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.     

Effects of systemic potato response to wounding and jasmonate on the aphid Macrosiphum euphorbiae (Sternorryncha: Aphididae)

Plant induced responses are activated by multiple biotic and abiotic stresses, and may affect the interactions between a plant and phytophagous insects. The objective of this work was to evaluate the effects of different stresses inflicted to potato plants (Solanum tuberosum) on the potato aphid (Macrosiphum euphorbiae). Abiotic wounding, biotic wounding by Leptinotarsa decemlineata and treatment with volatile methyl jasmonate (MeJA) were evaluated with regard to the orientation behaviour, the feeding behaviour and the development of the potato aphids. Dual‐choice olfactometry showed that plants treated with MeJA lost their attractiveness for the potato aphids, while both abiotic and biotic wounding did not alter the orientation of aphids. Electropenetrography revealed that the feeding behaviour of aphids was only slightly disturbed by a previous L. decemlineata wounding, while it was highly disturbed by mechanical wounding and MeJA treatment. Aphid nymph survival was reduced on mechanically wounded plants, the pre‐reproductive period was lengthened and the fecundity reduced on plants treated with MeJA. Our results bring new information about the effects of various stresses inflicted to S. tuberosum on M. euphorbiae. We showed that wounding and MeJA treatment induced an antixenosis resistance in potato plants against M. euphorbiae, which may influence aphid colonization processes.     

Vector activity of three aphid species (Hemiptera: Aphididae) modulated by host plant selection behaviour on potato (Solanales: Solanaceae)

Viral diseases non-persistently transmitted by aphids are of great economic importance in several annual crops. Transmission efficiency of these non-persistent phytoviruses is dependant on vector efficiency (i.e. vector intrinsic ability to transmit the virus) but also on the vector activity that implies the early steps of aphid host plant selection process (i.e. brief intracellular stylet punctures after landing) and to their interplant movement ability. In Europe, Macrosiphum euphorbiae (Thomas 1878) is considered as one of the most serious virus vectors on potato (Solanum tuberosum L. 1753). Nevertheless, several alate aphid species that do not colonise potato plants are trapped in potato crops. Therefore, we investigated, through laboratory experiments, vector activity of one potato colonising aphid, M. euphorbiae, and two non-colonising potato aphids, the bird cherry-oat aphid Rhopalosiphum padi (L. 1758) and the pea aphid Acyrthosiphon pisum (Harris 1776). A settling experiment was used to evaluate dispersal activity, and the electrical penetration graph (EPG) technique was used to investigate probing activity on potato plants. Results showed that M. euphorbiae exhibited a better vector activity than other two aphid species in terms of landing and probing. By contrast, interplant movements were only recorded on non-colonising aphids, suggesting a better vector activity than M. euphorbiae in terms of locomotive behaviour. These data confirm the involvement of A. pisum and R. padi in the spread of non-persistent viruses.     

Role of terpenes from aphid-infested potato on searching and oviposition behavior of Episyrphus balteatus

To cope with pathogen and insect attacks, plants develop different mechanisms of defence, in both direct （physical and chemical） and indirect ways （attractive volatiles to entomophagous beneficials）. Plants are then able to express traits that facilitate ＂top-down＂ control of pests by attracting herbivore predators. Here we investigate the indirect defence mechanism of potato plants by analyzing the volatile patterns of both healthy and aphid- infested plants. Important changes in the emitted terpene pattern by the Myzus persicae infested host plant were observed. Using Solid Phase MicroExtraction （SPME） and GC-MS, the （E）-fl-farnesene （EBF） appeared to be emitted by aphid-infested potato and not by healthy plants. To assess the infochemical role of these volatile releases after aphid damage on the aphidophagous predators Episyrphus balteams, the hoverfly foraging behavior was assessed using the Observer 5.0 software （Noldus, Wageningen, The Netherlands）. Aphidfree potato plants were also used as a control volatile source in the predator behavioral study. While aphid-infested plants induced efficient searching and acceptation behaviors leading to egg-laying, no kairomonal effect of healthy potato plants was observed, leading to longer immobility durations and shorter searching periods in the net cage. High oviposition rate of E. balteatus was observed when aphid-infested potato was used （mean of 48.9 eggs per laying and per female）. On the other hand, no egg was produced by the hoverfly on healthy aphid-free plants. The E. balteatus foraging and reproductive behaviors according to the volatile emission from aphid-infested plants are discussed in relation to the potential use of active infochemical molecules in integrated aphid pest management.     

