Showing papers on "Aphid published in 2001"
TL;DR: Phloem feeding on Arabidopsis leads to stimulation of response pathways associated with both pathogen infection and wounding, and application of the SA analog benzothiadiazole led to decreases in aphid reproduction on leaves of both wild-type plants and mutant plants deficient in responsiveness to SA.
Abstract: Little is known about molecular responses in plants to phloem feeding by insects. The induction of genes associated with wound and pathogen response pathways was investigated following green peach aphid (Myzus persicae) feeding on Arabidopsis. Aphid feeding on rosette leaves induced transcription of two genes associated with salicylic acid (SA)-dependent responses to pathogens (PR-1 and BGL2) 10- and 23-fold, respectively. Induction of PR-1 and BGL2 mRNA was reduced in npr1 mutant plants, which are deficient in SA signaling. Application of the SA analog benzothiadiazole led to decreases in aphid reproduction on leaves of both wild-type plants and mutant plants deficient in responsiveness to SA, suggesting that wild-type SA-dependent responses do not influence resistance to aphids. Two-fold increases occurred in mRNA levels of PDF1.2, which encodes defensin, a peptide involved in the jasmonate (JA)-/ethylene-dependent response pathway. Transcripts encoding JA-inducible lipoxygenase (LOX2) and SA/JA-inducible Phe-ammonia lyase increased 1.5- to 2-fold. PDF1.2 and LOX2 induction by aphids did not occur in infested leaves of the JA-resistant coi1-1 mutant. Aphid feeding induced 10-fold increases in mRNA levels of a stress-related monosaccharide symporter gene, STP4. Phloem feeding on Arabidopsis leads to stimulation of response pathways associated with both pathogen infection and wounding.
554 citations
TL;DR: Honeydew composition is an important factor in mediating ant–homopteran mutualisms and the trisaccharide melezitose is especially significant in this interaction, but it is shown for the first time that ant tending may itself influence honeyd Dew composition.
Abstract: Summary
1 Honeydew composition is an important factor in mediating ant–homopteran mutualisms. The trisaccharide melezitose is especially significant in this interaction. Honeydew of three Chaitophorus aphids (Homoptera: Aphididae), reared on two species of Populus (Salicaceae), was analysed to investigate factors that may influence honeydew composition.
2 Honeydew of Chaitophorus populialbae and C. populeti contained high proportions of the melezitose. These species are typically tended by ants. In contrast, C. tremulae honeydew contained low proportions of melezitose. This species is typically untended.
3 Chaitophorus populeti and C. populialbae produced higher proportions of melezitose when reared on Populus tremula than on P. alba.
4 Chaitophorus populeti and C. populialbae reduced their production of melezitose when reared in the absence of ants. The reverse was true in C. tremulae.
5 These results show that honeydew composition differs not only between aphid species but also within aphid species. They support known differences in ant preference for the different aphid species, and produce further predictions for ant preference for aphids on different host plants. In particular they show for the first time that ant tending may itself influence honeydew composition. They suggest that maintaining a honeydew composition attractive to ants may incur metabolic costs on aphids.
208 citations
TL;DR: Ants not only attended their aphid partners, but also preyed on them, and the average predation rate increased eightfold when ants were offered the alternative of sugar, whereas alternative prey had no significant effect.
Abstract: Nests of Lasius niger (L.) ants were given varied food regimens to test whether their behaviour towards an aphid partner, Aphis fabae (Scop.), changed with alternative food supplies. Honeydew collection and predation on aphids were measured by video monitoring the movement of ants between their nest and an aphid aggregation. Data collected from the aphid aggregations enabled comparisons between remaining aphid biomass and between the tending intensities of the ants. I tested how ant behaviour was influenced by their access to alternative prey and sugar. The results showed that ants accepted a honey solution as a substitute for the honeydew produced by aphids. Ants not only attended their aphid partners, but also preyed on them. The average predation rate increased eightfold when ants were offered the alternative of sugar, whereas alternative prey had no significant effect. In contrast, ant-tending intensity decreased with alternative sugar whereas alternative prey elicited no effect.
176 citations
TL;DR: The impact of introducing a predator, the convergent ladybird beetle, Hippodamia convergens, on the biological control of the cotton aphid, Aphis gossypii, by the parasitoid Lysiphlebus testaceipes, under field conditions is evaluated.
Abstract: Many predatory arthropods eat both unparasitized herbivores and herbivores that are parasitized and contain the immature stages of endoparasitoids, a form of intraguild predation. Thus, the biological control of herbivorous arthropods can be either enhanced or disrupted by introducing a predator species to an existing host-parasitoid system. We evaluate the impact of introducing a predator, the convergent ladybird beetle, Hippodamia convergens, on the biological control of the cotton aphid, Aphis gossypii, by the parasitoid Lysiphlebus testaceipes, under field conditions. Predation on immature parasitoids by H. convergens was intense: 98–100% of aphid mummies were consumed by the end of the experiment, and H. convergens substantially reduced immature parasitoid populations. Despite the negative impact of H. convergens on aphid parasitoids, aphid population suppression was greatest in treatments containing both H. convergens and parasitoids. The parasitoid alone or in combination with H. convergens suppressed cotton aphids in a density-dependent manner and increased total plant leaf area and biomass, H. convergens did not substantially alter the percentage of aphids mummified by parasitoids and showed a partial feeding preference for unparasitized aphids over aphid mummies. We conclude that under conditions where a predator shows both a partial preference for unparasitized hosts and high levels of predation on unparasitized hosts, we may expect the predator to improve suppression of herbivores even if it produces high levels of intraguild predation. While intraguild predation is an important ecological interaction in the early-season cotton agroecosystem, it does not disrupt cotton aphid biological control.
