Showing papers on "Aphididae published in 1998"
TL;DR: Volatiles obtained by air entrainment of aphid infested plants were more attractive to A. ervi than those from uninfested plants, in both behavioral bioassays and activity of pure compounds, which significantly increased parasitoid responses to these compounds.
Abstract: Herbivore induced release of plant volatiles mediating the foraging behavior of the aphid parasitoid Aphidius ervi was investigated using the pea aphid, Acyrthosiphon pisum, feeding on broad bean, Vicia faba. Behavioral responses were studied using an olfactometer and a wind tunnel. Volatiles obtained by air entrainment of aphid infested plants were more attractive to A. ervi than those from uninfested plants, in both behavioral bioassays. GC-EAG of both extracts showed a number of peaks associated with responses by A. ervi, but with some differences between extracts. Compounds giving these peaks were tentatively identified by GC-MS and confirmed by comparison with authentic samples on GC, using two columns of different polarity. The activity of pure compounds was further investigated by EAG and wind tunnel assays. Results showed that, of the compounds tested, 6-methyl-5-hepten-2-one was the most attractive for A. ervi females, with linalool, (Z)-3-hexen-1-yl acetate, (E)-β-ocimene, (Z)-3-hexen-1-ol, and (E)-β-farnesene all eliciting significantly more oriented flight behavior than a solvent control. Foraging experience significantly increased parasitoid responses to these compounds, with the exception of (E)-β-farnesene. Time-course GC analysis showed that feeding of A. pisum on V. faba induced or increased the release of several compounds. Release of two of these compounds (6-methyl-5-hepten-2-one and geranic acid) was not induced by the nonhost black bean aphid, Aphis fabae. During the analysis period, production of (E)-β-ocimene remained constant, but 6-methyl-5-hepten-2-one, linalool, geranic acid, and (E)-β-farnesene appeared during the first day after A. pisum infestation and increased in concentration with increasing time of aphid feeding.
446 citations
TL;DR: When maize plants are mechanically damaged and the damaged sites are treated with caterpillar regurgitant, the plants will release a specific blend of volatiles that constitute part of the induced plant defence and herbivores will be affected by the odours as well.
Abstract: When maize plants, Zea mays L., are mechanically damaged and the damaged sites are treated with caterpillar regurgitant, the plants will release a specific blend of volatiles. It is known that these volatiles can be attractive to natural enemies of herbivores. We hypothesise that the plant volatiles constitute part of the induced plant defence and that herbivores will be affected by the odours as well. In laboratory and semi-field studies this hypothesis was tested for the aphid Rhopalosiphum maidis (Fitch) (Rhynchota, Sternorrhyncha, Aphididae).
In a Y-tube olfactometer significantly more aphids chose the odour of healthy, undamaged maize seedlings when tested against clean air or plants treated with regurgitant. Clean air was chosen more often when tested next to the odour of treated plants. This apparently repellent effect of the odour of treated plants was significant for winged aphids, but not for the wingless aphids.
In field experiments aphids were released in the centre of circles of eight potted maize plants. Four plants in each circle were damaged and treated with caterpillar regurgitant while the other plants were left unharmed. At different intervals after aphid release, the number of aphids was counted on each plant. Significantly fewer winged and wingless aphids were found back on treated plants than on healthy plants.
We suggest that herbivores may be repelled by the odours because they could indicate that: 1) the plant has initiated the production of toxic compounds; 2) potential competitors are present on the plant; 3) the plant is attractive to parasitoids and predators. Aphids may be particularly sensitive to induced maize volatiles because one of the major compounds emitted by the plant is (E)-β-farnesene, which is a common alarm pheromone for aphids. Collections and analyses of the odours emitted by crushed R. maidis confirmed that it too emits (E)-β-farnesene when stressed. The results are discussed in context of plant defence strategies and their possible exploitation for the control of pest insects.
268 citations
TL;DR: The effects of predator species, aphid density, Aphid age, diel period, and habitat complexity on the dropping behaviour of the pea aphid Acyrthosiphon pisum were assessed in a series of laboratory and field‐cage experiments.
Abstract: 1. The effects of predator species, aphid density, aphid age, diel period, and habitat complexity on the dropping behaviour of the pea aphid Acyrthosiphon pisum were assessed in a series of laboratory and field-cage experiments. 2. The presence of foliar-foraging predators significantly increased the proportion of aphids that dropped from alfalfa plants. In the absence of predators, less than 7% of the aphids dropped. Dropping more than doubled (14%) when one of three hemipteran predators, N. americoferus, G. punctipes or O. insidiosus, was present. Nearly 60% of the aphids dropped when the ladybird beetle, Coccinella septempunctata, was present. 3. Adult aphids showed a significantly higher propensity to drop than immature aphids, regardless of the presence or absence of predators. Aphid density had no effect on dropping behaviour. 4. Neither diel period nor habitat complexity had an effect on aphid dropping behaviour. Aphids were significantly more likely to drop in the presence of predators during either the day or night and from either early or late regrowth alfalfa. 5. A review of the factors affecting dropping behaviour, including those elucidated in this study, indicates that the propensity to drop from a plant is influenced by three factors: the risk of predation on the plant, the quality of the resource to be abandoned, and the risk of mortality in the new microhabitat.
