Showing papers on "Aphid published in 1999"
TL;DR: Mummy parasitoids were the most important group linking different aphids, and common aphid species shared few strong, indirect links via primary parasitoid or hyperparasitoids, but could be strongly linked by mummy Parasitoids.
Abstract: 1 A quantitative parasitoid web was constructed describing the trophic relationships between the community of aphids, parasitoids and secondary parasitoids in an abandoned field in southern England Root aphids were omitted and secondary parasitoids were associated with aphids rather than primary parasitoids All aphids, parasitoids and trophic links were expressed in the same units (m−2) Over a 2-year period, separate webs were constructed for every month that aphids and parasitoids were active in the field
2 Twenty-six species of plants were attacked by 25 species of aphid which were parasitized by 18 species of primary parasitoids The primary parasitoids were attacked by 28 species of secondary parasitoids, of which 18 directly attacked the still living aphid (hyperparasitoids) and 10 attacked the aphid after mummification (mummy parasitoids) The aphids were attended by three species of ants
3 Eleven webs were constructed for the months May to September 1994 and May to October 1995 Aphids and primary parasitoids were most abundant and diverse in June, and secondary parasitoids one month later
4 The ratios of the number of aphid species to the number of species of primary parasitoid and hyperparasitoid were relatively constant across webs, as was the ratio of the number of links involving hyperparasitoids and mummy parasitoids The ratio of the total number of links to the total number of species increased with web size
5 The relative abundance of the species in the different webs was well described by a Dirichlet distribution with a common parameter This implies a gamma distribution of aphid abundances in the field with few common and many rare species
6 Predator (ie parasitoid) overlap graphs were constructed to assess the potential for indirect interactions between aphids Mummy parasitoids were the most important group linking different aphids A quantitative overlap diagram was developed to illustrate the potential strengths of indirect linkages Common aphid species shared few strong, indirect links via primary parasitoids or hyperparasitoids, but could be strongly linked by mummy parasitoids Symmetrical links were uncommon, and rare species were potentially strongly influenced by the presence of common aphids with which they shared parasitoids
7 Ant-attended aphids were attacked by fewer species of primary parasitoids and hyperparasitoids than those species not attended by ants Species of mummy parasitoids attack, on average, approximately twice the number of host species than species of either primary parasitoids or hyperparasitoids
376 citations
TL;DR: The honeydew composition and production of four aphid species feeding on Tanacetum vulgare, and mutualistic relationships with the ant Lasius niger were studied, showing consistent with the ants' preference for M. fuscoviride, which produced the largest amount of Honeydew including a considerable proportion of the trisaccharides melezitose and raffinose.
Abstract: The honeydew composition and production of four aphid species feeding on Tanacetum vulgare, and mutualistic relationships with the ant Lasius niger were studied. In honeydew of Metopeurum fuscoviride and Brachycaudus cardui, xylose, glucose, fructose, sucrose, maltose, melezitose, and raffinose were detected. The proportion of trisaccharides (melezitose, raffinose) ranged between 20% and 35%. No trisaccharides were found in honeydew of Aphis fabae, and honeydew of Macrosiphoniella tanacetaria consisted of only xylose, glucose and sucrose. M. fuscoviride produced by far the largest amounts of honeydew per time unit (880 μg/aphid per hour), followed by B. cardui (223 μg/aphid per hour), A. fabae (133 μg/aphid per hour) and M. tanacetaria (46 μg/aphid per hour). The qualitative and quantitative honeydew production of the aphid species corresponded well with the observed attendance by L. niger. L. niger workers preferred trisaccharides over disaccharides and monosaccharides when these sugars were offered in choice tests. The results are consistent with the ants' preference for M. fuscoviride, which produced the largest amount of honeydew including a considerable proportion of the trisaccharides melezitose and raffinose. The preference of L. niger for B. cardui over A. fabae, both producing similar amounts of honeydew, may be explained by the presence of trisaccharides and the higher total sugar concentration in B. cardui honeydew. M. tanacetaria, which produced only low quantities of honeydew with no trisaccharides was not attended at all by L. niger.
316 citations
TL;DR: The experiments indicate that aphids respond to the presence of a predator by producing the dispersal morph which can escape by flight to colonize other plants, but this shift in prey morphology does not lead to better protection against predator attack, but enables aphids to leave plants when mortality risks are high.
Abstract: Aphids exhibit a polymorphism whereby individual aphids are either winged or unwinged. The winged dispersal morph is mainly responsible for the colonization of new plants and, in many species, is produced in response to adverse environmental conditions. Aphids are attacked by a wide range of specialized predators and predation has been shown to strongly influence the growth and persistence of aphid colonies. In two experiments, we reared two clones of pea aphid ( Acyrthosiphon pisum ) in the presence and absence of predatory ladybirds ( Coccinella septempunctata or Adalia bipunctata ). In both experiments, the presence of a predator enhanced the proportion of winged morphs among the offspring produced by the aphids. The aphid clones differed in their reaction to the presence of a ladybird, suggesting the presence of genetic variation for this trait. A treatment that simulated disturbance caused by predators did not enhance winged offspring production. The experiments indicate that aphids respond to the presence of a predator by producing the dispersal morph which can escape by flight to colonize other plants. In contrast to previous examples of predator-induced defence this shift in prey morphology does not lead to better protection against predator attack, but enables aphids to leave plants when mortality risks are high.
217 citations
TL;DR: The results suggest that selection is important in structuring reproductive systems and genetic variation in French S. avenae, and there was substantial genic and genotypic diversity, even in the obligately asexual lineages.
