Direct and Indirect Impacts of Infestation of Tomato Plant by Myzus persicae (Hemiptera: Aphididae) on Bemisia tabaci (Hemiptera: Aleyrodidae)

The impacts of infestation by the green peach aphid (Myzus persicae) on sweetpotato whitefly (Bemisia tabaci) settling on tomato were determined in seven separate experiments with whole plants and with detached leaves through manipulation of four factors: durations of aphid infestation, density of aphids, intervals between aphid removal after different durations of infestation and the time of whitefly release, and leaf positions on the plants. The results demonstrated that B. tabaci preferred to settle on the plant leaves that had not been infested by aphids when they had a choice. The plant leaves on which aphids were still present (direct effect) had fewer whiteflies than those previously infested by aphids (indirect effect). The whiteflies were able to settle on the plant which aphids had previously infested, and also could settle on leaves with aphids if no uninfested plants were available. Tests of direct factors revealed that duration of aphid infestation had a stronger effect on whitefly landing preference than aphid density; whitefly preference was the least when 20 aphids fed on the leaves for 72 h. Tests of indirect effects revealed that the major factor that affected whitefly preference for a host plant was the interval between the time of aphid removal after infestation and the time of whitefly release. The importance of the four factors that affected the induced plant defense against whiteflies can be arranged in the following order: time intervals between aphid removal and whitefly release > durations of aphid infestation > density of aphids > leaf positions on the plants. In conclusion, the density of aphid infestation and time for which they were feeding influenced the production of induced compounds by tomatoes, the whitefly responses to the plants, and reduced interspecific competition.     

Changes in photosynthetic and transpiration rates of cotton leaves infested with the cotton aphid, Aphis gossypii: Unrestricted infestation

The influence of aphid, Aphis gossypii, feeding on photosynthesis and transpiration in cotton plants was investigated under greenhouse conditions. Four population densities of 0, 5, 10, and 25 aphids were used to infest individual cotton leaves. Gas exchange rates were determined for single attached cotton leaves after 9, 18, and 27 days of aphid infestation. Aphid feeding changed photosynthetic rates and transpiration rates. These changes were proportional to the number of aphids and the length of infestation period. Photosynthetic rates were significantly reduced in infested leaves with 25 aphids over 18 days, whereas significant reduction in photosynthetic rates was recorded within 27 days in infested leaves with 5, 10, and 25 aphids in comparison to their respective control. Initial population of 10 aphids increased significantly the transpiration rate of infested leaves over 9 and 27 days. Leaves of plants with 25 aphids had significantly greater transpiration rate than the control at all times.     

Evaluation of induced responses, insect population growth, and host-plant fitness may change the outcome of tests of the preference-performance hypothesis: a case study

The preference‐performance hypothesis predicts that insect preference should correspond to host suitability for offspring development. We studied the pattern of within‐plant preference in the aphid Sipha flava and its consequences for offspring performance on the host‐plant Sorghum halepense, regarding the role of induced responses of plants to aphid feeding. The consequences of within‐plant preference on aphid population growth and host‐plant traits were also evaluated. Our results showed that winged and wingless aphids preferred to settle on mature rather than young leaves. In contrast, aphid individual growth rate was higher on young leaves when compared with mature leaves, suggesting that the outcome of this test rejected the preference‐performance hypothesis. However, the inclusion of the factor ‘previous aphid infestation’ changed the outcome from a maladaptive choice to a neutral one. Thus, individual growth rates of S. flava increased when aphids developed on leaves that had been previously infested. Interestingly, aphid growth rate on previously infested leaves did not differ between young and mature leaves. On the other hand, aphid population reproductive rate was higher and the percentage of winged aphids lower when infestation occurred on mature rather than young leaves. Aphid infestation reduced plant and shoot biomass, and increased leaf mortality. These negative effects on plant traits related to plant fitness were greater when aphid infestation occurred on young leaves. Likewise, whereas infestation on mature leaves did not cause a significant reduction in the number of flowering plants compared with control plants, aphid infestation on young leaves did reduce the number of plants at the flowering stage. Consequently, if both the reproductive rate of aphids in the mid‐term, and host‐plant fitness are taken into account, the results indicate that aphid preference for mature leaves may be an adaptive choice, thus supporting the preference‐performance hypothesis.     