217 citations
TL;DR: It seems possible that, after seed treatment or soil application, a few of the biologically active metabolites arising are acting in concert with remaining levels of the parent compound imidacloprid, thus providing good control and long-lasting residual activity against plant-sucking pests in certain crops.
Abstract: The metabolism of the chloronicotinyl insecticide imidacloprid is strongly influenced by the method of application. Whilst in foliar application most of the residues on the leaf surface display unchanged parent compound, most of the imidacloprid administered to plants by soil application or seed treatment is metabolized more or less completely, depending on plant species and time. The present study revealed that certain metabolites of imidacloprid which have been described in crop plants are highly active against aphid pests in different types of bioassays. Some of these metabolites showed a high oral activity against the green peach aphid (Myzus persicae), and the cotton aphid (Aphis gossypii). The aphicidal potency of the metabolites investigated was weaker in aphid dip tests than in oral ingestion bioassays using artificial double membranes. The most active plant metabolite was the imidazoline derivative of imidacloprid. The LC50 values of this metabolite for M. persicae and A. gossypii in oral ingestion bioassays were in the lower ppb-range, i.e. 0·0044 and 0·0068 mg litre-1, respectively. Most of the other reported metabolites showed much weaker activity. Compared to imidacloprid, the imidazoline derivative showed superior affinity to housefly (Musca domestica) head nicotinic acetylcholine receptors, while all other metabolites were less specific than imidacloprid. It seems possible that, after seed treatment or soil application, a few of the biologically active metabolites arising are acting in concert with remaining levels of the parent compound imidacloprid, thus providing good control and long-lasting residual activity against plant-sucking pests in certain crops. © 1998 SCI.
213 citations
TL;DR: The results suggest that M. persicae, an important pest of many crops, might increase its abundance under conditions of climate change.
Abstract: Model terrestrial ecosystems were set-up in the Ecotron controlled environment facility. The effects of elevated CO2 (ambient + 200 mol/mol) and temperature (ambient + 2.0°C) on plant chemistry, the abundance of the peach potato aphid Myzus persicae, and on the performance of one of its parasitoids Aphidius matricariae, were studied. Total above-ground plant biomass at the end of the experiment was not affected by elevated atmospheric CO2, nor were foliar nitrogen and carbon concentrations. Elevated temperature decreased final plant biomass while leaf nitrogen concentrations increased. Aphid abundance was enhanced by both the␣CO2 and temperature treatment. Parasitism rates remained unchanged in elevated CO2, but showed an increasing trend in conditions of elevated temperature. Our results suggest that M. persicae, an important pest of many crops, might increase its abundance under conditions of climate change.
164 citations
TL;DR: Comparisons of aphid life history traits and population development between host plant genotypes showed that the effects of resistance act throughout aphid development and are highly effective at slowing down population increase.
Abstract: The feeding behaviour, excretion rate, and life history traits of the cotton-melon aphid, Aphis gossypii (Glover) (Homoptera, Aphididae), were measured on a resistant melon, Cucumis melo L., breeding line, AR 5. The site of resistance detection by the aphids was determined using the electrical penetration graph (EPG) technique. EPG recordings showed that resistance is expressed within the host plant, rather than on its surface, because the time to first stylet penetration was not significantly different between AR 5 and the closely related susceptible breeding line, PMR 5. EPG patterns associated with stylet pathway activities of the aphids were not significantly different between the resistant and susceptible lines. Significant behavioural differences were observed only after stylets contacted phloem sieve elements. On AR 5, the duration of salivation after sieve element puncture (waveform E1) was significantly longer, and the number of aphids showing phloem sap ingestion (waveform E2) was significantly reduced. We conclude that the resistance mechanism producing the effects seen in this study acts within the phloem sieve elements. Monitoring of excretion rates on the two genotypes showed that aphid feeding was delayed and greatly reduced on the resistant genotype. Comparisons of aphid life history traits and population development between host plant genotypes showed that the effects of resistance act throughout aphid development and are highly effective at slowing down population increase.
131 citations
TL;DR: The incidence of both mechanisms of carboxylesterase-based resistance to insecticides in Myzus persicae Sulzer is described and the implications for future recommendations for aphid control in the UK are discussed.
Abstract: The well-established carboxylesterase-based resistance to insecticides in Myzus persicae Sulzer has recently been accentuated by the appearance of aphids with a modified acetylcholinesterase (MACE) insensitive to pirimicarb and the novel aphicide, triazamate. This target site resistance mechanism was found in M. persicae from crops in the UK for the first time in 1996, together with especially large proportions of aphids with R2 and R3 levels of carboxylesterases, a combination that was associated with serious insecticide failures. This paper describes the incidence of both mechanisms and discusses the implications for future recommendations for aphid control in the UK.
73 citations
TL;DR: It is suggested that differences in the lesions caused by these aphids may be due to reaction kinetics rather than specific salivary toxins; that the rate of arrival ofSalivary components, possibly the oxidases, at phloem unloading sites may determine whether the plant's local defensive system is able to repress the immediate challenge or undergoes a run‐away reaction leading to necrosis.