Abstract: As French populations of the aphid Sitobion avenae exhibit a range of reproductive modes, this species provides a good opportunity for studying the evolution of breeding system variation. The present analysis combined ecological and genetic investigations into the spatial distribution of variation in reproductive mode. Reproductive mode was characterized in 277 lineages of S. avenae from France, and these aphids were scored for five microsatellite loci. The analyses revealed strong geographical partitioning of breeding systems, with obligate asexuals mostly restricted to the south of France, while lineages producing sexual forms were more common in the north. Contrary to what might be anticipated for organisms with frequent parthenogenesis, there was substantial genic and genotypic diversity, even in the obligately asexual lineages. More than 120 different genotypes were detected among the 277 aphid lineages, with an average of 5.9 alleles per locus (range four to 16) and heterozygosity of 56.7%. As with previous studies of allozyme variation in aphids, most loci showed heterozygote deficits, and disequilibrium was common among allelic variants at different loci, even after removal of replicate copies of genotypes that might have been derived through clonal reproduction. Our results suggest that selection is important in structuring reproductive systems and genetic variation in French S. avenae. Canonical correspondence analysis was employed to examine the associations between genotypic and phenotypic variables, enabling the identification of alleles correlated with life-history traits.
210 citations
TL;DR: It is concluded that inhibiting effects between Collembola and earthworms resulted from the use of a common resource, litter material rich in nitrogen.
Abstract: Effects of Collembola (Heteromurus nitidus and Onychiurus scotarius) and earthworms (Aporrectodea caliginosa and Octolasion tyrtaeum) on the growth of two plant species from different functional groups (Poa annua and Trifolium repens), and on the development of aphids (Myzus persicae) were investigated in a laboratory experiment lasting 20 weeks. Using soil from a fallow site which had been set aside for about 15 years, we expected that nitrogen would be of limited supply to plants and hypothesized that the soil animals studied, particularly earthworms, would increase nutrient availability to plants and thereby also modify aphid reproduction and development. Plant growth was modified strongly by the presence of soil animals. Earthworms caused a more than twofold increase in shoot and root mass of P. annua but increased that of T. repens by only 18% and 6%, respectively. However, earthworms neither affected plant shoot/root ratio nor the nitrogen concentration in plant tissue. In contrast, the presence of Collembola caused a reduction in plant biomass particularly that of P. annua roots, but plant tissue nitrogen concentration was increased, although only slightly. Aphid reproduction on T. repens was lowered in the presence of Collembola on average by 45% but on P. annua increased by a factor of about 3. It is concluded that Collembola decrease aphid reproduction on more palatable host plants like T. repens but increase that on less palatable ones like P. annua. Earthworm presence also affected aphid reproduction but the effect was less consistent than that of Collembola. In the presence of earthworms, aphid reproduction was in one experimental period increased by some 70%. Earthworms also modified the numbers of Collembola and their vertical distribution in experimental chambers. Exploitation of deeper soil layers by H. nitidus was increased but, generally, O. scotarius numbers were reduced whereas those of H. nitidus increased in earthworm treatments. The presence of Collembola also influenced earthworm body mass during the experiment. In general it declined, but in the presence of Collembola loss of body mass of A. caliginosa was more pronounced. We conclude that inhibiting effects between Collembola and earthworms resulted from the use of a common resource, litter material rich in nitrogen. This is supported by the higher C/N ratio of the litter material in the presence of earthworms and Collembola by the end of the experiment. Effects of soil invertebrates like Collembola and earthworms on plant performance and aphid development are assumed to be modified by complex direct and indirect interactions among soil animal groups.
195 citations
TL;DR: To find out the extent to which aphids depend on their symbionts for synthesis of individual essential amino acids, it is evaluated how well phloem sap amino acid composition matches the aphids' needs.
Abstract: Aphids harbour intracellular symbionts (Buchnera) that provide their host with amino acids present in low amounts in their diet, phloem sap. To find out the extent to which aphids depend on their symbionts for synthesis of individual essential amino acids, we have evaluated how well phloem sap amino acid composition matches the aphids’ needs. Amino acid compositions of the ingested phloem sap were compared to amino acids in aphid body proteins and also to available information about optimal diet composition for other plant feeding insects. Phloem sap data from severed stylets of two aphid species, Rhopalosiphum padi (L.) (Homoptera: Aphididae) feeding on wheat, and Uroleucon sonchi (L.) (Homoptera: Aphididae) feeding on Sonchus oleraceus (L.), together with published information on phloem sap compositions from other plant species were used.
186 citations
TL;DR: These extended laboratory studies are the first to demonstrate adverse tri-trophic interactions involving a lectin- expressing transgenic crop, a target pest aphid and a beneficial aphidophagous predator.
Abstract: Transgenic crops genetically engineered for enhanced insect resistance should be compatible with other components of IPM for the pest resistance to be durable and effective. An experimental potato line was genetically engineered to express an anti-aphid plant protein (snowdrop lectin, GNA), and assessed for possible interactions of the insect resistance gene with a beneficial pest predator. These extended laboratory studies are the first to demonstrate adverse tri-trophic interactions involving a lectin- expressing transgenic crop, a target pest aphid and a beneficial aphidophagous predator. When adult 2-spot ladybirds (Adalia bipunctata[L.]) were fed for 12 days on peach-potato aphids (Myzus persicae Sulzer) colonising transgenic potatoes expressing GNA in leaves, ladybird fecundity, egg viability and longevity significantly decreased over the following 2–3 weeks. No acute toxicity due to the transgenic plants was observed, although female ladybird longevity was reduced by up to 51%. Adverse effects on ladybird reproduction, caused by eating peach-potato aphids from transgenic potatoes, were reversed after switching ladybirds to feeding on pea aphids from non-transgenic bean plants. These results demonstrate that expression of a lectin gene for insect resistance in a transgenic potato line can cause adverse effects to a predatory ladybird via aphids in its food chain. The significance of these potential ecological risks under field conditions need to be further evaluated.
