Showing papers on "Aphid published in 2002"
TL;DR: Natural populations of pea aphids in California contain at least two facultative bacterial secondary symbionts (pea aphidsecondary symbiont, PASS, or pea Aphid rickettsia, PAR) in a range of frequencies throughout the state.
Abstract: 1. Natural populations of pea aphids in California contain at least two facultative bacterial secondary symbionts (pea aphid secondary symbiont, PASS, or pea aphid rickettsia, PAR) in a range of frequencies throughout the state.
2. Two pea aphid clones without either of these facultative associates failed to reproduce in the first 8 days after the final moult if they had been heat-stressed for a period of about 4 h at 39 °C as 1-day-old larvae in the laboratory.
3. Aphids infected artificially with PASS, however, were able to produce up to 48% of the normal complement of offspring produced by PASS-positive aphids that had not been heat-stressed. Clones infected artificially with PAR did not have the same advantage as those with PASS after heat stress.
4. In aphids without PASS or PAR, heat stress reduced the number of bacteriocytes (in which the obligate primary symbiont, Buchnera, resides) to 7% of non-heat-stressed aphids, while aphids with only PASS retained 70% of their bacteriocytes. Bacteriocytes in aphids with PAR but not PASS were reduced to 42% of controls.
5. When larvae were heat-stressed as older instars (5 days old), a similar pattern emerged, though the effect of heat stress was less extreme. Clones containing PASS produced the most offspring, three to 14 times as many as aphids without PASS or PAR. Aphids with PAR only, or PASS and PAR together, had reduced or no advantage over aphids without facultative symbionts.
6. Aphids of all clones that had been heat-stressed as later instars gave birth to a variable number of stillborn offspring. Aphids without facultative symbionts produced the most stillborn larvae.
7. Field studies showed a higher incidence of PASS in aphids collected in California in summer compared with aphids from the same sites collected 2–4 months earlier. The difference was significant in two of three widely dispersed locations.
657 citations
TL;DR: It is shown that previously reported preferential colonization of potatoes infected by potato leafroll virus by alatae of Myzus persicae, the principal aphid vector ofPLRV, is influenced by volatile emissions from PLRV–infected plants.
Abstract: The influence of viral disease symptoms on the behaviour of virus vectors has implications for disease epidemiology. Here we show that previously reported preferential colonization of potatoes infected by potato leafroll virus (genus Polerovirus) (luteovirus) (PLRV) by alatae of Myzus persicae, the principal aphid vector of PLRV, is influenced by volatile emissions from PLRV-infected plants. First, in our bioassays both differential immigration and emigration were involved in preferential colonization by aphids of PLRV-infected plants. Second, M. persicae apterae aggregated preferentially, on screening above leaflets of PLRV-infected potatoes as compared with leaflets from uninfected plants, or from plants infected with potato virus X (PVX) or potato virus Y (PVY). Third, the aphids aggregated preferentially on screening over leaflet models treated with volatiles collected from PLRV-infected plants as compared with those collected from uninfected plants. The specific cues eliciting the aphid responses were not determined, but differences between headspace volatiles of infected and uninfected plants suggest possible ones.
329 citations
TL;DR: Microarray and macroarray gene expression analyses of infested plants are used to better define the response profile of A. thaliana to M. persicae feeding and suggest that genes involved in oxidative stress, calcium-dependent signaling, pathogenesis-related responses, and signaling are key components of this profile in plants infested for 72 or 96 h.
Abstract: Phloem feeding involves unique biological interactions between the herbivore and its host plant. The economic importance of aphids, whiteflies, and other phloem-feeding insects as pests has prompted research to isolate sources of resistance to piercing-sucking insects in crops. However, little information exists about the molecular nature of plant sensitivity to phloem feeding. Recent discoveries involving elicitation by plant pathogens and chewing insects and limited studies on phloem feeders suggest that aphids are capable of inducing responses in plants broadly similar to those associated with pathogen infection and wounding. Our past work showed that compatible aphid feeding on leaves of Arabidopsis thaliana induces localized changes in levels of transcripts of genes that are also associated with infection, mechanical damage, chewing herbivory, or resource allocation shifts. We used microarray and macroarray gene expression analyses of infested plants to better define the response profile of A. thaliana to M. persicae feeding. The results suggest that genes involved in oxidative stress, calcium-dependent signaling, pathogenesis-related responses, and signaling are key components of this profile in plants infested for 72 or 96 h. The use of plant resistance to aphids in crops will benefit from a better understanding of induced responses. The establishment of links between insect elicitation, plant signaling associated with phloem feeding, and proximal resistance mechanisms is critical to further research progress in this area. Arch. Insect Biochem. Physiol. 51:182-203, 2002. Published 2002 Wiley-Liss, Inc. †
269 citations
TL;DR: The causal basis of the variation in aphid performance between host plants of different developmental ages was explored using the aphids Myzus persicae and Macrosiphum euphorbiae on potato plants, suggesting that amino acid composition of the phloem is one factor shaping the nutritional quality of plants for aphids.