Abstract: The spotted alfalfa aphid (SAA), Therioaphis trifolii maculata (B uckton), causes a characteristic veinal chlorosis and necrosis in the growing tips of susceptible cultivars of alfalfa. The pea aphid, Acyrthosiphon pisum (Harris), causes general degenerative changes in alfalfa but no specific, local symptoms. Biochemical and electrophoretic analyses detected similar enzymes in the ejected saliva of either species: pectin methylesterase, endopolygalacturonase and at least three isozymes of a copper dependent oxido-reductase that showed both catechol oxidase and peroxidase activity. Pectinase and catechol oxidase activities per unit of soluble protein were much greater in the saliva of pea aphid compared with that of SAA. The isozymes of the oxidase from SAA were roughly half the molecular weights of the corresponding isozymes from pea aphid, however, and radiotracer studies showed that soluble secretions injected into alfalfa by SAA travelled to growing tips considerably faster than the secretions of pea aphid. It is suggested that differences in the lesions caused by these aphids may be due to reaction kinetics rather than specific salivary toxins; that the rate of arrival of salivary components, possibly the oxidases, at phloem unloading sites may determine whether the plant's local defensive system is able to repress the immediate challenge or undergoes a run-away reaction leading to necrosis.
69 citations
TL;DR: The black bean aphid was heavily parasitized by the aphid parasitoid, Lysiphlebus fabarum both on agricultural crops and on associated weeds and Habitat diversity contributed to an increase of parasitism on fodder beet but not on broad bean.
Abstract: The black bean aphid (Aphis fabae) was heavily parasitized by the aphid parasitoid, Lysiphlebus fabarum both on agricultural crops (broad bean, fodder beet) and on associated weeds (goosefoot, chamomile, tansy). Parasitization rates increased during the season and were lower on broad bean than on other host plants. Habitat diversity contributed to an increase of parasitism on fodder beet but not on broad bean. Ant-attendance lead to increased parasitism on all host plants. The findings of the field studies were confirmed by laboratory experiments on foraging and oviposition behaviour of L. fabarum females on the various host plants.
67 citations
TL;DR: Information is summarized on the brown citrus aphid's distribution, host range, biology, population ecology, natural enemies, entomopathogens, transmission of plant viruses, and management.
Abstract: Literature is reviewed on the brown citrus aphid (BCA), Toxoptera citricida Kirkaldy, a serious pest of citrus recently introduced to Florida. Information is summarized on the aphid's distribution, host range, biology, population ecology, natural enemies, entomopathogens, transmission of plant viruses, and management.
66 citations
TL;DR: Positive responses of B. curculionis to sugar sprays recorded in this study suggest application of this material may be beneficial to the wasp throughout the 1st crop of alfalfa if aphid densities and associated availability of natural honeydew remain low.
Abstract: Sugar spray applied to crop foliage may serve as a surrogate for homopteran honeydew in meeting the nutritional needs for self-maintenance in adult parasitoids of crop pests. We tested the importance of timing of application of sugar spray and the interaction between sugar spray and naturally occurring aphid honeydew in influencing the local abundance of the alfalfa weevil parasitoid Bathyplectes curculionis (Thomson). Plots of hay alfalfa in northern Utah were sprayed with sucrose dissolved in water (sugar plots) or with water only (control plots) early, midway, or late during the preflowering period in the 5th yr of production. When sampled 2 d later, numbers of adult parasitoids were consistently higher in sugar plots than in control plots. Increased wasp density in response to local pea aphid density also occurred, but only in plots that did not receive sugar spray. Weevil parasitism was elevated in sugar plots compared with control plots only when sprays were applied late in the 1st crop. Lack of enhanced rates of wasp oviposition in sugar plots early and midway during the 1st crop may have resulted from poor weather, mutual interference among the wasps, or wasp feeding. Our study was conducted in a field harboring relatively low numbers of aphids. In general, sugar sprays may be redundant for adult parasitoids in a crop when naturally occurring homopteran honeydew is abundant. But the positive responses of B. curculionis to sugar sprays recorded in this study suggest application of this material may be beneficial to the wasp throughout the 1st crop of alfalfa if aphid densities (and associated availability of natural honeydew) remain low.
TL;DR: It is predicted that the parasitoid would be less willing to attack aphids in patches where a major predator, the coccinellid Coccinella septempunctata, was present or in patches which contained recent traces of predators.
Abstract: Most herbivores and many other insects are subject to attack by both parasitoids and predators. Members of these two guilds of natural enemies thus compete for resources (Rosenheim et al., 1995). However, competition is usually asymmetric because insects attacked by parasitoids are often as vulnerable to predation as unparasitized hosts (e.g., Lawton and Hassell, 1981). In such cases, we might expect parasitoids to evolve to avoid areas where predators are present. Aphids are attacked by large guilds of parasitoids and predators (Dixon, 1985: Minks and Harrewijg, 1988). Primary aphid parasitoids develop endoparasitically, pupating within the mummified remains of their host. Predators such as Coccinellidae appear not to distinguish between aphids with or without parasitoid larvae (Hagen and van den Bosch, 1968) and frequently consume mummified aphids. We studied the oviposition behavior of the parasitoid Aphidius ervi (Braconidae, Aphidiinae) attacking the pea aphid Acyrthosiphon pisum (aphididae, Macrosiphoninae). We predicted that the parasitoid would be less willing to attack aphids in patches where a major predator, the coccinellid Coccinella septempunctata, was present or in patches which contained recent traces of predators. METHODS
TL;DR: The results showed that the host plant may affect interspecific interactions between parasitoids and fungi and that these interactions depended on the timing of parasitoid oviposition and fungal infection.