171 citations
TL;DR: In this paper, a greenhouse study was conducted to characterize the reflectance spectra of wheat (Triticum aestivum L.) damaged by Russian wheat aphids (Diuraphis noxia Mordvilko) and greenbugs (Schizaphis graminum Rondani) and to determine those leaf reflectance wavelengths that were most responsive to crop stress imposed by these aphid pests.
Abstract: The efficiency of field monitoring for insect pests would be improved with knowledge of reflected solar radiation from crop canopies during insect outbreaks. The objectives of this greenhouse study were to characterize leaf reflectance spectra of wheat (Triticum aestivum L.) damaged by Russian wheat aphids (Diuraphis noxia Mordvilko) and greenbugs (Schizaphis graminum Rondani) and to determine those leaf reflectance wavelengths that were most responsive to crop stress imposed by these aphid pests. When the ligule was visible on second oldest leaf, wheat plants were infested with four wingless adult Russian wheat aphids, four wingless adult greenbugs, or left uninfested (four replicate plants per treatment). Plants and aphid populations were allowed to grow under greenhouse conditions for 3 wk, after which leaf-reflected radiation (from the adaxial surface across the 350-1075 nm range), dry weight, area, and chlorophyll concentrations were measured. When compared with the control, greenbug feeding damage caused general necrosis in oldest (first) leaves and dramatically lowered the dry weight, leaf area, and chlorophyll concentration of the second, third, and fourth leaves. Russian wheat aphid feeding resulted in a reduction in leaf dry weight and area in the third and fourth leaves, and a reduction in total chlorophyll concentration in all leaves. Leaf reflectance in the 625- to 635-nm and the 680- to 695-nm ranges, as well as the normalized total pigment to chlorophyll a ratio index (NPCI), were significantly correlated with total chlorophyll concentrations in both greenbug- and Russian wheat aphid-damaged plants. Thus, both of these wavelength ranges, as well as this reflectance index, were good indicators of chlorophyll loss and leaf senescence caused by the aphid feeding damage.
151 citations
TL;DR: In-flight orientation of the braconid Aphidius ervi in response to volatiles released from broad bean plants infested by the pea aphid, Acyrthosiphon pisum, was studied in a no-choice wind-tunnel bioassay and indicated the specificity of synomones elicited by different aphid species on the same plant species.
Abstract: In-flight orientation of the braconid Aphidius ervi in response to volatiles released from broad bean plants infested by the pea aphid, Acyrthosiphon pisum, was studied in a no-choice wind-tunnel bioassay. The role of aphid infestation level and duration, systemic production of volatiles by “insect-free” parts of the plant, and the specificity of aphid-induced volatiles on the flight behavior of the foraging female parasitoids were investigated. The upper insect-free part of a three-leaved broad bean plant, which was basally infested by a population of 40 A. pisum, released synomones detectable by A. ervi females after at least 48–72 hr of infestation, resulting in both significant increases in oriented flights and landings on the source compared with uninfested control plants. This suggests that volatiles involved in host-location by A. ervi are systemically released by broad bean plants either in response to circulation of aphid saliva, circulation of saliva-induced bioactive elicitors, or circulation of the synomones themselves. Air entrainment extracts of volatiles collected from a broad bean plant infested by the nonhost Aphis fabae or an uninfested broad bean plant elicited few oriented flights and landing responses by female parasitoids. These extracts were significantly less attractive than extracts collected from a broad bean plant infested by the host A. pisum, indicating the specificity of synomones elicited by different aphid species on the same plant species.
150 citations
TL;DR: The results presented below indicate that the pea aphid responded to the tracks left by ladybird larvae by producing a greater proportion of winged offspring, which avoid the impending increased risk of predation by dispersing.
Abstract: Predator–mediated plasticity in the morphology, life history and behaviour of prey organisms has been widely reported in freshwater ecosystems. Although clearly adaptive, similar responses have only recently been reported for terrestrial organisms. This is surprising as aphids are polyphenic and develop very rapidly compared with their predators and often produce very large colonies, which are attractive to predators. Therefore, one might expect terrestrial organisms like aphids to show a facultative change in their development in response to the presence of predators and other results have confirmed this. The results presented below indicate that the pea aphid responded to the tracks left by ladybird larvae by producing a greater proportion of winged offspring, which avoid the impending increased risk of predation by dispersing. Associated with this was a short–term increase in activity and reduction in fecundity. The black bean and vetch aphids, which are afforded some protection from ladybirds because they are ant attended and/or unpalatable, did not respond in this way to the presence of ladybird larvae.
140 citations
TL;DR: The fate of sucrose, the major nutrient of an aphid's natural food, was explored by radiolabeling, and the metabolic abilities of aphid are discussed from an adaptive point of view, with respect to their symbiotic status.