Abstract: To define plant 'nutritional quality' for aphids, the causal basis of the variation in aphid performance between host plants of different developmental ages was explored using the aphids Myzus persicae and Macrosiphum euphorbiae on potato plants (Solanum tuberosum). Both aphid species performed better on developmentally young ('pre-tuber-filling') plants than on mature ('tuber-filling') plants. Aphid performance did not vary with leaf phloem sucrose:amino acid ratio but could be related to changes in the amino acid composition of the phloem, which included a developmental shift from high glutamine levels in pre-tuber-filling plants to low glutamine levels in tuber-filling plants. Aphid performance on chemically defined 'young' and 'old' diets, with amino acid composition corresponding to that of phloem amino acid composition in pre-tuber-filling and tuber-filling plants, respectively, confirmed that phloem amino acid composition contributed to low aphid performance on tuber-filling plants. The relatively poor performance on 'old' diets could be accounted for, at least in part, by depressed feeding rates. These data suggest that amino acid composition of the phloem is one factor shaping the nutritional quality of plants for aphids.
266 citations
TL;DR: The results are discussed in terms of the peak activity periods of the different predatory groups and the consequences for integrated crop management (ICM).
217 citations
TL;DR: If, as reported here, the specialization on one kind of prey generally entails a tradeoff in performance on another, then the interactions between insect predators and their prey are more homologous to those of herbivorous insects and plants than previously thought.
Abstract: Summary 1. There are very few studies on prey specialization in predatory insects. Of the prey that the larvae of the generalist ladybird beetle Adalia bipunctata regularly feed on in the field, some are more suitable as food than others. A laboratory experiment was undertaken to determine whether it is possible to select for improved performance of this insect predator on a ‘poor quality’ prey, and the cost, if any, of such specialization. 2. The ladybird performed better when reared on the pea aphid Acyrthosiphon pisum than on the black bean aphid Aphis fabae . Over the course of six generations of selection there was a significant increase in performance on both species of aphid, especially the black bean aphid. 3. Ladybirds previously selected for five generations for better performance on the black bean aphid performed significantly worse when reared on pea aphid compared with those reared continuously for six generations on pea aphids, and vice versa. That is, specialization on one species of aphid resulted in a poorer performance on another. 4. If, as reported here, the specialization on one kind of prey generally entails a tradeoff in performance on another, then the interactions between insect predators and their prey are more homologous to those of herbivorous insects and plants than previously thought. The significance of this for prey specialization in ladybird beetles is discussed.
125 citations
TL;DR: Red imported fire ants enhance cotton aphid survival and density in the field through predator interference, and with the addition of fire ants to aphid-predator treatments, Aphid survival approximately doubled.
Abstract: Red imported Þre ants, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), are an invasive species found in high densities throughout southeastern agricultural systems. We tested the hypothesis that Þre ants tend cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), and thus release them from predation by lady beetle larvae, Coccinella septempunctata L. and Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae), and green lacewing larvae, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae). Fire ants preferentially foraged on aphid-infested cot- ton, Gossypium hirsutum L., plants (x 103 47 ants per plant) compared with plants without aphids (x 5 3 ants per plant). In caged greenhouse experiments, Þre ants reduced survival of lady beetle larvae by 92.9% and green lacewing larvae by 83.3%. Furthermore, strong mortality imposed on aphid predators by Þre ants affected aphid survival. With the addition of Þre ants to aphid-predator treatments, aphid survival approximately doubled. In a Þeld experiment, predator larvae were more abundant in cotton plots with experimentally suppressed densities of Þre ants (0.62 0.11 lady beetle larvae per sample; 0.06 0.02 lacewing larvae per sample) than in plots with high Þre ant densities (0.23 0.06 lady beetle larvae per sample; 0.01 0.01 lacewing larvae per sample). Conversely, cotton aphids were more abundant in high Þre ant density Þeld plots (x 6.83 0.03 aphids per leaf) than in low Þre ant density plots (x 4.04 0.03 aphids per leaf). These data suggest that red imported Þre ants enhance cotton aphid survival and density in the Þeld through predator interference.
124 citations
TL;DR: These experiments are the first to demonstrate a more indirect influence of parasites on insect polyphenism and the induction of wing development by parasitoids shows that host defences against parasites may also include an increased rate of dispersal away from infected habitats.
Abstract: In animals, inducible morphological defences against natural enemies mostly involve structures that are protective or make the individual invulnerable to future attack. In the majority of such examples, predators are the selecting agent while examples involving parasites are much less common. Aphids produce a winged dispersal morph under adverse conditions, such as crowding or poor plant quality. It has recently been demonstrated that pea aphids, Acyrthosiphon pisum, also produce winged offspring when exposed to predatory ladybirds, the first example of an enemy-induced morphological change facilitating dispersal. We examined the response of A. pisum to another important natural enemy, the parasitoid Aphidius ervi, in two sets of experiments. In the first set of experiments, two aphid clones both produced the highest proportion of winged offspring when exposed as colonies on plants to parasitoid females. In all cases, aphids exposed to male parasitoids produced a higher mean proportion of winged offspring than controls, but not significantly so. Aphid disturbance by parasitoids was greatest in female treatments, much less in male treatments and least in controls, tending to match the pattern of winged offspring production. In a second set of experiments, directly parasitised aphids produced no greater proportion of winged offspring than unparasitised controls, thus being parasitised itself is not used by aphids for induction of the winged morph. The induction of wing development by parasitoids shows that host defences against parasites may also include an increased rate of dispersal away from infected habitats. While previous work has shown that parasitism suppresses wing development in parasitised individuals, our experiments are the first to demonstrate a more indirect influence of parasites on insect polyphenism. Because predators and parasites differ fundamentally in a variety of attributes, our finding suggests that the wing production in response to natural enemies is of general occurrence in A. pisum and, perhaps, in other aphids.