The effect of co-infestation by conspecific and heterospecific aphids on the feeding behaviour of <Emphasis Type="Italic">Nasonovia ribisnigri</Emphasis> on resistant and susceptible lettuce cultivars

Aphid saliva can suppress the blocking of sieve elements, a reaction that plants employ to inhibit aphid feeding, but aphid saliva can also elicit plant defence responses. Such plant responses might affect interactions between different aphid species and intraspecifically, e.g. among different biotypes. The objectives of our study were to investigate if feeding behaviour and performance of two biotypes of the lettuce aphid Nasonovia ribisnigri are affected by (1) feeding by the other biotype and (2) feeding by the green peach aphid Myzus persicae or the potato aphid Macrosiphum euphorbiae. Additionally the effect of feeding in a group was studied. All experiments were performed on both a resistant and an isogenic susceptible lettuce cultivar. Feeding or probing by conspecific or heterospecific aphids had different effects on Nasonovia ribisnigri biotypes. Aphids were only slightly affected by feeding or probing of the same biotype on both susceptible and resistant lettuce. N. ribisnigri virulent biotype Nr:1 suppressed the resistance against Nr:0 in the resistant cultivar. In contrast, defence was induced by Nr:1 against Nr:0 in susceptible lettuce. Co-infestation by M. euphorbiae and M. persicae had minor effects on Nr:0. Defence against Nr:1 was induced on both susceptible lettuce and resistant lettuce by Nr:0 and M. euphorbiae. Additionally, M. persicae induced defence in resistant lettuce against Nr:1. Effectors in the saliva of Nr:1 aphids are likely responsible for the defence suppression in lettuce. Identification of these effectors could lead to a better understanding of the mechanism of virulence in N. ribisnigri.     

Host-locating response by the aphid parasitoid Aphidius ervi to tomato plant volatiles

Abstract

The blend of volatile compounds emitted by tomato plants (Solanum lycopersicum) infested with the potato aphid (Macrosiphum euphorbiae) has been studied comparatively with undamaged plants and aphids themselves. Aphid-infested plants were significantly more attractive towards Aphidius ervi than undamaged plants and aphids themselves. Oriented response towards host-damaged plant, from which aphids were removed just before running the bioassay, did not differ from that recorded for infested plants. Collection of the volatiles and analysis by gas chromatography revealed only quantitative differences between uninfested and aphid-infested plants. Nine compounds, α-pinene, (Z)-3-hexen-1-ol, α-phellandrene, limonene, (E)-β-ocimene, p-cymene, methyl salicylate, (E)-β-caryophyllene and an unknown compound, were emitted at higher levels from aphid-infested plants than from undamaged control plants, whilst no differences were noted for hexanal, 6-methyl-5-hepten-2-one, and humulene (=α-caryophyllene). Synthetic standards of these compounds were tested in wind tunnel bioassays and all elicited a significant increase in oriented flight and landings on the target by the aphid parasitoid Aphidius ervi. (E)-β-caryophyllene resulted the most attractive towards female wasps. These results corroborate the hypothesis that the volatiles produced by the plant in response to aphid attack derive from both jasmonic and salicylic acid pathways, and are exploited by A. ervi as olfactory cues to locate its hosts.     

