Showing papers on "Aphididae 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: 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: 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.
134 citations
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.
131 citations
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.
129 citations
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.
124 citations
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.
109 citations
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: 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: 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: Experiments with gynoparae of the black bean aphid, Aphis fabae Scopoli, show that these insects detect primary-host-specific cues during stylet penetration of peripheral plant tissues, and these stimuli promote settling and reproduction.
Abstract: The life cycle of some aphid species involves seasonal switches between unrelated summer (secondary) and winter (primary) host plants. Many of these “host-alternating” species, belonging to the sub-family Aphidinae, produce two return migrant forms on secondary host plants in autumn. Winged females (gynoparae) are produced first; these locate the primary host and deposit their sexual female offspring (oviparae). Later, males are produced on the secondary host and these locate the primary host independently before mating with the oviparae. The mechanisms of primary-host location by gynoparae and males are reviewed in this paper. Studies with several aphid species indicate that both forms are able to respond to volatile cues released by their specific primary host plant. Plant odours may also enhance or modify the responses of return migrants to the sex pheromone released by mature oviparae. Aphids are also able to sample non-volatile plant chemicals after landing, but there have been very few detailed investigations of the behaviour of return migrants at the primary-host-plant surface. Recent experiments with gynoparae of the black bean aphid, Aphis fabae Scopoli, show that these insects detect primary-host-specific cues during stylet penetration of peripheral plant tissues, and these stimuli promote settling and reproduction. Similar behavioural studies with males are required to shed light on the processes of speciation and reproductive isolation in host-alternating aphids.
TL;DR: The potential for indirect competition between two phloem-feeding aphids as mediated by a shared host, pecan Carya illinoensis, is evaluated in a greenhouse experiment.
Abstract: 1. This study evaluates the potential for indirect competition between two phloem-feeding aphids as mediated by a shared host, pecan Carya illinoensis. In a greenhouse experiment, one of two aphid species, Monellia caryella and Melanocallis caryaefoliae,
TL;DR: The results show the importance of screening cultivars against a wide variety of aphid clones when assessing aphid susceptibility in breeding programmes and the implications of these results on the adaptability of parthenogenetic aphids.
Abstract: The suitability of five grain legume species (narrow-leafed lupin, chickpea, faba bean, field pea, lentil) as hosts for three aphid species (green peach aphid, cowpea aphid, bluegreen aphid) was evaluated by measuring the mean relative growth rate (MRGR) and survivorship of nymphs over a 5 day period. For each aphid species, intraspecific (interclonal) variation was also determined by independently measuring the performance of 30 clones collected from a variety of hosts and from different parts of the Western Australia (WA) wheatbelt. The suitability of the grain legumes varied among aphid species. Chickpea was not a suitable host for any of the aphids tested. Averaged over all clones, lentil and faba bean were the most suitable hosts for cowpea aphid, and narrow-leafed lupin was the most suitable host for green peach aphid. Field pea was a suitable host for all three species, but only at a suboptimal level. Cowpea aphid showed the greatest amount of intraspecific variation, with significant variation in MRGR among clones on all hosts except chickpea and significant variation in survivorship on chickpea and lupin. For green peach aphid, there was significant variation in MRGR among clones on field pea and lupin, but in survivorship on lupin only. Bluegreen aphid clones showed significant variation only for MRGR on faba bean and lupin. There were positive correlations in performance of green peach aphid clones on faba bean and lentil, and of cowpea aphid clones on faba bean and lentil. Bluegreen aphid clones showed a negative correlation in performance on field pea and faba bean. These results show the importance of screening cultivars against a wide variety of aphid clones when assessing aphid susceptibility in breeding programmes. The implications of these results on the adaptability of parthenogenetic aphids are discussed.
TL;DR: The evidence for apparent competition in host-parasitoid communities is discussed and parasitism was highest in the presence of the treatment species and its host, intermediate when just the host was present, and lowest when both were absent.
Abstract: Summary
1
Two field manipulation experiments were performed to look for apparent competition between primary parasitoids of aphids, mediated by shared secondary parasitoids. In each case the frequency of secondary parasitism on a ‘focal’ species was compared in the presence or absence of a ‘treatment’ species and its aphid host.
2
In both experiments the focal species was Aphidius ervi (Haliday) attacking Acyrthosiphon pisum (Harris) (pea aphid). In the first experiment the treatment species was Aphidius rhopalosiphi (De Stefani-Perez) attacking Sitobion avenae (Fabricius) (a grass aphid) and in the second Aphidius microlophii (Pennachio & Tremblay) attacking Microlophium carnosum (Buckton) (nettle aphid).