118 citations
TL;DR: Wheat germ agglutinin, the chitin-binding lectin from wheat germ, has been shown to be antimetabolic, antifeedant and insecticidal to the mustard aphid.
Abstract: Wheat germ agglutinin (WGA), the chitin-binding lectin from wheat germ, has been shown to be antimetabolic, antifeedant and insecticidal to the mustard aphid (Lipaphis erysimi Kalt) A cDNA encoding WGA was transferred to Indian mustard (Brassica juncea cv RLM-198) through Agrobacterium-mediated transformation Southern analysis of the transgenics showed the integration of the transgene, while Northern and Western analyses demonstrated that the transgene was expressed in the transgenics Bioassays using leaf discs showed that feeding on transgenics induced high mortality and significantly reduced fecundity of aphids
106 citations
TL;DR: This is the first study to demonstrate that the relationship between herbivores, which increase the dispersal of a pathogen, and the pathogen itself can be mutualistic or antagonistic, depending on the species.
Abstract: Interactions between plants and their herbivores and pathogens are mostly analysed separately, thereby neglecting mutualistic or antagonistic interactions between these antagonists and possible joint effects on the host. We studied interactions between the weed Cirsium
arvense, the rust fungus Puccinia
punctiformis and three herbivorous insects, the aphids Aphis
fabae ssp. cirsiiacanthoidis and Uroleucon
cirsii, and the beetle Cassida
rubiginosa. All three insect species mechanically transported spore material and significantly increased rates of P.
punctiformis infection in healthy thistles. The interaction between C. rubiginosa and the fungus was antagonistic. Although C.
rubiginosa transferred spores, biomass of adults was significantly reduced, development of adults tended to be prolonged and mortality increased when feeding on plants infected with P.
punctiformis. In contrast, the relationship between the aphid U.
cirsii and P.
punctiformis was mutualistic: U.
cirsii profited by fungal infection and formed significantly larger colonies on fungus-infected plants. Although the differences in insect performance suggest that aphids may be better vectors than the beetle, infection rates were similar. This is the first study to demonstrate that the relationship between herbivores, which increase the dispersal of a pathogen, and the pathogen itself can be mutualistic or antagonistic, depending on the species.
105 citations
TL;DR: Age-related differences in honeydew production and composition and its effect on the mutualism between M. fuscoviride and the ant Lasius niger were studied and the intensity of ant-attendance was significantly lower in colonies of first and second instar larvae than in colony of older age classes.
TL;DR: It is demonstrated that tea shoot–aphid complexes emit volatile synomones, while the odors from tea aphids, aphid cuticle extracts, and tea aphid honeydew contain kairomones to which the natural enemies show a logistic dose–response.
Abstract: Olfactometer bioassays and electrophysiological studies showed that the lacewing, Chrysopa sinica, the aphid parasitoid, Aphidius sp., and the coccinellid, Coccinella septempunctata, all responded to volatiles from tea aphids, Toxoptera aurantii, to hexane or ether rinses of tea aphid cuticles, and to synomones released by aphid-damaged tea shoots, as well as to the tea shoot-aphid complex. Each natural enemy spent more time searching on a filter paper treated with tea aphid honeydew than on a blank control filter paper. The interaction between synomones from aphid-damaged shoots and kairomones from tea aphids enhanced the responses to the plant-host complex. There was a significant, logistic dose-response relationship between the number of natural enemies responding and the odor stimulus concentration. Volatile components from the plant-host complex, obtained by air entrainment, were identified by their mass spectra and retention times and confirmed by comparison with standard samples. These were (Z)-3-hexen-1-ol, benzaldehyde, (E)-2-hexenal, (Z)-3-hexenyl acetate, ocimene, linalool, geraniol, indole, and (E)-2-hexenoic acid. The main components in a hexane rinse from tea aphid cuticle were benzaldehyde, undecane, 2,5-hexanedione, 2,5-dihydrothiophene, linalool, 4-methyl-octane, and eicosane, whereas the main components from an ether rinse were (E)-2-hexenoic acid, heptadecane, pentadecane, eicosane, tetratetracontane, and nonadecane. Benzaldehyde elicited the strongest responses from natural enemies in theolfactometer and the largest electroantennogram (EAG) responses. While the amount of odor was small, Coccinella septempunctata was slightly more sensitive than Chrysopa sinica and Aphidius sp. An increase in doses of benzaldehyde, (E)-2-hexenal, and (Z)-3-hexenyl acetate caused the EAG responses of each natural enemy to decrease. When the doses of (Z)-3-hexen-1-ol, linalool, and geranoil increased, EAGs of Chrysopa sinica and Aphidius sp. increased, but EAGs of Coccinella septempunctata decreased. When the dose of indole increased, EAGs of Coccineila septempunctata decreased, but those of Aphidius sp. increased. This study demonstrates that tea shoot-aphid complexes emit volatile synomones, while the odors from tea aphids, aphidcuticle extracts, and tea aphid honeydew contain kairomones, to which the natulal enemies show a logistic dose-response.