Effect of black bean aphid, Aphis fabae, on transpiration, stomatal conductance and crude protein content of faba bean

This study was initiated to investigate effects of damage by 0, 5 and 10 aphids/plant on the physiology of faba bean plants throughout different feeding periods and at two plant development stages. Immediately following removal of Aphis fabae, measurements showed 84–229% increase in transpiration rate. These changes were proportional to the number of aphids and infestation duration. Injury by A. fabae caused the stomatal conductance to be much higher in the leaves of infested plants. Leaf stomatal conductance of the infested plants increased significantly by 51–224% depending on initial aphid densities and feeding intervals. This increase was proportional to the infestation level for each date. Length of infestation period and plant growth stage seemed to have no clear effect on stomatal apertures. Aphid feeding caused a damage of about 7–33% of crude protein levels in the leaf tissue. This reduction increased with increasing infestation levels and time, except for 28‐day‐old plants on 28 days. The physiological effects of aphid feeding on water vapour and chemical composition of damaged leaves are particularly serious when the population is high.     

Females of Cotesia vestalis,a parasitoid of diamondback moth larvae,learn to recognise cues from aphid‐infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non‐host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naïve parasitoids exhibited no preference between aphid‐infested and uninfested plants in a dual‐choice test, but those that had been previously fed aphid honeydew significantly preferred aphid‐infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid‐infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.     

Nutritional enhancement of host plants by aphids - a comparison of three aphid species on grasses

Three aphid species were compared with respect to ability of enhancing the nutritional quality of their host plants. Rhopalosiphum padi, which does not induce macroscopic changes in its host plants, was compared with Schizaphis graminum and Diuraphis noxia, both of which induce distinctive types of chlorotic lesions. Phloem sap samples were collected from severed stylets of feeding aphids and from exudates of cut leaves of plants uninfested or infested with each aphid species. Samples were analyzed for concentrations of individual amino acids.Compared to R. padi, S. graminum ingested phloem sap with a two-fold higher concentration of amino acids and a much higher proportion of essential amino acids. Similar differences between these two aphid species were observed on both wheat and barley. For each aphid species, the absolute concentrations of amino acids and the relative proportions of essential amino acids were similar between the two host plants. Effects of D. noxia were similar to those of S. graminum, though less dramatic. Exudates from leaves infested with each aphid species showed relative concentrations of individual amino acids that were similar to those in the corresponding stylet exudates. Based on comparison of stylet exudates and cut leaf exudates from infested and uninfested plants, R. padi seems to have little effect on amino acid composition of phloem. Changes in the phloem induced by both S. graminum and D. noxia appear to be systemic, affecting at least the whole leaf they are feeding on. The changes observed for D. noxia and for S. graminum are likely to be nutritionally advantageous for the aphids and are expected to affect the aphids' dependence on nutritional supplementation by intracellular symbionts (Buchnera).     

Changes in growth regulator content of radish seedlings, Raphanus sativus, infested with the aphid Myzus persicae

Following 10 days of infestation by the aphid Myzus persicae there was an increase in the amount of growth inhibiting substances and a decrease in cytokinins, gibberellins and auxins in infested as compared with similar uninfested radish seedlings. Even after previously infested seedlings have been freed of aphids for 10 days, differences in the hormone balance remained. The possible relationships between the changes in hormonal balance and the effect of the aphid infestation on growth, translocation and wilting are discussed.     

Comparison of chlorophyll and carotenoid concentrations among Russian wheat aphid (Homoptera: Aphididae)-infested wheat isolines

Russian wheat aphid, Diuraphis noxia (Mordvilko), feeding injury on 'Betta' wheat isolines with the Dn1 and Dn2 genes was compared by assessing chlorophyll and carotenoid concentrations, and aphid fecundity. The resistant Betta isolines (i.e., Betta-Dn1 and Betta-Dn2) supported similar numbers of aphids, but had significantly fewer than the susceptible Betta wheat, indicating these lines are resistant to aphid feeding. Diuraphis noxia feeding resulted in different responses in total chlorophyll and carotenoid concentrations among the Betta wheat isolines. The infested Betta-Dn2 plants had higher levels of chlorophylls and carotenoids in comparison with uninfested plants. In contrast, infested Betta-Dn1 plants had the same level of chlorophyll and carotenoid in comparison with uninfested plants. Our data provide essential information on the effect of D. noxia feeding on chlorophyll and carotenoid concentrations for Betta wheat and its isolines with D. noxia-resistant Dn1 and Dn2 genes.     