3
No significant effects of either the presence of A. rhopalosiphi or of its host on secondary parasitism of A. ervi were detected in the first experiment.
4
In the second experiment, rates of secondary parasitism were estimated twice: a significant effect of treatment was found on the first occasion but not the second. In the former, parasitism was highest in the presence of the treatment species and its host, intermediate when just the host was present, and lowest when both were absent.
5
We discuss the evidence for apparent competition in host-parasitoid communities.
TL;DR: The effects of two natural aphid enemies, adult Coccinella septempunctata Linneaus, a predator, and Aphidius rhopalosiphi de Stefani Perez, a parasitoid, on spread of barley yellow dwarf virus (BYDV) were studied under laboratory conditions.
Abstract: The effects of two natural aphid enemies, adult Coccinella septempunctata Linneaus, a predator, and Aphidius rhopalosiphi de Stefani Perez, a parasitoid, on spread of barley yellow dwarf virus (BYDV) transmitted by the bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) were studied under laboratory conditions. Predators or parasitoids were introduced to trays of durum wheat seedlings and the patterns of virus infection were observed after two, seven and 14 days of exposure. More plants were infected with BYDV in control trays without A. rhopalosiphi than in trays with the parasitoid present, both seven and 14 days after the introduction of parasitoids. Patterns of virus infection were found to be similar over time in trays with a parasitoid present and in control trays. More plants were infected in trays with C. septempunctata present than in control trays, both two and seven days after the introduction of the coccinellid. The spread of virus infections progressed differently over time for the two treatments (predator and parasitoid), differences between treatments being most marked after two days and seven days, when more plants exposed to predators but fewer exposed to parasitoids were infected with BYDV compared to their respective controls. However, by the 14th day 88% of all plants were infected and there was no significant difference between the two treatments. The role of natural enemies in spread of BYDV is discussed.
TL;DR: It is concluded that the reddish spot is correlated with, but is not itself responsible for, the observed induced resistance of S. halepense against S. flava.
Abstract: Feeding by the aphid Sipha flava produces a reddish spot on mature leaves of Sorghum halepense. The present work is aimed at determining whether this plant response entails induced resistance against the aphid. Old and young leaves showed the same response to aphid feeding (reddish coloration). Water-stressed plants displayed a similar reddish coloration to aphid-infested plants. This was verified by evaluation of absorbance peaks of the respective leaf extracts. Aphid fecundity was reduced on previously infested (and hence reddish colored) leaves. However, aphid fecundity was not affected on water stressed plants. Furthermore, aphid survival was not different on artificial diets containing increasing concentrations of the reddish pigment. It is concluded that the reddish spot is correlated with, but is not itself responsible for, the observed induced resistance of S. halepense against S. flava.
TL;DR: Results indicate that R. padi can play a significant role in the epidemiology of BYDV-RMV, and may be especially significant in regions where corn is a major source of virus and of aphids that can carry virus into a fall-planted wheat crop.
Abstract: The RMV strain of Barley yellow dwarf virus (BYDV-RMV) is an unassigned member of the Luteoviridae that causes barley yellow dwarf in various cereal crops. The virus is most efficiently vectored by the aphid Rhopalosiphum maidis, but can also be vectored with varying efficiency by R. padi and Schizaphis graminum. Field collections of alate aphids migrating into the emerging winter wheat crop in the fall of 1994 in central New York identified a high proportion of R. padi transmitting BYDV-RMV. This prompted a comparison of the BYDV-RMV isolates and the R. padi populations found in the field with type virus and aphid species maintained in the laboratory. A majority of the field isolates of BYDV-RMV were similar to each other and to the type BYDV-RMV isolate in disease severity on oat and in transmission by the laboratory-maintained population of R. maidis and a field-collected population of R. maidis. However, several field populations of R. padi differed in their ability to transmit the various BYDV-RMV isolates. The transmission efficiency of the R. padi clones was increased if acquisition and inoculation feeding periods were allowed at higher temperatures. In addition, the transmission efficiency of BYDV-RMV was significantly influenced by the aphid that inoculated the virus source tissue. In general, BYDV-RMV transmission by R. padi was higher when R. padi was the aphid that inoculated the source tissue than when R. maidis was the inoculating aphid. The magnitude of the change varied among virus isolates and R. padi clones. These results indicate that, under certain environmental conditions, R. padi can play a significant role in the epidemiology of BYDV-RMV. This may be especially significant in regions where corn is a major source of virus and of aphids that can carry virus into a fall-planted wheat crop.
TL;DR: Here, it is document that pea aphid populations that are more resistant to parasitism in laboratory assays exhibit lower rates of Parasitism in the field, suggesting that the genetically based differences in aphid resistance may influence rates of successful parasitism.