TL;DR: This study provides the first empirical evidence that changes in host plant quality mediated by increasing levels of CO2 can alter the outcome of interspecific competition among insect herbivores.
Abstract: We report the results of a study investigating the influence of elevated CO2 on species interactions across three trophic levels: a plant (Brassica oleracea), two aphid herbivores (the generalist Myzus persicae and the specialist Brevicoryne brassicae), and two natural enemies (the coccinellid Hippodamia convergens (ladybird) and the parasitoid wasp Diaeretiella rapae). Brassica oleracea plants reared under elevated CO2 conditions (650 ppmv vs. 350 ppmv) were larger and had decreased water and nitrogen content. Brevicoryne brassicae reared on plants grown in elevated CO2 were larger and accumulated more fat, while there was no change in M. persicae traits. Fecundity of individual aphids appeared to be increased when reared on plants grown in elevated CO2. However, these differences were generally lost when aphids were reared in colonies, suggesting that such changes in plant quality will have subtile effects on aphid intraspecific interactions. Nevertheless, CO2 treatment did influence aphid distribution on plants, with significantly fewer M. persicae found on the shoots, and B. brassicae was only found on senescing leaves, when colonies were reared on plants grown in elevated CO2. We reared B. brassicae and M. persicae in competition on plants grown at both the CO2 concentration treatments. We found a significantly lower ratio of M. persicae: B. brassicae on plants grown under elevated CO2 conditions, strongly suggesting that increasing CO2 concentrations can alter the outcome of competition among insect herbivores. This was also reflected in the distribution of the aphids on the plants. While the CO2 treatment did not influence where B. brassicae were found, fewer M. persicae were present on senescing leaves under elevated CO2 conditions. Changes in plant quality resulting from the CO2 treatments did not appear to alter aphid quality as prey species, as the number consumed by the ladybird H. convergens, and the number parasitised by the parasitoid wasp D. rapae, did not change. To our knowledge, this study provides the first empirical evidence that changes in host plant quality mediated by increasing levels of CO2 can alter the outcome of interspecific competition among insect herbivores.
TL;DR: Neem extract may be compatible with integrated pest management programs in citrus and should be evaluated for field efficacy because parasite emergences were similar between treated and untreated parasitized aphids.
Abstract: The biological effects of a commercially available neem seed extract (Neemix. 4.5, 4.5% azadirachtin, AZ) were assessed on the brown citrus aphid, Toxoptera citricida (Kirklady), a recently introduced insect pest of citrus in the United States and its parasitoid, Lysiphlebus testaceipes. When small citrus seedlings were dipped with the neem extract at 11–180 ppm AZ, 0–8% of nymphs and 0–17.5% of adults survived 7 d after the treatment while 95% of nymphs and 42.5% of adults in the control survived for the same period. The extract drastically reduced longevity of both adults and nymphs, adult fecundity, and molting of nymphs at all tested concentrations. Spraying neem extract (11–180 ppm AZ) onto potted citrus plants in the greenhouse also significantly reduced aphids by 20–100%, while control aphid populations increased by 950% 7 d after treatment. Application of the extract had little impact on the survival of adult parasitoids and developing parasitoids within aphids because parasite emergences...
TL;DR: Results indicate that plant-to-plant signaling in this tritrophic system may occur at the rhizosphere level and is most likely mediated by a systemically translocated elicitor.
Abstract: Broad bean plants (Vicia faba) infested by the pea aphid, Acyrthosiphon pisum, play a key role in the in-flight orientation of the parasitoid Aphidius ervi, by producing host-induced synomones (HIS). These volatiles are herbivore-specific and are systemically released from insect-free parts of an infested plant, suggesting the existence of an elicitor circulating throughout the plant. This study was designed to investigate whether the plant metabolic changes, leading to HIS biosynthesis and emission, can in some way trigger similar responses in neighboring plants through aerial and/or root communication. Uninfested broad bean plants maintained in the same pot together with plants infested by A. pisum became more attractive towards A. ervi females when tested in a wind-tunnel bioassay. This change was not observed when root contact was prevented among plants that had their aerial parts in close proximity, suggesting that an exudate from the roots of the infested plant may cause the induction of the attractive volatiles in uninfested plants. Broad bean plants grown hydroponically also produce pea aphid induced signals that attract A. ervi. When an intact (uninfested) plant was placed in a hydroponic solution previously used to grow a pea aphid-infested plant, it became attractive to parasitoids, while an intact plant placed in a solution previously used to grow an intact plant did not undergo such a change. These results indicate that plant-to-plant signaling in this tritrophic system may occur at the rhizosphere level and is most likely mediated by a systemically translocated elicitor.
TL;DR: Mutualistic interactions between aphids and ants are mediated by honeydew that aphids produce, and nymphs of the aphid Tuberculatus quercicola developed into significantly smaller adults with lower fecundity than did nymphS that were not ant attended.