170 citations
TL;DR: The hypothesis that mutualists, predators, and host plant quality act in concert to determine the distribution and abundance of a common herbivore is examined and mechanisms that de- termine arthropod community structure are uncovered.
Abstract: We examined the hypothesis that mutualists, predators, and host plant quality act in concert to determine the distribution and abundance of a common herbivore. The aphid, Chaitophorus populicola, is found only in association with ants, which provide tending services and protection from predators. As a consequence, aphid abundance declined by 88% on host plants located ?6 m from an ant mound. Differences in host plant quality resulted in aphid fecundity being greatest on narrowleaf cottonwoods, 7-22% less on back- cross hybrids, 37-46% less on F1 hybrids, and 57-61% less on Fremont cottonwoods. Due to the combined effects of these factors, we found that the realized aphid habitat was only 21% of their potential habitat. On trees where aphids and tending ants are present, aphids and ants greatly outnumber any other arthropod species; therefore, we examined the hypothesis that the factors affecting aphid density and distribution are also determinants of arthropod community structure. On a per-tree basis, observational data showed that arthropod species richness was 51% greater and abundance was 67% greater on trees where aphid-ant mutualists were absent relative to trees where they were present. When aphids were experimentally removed and ants abandoned the tree, we found the same pattern. On a per-tree basis, arthropod species richness increased by 57%, and abundance increased by 80% where aphid-ant mutualists were removed, relative to control trees. Overall, a total of 90 arthropod species were examined in this study: 56% were found only on trees without aphid-ant mutualists, 12% were found only on trees with aphid-ant mutualists, and 32% were common to both. Specific guilds were also affected; the aphid-ant mutualism had a negative effect on herbivores, generalist predators, and other species of tending ants, and a positive effect on specialist enemies of aphids. These results suggest that, by examining the factors responsible for the population dynamics of a common herbivore, we may also uncover mechanisms that de- termine arthropod community structure. Furthermore, studies that address the role of mu- tualism in shaping communities are underrepresented in the literature; these results em- phasize the importance of mutualism in ecological communities.
169 citations
TL;DR: The hypothesis that there might be trade-offs (negative covariation) in defensive ability against different natural enemies, but found no evidence for this, and the factors that might maintain clonal variation in natural enemy resistance are discussed.
Abstract: The potential rate of evolution of resistance to natural enemies depends on the genetic variation present in the population and any trade-offs between resistance and other components of fitness. We measured clonal variation and covariation in pea aphids (Acyrthosiphon pisum) for resistance to two parasitoid species (Aphidius ervi and A. eadyi) and a fungal pathogen (Erynia neoaphidis). We found significant clonal variation in resistance to all three natural enemies. We tested the hypothesis that there might be trade-offs (negative covariation) in defensive ability against different natural enemies, but found no evidence for this. All correlations in defensive ability were positive, that between the two parasitoid species significantly so. Defensive ability was not correlated with fecundity. A number of aphid clones were completely resistant to one parasitoid (A. eadyi), but a subset of these failed to reproduce subsequently. We discuss the factors that might maintain clonal variation in natural enemy resistance.
168 citations
TL;DR: The level ofCry1Ab in insects feeding on sources containing the Cry1Ab protein was uniformly low but varied with insect species as well as food source, and secondary exposure risk assessment for transgenic Bt crops is discussed.
Abstract: Enzyme-linked immunosorbent assays (ELISA) and bioassays were used to estimate levels of Cry1Ab protein in four species of phytophagous insects after feeding on transgenic Bt-corn plants expressing Cry1Ab protein or artificial diets containing Cry1Ab protein. The level of Cry1Ab in insects feeding on sources containing the Cry1Ab protein was uniformly low but varied with insect species as well as food source. For the corn leaf aphid, Rhopalosiphum maidis(Fitch), feeding on diet solutions containing Cry1Ab protein, the level of the protein in the aphid was 250‐500 times less than the original levels in the diet, whereas no Cry1Ab was detected by ELISA in aphids feeding on transgenic Bt-Corn plants. For the lepidopteran insects, Ostrinia nubilalis(Hubner), Helicoverpa zea (Boddie), and Agrotis ipsilon(Hufnagel), levels of Cry1Ab in larvae varied significantly with feeding treatment. When feeding for 24 h on artificial diets containing 20 and 100 ppm of Cry1Ab, the level of Cry1Ab in the larvae was about 57 and 142 times lower, respectively, than the original protein level in the diet for O. nubilalis ,2 0 and 34 times lower for H. zea, and 10 to 14 times lower for A. ipsilon. Diet incorporation bioassays with a susceptible insect (first instar O. nubilalis) showed significant Cry1Ab bioactivity present within whole body tissues of R. maidis and O. nubilalis that had fed on diet containing a minimum of 20 ppm or higher concentrations (100 or 200 ppm) of Cry1Ab, but no significant bioactivity within the tissues of these insects after feeding on transgenic Bt-corn plants. The relevance of these findings to secondary exposure risk assessment for transgenic Bt crops is discussed.