Abstract: The fate of sucrose, the major nutrient of an aphid's natural food, was explored by radiolabeling in the pea aphid Acyrthosiphon pisum. To investigate the influence of nitrogen quality of food on amino acid neosynthesis, pea aphids were reared on two artificial diets differing in their amino acid composition. The first (diet A) had an equilibrated amino acid balance, similar to that derived from analysis of aphid carcass, and the other (diet B) had an unbalanced amino acid composition similar to that of legume phloem sap. Aphids grown on either diet expired the same quantity of sucrose carbon as CO(2), amounting to 25-30 % of the ingested sucrose catabolized in oxidation pathways. On diet A, the aphids excreted through honeydew about twice as much sucrose carbon as on diet B (amounting to 12.6 % of the ingested sucrose for diet A and 8.4 % for diet B), while amounts of sucrose carbons incorporated into exuviae were almost identical (1.9 % of the ingested sucrose on diet A and 2.7 % on diet B). There was also no difference in the amounts of sucrose carbon incorporated into the aphid tissues, which represented close to 50 % of the ingested sucrose. Sucrose carbons in the aphid tissues were mainly incorporated into lipids and the quantities involved were the same in aphids reared on either diet. On diet B, we observed neosynthesis of all protein amino acids from sucrose carbons and, for the first time in an aphid, we directly demonstrated the synthesis of the essential amino acids leucine, valine and phenylalanine. Amino acid neosynthesis from sucrose was significantly higher on diet B (11.5 % of ingested sucrose carbons) than on diet A (5.4 %). On diet A, neosynthesis of most of the amino acids was significantly diminished, and synthesis of two of them (histidine and arginine) was completely suppressed. The origin of amino acids egested through honeydew was determined from the specific activity of the free amino acid pool in the aphid. Aphids are able to adjust to variation in dietary amino acids by independent egestion of each amino acid. While more than 80 % of excreted nitrogen was from food amino acids, different amino acids were excreted in honeydew of aphids reared on the two diets. The conversion yields of dietary sucrose into aphid amino acids determined in this study were combined with those obtained previously by studying the fate of amino acids in pea aphids reared on diet A. The origin of all the amino acid carbons in aphid tissues was thus computed, and the metabolic abilities of aphid are discussed from an adaptive point of view, with respect to their symbiotic status.
TL;DR: The positive effects of mycorrhizal colonization reported here are contrary to the majority of previous studies with chewing insects, which have reported negative effects.
Abstract: Two generations of two aphid species (Myzus ascalonicus and M. persicae) were reared on Plantago lanceolata plants, with and without root colonization by the arbuscular mycorrhizal fungus, Glomus intraradices. Life history traits of the aphids measured were nymphal development time, teneral adult weight, growth rate, total fecundity, adult longevity and duration of post-reproductive life. For both aphids in both generations, mycorrhizal colonization increased aphid weight and fecundity, while other traits were unaffected. The increases were consistent between generations. In a second experiment, M. persicae was reared on plants with and without the fungus, under varying N and P regimes. The results of N addition were inconclusive because there was high aphid mortality. However, under P supplementation, positive effects of the mycorrhiza on aphid growth were seen at low and medium P levels, while at high P levels these effects disappeared. The positive effects of mycorrhizal colonization reported here are contrary to the majority of previous studies with chewing insects, which have reported negative effects. A number of possible mechanisms for this apparent discrepancy are discussed.
TL;DR: ConA, a glucose/mannose-specific lectin from jackbean, has potential as a protective agent against insect pests in transgenic crops and is functionally active as a haemagglutinin.
Abstract: The effects of concanavalin A (ConA), a glucose/mannose-specific lectin from jackbean (Canavalia ensiformis), on insect crop pests from two different orders, Lepidoptera and Homoptera, were investigated. When fed to larvae of tomato moth (Lacanobia oleracea) at a range of concentrations (0.02–2.0% of total protein) in artificial diet, ConA decreased survival, with up to 90% mortality observed at the highest dose level, and retarded development, but had only a small effect on larval weight. When fed to peach-potato aphids (Myzus persicae) at a range of concentrations (1–9μM) in liquid artificial diet, ConA reduced aphid size by up to 30%, retarded development to maturity, and reduced fecundity (production of offspring) by >35%, but had little effect on survival. With both insects, there was a poor correlation between lectin dose and the quantitative effect. Constitutive expression of ConA in transgenic potatoes driven by the CaMV 35S promoter resulted in the protein accumulating to levels lower than predicted, possibly due to potato not being able to adequately reproduce the post-translational processing of this lectin which occurs in jackbean. However, the expressed lectin was functionally active as a haemagglutinin. Bioassay of L. oleracea larvae on ConA-expressing potato plants showed that the lectin retarded larval development, and decreased larval weights by >45%, but had no significant effect on survival. It also decreased consumption of plant tissue by the larvae. In agreement with the diet bioassay results, ConA-expressing potatoes decreased the fecundity of M. persicae by up to 45%. ConA thus has potential as a protective agent against insect pests in transgenic crops.
TL;DR: Host aphids of the parasitoid Diaeretiella rapae (M’Intosh,) are defined for Washington State, together with a listing of world findings, and D. rapae was shown to switch or alternate successfully between hosts, which suggests that certain host habitats might be used in conjunction with farmlands to enhance host opportunities for the Parasitoid and improve its population stability.