Abstract: 1. Mutualistic interactions between aphids and ants are mediated by honeydew that aphids produce. Previous work showed that when attended by the ant Formica yessensis Forel (Hymenoptera: Formicidae), nymphs of the aphid Tuberculatus quercicola (Matsumura) (Homoptera: Aphididae) developed into significantly smaller adults with lower fecundity than did nymphs that were not ant attended.
2. 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. The composition and concentration of amino acids were compared between the honeydew produced by ant-attended colonies and that produced by ant-excluded colonies.
3. The aphids excreted smaller droplets of honeydew, but also excreted them more frequently, in ant-attended colonies than in ant-excluded colonies. The honeydew of ant-attended aphids contained more types of amino acid, and a significantly higher total concentration of amino acids, than did the honeydew of ant-excluded aphids.
4. These results suggest that the increase in the concentration of amino acids in honeydew leads to a shortage of nitrogen available for aphid growth and reproduction, resulting in lower performance under ant attendance.
5. With the advance of seasons, a significant reduction was found in both the total free amino acid concentration in phloem sap and the frequency of honeydew excretion; however the total concentration of amino acids in the honeydew did not vary significantly during the seasons, suggesting that aphids keep the quality of honeydew constant in order to maintain ant visitation.
TL;DR: The results suggest that TGR-1551 has a resistance mechanism that prevents A. gossypii from initiating ingestion from the phloem, and support the hypothesis that Agr and Vat are coding for different kinds of resistance strategies.
Abstract: The feeding behavior of the melon aphidAphis gossypii Glover (Homoptera: Aphididae) was monitored using the electrical penetration graph (EPG) technique on different melon (Cucumis melo L.) genotypes showing resistance to the aphid. The aphid-resistant genotypes used were PI-161375 and PI-414723, sources of theVat andAgr genes, respectively. TGR-1551, a newC. melo accession from Zimbabwe, was also tested. Our goal was to localize the tissues where the resistance factors are expressed and to determine if the resistance mechanisms operating in the three aphid-resistant accessions were the same. Our results indicated that the three selected lines have resistant factors located at the epidermis, mesophyll and vascular tissues. However, the behavior ofA. gossypii on TGR-1551 was different from the two other resistant accessions, as indicated by a longer phloem salivation phase (E1 phase). Many of the E1 phases observed for aphids feeding on TGR-1551 were not followed by phloem ingestion (E2 phase). These results suggest that TGR-1551 has a resistance mechanism that preventsA. gossypii from initiating ingestion from the phloem. Preference tests under free choice conditions also showed that aphids rejected accessions TGR-1551 or PI-414723 faster than PI-161375. Our results support the hypothesis thatAgr andVat are coding for different kinds of resistance strategies. Comparisons of aphid life history parameters also indicated that TGR-1551 is a very promising new source to breed for resistance againstA. gossypii.
TL;DR: The hypothesis that multiple intracellular punctures of epidermal and mesophyll cells result in loading aphids with the CaMV-encoded aphid transmission factor (P2), and that aphids, in most cases, subsequently acquireCaMV particles during phloem sap ingestion, is supported.
Abstract: Cauliflower mosaic virus (CaMV) is transmitted in a non-circulative manner by aphids following the helper strategy. Helper proteins P2 and P3 act as a bridge between virions and the aphid cuticle. Electronic monitoring of aphid stylet activities (EPG technique), transmission tests and electron microscopy showed that CaMV is preferentially acquired from the phloem by its most common aphid vectors, Brevycorine brassicae and Myzus persicae. We also found that CaMV is semi- persistently transmitted and that the rate of acquisition does not follow a typical bimodal curve. Instead, the virus could be acquired from non-phloem tissues at a low and fairly constant rate after one or more intracellular punctures within a few minutes, but the probability of acquisition rose significantly when aphids reached the phase of committed ingestion from the phloem. The acquisition rate of CaMV did not increase with increasing number of intracellular punctures, but the total duration of intracellular puncture was one of the variables selected by the stepwise logistic regression model used to fit the data that best explained acquisition of CaMV. Furthermore, aphids reaching the phloem faster had a higher probability of acquiring the virus. Our results support the hypothesis that multiple intracellular punctures of epidermal and mesophyll cells result in loading aphids with the CaMV-encoded aphid transmission factor (P2), and that aphids, in most cases, subsequently acquire CaMV particles during phloem sap ingestion. Consistently, immunoelectron microscopy showed that P3-virions are frequently found in the sieve element lumen, whereas P2 could not be detected.
TL;DR: Results show that the hypothesis that plant/plant communication may release responses in neighbouring plants that change aphid host plant acceptance is supported and that this mechanism is not restricted to optimal growing conditions in the laboratory, although it may be modified under field conditions depending on plant genotype.