The molecular bases of plant resistance and defense responses to aphid feeding: current status

Plant genes participating in the recognition of aphid herbivory in concert with plant genes involved in defense against herbivores mediate plant resistance to aphids. Several such genes involved in plant disease and nematode resistance have been characterized in detail, but their existence has only recently begun to be determined for arthropod resistance. Hundreds of different genes are typically involved and the disruption of plant cell wall tissues during aphid feeding has been shown to induce defense responses in Arabidopsis, Triticum, Sorghum, and Nicotiana species. Mi‐1.2, a tomato gene for resistance to the potato aphid, Macrosiphum euphorbiae (Thomas), is a member of the nucleotide‐binding site and leucine‐rich region Class II family of disease, nematode, and arthropod resistance genes. Recent studies into the differential expression of Pto‐ and Pti1‐like kinase genes in wheat plants resistant to the Russian wheat aphid, Diuraphis noxia (Mordvilko), provide evidence of the involvement of the Pto class of resistance genes in arthropod resistance. An analysis of available data suggests that aphid feeding may trigger multiple signaling pathways in plants. Early signaling includes gene‐for‐gene recognition and defense signaling in aphid‐resistant plants, and recognition of aphid‐inflicted cell damage in both resistant and susceptible plants. Furthermore, signaling is mediated by several compounds, including jasmonic acid, salicylic acid, ethylene, abscisic acid, giberellic acid, nitric oxide, and auxin. These signals lead to the development of direct chemical defenses against aphids and general stress‐related responses that are well characterized for a number of abiotic and biotic stresses. In spite of major plant taxonomic differences, similarities exist in the types of plant genes expressed in response to feeding by different species of aphids. However, numerous differences in plant signaling and defense responses unique to specific aphid–plant interactions have been identified and warrant further investigation.     

The induction of top-roll symptoms on potato plants by the aphid Macrosiphum euphorbiae

In the field, caged potato plants of King Edward and Majestic cultivars infested with the potato aphid Macrosiphum euphorbiae developed top-roll symptoms, the proportion of affected plants increasing with the size and persistence of the aphid population. Yield of tubers from plots in which 90% of the plants had top-roll symptoms was 40% less than that from control plots; yield of saleable ware was even less. Foliage produced after the aphids had been killed was symptomless even when it arose from the axil of an affected leaf. Caged field plants treated with phorate granules to prevent aphid attack did not develop top-roll. Prolonged infestation of Pentland Crown, Majestic and King Edward plants by M. euphorbiae in a glasshouse induced rolling of upper leaves similar to top-roll of field plants. Experimental results suggest that rolling was directly attributable to heavy attack by M. euphorbiae, not to an aphid-transmitted pathogen.     

Genotypic variation in induced resistance and induced susceptibility in the peach-Myzus persicae aphid system

In response to herbivore damage or stress, plants may express physiological or morphological changes known as induced responses. We tested whether previous herbivory by the aphid Myzus persicae differentially altered the expression of resistance and susceptibility among five genotypes of peach that differ in their resistance phenotype (avoidance resistance, antibiosis resistance or susceptibility). We measured behavioural and performance parameters of aphid success on plants previously infested by conspecifics as compared to uninfested controls. Significant variation was found both among genotypes and among resistance phenotype, including between genotypes showing a same resistance phenotype. Genotypes with avoidance resistance showed either induced resistance to aphid settling or no response. Genotypes with antibiosis resistance showed induced susceptibility to aphid settling, but the effects of previous herbivory on aphid development were either positive or negative depending on the genotype. In the susceptible genotype, most parameters of aphid settlement and performance, including reproduction, were positively influenced by previous herbivory. Using electronic recording, the aphid probing behaviour was examined to tentatively identify host plant tissues most likely to play a role in induced defenses. Probing behaviour was significantly affected by plant genotype, previous herbivory, and their interaction, indicating complex relations between the two factors. In the genotypes with avoidance resistance, aphids were deterred before they reach the phloem. In the genotypes expressing susceptibility or antibiosis resistance, previous herbivory triggered instead the induction of a phloem‐mediated response, that however diverged depending on the resistance status (facilitation or reduction of phloem sap uptake respectively). Genotypic variation in induction found in the peach‐M. persicae system establishes a useful framework to improve our knowledge of the ecological role of induced plant responses to aphids.     