155 citations
TL;DR: Field-collected individuals of the seven-spotted ladybird responded positively to volatiles from aphid-infested plants and from previously aphid-, uninfested or from undisturbed aphids, but not to vol atiles from un infested plants or from Undisturbed Aphids.
149 citations
TL;DR: Three Brassicaceae species, Brassica napus (low glucosinolate content), Brassica nigra (including sinigrin), and Sinapis alba (including sinalbin) were used as host plants for two aphid species: the generalist Myzus persicae and the specialist Brevicoryne brassicae, which showed increased ladybird larval mortality at higher GLS concentrations.
Abstract: Three Brassicaceae species, Brassica napus (low glucosinolate content), Brassica nigra (including sinigrin), and Sinapis alba (including sinalbin) were used as host plants for two aphid species: the generalist Myzus persicae and the specialist Brevicoryne brassicae. Each combination of aphid species and prey host plant was used to feed the polyphagous ladybird beetle, Adalia bipunctata. Experiments with Brassicaceae species including different amounts and kinds of glucosinolates (GLS) showed increased ladybird larval mortality at higher GLS concentrations. When reared on plants with higher GLS concentrations, the specialist aphid, B. brassicae, was found to be more toxic than M. persicae. Identification of GLS and related degradation products, mainly isothiocyanates (ITC), was investigated in the first two trophic levels, plant and aphid species, by high-performance liquid chromatography and gas chromatography–mass spectrometry, respectively. While only GLS were detected in M. persicae on each Brassicaceae species, high amounts of ITC were identified in B. brassicae samples (allyl-ITC and benzyl-ITC from B. nigra and S. alba, respectively) from all host plants. Biological effects of allelochemicals from plants on predators through aphid prey are discussed in relation to aphid species to emphasize the role of the crop plant in integrated pest management in terms of biological control efficacy.
146 citations
TL;DR: The nutritional quality of the host plant on which the parent generation feeds has a stronger effect on the aphids than that of the quality of their own food plants, which may dampen the effect short-term fluctuations in host plant quality have on aphid performance.
Abstract: The effect of nitrogen fertilization on Aphis gossypii Glover color and size, fertility, and intrinsic rate of increase (rm) was studied on cotton plants. Nitrogen fertilization treatments consisted of 0, 50, 100, and 150% of the agronomic recommended level. Adult and nymph densities, as well as rm, were positively correlated with nitrogen fertilization. Aphid body length, head width, and darkness of color were recorded in populations on cotton plants fertilized with 100% nitrogen or with no nitrogen fertilization. Aphids on nitrogen-fertilized plants were significantly bigger and darker. All body size and darkness of color measurements were positively correlated with aphid fecundity. It was also found that the nutritional quality of the host plant on which the parent generation feeds has a stronger effect on the aphids than that of the quality of their own food plants. This phenomenon may dampen the effect short-term fluctuations in host plant quality have on aphid performance. Results are discussed in the context of aphid population biology, aphid–plant interactions and aphid population management.
146 citations
TL;DR: There is a competition for the mutualistic services of ants between aphid species exploiting the same resource and the outcome of this competition depends on the aphid's selective attractiveness to ants, which corresponded with already reported differences in honeydew quality and quantity.
Abstract: Workers of the ant species Lasius niger showed marked preferences when collecting honeydew from three aphid species living on tansy, Tanacetum vulgare. Colonies of Metopeurum fuscoviride were visited most intensively, Brachycaudus cardui had an intermediate position, and colonies of Aphis fabae were visited least intensively. L. niger abandoned colonies of the less preferred species as soon as colonies of a higher-ranked species were available on neighbouring tansy plants. As a consequence, the abandoned colonies suffered a higher predation by aphid predators and persisted for a shorter time than attended colonies of the same species. If two aphid species were present in a mixed colony on the same shoot, the preferred species increased in numbers, while the less preferred species decreased due to predation by L. niger. The results show that there is a competition for the mutualistic services of ants between aphid species exploiting the same resource. The outcome of this competition depends on the aphid's selective attractiveness to ants, which corresponded with already reported differences in honeydew quality and quantity.
TL;DR: The data suggest that the introduced A. glycines can be an efficient vector of SMV, but a less efficientvector of AMV, in the North Central region, and may increase SMV and AMV incidence.