Abstract: Four barley varieties with no significant difference in aphid acceptance were sown in pure stands and in pairwise combinations with varieties side by side in separate rows Settling tests were done in situ in the field plots with apterae of Rhopalosiphum padi (L) (Homoptera:Aphididae) and showed that aphid acceptance was changed in some combinations of cultivars In a laboratory test, in which plants of one cultivar were exposed to air from the other cultivars, aphid acceptance was significantly reduced in three of the four cultivars when treated with air from certain other cultivars Two of these three cultivars showed the same reduction under field conditions This supports the hypothesis that plant/plant communication may release responses in neighbouring plants that change aphid host plant acceptance The results also show that this mechanism is not restricted to optimal growing conditions in the laboratory, although it may be modified under field conditions depending on plant genotype
TL;DR: There is no evidence that the introduced wasps have become adapted to their local populations of pea aphid hosts, and the ability of the introduced parasitoids to develop successfully inpea aphids from alfalfa may have been compromised by the biological control introduction.
Abstract: Biological control systems can evolve; founder effects, drift, inbreeding, and adaptation to new environments can occur during the introduction and establishment of exotic pests and their natural enemies. It has been hypothesized that successful biological control agents are those that become locally adapted to their new environment or populations of hosts. However, there are no explicit comparisons of native and introduced populations of biological control agents testing for local adaptation. The pea aphid, Acyrthosiphon pisum, is an introduced pest of legumes. Aphidius ervi, a parasitoid wasp, was introduced from France to control pea aphids. Using reciprocal transplant experiments, I compared introduced populations of pea aphids and A. ervi from New York State with native populations from France. I documented patterns of aphid resistance to parasitism and A. ervi ability to overcome aphid resistance (virulence) in the two localities and explored whether the introduced parasitoids are locally adapted to the introduced pea aphids. I found that parasitoids from native French populations have high rates of parasitism on pea aphids specialized on clover and on pea aphids specialized on alfalfa, regardless of whether the aphids are collected from France or New York. Introduced parasitoids from New York have high rates of parasitism on pea aphids from clover, but low rates of parasitism on pea aphids from either New York or French alfalfa fields. Thus, there is no evidence that the introduced wasps have become adapted to their local populations of pea aphid hosts. On the contrary, the ability of the introduced parasitoids to develop successfully in pea aphids from alfalfa may have been compromised by the biological control introduction. This apparently nonadaptive evolution was cryptic until examined experimentally. A better understanding of the effects of biological control introductions on natural enemies will come through additional comparisons of native and introduced populations of biocontrol agents. Such comparisons may provide valuable insights into the role of microevolutionary change in biological control and suggest useful avenues to enhance the success of biological control introductions.
TL;DR: Tyrosine accumulation was the most prominent parasitoid-induced alteration, with a fourfold increase over control levels registered on day 6, and the amino acid biosynthetic capacity of Buchnera was unaltered, or even enhanced for the phenolic pool, and contributed greatly to the definition and maintainance of host free amino acid pools.
TL;DR: A reverse transcription-polymerase chain reaction (RT-PCR) assay was developed to detect SMV in single soybean aphids using a pair of primers designed to amplify a 469-bp PCR fragment in the coding region of SMV coat protein, and found 100% of these aphids to be SMV-infected.
Abstract: The soybean aphid (Aphis glycines) was a poor vector (0.83% transmission) when the aphids were allowed overnight acquisition feed on Soybean mosaic virus (SMV)-infected soybean leaves. However, A. glycines was shown to be a very efficient vector (34.72% transmission) when individual aphids were allowed a 1-min acquisition probe on the same infected leaves used for the feeding treatment. Similar results were obtained with Myzus persicae and tobacco in transmission experiments of the potyviruses Tobacco etch virus (feeding: 1.36%; probing: 45.5%) and Tobacco vein mottling virus (feeding: 2.0%; probing: 47.5%). A reverse transcription-polymerase chain reaction (RT-PCR) assay was developed to detect SMV in single soybean aphids using a pair of primers designed to amplify a 469-bp PCR fragment in the coding region of SMV coat protein. In contrast to the low transmission rate obtained with the soybean aphids that acquired virus through overnight feeding, RT-PCR detected SMV in 100% of these aphids. Interestingly, the rate of SMV detection by RT-PCR in aphids that were allowed a 1-min acquisition probe (31.67%) coincided with percent transmission (34.72%). The practical application of RT-PCR in detecting nonpersistently transmitted viruses and its implications for virus epidemiology are discussed.
TL;DR: In this article, the interactions among host plants (Medicago sativa L., cv. ''Windsor'), aphid prey (Acyrthosiphon pisum Harris, Homoptera:Aphididae), and Coccinella septempunctata L. preimaginal biology were evaluated.
Abstract: The interactions among host plants(Medicago sativa L., cv. `OKO8' and Vicia faba L., cv. `Windsor'), aphid prey(Acyrthosiphon pisum Harris, Homoptera:Aphididae), and Coccinella septempunctata L. (Coleoptera: Coccinellidae) preimaginal biology were evaluated. Interactions were measured over a range of limiting daily prey levels (1.2 mg–16.4 mg)from each host plant colony. Compared withA. pisum reared on V. faba, A. pisum reared on M. sativa storedsignificantly more fatty acids which resultedin a 1.17-fold increase in available caloriesfor developing C. septempunctata. Theincreased survival, decreased developmentaltimes, and larger size of C.septempunctata supplied with A. pisumreared on M. sativa clearly demonstratehost plant effects at the third trophic level. At low very limiting daily prey levels, A. pisum reared on M. sativa were moresuitable prey for C. septempunctatasurvival, development, and adult size thanA. pisum reared on V. faba. Coccinella septempunctata survival ratios(larval), developmental times, and adult sizeconverged (were not statistically different)between host plants at higher daily A.pisum levels. These convergence's supportthe hypothesis that there were quantitativedifferences in the nutritional value ofaphids, as influenced by differences in fattyacids and subsequent nutritional levels(calories), between aphids reared on separateplant hosts. The observed tritrophicinteractions appear to be modulated by thebiochemical response of A. pisum to hostplants.