UV‐B impact on aphid performance mediated by plant quality and plant changes induced by aphids

Plants face various abiotic and biotic environmental factors and therefore need to adjust their phenotypic traits on several levels. UV‐B radiation is believed to impact herbivorous insects via host plant changes. Plant responses to abiotic challenges (UV‐B radiation) and their interaction with two aphid species were explored in a multifactor approach. Broccoli plants [Brassica oleracea L. convar. botrytis (L.), Brassicaceae] were grown in two differently covered greenhouses, transmitting either 80% (high UV‐B) or 4% (low UV‐B) of ambient UV‐B. Three‐week‐old plants were infested with either specialist cabbage aphids [Brevicoryne brassicae (L.), Sternorrhyncha, Aphididae] or generalist green peach aphids [Myzus persicae (Sulzer), Sternorrhyncha, Aphididae]. Plants grown under high‐UV‐B intensities were smaller and had higher flavonoid concentrations. Furthermore, these plants had reduced cuticular wax coverage, whereas amino acid concentrations of the phloem sap were little influenced by different UV‐B intensities. Cabbage aphids reproduced less on plants grown under high UV‐B than on plants grown under low UV‐B, whereas reproduction of green peach aphids in both plant light sources was equally poor. These results are likely related to the different specialisation‐dependent sensitivities of the two species. The aphids also affected plant chemistry. High numbers of cabbage aphid progeny on low‐UV‐B plants led to decreased indolyl glucosinolate concentrations. The induced change in these glucosinolates may depend on an infestation threshold. UV‐B radiation considerably impacts plant traits and subsequently affects specialist phloem‐feeding aphids, whereas aphid growth forces broccoli to generate specific defence responses.     

Modification of Macrosiphum euphorbiae colonisation behaviour and reproduction on potato plants treated by mineral oil

Although mineral oil spray is one of the most effective ways to control the transmission of non‐persistent aphid‐borne viruses in the field, its mode of action is poorly understood. In this study, the effects of mineral oil treatment of potato plants on host selection behaviour, growth, and reproduction of potato aphids, Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae), were investigated. The effects were assessed 30 min, 1 day, and 7 days after treatment, (1) on aphid orientation behaviour by using a Y‐tube olfactometer, and (2) on aphid feeding behaviour by using the electrical penetration graph (EPG) technique. Olfactory experiments showed that the oil had a repulsive effect only 30 min after spraying. EPG experiments showed a slight modification of the aphid feeding behaviour mainly 7 days after treatment. The number of both salivation and sap ingestion events during the phloem phases were increased 7 days after treatment. In addition, irrespective of the time after treatment, xylem ingestion time was increased. Clip cage experiments were set up to assess potential effects of the oil treatment on aphid survival and population parameters. Nymphal mortality was increased on treated plants, whereas fecundity of surviving insects was enhanced. The antagonistic effects of oil treatment on aphids are discussed in a plant protection context.     

Behavioural responses of the aphid parasitoid Diaeretiella rapae to volatiles from Arabidopsis thaliana induced by Myzus persicae

In response to herbivory by insects, several plant species have been shown to produce volatiles that attract the natural enemies of those herbivores. Using a Y‐tube olfactometer, we investigated responses of the aphid parasitoid Diaeretiella rapae MacIntosh (Hymenoptera: Aphidiidae) to volatiles from Arabidopsis thaliana Columbia (Brassicaceae) plants that were either undamaged, infested by the peach‐potato aphid, Myzus persicae Sulzer (Homoptera: Aphididae), or mechanically damaged, as well as to volatiles from just the aphid or its honeydew. In dual‐choice experiments, female D. rapae given oviposition experience on A. thaliana infested with M. persicae were significantly attracted to volatiles from A. thaliana infested with M. persicae over volatiles from undamaged A. thaliana and similarly were significantly attracted to plants that had been previously infested by M. persicae, but from which the aphids were removed, over undamaged plants. Diaeretiella rapae did not respond to volatiles from M. persicae alone, their honeydew, or plants mechanically damaged with either a pin or scissors. We conclude that an interaction between the plant and the aphid induces A. thaliana to produce volatiles, which D. rapae can learn and respond to. Poor responses of D. rapae to volatiles from an A. thaliana plant that had two leaves infested with M. persicae, with the two infested leaves being removed before testing, suggested the possibility that, at this stage of infestation, the majority of volatile production induced by M. persicae may be localized to the infested tissues of the plant. We conclude that this tritrophic interaction is a suitable model system for future investigations of the biochemical pathways involved in the production of aphid‐induced volatiles attractive to natural enemies.     