Abstract: Host-plant resistance can affect herbivorous insects and their natural enemies such as parasitoids and entomopathogenic fungi. This tritrophic effect acts on interspecific interactions between the two groups of natural enemies distantly related in phylogenetic terms. The intra- and extra-host aspects of the interaction between the cereal aphid parasitoid Aphidius rhopalosiphi and the entomopathogenic fungus Erynia neoaphidis developing on the grain aphid, Sitobion avenae, on resistant and susceptible wheat (Triticum aestivum) cultivars, were studied. The competitive outcome of the intra-host interaction depended on the timing of parasitoid oviposition and fungal infection and was affected by wheat resistance. In particular, survival of the parasitoid was lower on the resistant wheat cultivar than the susceptible wheat cultivar, when the competitive outcome of the interaction was favourable for either parasitoid or fungal development. Before and after this period the influence of plant resistance was not significant. Furthermore, the extra-host interaction was not affected by the wheat cultivar, although an increase in fungal infection of S. avenae was observed when parasitoids foraged in the experimental arena with sporulating aphid cadavers compared with foraging in the absence of sporulating cadavers. Our results showed that the host plant may affect interspecific interactions between parasitoids and fungi and that these interactions depended on the timing of parasitoid oviposition and fungal infection.
TL;DR: The role of the kairomone in foraging decisions by the parasitic wasp was explored by manipulating the amount of honeydew and the number of aphids in a colony independently and the count‐down patch‐exploitation mechanism was employed to predict the results.
Abstract: 1. The wasp Diaeretiella rapae uses honeydew emitted by its host, the cabbage aphid Brevicoryne brassica, as a kairomone (chemicals emitted by an organism as part of its activity and used by its natural enemies to their advantage). The role of the kairomone in foraging decisions by the parasitic wasp was explored by manipulating the amount of honeydew and the number of aphids in a colony independently. The count-down patch-exploitation mechanism (Iwasa et al., 1981) was employed to predict the results of these manipulations and contrast them with the predictions of Waage's (1979) model.
2. Kairomonal activity of honeydew decreased as the honeydew aged and lost its activity completely within 72 h.
3. The wasp was exposed to different amounts of honeydew on (a) aphid-free leaves and (b) leaves bearing colonies of 150 aphids. The parasitoid search time on both leaf types increased with increasing honeydew contamination. On aphid-bearing leaves, the number of attacked aphids in the colonies also increased with increasing honeydew contamination. The presence of aphids reduced the parasitoid search time compared to search time on aphid-bearing leaves with the same level of honeydew contamination, as predicted by the count-down model.
4. Parasitoids exposed to the same amount of honeydew, but a different number of aphids in a colony on the leaf, first increased the number of aphids attacked in relation to the number of aphids in the colony. But as the colony reached a certain size, the number of aphids attacked levelled off, despite the increase in the number of aphids in the colony. Search time was variable but did not exhibit any trend as the number of aphids in the colonies increased.
5. These results suggest that honeydew level is used by D. rapae as a cue for assessment of the number of aphids in the colony. In such cases, a count-down exploitation mechanism gives the best results to a forager. Many parasitoids may use kairomones for patch assessment and will therefore employ a count-down rule during patch exploitation.
TL;DR: Both apterae and alatae showed a general attraction to green plants and were also able to distinguish between other host plants and cowpea, which was the original host of the aphid clone used in the experiments.
Abstract: Olfactometer experiments were conducted with apterae and alatae of the cowpea aphid, Aphis craccivora, Koch (Hom.:Aphidoidea). The occurrence of density dependent related pheromones and odour response to their host plant Vigna unguiculata was studied. Apterae responded with positive anemotaxis to air passed over both small groups of apterae and alatae (≤10 individuals) but negatively to air that passed over a bigger group (≥20 individuals). Alatae responded in the same way to groups of apterae but were repelled by alatae independent of the size of the group applied as odour source in the olfactometer, except when exposed to air passing ten alatae feeding on cowpea leaves. This may be due to interaction between aphid pheromones and host plant odour. Both apterae and alatae showed a general attraction to green plants and were also able to distinguish between other host plants and cowpea, which was the original host of the aphid clone used in the experiments. When attacked by aphids, the cowpea plant responded with a temporal increase in attractivity that reached a maximum after 48 h and had disappeared after one week.
TL;DR: In this paper, four polymorphic enzymes (PEP, PGI, PGM and IDH) were separated from adult individuals of five parasitoid species of the genus Aphidius Nees (A. ervi Haliday, A. eadyi Starý, Gonzalez & Hall, A picipes Nees and A. urticae Haliday) using horizontal cellulose acetate plate electrophoresis.
