon occidentaleBaker, and Praon sp. were also detected. Numbers of both D. noxia and D.rapae were significantly greater on Centennialthan on IDO488 in both years. When all speciesof cereal aphids and parasitoids areconsidered, the total percentage parasitism wasnot significantly different between thegenotypes. There was no interaction betweenD. noxia resistance and the populationdensity of the predators or parasitoidsmonitored. These results suggest that the D. noxia resistant line had no adverse impacton natural enemies under the conditions ofthese field experiments.

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

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

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

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

Identifying key cereal aphid predators by molecular gut analysis.

We describe polymerase chain reaction (PCR) primers for gut analysis of aphid predators. The primers amplify aphid mitochondrial COII fragments ranging in size from 77 to 386 bp. Using these primers, we were able to distinguish six species of US Great Plains cereal aphids, including two congeners, Rhopalosiphum maidis (Fitch) and R. padi (L.), and to detect them in extracts of coccinellid and chrysopid predators. We devised a protocol for deriving half-lives of detectability for the DNA of a single aphid consumed by predators maintained under simulated field dietary and temperature conditions. Using this protocol and primers that amplify a 198-bp fragment, we determined statistically different half-lives of detectability for a single R. maidis of 3.95 h in Chrysoperla plorabunda (Fitch) and 8. 78 h in Hippodamia convergens Guerin. The detectability half-life for a 339-bp R. maidis fragment was statistically longer in C. plorabunda but not in H. convergens. The sensitivity of the assay for the 198-bp fragment is 10-7 aphid equivalents. For species-specific predator gut analysis, PCR is superior to monoclonal antibody technology, giving comparable detectability half-lives with lower expense, much shorter development times, and greater certainty of a successful outcome.

The Effects of Cultural Measures on Cereal Pests and Their Role in Integrated Pest Management

The influences of cultural control measures on invertebrate pests and their natural enemies in cereals (wheat, barley and oats) are described and discussed, with emphasis on the major pests in north-west Europe. Possibilities for additive and synergistic combinations of cultural measures are identified, together with opportunities for integrating cultural measures with chemical and biological control where appropriate. Recent studies confirm the central role of cultural control measures in integrated pest management and integrated production of cereal crops. However, cultural measures often have opposing effects on different pests as well as diseases and weeds, so that appropriate measures must be selected on the basis of an assessment of the risks from key pests, diseases and weeds. Crop rotation is not an important means of controlling cereal pests, but its use is recommended for control of cereal diseases and weeds, as well as pests of crops grown in rotation with cereals. Diversification of crops and non-crop habitats in predominantly cereal growing areas is thought to increase numbers of certain parasitoids and polyphagous predators of cereal pests. The presence of weeds or an intercrop in a field together with cereals may reduce the severity of aphid and slug damage to cereals. Trap cropping has not yet been adequately tested in wheat, barley or oats. Cover crops reduce damage by wheat bulb fly in a following wheat crop, but increase the risk of slug damage. Resistance to a wide range of cereal aphid species has been identified in wheat and barley, but in Europe, more emphasis is placed on selecting cultivars with resistance to cereal diseases rather than pest resistance. Resistance in wheat to wheat bulb fly and wheat blossom midge is recorded, and resistance to slug damage has been reported in some laboratory studies. Early sowing of winter cereals results in more damage by certain dipterous pests and increased numbers of the aphid vectors of barley yellow dwarf virus (BYDV), but early sowing results in less damage by wheat bulb fly and slugs in autumn/winter and by late infestations of aphids in summer. Avoidance of ploughing results in reduced incidence of wheat bulb fly, yellow cereal fly and aphids, but increased numbers of slugs, wheat blossom midge and bibionid larvae. Avoidance of ploughing can result in greater numbers of certain polyphagous predators, particularly in the first weeks following crop establishment. The presence of straw residues results in increased slug populations, but reduced incidence of yellow cereal fly and wheat blossom midge. Preparation of fine, firm seedbeds discourages attack by slugs and wheat bulb fly on cereals. Drilling at slightly greater depth in rough cloddy seedbeds helps to protect wheat seeds from slug damage. Nitrogen fertiliser applied in spring can help cereal plants compensate for losses by wheat bulb fly or slugs. However, nitrogen applications tend to result in increased summer infestations of aphids.