Local and systemic responses induced by aphids in Solanum tuberosum plants

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Homoptera: Aphididae) are serious pests of potato (Solanum tuberosum L.) (Solanaceae), notably in transmitting several plant viruses. Heterospecific interactions may occur between these two species as they are often seen at the same time on the same potato plant in the field. As aphid infestation is known to induce both local and systemic changes, we conducted experiments to determine the effect of previous infestation on probing behaviour and feeding‐related parameters. We used the DC electrical penetration graph technique to characterize the influence of previous infestation by conspecific M. persicae or by heterospecific Ma. euphorbiae on M. persicae feeding behaviour at both local and systemic levels, i.e., on previously infested leaves and on non‐previously infested leaves of infested plants, respectively. Conspecific and heterospecific infestation led to similar modification of M. persicae feeding activities. However, the effects of previous infestation occurring at the local level were opposite to those observed at the systemic level. Myzus persicae food acceptance was slightly enhanced on previously infested leaves, whereas it was inhibited on non‐infested leaves of infested plants, which indicated an induced resistance mechanism. Our results advance the understanding of the mechanisms involved in aphid–host plant acceptance and colonization processes on potato plants in conspecific and heterospecific situations.     

Pea aphids (Acyrthosiphon pisum Harris) reduce secretion of extrafloral nectar in broad bean (Vicia faba)

1. Herbivores sometimes suppress plant defences. This study tested whether the presence of pea aphids (Acyrthosiphon pisum Harris) on broad bean (Vicia faba) led to decreased secretion of extrafloral nectar (EFN) which functions as an indirect plant defence against herbivores. 2. To determine effects of aphid infestation on EFN secretion, a comparison was done between EFN secretion in uninfested plants and that in plants infested by A. pisum and another aphid species (Aphis craccivora Koch). 3. When broad bean plants were infested by A. pisum, they secreted significantly smaller amounts of EFN than did uninfested plants and A. craccivora‐infested plants. There was no significant difference in EFN secretion between uninfested plants and A. craccivora‐infested plants. The number of extrafloral nectaries did not differ among the three treatments. 4. These results suggest that A. pisum reduced EFN production in broad bean plants.     

The influence of size and duration of aphid infestation on host plant quality, and its effect on sugar beet yellowing virus epidemiology

This paper studies the influence of previous infestation on the host quality of sugar beet (Beta vulgaris L.) for aphids and the influence of previous infestation on sugar beet yellowing virus epidemiology. Sugar beet previously infested with Myzus persicae (Sulzer) or Aphis fabae Scopoli (Homoptera: Aphididae) had an improved host quality for subsequently infesting aphids of the same species. There was a significant negative relationship between the number of M. persicae infesting a plant and the proportion of those that died with a dark deposit in their stomachs, and a significant positive relationship between the number that settled on a plant and the number that infested it previously. Nymphs feeding on previously infested plants grew more rapidly than those on control plants. The beneficial effect of previous infestation persisted for at least 2 weeks and prolongation of the infestation beyond 2 weeks was of no further benefit to the aphids. Field grown sugar beet, previously colonised by M. persicae, was more susceptible to natural infestation by M. persicae up to 5 days after exposure. Previously infested plants were also more susceptible to infection with beet mild yellowing virus (BMYV) but not beet yellows virus (BYV), suggesting that the aphids on the previously infested sugar beet settled more readily and were more inclined to feed (and thus transmit BMYV) than aphids on the previously uninfested plants. The consequences for the control of sugar beet yellowing virus vectors are discussed.     

Involvement of ethylene in aphid infestation of barley

The recently arrived Russian wheat aphid (RWA) is a major pest of wheat and barley in the United States. RWA induced ethylene production in Morex, a barley variety susceptible to RWA, but induced little ethylene production in PI 366450, a barley resistant to RWA. Greenbugs, another aphid pest, induced ethylene production in PI 366450 and Morex, both of which are susceptible to greenbugs. RWA infestation results in pronounced symptoms on barley including leaf streaking, stunting of growth, and rolled leaves. Incubation of barley in ethylene (5 and 50 l/l) or other plant hormones (auxin, gibberellic acid, zeatin, kinetin, and abscisic acid at 10^-4 M) failed to produce streaking or rolling in uninfested plants or to alter the production of these symptoms in infested plants. Incubation of Morex and PI 366450 in ethylene caused some stunting of the leaves and internodes that emerged during or soon after ethylene incubation. However, the leaf and internode that emerged 9 days after incubation showed some compensatory, or increased, growth.Mention of specific product name by the United States Department of Agriculture does not constitute an endorsement and does not imply a recommendation over other suitable products.     