Abstract: Four polymorphic enzymes (PEP, PGI, PGM and IDH) were separated from adult individuals of five aphid parasitoid species of the genus Aphidius Nees (A. ervi Haliday, A. microlophii Pennacchio & Tremblay, A. eadyi Starý, Gonzalez & Hall, A. picipes Nees and A. urticae Haliday) using horizontal cellulose acetate plate electrophoresis. These markers were used to investigate the genetic relationships, including reproductive isolation and host adaptation/specificity, in laboratory and field populations. Samples were collected from the pea aphid, Acyrthosiphon pisum (Harris) and/or the nettle aphid, Microlophium carnosum (Buckton) in the UK and Bulgaria between 1991 and 1994. Whilst all loci discriminated between some species, PGM discriminated all five species, one species (A. eadyi) bearing two unique alleles (PGMa and PGMc). Aphidius microlophii (from nettle aphid) and A. ervi (from pea aphid), which are difficult to separate morphologically, possessed unique PGM alleles – PGMb and PGMe, respectively. Both parasitoids occur sympatrically, and whilst hybrids heterozygous for PGM were produced in the laboratory (PGMb,e), such genotypes were not observed in the field populations sampled. Hence, the species appear to be reproductively isolated. Most parasitoid populations studied showed mean heterozygote deficiencies per locus (homozygote excess) compared with Hardy-Weinberg expectations. In particular, A. eadyi bearing PGMa alleles were always homozygous whilst additionally, many were homozygous for another allele, PGIb. This is evidence for the existence of one or more morphologically-indistinguishable ‘cryptic’ species occurring sympatrically within European field populations. A dendrogram of relatedness was produced following calculation of Nei's genetic identity coefficient, I from the parasitoid population allele frequency data. All species showed very high similarity between populations at the intraspecific level (>0.9), but fewer interspecific similarities (0.23–0.63). These values compare well with previously published values for Aphidius populations and for other insects.
TL;DR: Castilleja growth and reproductive performance were greatly improved by the simultaneous attack of two distinct host species, even though Castilleja grown with two Lupinus hosts had significantly higher nitrogen content.
Abstract: I examined how the performance of Castilleja wightii (Scrophulariaceae), a generalist root parasite, is affected by the availability of different combinations of host species. In this greenhouse study, I focused on pairs of hosts consisting of either two leguminous host individuals (Lupinus arboreus; Fabaceae), two non-nitrogen-fixing hosts (Eriophyllum stachaedifolium; Asteraceae), or one individual of each of these species. Castilleja growth and reproductive performance were greatly improved by the simultaneous attack of two distinct host species, even though Castilleja grown with two Lupinus hosts had significantly higher nitrogen content. Different combinations of host species also strongly affected the growth of aphid colonies feeding on the Castilleja used in this experiment. Across all treatments, the growth of aphid colonies was positively correlated with the nitrogen content of the parasitic plants, which, in turn depended on the combination of hosts attacked. Aphid colonies feeding on parasites ...
TL;DR: The hypothesis is that an aphid specialist predator as C. septempunctata, may gain advantage from developing on a diversified diet, compared to a singlespecies aphid diet, because different species of aphids may have a different composition of nutrients, thus satisfying better a varied nutrient demand.
Abstract: The developmental time, weight and fecundity of the aphid specialist predator the seven spotted ladybird (Coccinella septempunctata L.) vary considerably according to the species of aphid they are raised on (Blackman, 1967a; Ghanim et al., 1984; Malcolm, 1992). The results of these studies showed that prey of low food quality slowed larval development and produced smaller adult animals. The experiments were carried out with single-species diets. So far there seems to be no studies on the possible benefits of diet mixing in coccinellid beetles (Hodek & Hon ěk 1996). Hodek (1956) and Blackman (1967b) found evidence that C. septempunctata is unselective in its choice of prey; it cannot recognise and avoid unsuitable or toxic species of aphids. ̧ Sengonca & Liu (1994) noticed that the larvae ofC. septempunctata revealed no difference in responding to the kairomones from four different species of aphid prey. It is therefore likely that the larvae ofC. septempunctata just eat the aphids that they meet. This may be an optimal foraging strategy, when the prey is clumped and unpredictable and acceptance of toxic prey is no worse than starvation. Even if coccinellids are unselective in a choice situation, a mixture of prey species may provide a higher nutritional diversity and thus be beneficial in terms of improved performance i.e. a lower mortality, a faster development and a higher adult body weight. We used three cereal aphid species Sitobion avenae(F.), Rhopalosiphum padi (L.) and Metopolophium dirhodum(Walker) and an equal number mixture of these three species as prey and compared the performance of C. septempunctata larvae. The three cereal aphid species all have grasses as their host plants, thus the coccinellid larvae may encounter all three species on the same plant. It is therefore ecologically relevant to examine if there is an advantage of a mixed diet of these three aphid species. Our hypothesis is that an aphid specialist predator as C.septempunctata , may gain advantage from developing on a diversified diet, compared to a singlespecies aphid diet, because different species of aphids may have a different composition of nutrients, thus satisfying better a varied nutrient demand. This should be revealed by better performance of the larvae, indicating a higher food value of the mixed diet. Such relationships are known for a wide range of generalist consumers (Reichert & Harp, 1987; Waldbauer & Friedman, 1991; Wallin et al., 1992; Bernays et al., 1994).