Abstract: The recent discovery of the soybean aphid, Aphis glycines Matsamura, in the North Central region of the United States is significant because it is the first time that a soybean-colonizing aphid has been detected in the New World. Although the aphid has the potential to cause physiological loss of up to 52% on soybeans (4), it can also transmit Soybean mosaic virus (SMV). Transmission of Alfalfa mosaic virus (AMV) has not been reported. SMV, and less commonly AMV, are found in soybeans in the North Central states and are transmitted by numerous aphids in a nonpersistent manner (2; Grau, unpublished). For SMV, potential exists for specificity of transmission between virus strain and aphid species (3). For these reasons, it was important to determine if an endemic isolate of these viruses could be transmitted by this introduced species of aphid in the North Central region. Transmission experiments were conducted as described (3), using 3, 5, and 10 aphids per plant. Ten plants of the soybean cultivar Williams 82 were used for each treatment. To preclude confounding results by possible seed transmission, plants used in all tests were grown from seeds harvested from virus-indexed plants grown in the greenhouse. For experiments involving SMV, the aphid-transmissible field isolate Al5 (GeneBank Accession no. AF242844) and, as a negative control, the non-aphid transmissible isolate N (GeneBank Accession no. D500507) were used. For experiments involving AMV, a field isolate of AMV, confirmed by ELISA and host range, was used. The aphid species Myzus persicae was maintained on broad bean and A. glycines was maintained on virus-free soybean. The protocol for transmission studies of AMV was identical to that used in the SMV study, except only A. glycines was tested. For experiments, plants were periodically observed for symptom development and tested by ELISA 4 to 5 weeks after inoculation access. No transmission of SMV-N occurred in any tests, which together involved 180 aphids each of M. persicae or A. glycines. For the Al5 isolate, transmission efficiencies of 30, 50, and 50% were obtained with 3, 5, and 10 individuals, respectively, of M. persicae per plant. Efficiencies for A. glycines were 30, 40, and 40%. Transmission levels by the two aphid species did not differ significantly (t-test, P = 0.01). For AMV, corresponding transmission efficiencies were 0, 0, and 20%. The data suggest that the introduced A. glycines can be an efficient vector of SMV, but a less efficient vector of AMV, in the North Central region. Transmission of AMV by M. persicae has been documented (1) but was not examined in this study. Transmission of SMV and AMV by A. glycines is of concern because it may increase SMV and AMV incidence. With the recent outbreak of Bean pod mottle virus (BPMV) in the region, the potential for synergism of SMV and BPMV is increased (2). References: (1) M. B. Castillo and G. G. Orlob. Phytopathology 56:1028, 1966. (2) G. L. Hartman et al., eds. 1999. Compendium of Soybean Diseases, 4th Ed. American Phytopathological Society, St. Paul, MN. (3) B. S. Lucas and J. H. Hill. Phytopathol. Z. 99:47, 1980. (4) C. L. Wang et al. Plant Prot. 20:12, 1994.
TL;DR: Different enzymatic responses in wheat, barley, and oat to D. noxia and R. padi feeding indicate the cereals have different mechanisms of aphid resistance, suggesting oxidative stress in plants is likely.
Abstract: The impact of the leaf-chlorosis-eliciting Russian wheat aphid, Diuraphis noxia (Mordvilko), and the nonchlorosis-eliciting bird cherry-oat aphid, Rhopalosiphum padi (L.), feeding on D. noxia-susceptible and -resistant cereals was examined during the period (i.e., 3, 6, and 9 d after aphid infestation) that leaf chlorosis developed. After aphid number, leaf rolling and chlorosis ratings, and fresh leaf weight were recorded on each sampling date, total protein content, peroxidase, catalase, and polyphenol oxidase activities of each plant sample were determined spectrophotometrically. Although R. padi and D. noxia feeding caused significant increase of total protein content in comparison with the control cereal leaves, the difference in total protein content between R. padi and D. noxia-infested leaves was not significant. Although R. padi-feeding did not elicit any changes of peroxidase specific activity in any of the four cereals in comparison with the control leaves, D. noxia feeding elicited greater increases of peroxidase specific activity only on resistant 'Halt' wheat (Triticum aestivum L.) and susceptible 'Morex' barley (Hordeum vulgare L.), but not on susceptible 'Arapahoe' and resistant 'Border' oat (Avena sativa L.). D. noxia-feeding elicited a ninefold increase in peroxidase specific activity on Morex barley and a threefold on Halt wheat 9 d after the initial infestation in comparison with control leaves. Furthermore, D. noxia feeding did not elicit any differential changes of catalase and polyphenol oxidase activities in comparison with either R. padi feeding or control leaves. The findings suggest that D. noxia feeding probably results in oxidative stress in plants. Moderate increase of peroxidase activity (approximately threefold) in resistant Halt compared with susceptible Arapahoe wheat might have contributed to its resistance to D. noxia, whereas the ninefold peroxidase activity increase may have possibly contributed to barley's susceptibility. Different enzymatic responses in wheat, barley, and oat to D. noxia and R. padi feeding indicate the cereals have different mechanisms of aphid resistance.
TL;DR: Host plants grown at elevated CO2 generally had greater biomass, leaf area and C:N ratios than those grown at ambient CO2, while plants with aphids had lower biomass and leaf area than those without aphids.
Abstract: We investigated interactions between five species of phloem-feeding aphids (Homoptera: Aphididae) and their host plants at elevated CO2; Acyrthosiphon pisum (Harris) on Vicia faba L., Aphis nerii Boyer de Fonscolombe on Asclepias syriaca L., Aphis oenotherae Oestlund on Oenothera biennis L., Aulacorthum solani (Kaltenbach) on Nicotiana sylvestris Speg. & Comes and Myzus persicae (Sulzer) on Solanum dulcamara L. Host plants grown at elevated CO2 generally had greater biomass, leaf area and C:N ratios than those grown at ambient CO2, while plants with aphids had lower biomass and leaf area than those without aphids.
The responses of aphid populations to elevated CO2 were species-specific with one species increasing (M. persicae), one decreasing (A. pisum), and the other three being unaffected. CO2 treatment did not affect the proportion of alate individuals produced. In general, aphid abundance was not significantly related to foliar nitrogen concentration.