The effect of previously infested spruce needles on the growth of the green spruce aphid, Elatobium abietinum, and the effect of the aphid on the amino acid balance of the host plant

The effect of chlorosis induced in needles of Sitka and Norway spruce by the green spruce aphid on growth of the aphid is investigated, and the effect of infestation of the aphid on amino acid levels in Sitka spruce foliage is reported. On both Sitka and Norway spruce green spruce aphids were heavier when reared on chlorotic (previously infested) needles than when reared on green (previously uninfested) needles. The effect was more pronounced on Sitka than on Norway spruce. Infestation of the aphid altered the amino acid balance of Sitka spruce foliage but not the concentration of total amino acids. Possible causes of chlorosis, the influence of individual amino acids on aphid growth, the potential effect of chlorosis on outbreaks of the aphid and the differences in susceptibility of Sitka and Norway spruce to damage by the aphid are discussed.     

Plant‐mediated species networks: the modulating role of herbivore density

1. When herbivores of distinct feeding guilds, such as phloem feeders and leaf chewers, interact, the outcome of these interactions often shows facilitation. However, whether this facilitation turns into competition at stronger herbivory pressure remains unknown. 2. Using an integrative approach that links ecological processes (behavioural choices of insects) with physiological plant mechanisms (nutrient and phytohormone levels) for the wild crucifer Brassica nigra (L.) Koch., this study evaluates preferences of leaf chewers for plants previously infested with several densities of the specialist aphid Brevicoryne brassicae L. (Hemiptera, Aphididae). As leaf chewers, four species of caterpillars (Lepidoptera) were selected that differ in their degree of specialisation in crucifers. 3. These results show that, whereas at low and medium aphid densities caterpillars displayed a preference for aphid‐infested plants or no preference, at high aphid infestation density, all four species of caterpillar preferred uninfested plants, with a significant difference for Pieris rapae and Mamestra brassicae. 4. In contrast to our expectation, the consistent preference for uninfested plants at a high aphid density could not be associated with a decrease in plant nutrition. However, while jasmonate concentrations [i.e. 12‐oxo‐phytodienoic acid and jasmonic acid (JA)] at medium aphid‐density infestation decreased compared with low levels of infestation, at high infestation level, the jasmonates JA as well as JA conjugated with the amino acid isoleucine were present at higher levels compared with low‐infestation treatments. 5. This work provides evidence that positive interactions observed in herbivore communities can be transient, leading to negative interactions mediated by changes in plant defences rather than in plant nutrition.     

Aphelinus albipodus(Hymenoptera: Aphelinidae) andDiaeretiella rapae(Hymenoptera: Braconidae) Parasitism onDiuraphis noxia(Homoptera: Aphididae) Infesting Barley Plants Differing in Plant Resistance to Aphids

Russian wheat aphid,Diuraphis noxia(Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid byAphelinus albipodusHayat & Fatima andDiaeretiella rapaeMcIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the largerD. rapaewas more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism byA. albipodusdid not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism byD. rapaewas greater thanA. albipodus.These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.     

Oviposition preferences of Maculinea alcon as influenced by aphid (Aphis gentianae) and fungal (Puccinia gentianae) infestation of larval host plants

Abstract 1. The influence of infestation of the larval host plant Gentiana cruciata on the egg‐laying preferences of the xerophilous ecotype of Alcon Blue butterfly (Maculinea alcon) was studied in a semi‐dry grassland area (Aggtelek Karst Region, Northern Hungary). 2. We examined whether oviposition patterns of females differed when G. cruciata stems were uninfested compared with when they were infested by an aphid (Aphis gentianae) or a rust (Puccinia gentianae) species. 3. Females laid more than 90% of their eggs on fertile, uninfested G. cruciata stems, although these stems comprised only ～ 50% of the total stems available. Stems infested by aphids were similar to uninfested ones in properties that had a strong correlation with egg numbers, and yet there were significantly fewer eggs on infested stems than on intact ones. 4. Females never laid eggs on parts of Gentiana stems infested by aphids, and the presence of Lasius paralienus ants, which have a mutualistic interaction with Aphis gentianae, did not increase the repulsive effect of aphids. Infection of Gentiana by Puccinia did not influence the egg‐laying behaviour of females, even though the flowers and buds of infested stems exhibited a delayed development. 5. Aphid infestation can influence butterfly oviposition patterns through both direct and indirect effects. The presence of aphids directly excluded oviposition, but our data also indicated the possibility of an indirect effect of aphid infestation. Stems that had no aphids at the last egg counting, but were infested prior to it, had significantly fewer eggs than those that were never infested.     