Population density of cereal aphids parasitoids and their rolein suppressing cereal aphids on wheat plantations at Mansoura district

Experiments were carried out in wheat fields of Economic Entomology Department, Faculty of Agriculture, Mansoura‐University, during two successive seasons 1997 and 1998. The cereal aphids, Schizaphis graminum (Rond.), Sitobion avenae (Fabr.), Rhopalosiphum padi (L.) and Rhopalosiphum maidis (Fitch.) are the serious pests of the wheat crop at Mansoura district. Four hymenopterous parasitoid species, namely Aphidius uzbekistanicus Luz., Aphidius matricariae Hal., Praon gallicum Hal. and Aphidius rhopalosiphi De Stefani, were recorded as primary parasitoids on the cereal aphid species. The numbers and ratios of these species were as follows: A. uzbekistanicus 516 individuals (40.8%) in 1997 and 488 individuals (44.2%) in 1998, A. matricariae 350 individuals (27.6%) in 1997 and 286 individuals (25.9%) in 1998, Praon gallicum 231 individuals (18.3%) in 1997 and 192 individuals (17.4%) in 1998, A. rhopalosiphi 168 individuals (13.3%) in 1997 and 139 individuals (12.6%) in 1998. The dominant aphid parasitoids species among them was A. uzbekistanicus during the two seasons of study.

Abundance of cereal aphids (Hemiptera: Aphididae) within wild Triticum and Aegi­lops spp., and cultivated wheat

Accessions of the wild Triticum species: T. boeticum, T. dicoccoides, T. urartu, and the Aegilops species: Ae. columnaris, Ae. geniculata, Ae. markgrafii, Ae. neglecta and Ae. triuncialis in the collection of the Gene Bank of RICP Prague-Ruzyně, with T. aestivum cv. Sandra as control, were evaluated for cereal aphid occurrence in the open during 1995–1998 period. The cereal aphid species Rhopalosiphum padi (RP), Metopolophium dirhodum (MD) and Sitobion avenae (SA) were predominant on the plants. Variations in the abundance of individual aphid species in each year were found. The results from 1997, the optimal year for aphid occurrence, showed differences between both aphid and plant species. RP significantly dominated in Triticum species, while SA preferred Aegilops accessions. A significant negative correlation was found between RP and MD densities in the Triti­ cum spp., while MD and SA occurrence showed a negative relation to that of RP and SA in the Aegilops accessions. The individual aphid species showed a similar pattern of infestation in several genomically close accessions.

The influence of three cereal aphid species and mixed diet on larval survival, development and adult weight of Coccinella septempunctata

Entomologia Experimentalis et ApplicataVolume 89, Issue 3 p. 319-322 The influence of three cereal aphid species and mixed diet on larval survival, development and adult weight of Coccinella septempunctata Mikael S. Hauge, Mikael S. Hauge Department of Zoology, University of Aarhus, Building 135, DK- 8000 Århus C, DenmarkSearch for more papers by this authorFrederik H. Nielsen, Frederik H. Nielsen Department of Zoology, University of Aarhus, Building 135, DK- 8000 Århus C, DenmarkSearch for more papers by this authorSøren Toft, Søren Toft Department of Zoology, University of Aarhus, Building 135, DK- 8000 Århus C, DenmarkSearch for more papers by this author Mikael S. Hauge, Mikael S. Hauge Department of Zoology, University of Aarhus, Building 135, DK- 8000 Århus C, DenmarkSearch for more papers by this authorFrederik H. Nielsen, Frederik H. Nielsen Department of Zoology, University of Aarhus, Building 135, DK- 8000 Århus C, DenmarkSearch for more papers by this authorSøren Toft, Søren Toft Department of Zoology, University of Aarhus, Building 135, DK- 8000 Århus C, DenmarkSearch for more papers by this author First published: 17 October 2003 https://doi.org/10.1046/j.1570-7458.1998.00415.xCitations: 42AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume89, Issue3December 1998Pages 319-322 RelatedInformation

SPATIAL DISTRIBUTION AND SAMPLING PLANS WITH FIXED LEVELS OF PRECISION FOR CEREAL APHIDS (HOMOPTERA: APHIDIDAE) INFESTING SPRING WHEAT