We performed separate analyses to test whether either aphid presence or aphid abundance modified the response of host plants to elevated CO2. In terms of aphid presence, only three of the potential 15 interactions (five aphid species x three plant traits) were significant; A. solani slightly modified the response of the plant biomass to elevated CO2 and M. persicae affected the response of leaf area and allocation. In terms of aphid abundance, only two of the potential 15 interactions were significant with A. nerii modifying the plant response to CO2 in terms of total leaf area and allocation.
We conclude that, in contrast to other insect groups such as leaf chewers, populations of most phloem-feeders may not be negatively affected by increased CO2 concentrations in the future. The reasons for this difference include the possibility that aphids may be able to compensate for changes in host plant quality by altering feeding behaviour or by synthesizing amino acids. In addition, there is little evidence that aphid herbivory, even at high levels, will substantially modify the response of plants to elevated CO2.
TL;DR: The ability of aphid populations to adapt to high temperatures in the Iberia peninsula is suggested, suggesting the role of temperature as a key factor in determining aphid population dynamics in the northeastern Iberian peninsula.
Abstract: The development, reproduction and longevity of corn aphids Rhopalosiphum padi (L.), Sitobion avenae (Fabricius) and Metopolophium dirhodum (Walker) were studied at 18, 22, 25, 27.5 and 30°C. Only nymphs of R. padi survived at 30°C, but the adult reproductive capacity was very low. Rhopalosiphum padi performed better than M. dirhodum at all temperatures tested, and better than S.avenae over the range of 22–27.5°C. The better performance of R. padi was due to a lower nymphal mortality, lower developmental and prereproductive times and a higher intrinsic rate of increase (rm). Sitobion avenae had a higher rm than M. dirhodum at all temperatures. The most suitable temperature for population development was ≈28.5°C for R. padi, 26.5°C for S. avenae and 24.5°C for M. dirhodum, suggesting the ability of aphid populations to adapt to high temperatures in the Iberian peninsula. The role of temperature as a key factor in determining aphid population dynamics in the northeastern Iberian peninsula is discussed.
TL;DR: Transgenic Bt potato, Bt‐based microbial formulations and systemic insecticides appeared to be compatible with the development of integrated pest management (IPM) against other potato pests such as GPA because these CPB control measures have little impact on major natural enemies.
Abstract: Field studies were conducted in 1992 and 1993 in Hermiston, Oregon, to evaluate the efficacy of transgenic Bt potato (Newleaf®, which expresses the insecticidal protein Cry3Aa) and conventional insecticide spray programs against the important potato pest, Leptinotarsa decemlineata (Say), Colorado potato beetle (CPB), and their relative impact on non-target arthropods in potato ecosystems. Results from the two years of field trials demonstrated that Newleaf potato plants were highly effective in suppressing populations of CPB, and provided better CPB control than weekly sprays of a microbial Bt-based formulation containing Cry3Aa, bi-weekly applications of permethrin, or early- and mid-season applications of systemic insecticides (phorate and disulfoton). When compared with conventional potato plants not treated with any insecticides, the effective control of CPB by Newleaf potato plants or weekly sprays of a Bt-based formulation did not significantly impact the abundance of beneficial predators or secondary potato pests. In contrast to Newleaf potato plants or microbial Bt formulations, however, bi-weekly applications of permethrin significantly reduced the abundance of several major generalist predators such as spiders (Araneae), big-eyed bugs (Geocorus sp.), damsel bugs (Nabid sp.), and minute pirate bugs (Orius sp.), and resulted in significant increases in the abundance of green peach aphid (GPA), Myzus persicae (Sulzer) – vector of viral diseases, on the treated potato plots. While systemic insecticides appeared to have reduced the abundance of some plant sap-feeding insects such as GPA, lygus bugs, and leafhoppers, early and mid-season applications of these insecticides had no significant impact on populations of the major beneficial predators. Thus, transgenic Bt potato, Bt-based microbial formulations and systemic insecticides appeared to be compatible with the development of integrated pest management (IPM) against other potato pests such as GPA because these CPB control measures have little impact on major natural enemies. In contrast, the broad-spectrum pyrethroid insecticide (permethrin) is less compatible with IPM programs against GPA and the potato leafroll viral disease.
TL;DR: Aphid performance was strongly influenced by the presence of protozoa, but not by earthworms, and the numbers and biomass of adult and juvenile aphids were significantly increased, likely due to an increased N content in barley plants and consequently increased nitrogen availability to aphids.
Abstract: We investigated if the activity of soil invertebrates (protozoa and earthworms) affected the performance of barley and if effects propagated higher up the above-ground food chain into herbivores (cereal aphid, Sitobion avenae). Barley plants were grown individually in microcosms containing defaunated soil and grass residues. Plants were grown in soil containing: a) no added fauna, b) protozoa, c) earthworms, or d) protozoa and earthworms. After 7 weeks growth at 20°C three adult cereal aphids were added to each plant on separate leaves. The aphids were allowed to grow and reproduce for another 2 weeks before the experiment was destructively sampled. Amounts of mineral N in the soil and leached from the microcosms were significantly reduced by the presence of soil animals. Correspondingly plant biomass and total plant N content were increased significantly by soil animals, protozoa in particular. The different mechanisms responsible for changes in nutrient turnover in presence of protozoa and earthworms are discussed. Aphid performance was strongly influenced by the presence of protozoa, but not by earthworms. In the presence of protozoa the numbers and biomass of adult and juvenile aphids were significantly increased. These effects are likely due to an increased N content in barley plants and consequently increased nitrogen availability to aphids. The results underline that the detritivore and herbivore systems are intimately linked.