TL;DR: The results showed that distinct mechanisms were involved in the sources of resistance studied and the ranking of the genotypes on their resistance/susceptibility status remained roughly stable throughout the experiments, providing evidence that aphids on this genotype lacked sufficient ressources to be directed both towards production and growth of embryos.
Abstract: Discovery in the late seventies of resistance to the green peach aphid Myzus persicae (Sulzer) (Homoptera: Aphididae) in Prunus species was based on screening in the field or in greenhouses with natural aphid populations. Here, we assess the impact of these wild and domesticated peach trees on the behaviour, development, reproductive performance and demography of cloned aphids under controlled light and temperature. Four peach varieties, i.e., Rubira, Weeping Flower Peach, Summergrand and Malo konare and the clone P1908 of the related species Prunus davidiana were tested against the highly susceptible cultivar GF305. Besides a variability in the performance of aphids among experiments, our results showed that (i) distinct mechanisms were involved in the sources of resistance studied and (ii) the ranking of the genotypes on their resistance/susceptibility status remained roughly stable throughout the experiments. Observations on the settling behaviour of first instar nymphs demonstrated antixenosis components in the resistance conferred by Rubira and Weeping Flower Peach. Nymphs began to leave the plants after a short exposure (19–21 h) and no aphid was left after 4 days. Nymphal mortality remained rather low (16%) compared to the repellent effect on aphids of both genotypes. Nymphs disappeared from Weeping Flower Peach significantly earlier than from Rubira. Summergrand, Malo konare and P. davidiana clone P1908 were accepted as host plants by aphids. On P. davidiana, decreased fecundity and intrinsic rate of natural increase (rm= 0.20, averaged on all experiments) were clear expression of antibiosis. In addition, the mean length of the mature embryos within the gonads of the females on the day of adult moult was negatively correlated with the total number of embryos, providing evidence that aphids on this genotype lacked sufficient ressources to be directed both towards production and growth of embryos. Compared to the most susceptible cultivar GF305 (rm= 0.36), Summergrand (rm= 0.26) and Malo konare (rm= 0.28) had, to a lesser extent, a negative impact on nymph production and rate of increase.
TL;DR: The results indicate that reduced waxbloom in peas could improve the effectiveness of H. convergens on peas at low prey densities.
Abstract: Adult females of the coccinellid predator Hippodamia convergens (Say) spent more time walking and less time grooming on a line of peas, Pisum sativum L., that has reduced waxbloom on all parts of the plant (due to the mutation wel ) compared with a near-isogenic sister line with normal waxbloom. H. convergens walking was distributed over all parts of the low-wax plants, whereas on normal-wax plants walking occurred mostly on stems and the edges of leaves and stipules. The beetles were able to generate 30 times the adhesive traction force on leaf surfaces of low-wax plants compared with normal-wax plants. In cage studies, H. convergens (4 adults per plant) were more effective at reducing population growth of pea aphid, Acyrthosiphon pisum (Harris), on low-wax plants than on normal-wax plants, but only at initial aphid densities of 10 aphids per plant. At higher initial densities (20 and 40 aphids per plant), differential impact of H. convergens was not observed or disappeared after 4–5 d. The results indicate that reduced waxbloom in peas could improve the effectiveness of H. convergens on peas at low prey densities.
TL;DR: Electrical penetration graphs of Myzus persicae (Sulzer) (Homoptera: Aphididae) feeding behaviour on four resistant and two susceptible genotypes of peach showed that resistance was mainly linked to reduced duration of phloem sap uptake, and evidence for the existence of different mechanisms underlying resistance in the tested genotypes against M. Persicae was given.