Abstract: Host aphids of the parasitoid Diaeretiella rapae (M’Intosh,) are defined for Washington State, together with a listing of world findings. Specifics are given on host habitats frequented by the parasitoid, comparative population abundance, associated parasitoid species, and host switching. D. rapae is a common parasitoid of Brachycorynella asparagi (Mordvilko), Hayhurstia atriplicis (L.), Brevicoryne brassicae (L.), Diuraphis noxia (Kurdjumov), and sometimes Myzus persicae (Sulzer). In total, 19 species of aphids were positively linked with D. rapae and 6 are reported as hosts for the first time— Acyrthosiphon lactucae (Passerini), Phorodon humuli (Schrank), Dysaphis plantaginea (Passerini), Brachycaudus tragopogonis (Kaltenbach), Uroleucon ivae Robinson, and Braggia sp. D. rapae was shown to switch or alternate successfully between hosts, which suggests that certain host habitats might be used in conjunction with farmlands to enhance host opportunities for the parasitoid and improve its population stability. Two of its primary aphid hosts, B. asparagi and D. noxia, reached pest status shortly after their arrival in Washington but are less problematic today, in part at least because of host switching and acceptance by D. rapae.
TL;DR: This analysis, which was based on the results from seven microsatellite loci, has confirmed that A. gossypii populations in southern France are primarily asexual, as only 12 nonrecombinant genotypic classes (clones) were identified from 694 aphids.
Abstract: Aphis gossypii is an aphid species that is found throughout the world and is extremely polyphagous. It is considered a major pest of cotton and cucurbit species. In Europe, A. gossypii is assumed to reproduce exclusively by apomictic parthenogenesis. The present study investigates the genetic diversity of A. gossypii in a microgeographic, fragmented habitat consisting of eight glasshouses of cucurbit crops. This analysis, which was based on the results from seven microsatellite loci, has confirmed that A. gossypii populations in southern France are primarily asexual, as only 12 nonrecombinant genotypic classes (clones) were identified from 694 aphids. Moreover, a high proportion of the aphids (87%) had one of three common genotypes. No significant correlation was found between genotypic class and host plant species. Within a glasshouse population of A. gossypii, a significant reduction in clonal diversity was observed as the spring/summer season progressed. The final predominance of a clone could result from interclonal competition. At the microgeographic level (i.e. glasshouses within a 500-m radius), significant genetic subdivision was detected and could be attributed to founder effects and the limitation of gene flow imposed by the enclosed nature of the glasshouse structure. Finally, the three common clones of A. gossypii detected in 1996 reappeared in spring 1997 following the winter extinction, together with rare clones that had not previously been seen. The probability that A. gossypii overwinters within refuges at a microgeographic scale from which populations are renewed each spring is discussed.
TL;DR: Variability in attack rates among aphids both among and within plants decreased parasitoid foraging efficiency, with the greatest decrease caused by among‐plant variability.
Abstract: When a parasitoid is searching for hosts, not all hosts are equally likely to be attacked. This variability in attack probability may affect the parasitoid functional response. Using a collection of experiments, we quantified the functional response of Aphidius ervi (Hymenoptera: Braconidae), an insect parasitoid of the pea aphid Acyrthosiphon pisum (Homoptera: Aphididae). We measured variability in the number of hosts attacked by a foraging parasitoid both among plants and within plants. At the first scale, A. ervi, searching among plants containing different numbers of aphids, showed both aphid‐density‐dependent and aphid‐density‐independent variability in the number of aphids attacked per plant. Within plants, A. ervi selectively attacked second and third instar aphids relative to other instars. Furthermore, there was variability in the susceptibility of attack among aphids independent of instar. Variability in attack rates among aphids both among and within plants decreased parasitoid foragi...
TL;DR: It is demonstrated that pea aphid populations that are specialized on alfalfa are successfully parasitized less often than are populations specialized on clover, and the difference in resistance on the two crops appears to be genetically based.
Abstract: The evolution of associations between herbivorous insects and their parasitoids is likely to be influenced by the relationship between the herbivore and its host plants. If populations of specialized herbivorous insects are structured by their host plants such that populations on different hosts are genetically differentiated, then the traits affecting insect-parasitoid interactions may exhibit an associated structure. The pea aphid (Acyrthosiphon pisum) is a herbivorous insect species comprised of genetically distinct groups that are specialized on different host plants (Via 1991a, 1994). Here, we examine how the genetic differentiation of pea aphid populations on different host plants affects their interaction with a parasitoid wasp, Aphidius ervi. We performed four experiments. (1) By exposing pea aphids from both alfalfa and clover to parasitoids from both crops, we demonstrate that pea aphid populations that are specialized on alfalfa are successfully parasitized less often than are populations specialized on clover. This difference in parasitism rate does not depend upon whether the wasps were collected from alfalfa or clover fields. (2) When we controlled for potential differences in aphid and parasitoid behavior between the two host plants and ensured that aphids were attacked, we found that pea aphids from alfalfa were still parasitized less often than pea aphids from clover. Thus, the difference in parasitism rates is not due to behavior of either aphids or wasps, but appears to be a physiologically based difference in resistance to parasitism. (3) Replicates of pea aphid clones reared on their own host plant and on a common host plant, fava bean, exhibited the same pattern of resistance as above. Thus, there do not appear to be nutritional or secondary chemical effects on the level of physiological resistance in the aphids due to feeding on clover or alfalfa, and therefore the difference in resistance on the two crops appears to be genetically based. (4) We assayed for genetic variation in resistance among individual pea aphid clones collected from clover fields and found no detectable genetic variation for resistance to parasitism within two populations sampled from clover. This is in contrast to Henter and Via's (1995) report of abundant genetic variation in resistance to this parasitoid within a pea aphid population on alfalfa. Low levels of genetic variation may be one factor that constrains the evolution of resistance to parasitism in the populations of pea aphids from clover, leading them to remain more susceptible than populations of the same species from alfalfa.