AbstractThree cereal aphids, Rhopalosiphum padi (L.), Schizaphis graminum (Rondani), and Sitobion avenae (F.), invade wheat fields in the northern Great Plains each spring, and populations occasionally reach economic levels. The first objective of this study was to describe the spatial distribution of three species of cereal aphids infesting hard red spring wheat (Triticum aestivum L.). The second objective was to develop two sampling plans for cereal aphids using individual stems as the sampling unit, a sampling plan with fixed levels of precision and a sequential sampling decision plan based on total numbers of aphids present. Aphid population estimates were collected from 47 eastern North Dakota spring wheat fields during 1993–1995. The number of aphids per stem were counted on 100–350 stems per field. Taylor’s power law and Iwao’s patchiness regression were used to analyze the spatial distribution of the aphids. Rhopalosiphum padi and S. avenae exhibited an aggregated distribution, whereas S. graminum was distributed randomly in the field. Taylor’s power law provided a better fit to the data than Iwao’s patchiness regression. Sample size requirements for precision levels of 0.10, 0.15, and 0.25 were estimated with Taylor’s regression coefficients. Required sample sizes increased with decreased aphid populations and increased levels of precision. The two sampling plans presented should be useful for research on cereal aphid population dynamics and pest management decision making in spring wheat.

Relationships between primary and secondary parasitoids of cereal aphids

Abstract: The aim of the study was to compare relationships between primary and secondary parasitoids associated with cereal aphids on winter as well as on spring crops. The study was carried out between 1991–1994 in two regions in Poland, 400 km apart (vicinities of Warsaw and Wrocław). It has been found that in both regions, there occurred three cereal aphid species Sitobion avenae F., Rhopalosiphum padi L. and Metopolophium dirhodum Walk. The groups of parasitic Hymenoptera associated with cereal aphids, and mainly with S. avenae which showed a highest degree of parasitization, were similar in both regions. Although more species of parasitoids were found in the Wrocław region (nine species of primary and 11 species of secondary parasitoids) as compared to the Warsaw region (six and nine, respectively), the species composition was similar in both regions. There were big differences in proportion between primary and secondary parasitoids on spring and winter cereals at both localities. In the case of winter cereals, there were more hyperparasitoids among parasitic Hymenoptera reared from mummified aphids. The primary parasitoids constituted 30% on average while the hyperparasitoids constituted 70%. Aphidius uzbekistanicus Luzh. predominates over other primary parasitoids and Dendrocerus carpenteri Curtis is a dominant species among hyperparasitoids. In the case of spring cereals, the primary/secondary parasitoid ratio is different (primary parasitoids make up to 72% on average, with the secondary parasitoids 28%). Most often, A. uzbekistanicus is a dominating species but in certain years the dominance is not as clear as in winter cereals. The dominance hierarchy within hyperparasitoids is different in different years. The presented results demonstrate that in spite of a great distance between the study areas, the relationships between the cereal aphids' primary and secondary parasitoids show similar trends.

Plant Proteinase Inhibitors Are Potential Anticereal Aphid Compounds

Trials were conducted to identify new compounds that may be useful in the control of cereal aphids on wheat, Triticum aestivum (L.). Five plant proteinase inhibitors were tested for their ability to control 3 species of cereal aphids in feeding trials. The proteinase inhibitors were tested against the Russian wheat aphid, Diuraphis noxia (Mordvilko), the green bug, Schizaphis graminum (Rondani), and the bird cherry-oat aphid, Rhoalosiphum padi (L.). Two of these compounds, potato proteinase inhibitors I and II, increased mortality among late instar aphids and reduced production of nymphs in feeding trials. Potato carboxypeptidase inhibitor and soybean trypsin inhibitor showed variable effects ranging from significant to nonsignificant abiosis, depending on the species of aphid examined. The lima bean proteinase inhibitor showed little effect on any of the 3 species. Though the effectiveness of the inhibitors varied, it appears that the proteinase inhibitors from potato are potentially effective proteins for the control of these species.