Abstract: Key words: Aphididae, EPG, Myzus persicae, peach, phloem, plant resistance mechanismsAbstractElectrical penetration graphs of Myzus persicae (Sulzer) (Homoptera: Aphididae) feeding behaviour on four resis-tant and two susceptible genotypes of peach (Prunus persica L. Batsch) and related species showed that resistancewas mainly linked to (i) reduced duration of phloem sap uptake, (ii) reduced percentage of pattern E1 (salivarysecretion into sieve elements) followed by pattern E2 (sap ingestion) and (iii) increased number of shifts fromE1 to E2 and back. These results suggest the unsuitability of phloem sap, and thus repetitive failures to initiatesustained ingestion. Extensive comparisons of the EPGs also revealed more specific trends. Aphids on the mostsusceptible cultivar GF305 produced significantly longer potential drops than on other peach genotypes. On theresistant Rubira, aphids generated more penetrationsbefore the first E occurred, indicating the possible presence ofa resistance factor beforethe phloemwas reached. The clone P1908of the wild speciesPrunusdavidianadisplayedtraits of both susceptibility (less but longer probes) and resistance. In particular, aphids produced more E1, sug-gesting difficulties in preparing sieve elements before feeding. The aphid probing process could be correlated withaphid settling behaviour and bionomics, as previously reported, and gave evidence for the existence of differentmechanisms underlying resistance in the tested genotypes againstM. persicae.IntroductionThe green peach aphid Myzus persicae (Sulzer) is oneof the major pests in peach orchards of France andsouthern Europe (Leclant, 1973; Sacchetti & Niccoli,1995). It causes direct damage to peaches, and is alsoone of the vectors of the plum pox virus, responsi-ble for the sharka disease (Kassanis & Sutic, 1965).Due to the limited efficiency of both biological andchemical controls, sources of host plant resistance toM. persicae have been screened for within the genusPrunus (Massonie et al., 1982). The genotypes testedin our study are listed in Table 1.The development of aphid colonies and plant re-actions after artificial infestation of these genotypesunder semi-natural conditions have been describedpreviously. This was followed by the detailed analy-sis of behavioural traits and bionomics of M. persicaein growth chambers (Sauge et al., 1998). Differentmechanisms of host plant resistance have been charac-terized. On Rubira and Weeping Flower Peach (WFP),red or yellow coloured spots are induced by aphidfeeding, sometimes followed by withering of termi-nal leaves. Moreover, aphids begin to leave the plantswithin 3 days (Massonie et al., 1982, 1984; Monet &Massonie, 1994). On Malo konare, artificial contami-nation by aphids resulted in the delayed developmentof colonies. Finally, on the clone P1908 of the wildspecies P. davidiana, as well as on some interspecifichybrids between this clone and a susceptible cultivar,aphids are able to settle but colonies declined aftersome weeks (Massonie et al., 1982). P1908 and thehybridsalsoexhibitstronglyreducedsymptomsofleafcurling.In this work, we further investigated these resis-tances using the Electrical Penetration Graph (EPG,
TL;DR: It is concluded that the resistance of P. sativum to certain A. pisum clones does not arise from factors impeding either stylet penetration through the plant tissues or the maintenance of feeding from the sieve elements, and it is proposed that host plant affiliation of A.pisum may be mediated primarily by specific olfactory or gustatory cues, before the aphid initiates Stylet penetration of the plant.
Abstract: Plant penetration by the stylets of six clones of the pea aphid, Acyrthosiphon pisum, on Vicia faba (acceptable to all clones) and Pisum sativum (acceptable to 3/6 clones) was investigated by the DC electrical penetration graph technique. In a 10 h recording period, 93% of 144 aphids exhibited sustained feeding on phloem sap. Significant interclonal differences were observed for the incidence of potential drops (indicative of brief punctures of plant cells) and the duration of waveform E1 (insect salivation into a sieve element). In addition, the total duration of the sieve element phase and the duration of completed ‘bouts’ of sustained feeding differed between the two test plants, in a fashion varying between clones. However, these differences could not be related to the acceptability of plants to the different aphid clones. The duration of the stylet pathway phase preceding the first sustained feeding on phloem sap did not vary significantly with either aphid clone or plant. It is concluded that the resistance of P. sativum to certain A. pisum clones does not arise from factors impeding either stylet penetration through the plant tissues or the maintenance of feeding from the sieve elements. It is proposed that host plant affiliation of A. pisum may be mediated primarily by specific olfactory or gustatory cues, before the aphid initiates stylet penetration of the plant.
TL;DR: No single growth stage of chrysanthemum for maximal aphid population growth can be assigned, but the budding and flowering stage are the most suitable in three out of four aphid × cultivar combinations.
Abstract: Realistic values of population growth rates are needed when used in forecasting programmes, e.g., in a programme of integrated control. Therefore, comparisons were made in a chrysanthemum - aphid system between different methods of assessing population growth rates. The reproductive performances of the aphid species Aphis gossypii and Myzus persicae were measured on two chrysanthemum cultivars using three plant growth stages (young vegetative, budding and flowering). In the first set of experiments, development time and reproduction were used to estimate the population growth rate r m . The mean relative growth rates (MRGR) were also assessed. It was shown for the first time that the relationship between r m and MRGR was influenced by aphid species. In a second experiment, the aphid population increase on a whole plant was measured and r m was estimated by calculating the slope of the (In transformed) population increase. It is shown that population growth rate is affected by the growth stage of the plant, and that cultivar and aphid species interact with plant growth stage in influencing population growth rate. Thus, no single growth stage of chrysanthemum for maximal aphid population growth can be assigned, but the budding and flowering stage are the most suitable in three out of four aphid x cultivar combinations. Comparison between the results from both experiments demonstrates clearly that more realistic values for r m are obtained when measured on whole plants.
TL;DR: Two methods of establishing the parasitoids in cucumber crops prior to invasion of the aphids were developed and were found to be more efficient in summer than in late spring.
Abstract: Aphis gossypii Glover (Hom.: Aphididae) is a damaging pest of protected cucumbers in the UK, and control measures are required which are compatible with other components in the overall cucumber integrated pest management programme. Two methods of establishing the parasitoids, Aphidius colemani Viereck (Hym.: Braconidae), in cucumber crops prior to invasion of the aphids were developed. The first involved weekly releases of small numbers of parasitoids beginning before A. gossypii became established on the plants. The second method used open-rearing units based on maize, wheat and rygrass plants infested with Rhopalosiphum padi L (Hom.: Aphididae), which is a common host to many natural enemies of A. gossypii but not a threat to the cucumber crop. Both methods were found to be more efficient in summer than in late spring. Parasitoid release rates were established for the two control methods at both of these times of the year. Like all biological control measures, these methods will require careful manageme...