TL;DR: The objective was to determine whether color or odor-mediated cues of plants infected with Potyviridae mediate aphid attraction, and it was found that Myzus persicae and Rhopalosiphum maidis preferred alighting on intensely yellow than on green or brown ceramic tiles, and expressed no preference for landing on leaves infected with soybean mosaic virus.
Abstract: The progress of nonpersistently transmitted virus epidemics can be substantially altered by the degree of aphid attraction and preference for virus-infected plants. Our objective was to determine whether color or odor-mediated cues of plants infected with Potyviridae mediate aphid attraction. We found that Myzus persicae (Sulzer) and Rhopalosiphum maidis (Fitch) preferred alighting on intensely (highly saturated) yellow than on green (plant-like) or brown (soil-like) ceramic tiles, and expressed no preference for landing on leaves infected with soybean mosaic virus (SMV) or on chlorophyll-deficient soybean leaves. Furthermore, neither aphid species showed odor-mediated attraction to leaf extracts of SMV-infected leaves. Also, R. maidis remained longer on uninfected than on SMV-infected soybean plants before taking flight, although M. periscae exhibited no preference. Neither aphid species had a preference to remain on healthy or potato virus Y-infected plants. Therefore, we conclude that both aphid species when landing are equally likely to alight on healthy or SMV-infected soybean plants in the field, but R. maidis is likely to remain a shorter time on SMV-infected than on healthy plants before taking off. The fact that aphids leave the infected plant soon after probing increases the probability of finding another plant and making an infective probe before the vector loses its potential to inoculate the virus. These results could be used to increase the precision of existing simulations models, such as the one previously developed for SMV.
TL;DR: It is demonstrated that photosynthetic adjustments can significantly contribute to plant tolerance resulting from arthropod injury, and evidence here indicates that an active plant defense through antibiosis comes at the cost of reduced capacity for physiological tolerance and compensation.
Abstract: Plant tolerance to injury from insect herbivores has several advantages as a pest management approach. However, its use is limited because mechanisms conferring plant tolerance are not well understood. We hypothesize that plant physiological responses, specifically photosynthesis, substantially contribute to plant tolerance to arthropod injury. This hypothesis was tested on 3 wheat ( Triticum eastivum L.) lines that differed in their mode of resistance to the Russian wheat aphid, Diuraphis noxia (Mordvilko). The lines were ‘Arapahoe’ (a susceptible line), PI 137739 (an antibiotic line), and PI 262660 (a tolerant line). These lines were grown in a greenhouse, aphids were maintained on plants for 1 wk, and physiological responses of these lines were determined. Light curve and fluorescence data indicated that the primary mechanism for photosynthetic rate reduction in aphid-injured leaves is via interference of the photochemical efficiency at the initial stage of photosynthesis. Aphid-injured seedlings had lower light-saturation points, which suggested less efficient use of light energy compared with control seedlings. Immediately after aphid removal, aphid injury reduced chlorophyll fluorescence and photosynthetic rates in all lines, but PI 137739 (with antibiosis) had significantly greater photosynthetic rate reduction. Photosynthetic rates of the tolerant line, PI 262660, began recovering 3 d after aphid removal with complete photosynthetic recovery 7 d after aphid removal. This gradual photosynthetic compensation did not occur in the other 2 lines. PI 262660 also had greater leaf area and more dry matter when compared with the other cultivars. This study demonstrates that photosynthetic adjustments can significantly contribute to plant tolerance resulting from arthropod injury. Moreover, evidence here indicates that an active plant defense through antibiosis comes at the cost of reduced capacity for physiological tolerance and compensation.
TL;DR: It is concluded that the absence of the two species of aphid in the study site is influenced by the resident predator community, and by the availability of mutualists.
Abstract: We investigated why two species of aphids (Aphis jacobaeae and Brachycaudus cardui) were very rare in a study site despite their abundance in the surrounding area. The study site contained many common species of aphid and we tested the hypothesis that the community of aphid predators in the field excluded the missing species. Colonies of the two aphid species were artificially initiated in the experimental site and allocated to one of four treatments: control; ground predator exclusion; total predator exclusion, and provision of mutualist ants. Two measures of colony performance were analysed: longevity and cumulative aphid density. Colonies decline naturally in late summer but control colonies disappeared very quickly while colonies protected from all predators survived the longest. The performance of colonies protected from just ground predators was intermediate. We failed to persuade ants to tend A. jacobaeae. Colonies of B. cardui attended by ants performed better than controls and those with ground predators excluded, but not as well as those with all predators excluded. We conclude that the absence of the two species of aphid in the study site is influenced by the resident predator community, and by the availability of mutualists.
TL;DR: The allometry of body size and body mass in relation to parasitoid fitness is discussed and individuals developing in pea aphid were absolutely larger in dry mass as well as proportionately larger relative to their hind‐tibia length.