Abstract: In insect host-parasitoid systems, successful immune responses of the host kill the parasitoid, and successful development of the parasitoid will kill the host. Thus, hosts and their parasitoids can exert strong selection on each other that may lead to the coevolution of host defense traits and parasitoid counter-defenses. In upstate New York, pea aphids (Acyrthosiphon pisum) specialized on alfalfa are, on average, two times more physiologically resistant to parasitism by Aphidius ervi parasitoids than pea aphids spe- cialized on clover. There is genetic variation within populations of Aphidius ervi in the ability to overcome pea aphid resistance; thus an evolutionary response to the differences in aphid resistance is possible. Here, I document that pea aphid populations that are more resistant to parasitism in laboratory assays exhibit lower rates of parasitism in the field, suggesting that the genetically based differences in aphid resistance may influence rates of successful parasitism. I found that the difference in resistance between pea aphids spe- cialized on alfalfa or on clover in New York is present in additional populations of pea aphids assayed over several years and is present in Maryland as well as New York. However, despite the potentially large difference in selective regimes due to differences in aphid resistance, parasitoids collected from alfalfa fields and clover fields do not differ in their ability to overcome pea aphid resistance. There is no evidence that they are adapted to aphids from their home crop, or locally adapted to aphids from their home field. The mobility of this parasitoid, and its relatively recent introduction to North America as a biological control agent, may contribute to the lack of adaptation.
TL;DR: Pest management efforts should focus on sampling for and suppressing this aphid species, which is unlikely to cause economic loss on wheat in South Carolina, thus crop managers should not have to sample for the subterranean R. rufiabdominalis colonies.
Abstract: Aphid (Homoptera: Aphididae) seasonal flight activity and abundance in wheat, Triticum aestivum L., and the significance of aphid species as vectors of barley yellow dwarf virus were studied over a nine-year period in the South Carolina coastal plain. Four aphid species colonized wheat in a consistent seasonal pattern. Greenbug, Schizaphis graminum (Rondani), and rice root aphid, Rhopalosiphum rufiabdominalis (Sasaki), colonized seedling wheat immediately after crop emergence, with apterous colonies usually peaking in December or January and then declining for the remainder of the season. These two aphid species are unlikely to cause economic loss on wheat in South Carolina, thus crop managers should not have to sample for the subterranean R. rufiabdominalis colonies. Bird cherry-oat aphid, Rhopalosiphum padi (L.), was the second most abundant species and the most economically important. Rhopalosiphum padi colonies usually remained below 10/row-meter until peaking in February or March. Barley yellow dwarf incidence and wheat yield loss were significantly correlated with R. padi peak abundance and aphid-day accumulation on the crop. Based on transmission assays, R. padi was primarily responsible for vectoring the predominant virus serotype (PAV) we found in wheat. Pest management efforts should focus on sampling for and suppressing this aphid species. December planting reduced aphid-day accumulation and barley yellow dwarf incidence, but delayed planting is not a practical management option. English grain aphid, Sitobion avenae (F.), was the last species to colonize wheat each season, and the most abundant. Sitobion avenae was responsible for late-season virus transmission and caused direct yield loss by feeding on heads and flag leaves during an outbreak year.
TL;DR: How drought-stress in host plants affects populations of A. pisum outside the laboratory is examined by comparing the growth of aphid populations on watered and experimentally drought-stressed pea plants and the hypotheses tested were that drought- stress reduces the rate at which aphids numbers increase and that aphid numbers decline at a younger plant growth stage on drought-Stressed plants than on non-stress plants.