Binomial Sequential Sampling Plans for Cereal Aphids (Homoptera: Aphididae) in Spring Wheat

Binomial sequential sampling plans usually are more efficient than sampling plans based on counting the number of insects per sample. Our objective was to develop robust binomial sequential sampling plans based on a range of action thresholds for 3 species of cereal aphids, Rhopalosiphum padi (L), Sitobion avenae (F.), and Schizaphis graminum (Rondani). Aphid population data were collected from 45 eastern North Dakota spring wheat fields during 1993-1995. The proportion of infested stems (P T ) with more than T (tally threshold) aphids was related to mean aphid density (m) with the empirical model ln[-ln(1 - P T )] = a + bln(m). The P T -m relationship fit the data well for T values of 0-4, with T = 3 having the best fit. Binomial sequential sampling plans were developed using a Monte-Carlo computer program based on the empirical model. Tally thresholds were evaluated with operating characteristic and average sample number functions. Increasing the tally threshold from 0 to 3 improved the accuracy of the sampling plans but also increased the average sample number required to make a decision. Sampling stop lines for binomial sequential sampling plans with tally thresholds of and 3 and action thresholds of 9 and 13 aphids per stem, and with a tally threshold of 3 and an action threshold of 17 aphids per stem, are provided for use in spring wheat. Sampling plans should be useful tools for spring wheat growers and crop consultants in the northern Great Plains and be applicable over a range of crop values and management costs.

Acquisition d’une aversion alimentaire à trois espèces de pucerons des céréales chez l’araignéePardosa prativaga: effets intra- et interspécifiques

Naive spiders usually accept aphids though these are low quality food, but they subsequently develop aversions as a result of experience. An aversion induced by one species of cereal aphid will be effective with the same strength also against two other species, no matter which of the three species induces the aversions; thus, it plays no role which species the spider encounters. However, the strength of the aversions is significantly dependent on which species induces them. With the three species of aphids tested, it turned out that the aphid of lowest quality as food for the spider created the weakest aversions, while the relatively higher quality aphids produced stronger aversions. Hypothetical explanations for these findings are discussed.

Variability in the Development of Cereal Aphid Parasitoids and Hyperparasitoids in Oceanic Regions as a Response to Climate and Abundance of Hosts

Experiments were conducted to understand how parasitoids and hyperparasitoids of cereal aphids in oceanic regions survive the periodic disappearance of their hosts. We recorded the number of parasitoids and hyperparasitoids emerging from mummies collected in summer on winter wheat and corn and in winter on cereal volunteers. In addition, we studied the duration of both summer and winter development of Aphidius rhopalosiphi De Stefani-Perez, the main parasitoid species of cereal aphids. In summer, interruption in development occurred in primary parasitoids which resulted in a longer development time (up to 4 m). These interruptions were fairly infrequent but they did ensure the survival of part of the population when there was a large decrease or disappearance of the aphid population. A longer duration of summer development also was recorded in a few hyperparasitoids. In winter, an important variability in the length of the development of primary parasitoids was noted which reflected their adaptive closeness to the aphid cycle. All hyperparasitoids studied here had long interruptions in their development and emerged only at the end of winter.

Genotypic variation among different phenotypes within aphid clones.

Most aphid species Hemiptera: Aphididae are parthenogenetic between periods of sexual reproduction. They are also highly polyphenic, with different adult morphs occurring in the life cycle, piz. winged, wingless, asexual and sexual. It is assumed that aphids born in a parthenogenetic clonal lineage are genetically identical regardless of the final adult form with the exception of sexual forms). Using the randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) we have found that different asexual adult phenotypes winged and wingless of some clones of two cereal aphid species (the grain aphid, Sitobion avenae (F.) and the bird-cherry aphid. Rhopalosiphum padi (L.) may be distinguished by the presence or absence of one or more RAPD-PCR bands. In three of nine clones examined, such differences were found, and Southern blotting and hybridization of the discriminating bands confirmed these to be of aphid origin, rather than due to endosymbiotic bacteria or contaminating fungi. The main 248 and 296 bp bands, in the two species respectively, were sequenced and found to be A/T rich. The smaller band showed 57% homology with white striated muscle over a stretch of 90 bp. Genomic DNA treated with dimethyl sulphoxide to remove secondary structures still showed differences in RAPD-PCR profiles between winged and wingless morphs within the unusual clones. This discovery may be widespread and therefore it is important to understand the phenomenon in relation to clonal organisms.