TL;DR: The effect of a previous infestation by the green peach aphid Myzus persicae (Sulzer) on the settling behaviour and reproduction of the same aphid species was investigated in the resistant peach cultivar Rubira, and compared with that observed in the susceptible control cultivar GF305.
Abstract: The effect of a previous infestation by the green peach aphid Myzus persicae (Sulzer) on the settling behaviour and reproduction of the same aphid species was investigated in the resistant peach cultivar Rubira, and compared with that observed in the susceptible control cultivar GF305. A previous infestation of 48 h triggered induced resistance in Rubira. There were significantly fewer aphids settling on preinfested than on uninfested plants, indicating an increased rejection of Rubira as a host plant. The level of induced resistance in preinfested plants was positively related to the duration of the first infestation. In GF305, previous infestation had no detrimental effect on aphid settlement and even slightly enhanced larviposition by adult females. The aphid probing behaviour after a 48-h preinfestation was also monitored for 8 h with the electrical peneration graph (EPG) technique. On preinfested GF305, most EPG parameters indicated an enhanced host plant acceptance. On preinfested GF305, aphids produced less sieve element salivation and more continuous sap ingestion than on uninfested GF305, indicating that the previous aphids provoked changes in plant properties beneficial to the test aphids. In Rubira, a major induced factor of resistance was thought to be expressed in the sieve element as phloem sap ingestion was 4-fold shorter on preinfested than on uninfested plants. The time taken by the aphid stylets to reach a sieve element was also significantly increased on preinfested Rubira, suggesting the induction of resistance factors outside the phloem. The originality of the Rubira/M. persicae interaction is discussed in the perspective of a better understanding of plant induced responses to aphids.
TL;DR: This paper summarises the results of two long-term surveys of resistance dynamics in M persicae in England, based on samples collected directly from field and glasshouse crops or from four 12.2-m suction traps, and showed marked fluctuations in resistance frequencies.
Abstract: Advances in understanding insecticide resistance in the peach-potato aphid, Myzus persicae (Sulzer), at the genotypic, biochemical and molecular levels have led to rapid and precise methods for the detection of several resistance mechanisms (elevated carboxylesterase, modified acetylcholinesterase or MACE, and knockdown resistance or kdr) in individual insects, and for monitoring their frequencies over space and time. This paper summarises the results of two long-term surveys of resistance dynamics in M persicae in England, based on samples collected directly from field and glasshouse crops or from four 12.2-m suction traps. The study showed marked fluctuations in resistance frequencies that probably reflect the counteracting forces of selection imposed by insecticides for aphids possessing more copies of esterase resistance genes, and selection against these forms when insecticide use is relaxed. There is growing evidence that several different resistance mechanisms in M persicae have associated fitness costs. In the case of esterase and MACE, these costs are apparently strong enough to effect a decline in resistance frequency over winter, and a more prolonged decline over successive cropping seasons when aphid numbers are insufficient to trigger intensive chemical applications. Changes in the overall frequency of resistance genotypes may also be influenced by the predominance of year-round parthenogenesis in M persicae in the UK, leading to non-random associations between mechanisms and selection operating on clonal lineages rather than individual genotypes.
TL;DR: The hypothesis is that aphids may recognise their host plants as soon as they probe the mesophyll tissue and before they start ingestion from phloem vessels.
Abstract: Plant penetration behaviour (probing) of the cabbage aphid, Brevicoryne brassicae, and the pea aphid, Acyrthosiphon pisum, was studied on excised leaves of broad beans, Vicia faba, kept in water or in a 1% aqueous solution of sinigrin. Using the DC EPG (Electrical Penetration Graph) technique it was shown that the cabbage aphid on sinigrin-untreated bean leaves showed numerous short probes into epidermis and mesophyll. None of these aphids showed either phloem salivation or ingestion waveforms on untreated leaves. In contrast, on sinigrintreated bean leaves, 35% of the probing time was spent on phloem sap ingestion (E2) and almost all aphids reached phloem vessels and started feeding. The duration of phloem salivation before phloem ingestion and the mean duration of phloem ingestion periods were similar on a host and a sinigrin-treated non-host plant. However, the total probing time by B. brassicae was 10% longer, the total phloem sap ingestion time was twice as long, and the time to the first phloem phase within a probe was three times shorter on the host plant compared to sinigrintreated broad beans. Acyrthosiphon pisum also responded to the addition of sinigrin to broad beans, but in this case sinigrin acted as a deterrent. On sinigrin-treated leaves, A. pisum terminated probes before ingestion from phloem vessels, and none of these aphids showed phloem salivation and ingestion on treated leaves. Glucosinolates were detected in the mesophyll cells of the brassicaceous plant, Sinapis alba. Based on this finding and in addition to the foregoing EPG analysis of aphid probing on these plants and broad beans, our hypothesis is that aphids may recognise their host plants as soon as they probe the mesophyll tissue and before they start ingestion from phloem vessels.