TL;DR: Recent cultural practices in California cotton include higher rates of nitrogen fertilization, which increases nitrogen content of plants, which is an important factor contributing to the increased severity of the cotton aphid as a pest of California cotton during the midseason.
Abstract: Field experiments were conducted from 1996 to 1998 to assess the effects of nitrogen fertilization rates and planting dates on the population dynamics of the cotton aphid, Aphis gossypii Glover, during the midgrowing season of California cotton. Cotton aphids reached higher densities in high nitrogen fertilized plants (227 kg N/ha, rate currently used by cotton growers) than in low nitrogen fertilized plants (57 kg N/ha). In addition, late-planted cotton (May–June), which had more nitrogen content, also harbored higher aphid populations than early plantings (April). Overall, aphid abundance was positively correlated with plant nitrogen content. In a moderate aphid pressure year (1996), planting the cotton early (April) was effective in keeping the aphid population below the midseason economic threshold. However, in a high aphid pressure year (1997), it was necessary to drastically reduce the nitrogen fertilization to 57 kg N/ha to maintain the aphid density under this threshold. Recent cultural practices in California cotton include higher rates of nitrogen fertilization, which increases nitrogen content of plants. The current data suggest that this practice (i.e., high fertilization) is an important factor contributing to the increased severity of the cotton aphid as a pest of California cotton during the midseason.
TL;DR: Results suggest that ethylene is involved in the oxidative responses of barley plants induced by infestation, and increases with the degree of infestation.
Abstract: The purpose of this work was to investigate whether ethylene is involved in the oxidative and defensive responses of barley to the aphids Schizaphis graminum (biotype C) and Rhopalophum padi. The effect of aphid infestation on ethylene production was measured in two barley cultivars (Frontera and Aramir) that differ in their susceptibility to aphids. Ethylene evolution was higher in plants infested for 16 hr than in plants infested for 4 hr in both cultivars. Under aphid infestation, the production of ethylene was higher in cv. Frontera than in Aramir, the more aphid susceptible cultivar. Ethylene production also increases with the degree of infestation. Maximum ethylene evolution was detected after 16 hr when plants were infested with 10 or more aphids. Comparing the two species of aphids, Schizaphis graminum induced more ethylene evolution than Rhopalosiphum padi. Infestation with S. graminum increased hydrogen peroxide content and total soluble peroxidase activity in cv. Frontera, with a maximum level of H2O2 observed after 20 min of infestation and the maximum in soluble peroxidase activity after 30 min of infestation. When noninfested barley seedlings from cv. Frontera were exposed to ethylene, an increase in hydrogen peroxide and in total peroxidase activity was detected at levels similar to those of infested plants from cv. Frontera. When noninfested plants were treated with 40 ppm of ethylene, the maximum levels of H2O2 and soluble peroxidase activity were at 10 and 40 min, respectively. Ethylene also increased the activity of both cell-wall-bound peroxidases types (ionically and covalently bound), comparable with infestation. These results suggest that ethylene is involved in the oxidative responses of barley plants induced by infestation.
TL;DR: It is suggested that the increase in the proportions of sucrose and trehalose in honeydew leads to a shortage of carbohydrates available for energy metabolism, resulting in lower performance of the aphids under ant attendance.
Abstract: Mutualistic interactions between aphids and ants are mediated by the honeydew produced by aphids. Previous work showed that when attended by the ant Formica yessensis, nymphs of the aphid Tuberculatus quercicola developed into significantly smaller adults with lower fecundity than when not ant-attended. This study tested the hypothesis that this cost of ant attendance arises through changes in the quality and quantity of honeydew. Ant-attended and ant-excluded aphid colonies were prepared in the field, and the sugar concentration and sugar composition of the honeydew of ant-attended colonies were compared with those of ant-excluded colonies. The frequency and amount of honeydew excretion were also quantified in the two types of colonies. The aphids excreted smaller droplets of honeydew more frequently in ant-attended colonies than in ant-excluded colonies. There was no significant difference in total sugar concentration between the honeydew of ant-attended aphids and ant-excluded aphids. However, ant-attended aphids produced honeydew containing a significantly lower proportion of glucose and higher proportions of sucrose and trehalose than did ant-excluded aphids. These results suggest that the enhanced rate of honeydew-excretion behavior under ant attendance led to changes in the aphid's physiological status. We suggest that the increase in the proportions of sucrose and trehalose in honeydew leads to a shortage of carbohydrates available for energy metabolism, resulting in lower performance of the aphids under ant attendance.
TL;DR: It is demonstrated that Mi-mediated aphid resistance is isolate-specific, and it may not extend to all aphid species, and that virulent potato aphids are geographically widespread, and, unlike virulent nematode isolates, are relatively common.
Abstract: Mi is a dominant locus in tomato that confers resistance to both root knot nematodes, Meloidogyne spp., and potato aphids, Macrosiphum euphorbiae (Thomas). The goal of this study was to investigate the breadth of Mi-mediated aphid resistance. To examine variability in potato aphid response, the effect of Mi on seven isolates of the potato aphid from California, New Jersey, North Carolina, France, and The Netherlands was measured in greenhouse bioassays. Assays were also performed to determine if Mi impacted another aphid species that attacks tomato, Myzus persicae (Sulzer). Tomato varieties carrying Mi had a profound negative impact on the potato aphid isolates from France and The Netherlands. In contrast, other potato aphid isolates from New Jersey, North Carolina, and California proved to be virulent, or capable of overcoming Mi. Mi-mediated resistance also did not extend to the green peach aphid isolates tested. These results demonstrate that Mi-mediated aphid resistance is isolate-specific, a...