Abstract: We describe the allometry of body mass and body size as measured by hind-tibia length in males of Monoctonus paulensis (Ashmead) (Hymenoptera: Braconidae, Aphidiinae), a solitary parasitoid of aphids To assess the influence of host quality on allometric relationships, we reared parasitoids on second and fourth nymphal instars of four different aphid species, Acyrthosiphon pisum (Harris), Macrosiphum creelii Davis, Myzus persicae (Sulzer) and Sitobion avenae (F), under controlled conditions in the laboratory Dry mass was positively correlated with hind-tibia length, and could be predicted from it, in unparasitized aphids, in aphid mummies containing parasitoid pupae, and in the parasitoid The reduced-major-axis scaling exponents for the regression of dry mass on hind-tibia length were species-specific in aphids, reflecting differences in volume and shape between species In mummified aphids, the stage at death influenced the size/mass relationship In males of M paulensis, the allometric exponent varied between parasitoids developing in different kinds of host Individuals developing in pea aphid were absolutely larger in dry mass as well as proportionately larger relative to their hind-tibia length We discuss the allometry of body size and body mass in relation to parasitoid fitness
TL;DR: The selection of pubescent leaves infested with aphids by ovipositing females reflects both the food dependence and predation risk constraints of immature midges.
Abstract: Eggs and neonate larvae of the aphidophagous midge Aphidoletes aphidimyza Rondani are vulnerable to intraguild predation and starvation. The role of A. aphidimyza females in selecting suitable oviposition sites for offspring survival and development was investigated in the laboratory on potato. Oviposition preference, measured as the number of eggs laid in different microhabitats, increased with density of the potato aphid, Macrosiphum euphorbiae (Thomas), and plant pubescence. However, midge females do not discriminate between plants colonized by the coccinellid predator Coleomegilla maculata lengi Timberlake and those that are not. A. aphidimyza egg survival in the presence of C. macula larvae and adults was higher in sites characterized by a high density of trichomes than in other microhabitats. The selection of pubescent leaves infested with aphids by ovipositing females reflects both the food dependence and predation risk constraints of immature midges.
TL;DR: Comparisons between different experimental systems show that long-term population responses to elevated CO2 can not be reliably predicted from detailed measurements on individual aphids.
Abstract: We studied the impact of elevated CO2 on 2 aphid pest species, Myzus persicae and Brevicoryne brassicae (Homoptera: Aphididae), on a series of host plants in 3 independent studies each differing in experimental complexity. Measurements on individual aphids showed that host plant and aphid species significantly influenced the response to elevated CO2. These differences occurred not only in the level of responsiveness but also directionally. B. brassicae reared on Brassica oleracea produced significantly less offspring at elevated CO2, whereas the opposite was found for M. persicae on the same host. No response was found for M. persicae on Senecio vulgaris. When populations of B. brassicae and M. persicae were followed for a longer period, no differences were observed in population sizes. Comparisons between different experimental systems show that long-term population responses to elevated CO2 can not be reliably predicted from detailed measurements on individual aphids. The consequences of these findings for climate change research are discussed.
TL;DR: Significant changes in leaf temperature were recorded in 11 combinations, indicating that the aphid response is part of a broader effect of plant‐plant communication.
Abstract: Effects of volatiles from one plant on the aphid acceptance of a neighbouring plant were studied in laboratory experiments with four barley cultivars. With a compressor‐supported system, air was led over one plant and then over a test plant. After treatment, settling of apterae of Rhopalosiphum padi (L.) on the responding test plants was compared with that on control plants treated with air from no other plant or air from a plant of the same cultivar. In an untreated state the four barley cultivars did not show differences with regard to aphid acceptance. However, after exposure to air from another plant significant changes in aphid acceptance were found in seven of the 16 possible cultivar combinations of inducing and responding plants. Significant changes in leaf temperature were recorded in 11 combinations, indicating that the aphid response is part of a broader effect of plant‐plant communication. Two of the four cultivars showed significant intracultivar communication. The congruence between changes ...
TL;DR: A complex of large coccinellid species was inferred to have the greatest potential for impact on BCA populations in Puerto Rico, and Predation by syrphid larvae was another important source of BCA mortality.
Abstract: Populations of the brown citrus aphid (BCA), Toxoptera citricida (Kirkaldy), and associated insects were monitored in citrus groves in western Puerto Rico in 1996 and 1997. Peak populations of the aphid were observed in spring and fall of both years. A total of 6,737 infested citrus terminals were examined and categorized by growth stage and BCA colony size. Natural enemies, primarily coccinellids, syrphids, chrysopids, and aphidiids, were recorded when present in BCA colonies and a list of species is presented. A complex of large coccinellid species was inferred to have the greatest potential for impact on BCA populations in Puerto Rico. Predation by syrphid larvae was another important source of BCA mortality. The parasitoid, Lysiphlebus testaceipes (Cresson), was abundant in some samples, but usually parasitized only a small percentage of aphids within colonies. The fungus, Verticillium lecanii (Zimm.), infected BCA colonies sporadically. The red imported fire ant, Solenopsis invicta Buren, was often observed harvesting honeydew from BCA colonies and interfering with natural enemies.
TL;DR: The results show that larval and pupal cannibalism and interspecific predation occur more frequently when aphid populations crash, but there is no evidence of coccinellid density-dependent mortality or density- dependent larval dispersal among species.