TL;DR: This study highlights the importance of understanding not only the demographic parameters to genetic diversity, but also the more intricate correlation of genetic diversity to host types in agricultural environments.
Abstract: Elucidation of the genetic variability of a model insect species, the grain aphid, Sitobion avenae (Fabricius), a predominantly asexual herbivore within the temperate agro-ecosystem tested, was initiated using molecular DNA markers (RAPDs). This revealed genetic profiles that appeared related to host adaptation at the specific level amongst the natural populations colonizing different grasses and cereals (Poaceae) within the same geographic location. These profiles were recorded either as 'specialist' genotypes found on specific grasses, or as 'generalist' genotypes colonizing several host types including cultivated cereals or native grasses. These findings are compared with analogous systems found amongst insect species, including at a higher trophic level, i.e. interactions between hymenopterous aphid parasitoids. As the aphids and their respective plant hosts occur in the same geographical region at the same time, this appears to be a rare example of the evolutionary transition leading to sympatric speciation in insects. Hence, this study highlights the importance of understanding not only the demographic parameters to genetic diversity, but also the more intricate correlation of genetic diversity to host types in agricultural environments.
TL;DR: In 1996 and 1997 a field survey of the abundance and species composition of cereal aphid primary and secondary parasitoids in spring barley, winter wheat and durum wheat was conducted in Zealand, Denmark to create a better understanding of the mechanisms underlying aphid–parasitoid dynamics in the field.
Abstract: In 1996 and 1997 a field survey of the abundance and species composition of cereal aphid primary and secondary parasitoids in spring barley, winter wheat and durum wheat was conducted in Zealand, Denmark. The purpose was to create a better understanding of the mechanisms underlying aphid-parasitoid dynamics in the field. Such an understanding can be used when developing biological control methods in cereals. In both years aphid attacks in cereals began in late June and never exceeded the economic threshold. In 1996 the first aphids were found in wheat on 26 June; in 1997 the first aphids were found on 24 June on both crops. The highest densities reached in 1996 were an average of six aphids per shoot in winter wheat and one aphid per shoot in spring barley. In 1997 the highest densities reached were 11 aphids per shoot in winter wheat and four aphids per shoot in spring barley. The aphid population collapsed by the end of July to early August in 1996, but it collapsed by mid-July in 1997. The onset and peak of parasitization were delayed in comparison to aphid infestation. Parasitism was 20-60% by the end of the cropping season in spring barley, and 30-80% in winter wheat and durum wheat in 1996. In 1997 parasitism did not exceed 3-11% in barley and was less than 2% in one winter wheat field but more than 40% in the other winter wheat field sampled. In both years most parasitism was due to Aphidiidae (Hymenoptera). The two dominant species were Aphidius ervi Haliday and Aphidius rhopalosiphi De Stefani-Perez. Hyperparasitism began after primary parasitism and increased progressively during the cropping season. The two years were similar in many respects, including for species composition of aphids and parasitoids. The late start of the aphid infestation may have contributed to the high level of parasitization found in 1996, but in 1997 the aphid infestation period was so short that a parasitoid population did not have time to build up.
TL;DR: Paecilomyces fumosoroseus (Wize) Brown & Smith is under development as a mycoinsecticide for control of the Russian wheat aphid, Diuraphis noxia Kurdjumov as discussed by the authors.
Abstract: Paecilomyces fumosoroseus (Wize) Brown & Smith is under development as a mycoinsecticide for control of the Russian wheat aphid, Diuraphis noxia Kurdjumov. Interactions with other natural enemies within the agro-ecosystem, such as the coccinellid Hippodamia convergens Guerin, require evaluation before its potential can be realized. In laboratory bioassays H. convergens adults were sprayed with suspensions of P. fumosoroseus conidia at different concentrations (including potential field rates) and mortality assessed. Although a proportion of coccinellids succumbed to infection (the greatest proportion was 22% when the ladybirds had suffered stress) it is unlikely that they would be at risk from infection as a direct result of a spray application unless there were prolonged periods of high humidity or the coccinellids were stressed. When provided with uninfected or P. fumosoroseus -infected D. noxia cadavers as prey, coccinellids consumed more uninfected aphids. The predators never consumed aphid cadavers f...
TL;DR: The complexity of plant nutrient content on aphid performance suggests that not only nutrient levels but also ratios of nutrients must be considered.
Abstract: Three experiments were conducted to study how nutrient content of the host plant, Petunia axillaris hybrida Villm Grandiflora Group, affects the performance of Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae). Aphid performance was analysed in relation to plant nutrient levels and the ratio of nitrogen to potassium (N/K). Phosphorus (P) had a positive effect on several parameters of aphid performance. Both P and K were associated with a short development time but a strong correlation between P and K content made it impossible to detect their relative importance. In one experiment aphid performance was significantly lower on unfertilised plants with low N content, suggesting a positive effect of N. A high N/K ratio did not, in general, increase aphid performance. The complexity of plant nutrient content on aphid performance suggests that not only nutrient levels but also ratios of nutrients must be considered.