Assessing the risk of primary infection of cereals by barley yellow dwarf virus in autumn in the Rennes basin of France

In the Rennes basin, Rhopalosiphum padi is anholocyclic and represents more than 90% of suction trap catches of potential vectors of barley yellow dwarf virus (BYDV) during autumn. From 1983 to 1987 the possibility of predicting the risk of BYDV infection of batches of barley test seedlings (sampling units) exposed each week from September to December near a 12.2 m high suction trap was investigated. Three kinds of variables were checked as possible predictors: weekly mean or maximum temperatures; weekly catches of R. padi (including or excluding males); and percentage of sampling units infested by aphids. Three contrasting examples were observed: during the first three years (1983–1985), infection was high and its change with time followed temperature, aphid catches and plant infestation changes; in 1986, high numbers of aphids caught and a high proportion of plants infested resulted in only low infection and in 1987, both infestation and infection were very low. Simple linear regression analysis showed that the more reliable predictors of infection were the proportion of infested plants and to a lesser extent the numbers of trapped aphids. Multiple linear regressions including either of the three groups of ‘predicting’ variables did not result in any improvement in the prediction. At a practical level, the use of counts of aphid catches would seem a better compromise between accuracy and consistency of prediction and ease of gathering data than that of plant infestation but any significant improvement of the prediction should be sought in an early estimate of the amount of virus available to aphids before they colonise the plants.     

Characteristics of the population build-up of the Russian wheat aphid Diuraphis noxia and the effect on wheat yield in the eastern Orange Free State

Diuraphis noxia infestations were monitored in early winter and winter wheat during 1983–1985. The aphid population increase was logarithmic in all three years and on both cultivars 100 % infestation levels were recorded. The period of exponential increase in both percentage infestation and in the number of D. noxia per stem took place when the plants had reached the stem elongation stage. The mean number recorded at peak population levels was 150–160 aphids per stem. During the period of plant senescence numbers dropped rapidly. Large reductions in yield were recorded on all infested plants. Single-plant data showed that yield reductions in the early winter cv. Betta were related to the duration of infestation. Relative to sprayed controls, reduction in kernel mass ranged from 25–80% and in 1000-kernel mass from 15–45%. However, the yield reductions of the faster-growing cv. Flamink, appeared to be dependent on the number of aphids per plant during the later growth stages and not the duration of infestation.     

Increased feeding damage under elevated Co2: The case of the Russian wheat aphid

We report the results of a baseline study on the effects of Russian wheat aphid infestation on barley lines grown under ambient and elevated (450 and 550 μmol mol^− 1) CO₂ concentrations [CO₂]. Elevated CO₂ impacted on plant biomass, C:N ratios and leaf nitrogen concentrations. Visible manifestation of aphid feeding related damage was assessed by examining resultant chlorosis and leaf roll under ambient and two elevated [CO₂] levels using a control and three resistant barley host combinations. Elevated [CO₂] had a significant positive effect on the growth of the four barley lines that were not infested by the aphids. However under the same conditions aphid feeding under elevated CO₂ conditions caused very high biomass loss, which was more noticeable in experiments involving non-resistant PUMA than in the resistant barley lines. The results of this study demonstrate that CO₂ enrichment substantially increases aphid populations of RWASA1 and RWASA2 on the four barley lines investigated. Furthermore, aphid populations were higher on non-resistant PUMA than the three resistant lines and the RWASA2 biotype out-performed RWASA1 in each case. Under elevated [CO₂], aphid feeding, resulted in a significant increase in the leaf C:N ratios (as a percentage change) in most treatments, compared to levels recorded on uninfested plants. The resistant lines also showed a significant reduction in leaf nitrogen (~ 40% for PUMA and not less than 30% for the resistant STARS lines tested). C:N ratio changes and N loss correlated to [CO₂] and aphid biotype. By 28 days of infestation, most of the non-resistant PUMA line in particular showed significant irrecoverable levels of leaf chlorosis. At level 9 rating on the chlorosis scale (i.e. plant death when recovery was not possible), experiments were terminated. As aphid success is unlikely to be the sole product of [CO₂], but also of other limiting nutrients such as N, it may be worth further investigating the effect of plant quality and ultimately plant nutrition on the population growth of aphids.