Abstract: Coccinellid larvae are known to prey upon conspecific and heterospecific eggs, larvae, prepupae, and pupae. This behavior may depend on both the aggregation and intensive search of potential cannibals and predators near aphid colonies and the disappearance of aphids before coccinellid larvae have completed their development. We examined how coccinellid density and prey availability influence cannibalism and interspecific predation of larvae and pupae of 4 species of coccinellids. We determined whether coccinellid mortality and dispersal were density-dependent when prey become scarce, and estimated the leaving rates of Coleomegilla maculata (DeGeer), Adalia bipunctata (L.), and Hippodamia convergens (Guerin) larvae from plants with aphids and plants without aphids. Our results show that larval and pupal cannibalism and interspecific predation occur more frequently when aphid populations crash, but we found no evidence of coccinellid density-dependent mortality or density-dependent larval dispersal among species. However, A. bipunctata and H. convergens were significantly more aggressive and more likely to leave a plant without aphids than was C. maculata. These results suggest that the decision to stay on a plant is not strongly aphid- or pollen-mediated for C. maculata, but the decision to stay or leave does appear to be aphid-mediated for H. convergens and to some extent A. bipunctata. Whether a coccinellid larva stays or leaves and its tendency to cannibalize can affect larval and pupal survival and the population dynamics of each species.
TL;DR: An augmentative release of larvae significantly prevented the build‐up of colonies of D. plantaginea and significant reductions in aphid numbers were recorded at the two highest predator‐prey ratios, 1:1 and 5:1.
Abstract: The impact of augmentative releases of larvae and eggs of the indigenous ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) against the rosy apple aphid Dysaphis plantaginea Pass. (Homoptera: Aphididae), a major pest insect on apple trees, was assessed in field experiments in Switzerland, during 1997. In a first experiment, eggs and larvae were released on 3-year old apple trees infested with five aphids at four different predator-prey ratios (0:5, 1:5, 1:1, 5:1). In a second experiment, eggs and larvae were released at a predator-prey ratio of 5:1 on branches of apple trees naturally infested with aphids. In both experiments, the interaction with ants was taken into account and the releases were done at two different times in spring. The results showed that an augmentative release of larvae significantly prevented the build-up of colonies of D. plantaginea. Significant reductions in aphid numbers were recorded at the two highest predator-prey ratios, 1:1 and 5:1. Larvae were efficient just before flowering of apple trees at a time when growers normally have to spray their trees. On trees where ants were present the larvae of A. bipunctata were significantly less efficient. Effects of eggs of A. bipunctata, however, were less reliable. At the first date of release (5 April), they did not hatch, probably as a consequence of bad weather conditions.
TL;DR: Coccinellidae were the most efficient predators of T. citricida, and Syrphid flies were other important predators, especially Pseudodorus clavatus (Florida and Puerto Rico) and Ocyptamus fuscipennis (Puerto Rico).
Abstract: Sixteen cohorts of the brown citrus aphid, Toxoptera citricida, were followed from colony initiation to maturation/extinction in citrus groves at two sites in Puerto Rico and nine sites in Florida, USA. Infested citrus terminals were sampled repeatedly in a non-destructive manner and data recorded on the recruitment of natural enemies and the fate of aphid colonies. Coccinellidae were the most efficient predators of T. citricida, primarily Cycloneda sanguinea, and Coelophora inaequalis (Puerto Rico), C. sanguinea, Harmonia axyridis (Florida). Coccinellids were abundant in citrus year-round in Puerto Rico, but in Florida citrus their abundance peaked in spring and declined thereafter. Syrphid flies were other important predators, especially Pseudodorus clavatus (Florida and Puerto Rico) and Ocyptamus fuscipennis (Puerto Rico). Syrphids increased in abundance from spring to fall in both regions. Other predators included Cereaochrysa lineaticornis, Chrysoperla rufilabris (Chrysopidae) and Micromus posticus (Hemerobiidae). The parasitoid Lysiphlebus testaceipes was ubiquitous in T. citricida cohorts, but its impact on colony survival was usually low. The fungal pathogen Verticillium lecanii was a significant source of colony mortality at one site in Puerto Rico, but was not observed on T. citricida in Florida.
TL;DR: The number of species of fungi collected reflects a great diversity in the aphid-pathogenic flora from South Africa, including six Entomophthorales and two Hyphomycetes.
TL;DR: S. alba has good potential as an alternative crop suitable for northern Idaho because it can be grown with reduced late season insecticide application and is completely resistant to cabbage seedpod weevil, and Aphid colonization was observed on plants from all species.
Abstract: The effect of late season insect infestation on seed yield, yield components, oil content and oil quality of two canola species (Brassica napus L. and B. rapa L.) and two mustard species (B. juncea L. and Sinapis alba L.) was examined over 2 years. In each year, ten genotypes from each species were evaluated with late season insects controlled with either methyl parathion or endosulfan insecticides, and without insecticides. Major late season insect damage in 1992 was caused by cabbage seedpod weevil (Ceutorhynchus assimilis Paykull), while diamondback moth (Plutella xylostella L.) and aphids (primarily cabbage aphids, Brevicoryne brassicae L.) were major insect pests in 1993. Insecticide application was very effective in controlling diamondback moth larvae and adult cabbage seedpod weevils, but only partially effective in controlling aphids. Higher numbers of diamondback moth larvae were observed on mustard species compared to canola species. S. alba was completely resistant to cabbage seedpod weevil and there was no damage due to this pest observed. Aphid colonization was observed on plants from all species, but infestation on S. alba and B. rapa occurred too late to have a major effect on seed yield. Seed oil content of canola species was significantly reduced by insect damage although oil quality (indicated by fatty acid profile) was not affected by insect attack. Uncontrolled insect infestation reduced seed yield of canola species by 37 and 32 % in B. napus and B. rapa, respectively. Least yield reduction occurred in S. alba, where average yield reduction from plants in untreated control plots was < 10 % of insecticide treated plants. S. alba, therefore, has good potential as an alternative crop suitable for northern Idaho because it can be grown with reduced late season insecticide application.