TL;DR: It is suggested that the incidence of PABS in pea aphids is determined by the balance between loss (processes may include occasional failure of vertical transmission and selection against PABS-positive aphids) and horizontal transfer between insects.
TL;DR: A laboratory method using large population cages that represent an intermediate experimental scale is presented, allowing the study of ecological and behavioural interactions between transgenic plants, pests and their natural enemies under more controlled conditions than is possible in the field.
Abstract: Studies of the effects of insect-resistant transgenic plants on beneficial insects have, to date, concentrated mainly on either small-scale ‘worst case scenario’ laboratory experiments or on field trials. We present a laboratory method using large population cages that represent an intermediate experimental scale, allowing the study of ecological and behavioural interactions between transgenic plants, pests and their natural enemies under more controlled conditions than is possible in the field. Previous studies have also concentrated on natural enemies of lepidopteran and coleopteran target pests. However, natural enemies of other pests, which are not controlled by the transgenic plants, are also potentially exposed to the transgene product when feeding on hosts. The reduction in the use of insecticides on transgenic crops could lead to increasing problems with such nontarget pests, normally controlled by sprays, especially if there are any negative effects of the transgenic plant on their natural enemies. This study tested two lines of insect-resistant transgenic oilseed rape
(Brassica napus) for side-effects on the hymenopteran parasitoid
Diaeretiella rapae and its aphid host, Myzus persicae. One transgenic line expressed the d-endotoxin Cry1Ac from Bacillus thuringiensis
(Bt) and a second expressed the proteinase inhibitor oryzacystatin I
(OC-I) from rice. These transgenic plant lines were developed to provide resistance to lepidopteran and coleopteran pests, respectively. No detrimental effects of the transgenic oilseed rape lines on the ability of the parasitoid to control aphid populations were observed. Adult parasitoid emergence and sex ratio were also not consistently altered on the transgenic oilseed rape lines compared with the wild-type lines.
TL;DR: Densities declined in fields harboring intermediate aphid densities when lacewing subpopulations were experimentally caged to block immigration and emigration, suggesting that Chrysoperla spp.
Abstract: The functional importance of higher-order predators in terrestrial ecosystems is currently an area of active inquiry. In particular, an understanding of the relative influences of prey availability and higher-order predation on predator populations is of immediate relevance to the theory of biological control of herbivorous arthropods. Biological control workers have repeatedly speculated that one cause of failure to establish predators and parasitoids in novel environments is the strong mortality imposed on released agents by higher-order predators. Nevertheless, the ability of higher-order predators to create a habitat where mortality exceeds natality (a “sink” habitat) has never been tested experimentally with a biological control agent in nature.
Although in isolation the predatory lacewing Chrysoperla carnea can consistently produce strong suppression of populations of the aphid Aphis gossypii, the full community of predators when tested together exerts minimal aphid control. The age structure of Chrysoperla spp. populations in cotton fields harboring low to intermediate densities of aphid prey is characterized by a sharp drop in densities from the egg to the first larval instar; this observation is consistent with heavy mortality during either the egg or first larval stage. Egg cohorts followed under unmanipulated field conditions showed relatively high rates of successful hatch, suggesting that the vulnerable developmental stage is the young larva. Larval survival is relatively high in the absence of hemipteran predators, suggesting that prey availability is not the primary limiting factor. Depressed survival is observed in the presence of Geocoris spp., Nabis spp., and Zelus renardii, all common hemipteran predators in cotton. Predation on lacewing larvae appears to disrupt the strong top-down control of aphid populations in cotton.
Chrysoperla spp. densities declined in fields harboring intermediate aphid densities when lacewing subpopulations were experimentally caged to block immigration and emigration. In one year (1993) Chrysoperla spp. densities fell to very low levels, suggesting that the field was either a true sink habitat or a pseudosink with a very low equilibrium density. In a second year (1994), densities declined to what appeared to be a lower but stable density, suggesting that the habitat was a pseudosink. Thus, in both years, declines in Chrysoperla spp. densities were observed following caging, suggesting that Chrysoperla spp. populations are spatially subsidized. Aphid prey availability and higher-order predation interacted strongly in their influence on C. carnea survival: larval survival in the presence of higher-order predators was 5.6% when prey availability was intermediate and 40.5% when prey were superabundant. Spatial heterogeneity in aphid prey densities modulates the intensity of higher-order predation and thereby appears to produce source–sink dynamics of Chrysoperla spp. in cotton fields.
TL;DR: Broad bean (Vicia faba), an annual plant bearing extrafloral nectaries, is regularly infested by two aphid species, Aphis fabae and Acyrthosiphon pisum, and it is suggested that EFN may provide some degree of protection for V. faba against those sucking herbivores that are not able to attract ants.