TL;DR: Interactions between barley yellow dwarf luteovirus (BYDV) and the aphid parasitoid, Aphidius ervi Haliday, were investigated while sharing the vector/host, Sitobion avenae (F.) (Homoptera: Aphididae).
Abstract: Interactions between barley yellow dwarf luteovirus (BYDV) and the aphid parasitoid, Aphidius ervi Haliday (Hymenoptera: Aphidiidae), were investigated while sharing the vector/host, Sitobion avenae (F.) (Homoptera: Aphididae). Aphids, which were parasitized during their second larval stadium, had access to virus-infected plants before, immediately after, or several days after parasitoid attack. The larval development of A. ervi in S. avenae was significantly delayed when virus acquisition took place before or shortly after the parasitoid had hatched, but not when the parasitoid was at the second larval stage during virus acquisition. Similarly, the presence of BYDV led to a significantly higher aphid mortality when they acquired virus up to and including the time that A. ervi was at the first larval stage. Adult female parasitoids deposited fewer eggs in viruliferous aphids. Virus transmission was not reduced by parasitization, and in some experiments aphids which were subjected to parasitoid attack transmitted BYDV more efficiently than unattacked insects.
Journal Article•
TL;DR: Plant‐derived antifeedant compounds and mineral oil were applied to tobacco leaves infected by potato virus Y in order to assess the effects on stylet penetration behaviour and subsequent transmission of the virus by the aphid vector, Myzus persicae.
Abstract: Plant-derived antifeedant compounds and mineral oil were applied to tobacco leaves infected by potato virus Y (PVY), in order to assess the effects on stylet penetration behaviour and subsequent transmission of the virus by the aphid vector, Myzus persicae. Video recordings of insect movements at the leaf surface showed that the initiation of stylet penetration was significantly delayed when mineral oil (Sunoco 7E) was present, but behaviour was not affected by any of three antifeedant treatments (quassin, hop α-acids or hop β-acids). Each insect was monitored until it had withdrawn its stylets from the leaf, and was then transferred to a healthy tobacco test seedling in order to determine its ability to transmit the virus. The proportion of aphids transmitting PVY from antifeedant-treated plants was similar to that from solvent-treated control plants, but the mineral oil caused a clear reduction in virus transmission efficiency.
TL;DR: Results suggest that inactive and active vectors came from the active and highly active alate populations, respectively and provide confirmation that lowM.
Abstract: Alate green peach aphids,Myzus persicae (Sulzer), tested in a flight chamber during their maiden flight period displayed behaviours ranging from repeated trivial flights to settling on the plants. The interaction of alate vector density and PVYn spread was dichotomous, virus spread was significantly related to vector density in some trials but virus spread was nil or limited and not significantly dependent on vector density in others. The green peach aphid colony used in these experiments provided a mixture of active and highly active alate populations. Results suggest that inactive and active vectors came from the active and highly active alate populations, respectively. Therefore, winged aphids within a species cannot all be attributed the same vector efficiency unless known to originate from the same population. At a 15% inoculum level the intercept for the regression model for the spread of PVYn was 5.03% indicating that there is a significant probability of propagation at aphid densities as low as one. However, over the range of aphid densities tested, the rate of spread per aphid was low, 0.08%, suggesting that reinfection of newly infected plants or movement interference between aphid vectors rapidly became important factors negatively affecting virus spread. Although these results cannot be directly transferred to field conditions they provide confirmation that lowM. persicae numbers can transmit unacceptable levels of mosaic and that low inoculum levels are required to decrease the risk of transmission by the small aphid numbers which cannot be realistically controlled.
TL;DR: Spinach, Spinacia oleracea L., produced for processing in the Arkansas River Valley of western Arkansas was sampled for live and diseased aphids from 1990 to 1993 and the green peach aphid was the only aphid detected and its occurrence was highly variable.
Abstract: Spinach, Spinacia oleracea L., produced for processing in the Arkansas River Valley of western Arkansas was sampled for live and diseased aphids from 1990 to 1993. The green peach aphid, Myzus persicae (Sulzer), was the only aphid detected and its occurrence was highly variable. No aphids were detected in 14 of the 24 sampled fields. Nine of the 10 fields in which aphids were detected had individuals infected with the fungus Erynia neoaphidis (Remaudiere & Hennebert). No other fungal pathogens were observed. Infected aphids were detected in each of the 3 spinach production seasons (fall, winter, and spring). In several fields, especially during the winter of 1992, aphid populations declined with increased E. neoaphidis incidence. However, in fields with relatively high numbers of aphids this population decline occurred at or after the normal spinach harvest period. Aphids killed by E. neoaphidis were tightly held to spinach foliage and, when epizootics occurred at harvest, the spinach was rejected by the processor due to difficulty in washing the aphid cadavers from the product.