Abstract: Most studies on the relationship between drought-stress in host plants and aphids have been carried out in the laboratory. These experiments have usually shown that drought-stress results in a decrease in the abundance, survival, and fecundity of aphids (Kennedy et al., 1958; Wearing & van Emden, 1967; Wearing, 1972; Miles et al., 1982; Sumner et al., 1983, 1986a,b; Behle & Michels, 1988; Fereres et al., 1988; Pons & Tatchell, 1995), together with an increase in the proportion of aphids that are winged (alatae) and therefore capable of long distance migration (Stadler, 1990; Baugh & Phillips, 1991; Pons & Tatchell, 1995), although in some cases little effect on the aphids was observed (McMurtry, 1962; Lorenz De Vries & Manglitz, 1982; Salas & Corcuera, 1991). A few contradictory studies have reported increased abundance, fecundity, or survival of aphids on drought-stressed plants (Wearing, 1967, 1972; Miles et al., 1982; Dorschner et al., 1986), which may have been due to reduced transpirational cooling leading to raised leaf temperatures (Mattson & Haack, 1987). The few manipulative studies conducted outside the laboratory have mostly shown that host plant drought-stress decreases aphid abundance (Kennedy & Booth, 1959; Michels & Undersander, 1986; Oswald & Brewer, 1997). The pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) causes extensive damage to pea crops in Europe (Bournoville, 1973; Lane & Walters, 1991; Bommarco & Ekbom, 1995) and North America (Maiteki et al., 1986). The crop growth stage at which aphid numbers begin to decline is variable but always occurs after ̄owering (Lane & Walters, 1991; Walters et al., 1994; McVean & Dixon, 1999) when peas become particularly susceptible to drought-stress (Salter & Drew, 1965; Pate, 1975; Biddle et al., 1988). The work reported here was designed to examine how drought-stress in host plants affects populations of A. pisum outside the laboratory by comparing the growth of aphid populations on watered and experimentally drought-stressed pea plants. The hypotheses tested were that drought-stress reduces the rate at which aphid numbers increase and that aphid numbers decline at a younger plant growth stage on drought-stressed plants than on non-stressed plants. The importance of aphid population density (natural rather than manipulated) to this process was also considered. There is no universally accepted de®nition of plant droughtstress (Larsson, 1989). Speight (1986) suggested that host plant drought-stress should be described as a decrease in plant growth and reproduction. Larsson (1989) proposed that host plant drought-stress should be based solely on insect performance. In the study reported here, when plants are described as drought-stressed, both these criteria of plant stress are met. Changes in both insect performance and in plant productivity followed when the amount of water available to the plant was reduced.
TL;DR: The results illustrate that the performance of a secondary pest of potato can vary unpredictably, depending on the nature of the resistance factors involved in developing specific resistance to a primary pest.
Abstract: Improving the use of bioctechnological and classical plant resistance for herbivore pest control with less reliance on chemicals critically depends on predictable interactions with secondary pests. Performance of the potato aphid Macrosiphum euphorbiae (Thomas), a secondary pest of potato in eastern North America, was studied on potato, Solanum tuberosum L., lines with traits of potential resistance to primary pests. The lines tested were ‘Newleaf’, a transgenic ‘Superior’ cultivar expressing the Bacillus thuringiensis Berliner CryIIIA toxin, which is highly resistant to the Colorado potato beetle, Leptinotarsa decemlineata (Say); a transgenic ‘Kennebec’ cultivar expressing rice cystatin I, a protease inhibitor previously shown to inhibit cathepsin like digestive enzymes in the Colorado potato beetle; NYL 235–4, a potato derived by selective breeding following hybridization with S. berthaulthii, with a moderate density of glandular trichomes providing resistance to small insects by contact; and t...
TL;DR: A detailed population dynamics model was devised to provide a tool for integrated pest management against the cereal aphid Sitobion avenae on winter wheat.
Abstract: Summary
1. A detailed population dynamics model was devised to provide a tool for integrated pest management against the cereal aphid Sitobion avenae on winter wheat.
2. This model allowed investigation of the relative impact of different natural enemies on aphid population dynamics.
3. The output of the model was compared with a set of data collected in the western part of France from 1976 to 1986.
4. Fungal diseases accounted for 75% of the reduction in peak aphid density and were the key factor acting on aphid dynamics in this region.
5. This study highlights the importance of detailed population dynamics modelling of keystone species, like aphids, for elucidation of the relations between the keystone species and other species associated in the ecosystem.
TL;DR: This work tested for the occurrence of genetic variation in winged morph production by rearing individuals from red and green clones of pea aphid under wing‐inducing (crowding) and control conditions, and scored the phenotypes of their offspring.
Abstract: Aphids (Homoptera: Aphidoidea) produce a number of different phenotypes in their life-cycle, among which are winged (alate) and wingless (apterous) morphs. Lowe & Taylor (1964) and Sutherland (1969a, b) were the first to suggest that aphid clones differ in their propensity to produce the winged morph and that in the pea aphid (Acyrthosiphon pisum Harris), this propensity is linked to the colour of the phenotype. We tested for the occurrence of genetic variation in winged morph production by rearing individuals from red and green clones of pea aphid under wing-inducing (crowding) and control conditions, and scored the phenotypes of their offspring. Clones differed significantly in alate production and red clones produced on average a higher proportion of winged morphs than green clones. Importantly, however, there was considerable variation between clones of the same colour. Broad-sense heritabilities of winged morph production were 0.69 (crowding treatment) and 0.63 (control). Clones also differed in the number of offspring they produced. When exposed to the crowding stimulus, aphids deferred offspring production, resulting in a higher number of offspring produced in the crowding treatment than in the control.