Abstract: Broad bean (Vicia faba), an annual plant bearing extrafloral nectaries (EFN) at the base of the upper leaves, is regularly infested by two aphid species, Aphis fabae and Acyrthosiphon pisum. EFN and A. fabae are commonly attended by the ant, Lasius niger, while Ac. pisum usually remains uninfested. Sugar concentration and sugar composition of extrafloral nectar did not change significantly after aphid infestation. The sugar concentration was significantly higher in EFN (c. 271 µg µl–1) than in the honeydew of A. fabae (37.5 µg µl–1). The presence of small A. fabae colonies had no significant effect on ant attendance of EFN, which remained at the same level as that on plants without A. fabae. Obviously, there was no significant competitive effect between the two sugar sources. We suggest that the high sugar concentration in the extrafloral nectar may outweigh the higher quality (due to the presence of melezitose) and quantity of aphid honeydew. Ants and the presence of EFN influenced aphid colony growth. While A. fabae colonies generally grew better in the presence of ants, Ac. pisum colonies declined on plants with EFN or A. fabae colonies. We conclude that EFN may provide some degree of protection for V. faba against those sucking herbivores that are not able to attract ants.
TL;DR: It has been shown that exudates from the roots of aphid-infested plants, grown hydroponically or in soil, cause intact plants to become more attractive to parasitoids, and aerial interactions between intact barley plants from different cultivars can also influence acceptability to aphids.
TL;DR: The effects of induced resistance to cotton aphids, two-spotted spider mites, and western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in cotton plants were investigated using applications of the natural plant inducer, jasmonic acid (JA).
Abstract: Plants can be treated with natural elicitors to induce resistance to herbivores. The effects of induced resistance to cotton aphids Aphis gossypii Glover (Homoptera: Aphididae), two-spotted spider mites Tetranychus urticae Koch (Acari: Tetranychidae), and western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in cotton plants were investigated using applications of the natural plant inducer, jasmonic acid (JA). Preference was reduced by more than 60% for aphids and spider mites, and more than 90% for thrips on JA-induced leaves compared with control leaves. Survival of aphid nymphs was reduced by two-fold and percentage of nymphs attaining the adult stage was reduced by about eight-fold on induced leaves compared with controls. Induction reduced survival and reproduction of adult aphids by about 40% and 75%, respectively. Induction did not affect survival in spider mites or thrips. However, induction reduced egg production in spider mites by more than 75% and feeding in thri...
TL;DR: Results indicate that Rme1 does not play a general role in disease resistance but may be specific for Mi-1-mediated resistance, and the response against Fusarium oxysporum f.sp.
Abstract: The tomato Mi-1 gene confers resistance against root-knot nematodes (Meloidogyne spp.) and a biotype of the potato aphid (Macrosiphum euphorbiae). Four mutagenized Mi-1/Mi-1 tomato populations were generated and screened for altered root-knot nematode resistance. Four independent mutants belonging to two phenotypic classes were isolated. One mutant was chosen for further analyzes; rme1 (for resistance to Meloidogyne) exhibited levels of infection comparable with those found on susceptible controls. Molecular and genetic data confirmed that rme1 has a single recessive mutation in a locus different from Mi-1. Cross-sections through galls formed by feeding nematodes on rme1 roots were identical to sections from galls of susceptible tomato roots. In addition to nematode susceptibility, infestation of rme1 plants with the potato aphid showed that this mutation also abolished aphid resistance. To determine whether Rme1 functions in a general disease-resistance pathway, the response against Fusarium oxysporum f.sp. lycopersici race 2, mediated by the I-2 resistance gene, was studied. Both rme1 and the wild type plants were equally resistant to the fungal pathogen. These results indicate that Rme1 does not play a general role in disease resistance but may be specific for Mi-1-mediated resistance.
TL;DR: Host choice by Monoctonus paulensis was qualitatively the same as host order based on estimated fitness returns, and A. pisum was the “best” host in terms of successful oviposition, eclosion from mummies, and offspring sex ratio.
TL;DR: Changes in phloem content, combined with differences in ingestion rates, resulted in large differences among aphids in estimated rates of ingestion of individual amino acids, implying dependence on symbiont provisioning.
Abstract: . Nutrient provisioning in aphids depends both on the composition of ingested phloem sap and on the biosynthetic capabilities of the aphid and its intracellular symbionts. Amino acid budgets for three aphid species, Rhopalosiphum padi (L.), Schizaphis graminum (Rondani) and Diuraphis noxia (Mordvilko), were compared on a single host plant species, wheat Triticum aestivum L. Ingestion of amino acids from phloem, elimination of amino acids in honeydew, and the content of amino acids in aphids tissue were measured. From these values, ingestion rates were estimated and compared to honeydew and to estimated composition of aphid proteins. Ingestion rate was lowest in D. noxia due to low growth rate and low honeydew production; intermediate in S. graminum due to higher growth rate and intermediate honeydew production; and highest in R. padi, which had the highest rates for both variables. Both D. noxia and S. graminum induced increases in the amino acid content of ingested phloem. These changes in phloem content, combined with differences in ingestion rates, resulted in large differences among aphids in estimated rates of ingestion of individual amino acids. In honeydew, most essential amino acids were found in low amounts compared with the amounts ingested, especially for methionine and lysine. A few amino acids (arginine, cystine, histidine and tryptophan) were more abundant in honeydew of some aphids, suggesting oversupply. Aphid species differed in the composition of free amino acids in tissue but showed very similar composition in protein, implying similar requirements among the aphids. In R. padi and D. noxia, most essential amino acids were ingested in amounts insufficient for growth, implying dependence on symbiont provisioning. In S. graminum, most amino acids were ingested in amounts apparently sufficient for growth.