Behavioural responses of the seven‐spot ladybird Coccinella septempunctata to plant headspace chemicals collected from four crop Brassicas and Arabidopsis thaliana,infested with Myzus persicae

1 Insects using olfactory stimuli to forage for prey/hosts are proposed to encounter a ‘reliability–detectability problem’, where the usability of a stimulus depends on its reliability as an indicator of herbivore presence and its detectability. 2 We investigated this theory using the responses of female seven‐spot ladybirds Coccinella septempunctata (Coleoptera: Coccinellidae) to plant headspace chemicals collected from the peach‐potato aphid Myzus persicae and four commercially available Brassica cultivars; Brassica rapa L. cultivar ‘turnip purple top’, Brassica juncea L. cultivar ‘red giant mustard’, Brassica napus L. cultivar ‘Apex’, Brassica napus L. cultivar ‘Courage’ and Arabidopsis thaliana. For each cultivar/species, responses to plants that were undamaged, previously infested by M. persicae and infested with M. persicae, were investigated using dual‐choice Petri dish bioassays and circular arenas. 3 There was no evidence that ladybirds responded to headspace chemicals from aphids alone. Ladybirds significantly preferred headspace chemicals from B. napus cv. Apex that were undamaged compared with those from plants infested with aphids. For the other four species/cultivars, there was a consistent trend of the predators being recorded more often in the half of the Petri dish containing plant headspace chemicals from previously damaged and infested plants compared with those from undamaged ones. Furthermore, the mean distance ladybirds walked to reach aphid‐infested A. thaliana was significantly shorter than to reach undamaged plants. These results suggest that aphid‐induced plant chemicals could act as an arrestment or possibly an attractant stimulus to C. septempunctata. However, it is also possible that C. septempunctata could have been responding to aphid products, such as honeydew, transferred to the previously damaged and infested plants. 4 The results provide evidence to support the ‘reliability–detectability’ theory and suggest that the effectiveness of C. septempunctata as a natural enemy of aphids may be strongly affected by which species and cultivar of Brassica are being grown.     

Attraction of pepper weevil to volatiles from damaged pepper plants

Pioneer herbivorous insects may find their host plants through a combination of visual and constitutive host‐plant volatile cues, but once a site has been colonized, feeding damage changes the quantity and quality of plant volatiles released, potentially altering the behavior of conspecifics who detect them. Previous work on the pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae), demonstrated that this insect can detect and orient to constitutive host plant volatiles released from pepper [Capsicum annuum L. (Solanaceae)]. Here we investigated the response of the weevil to whole plants and headspace collections of plants damaged by conspecifics. Mated weevils preferred damaged flowering as well as damaged fruiting plants over undamaged plants in a Y‐tube olfactometer. They also preferred volatiles from flowering and fruiting plants with actively feeding weevils over plants with old feeding damage. Both sexes preferred volatiles from fruiting plants with actively feeding weevils over flowering plants with actively feeding weevils. Females preferred plants with 48 h of prior feeding damage over plants subjected to weevil feeding for only 1 h, whereas males showed no preference. When attraction to male‐ and female‐inflicted feeding damage was compared in the Y‐tube, males and females showed no significant preference. Wind tunnel plant assays and four‐choice olfactometer assays using headspace volatiles confirmed the attraction of weevils to active feeding damage on fruiting plants. In a final four‐choice olfactometer assay using headspace collections, we tested the attraction of mated males and virgin and mated females to male and female feeding damage. In these headspace volatile assays, mated females again showed no preference for male feeding; however, virgin females and males preferred the headspace volatiles of plants fed on by males, which contained the male aggregation pheromone in addition to plant volatiles. The potential for using plant volatile lures to improve pepper weevil monitoring and management is discussed.     

Olfactory responses of Aphidius gifuensis to odors of host plants and aphid‐plant complexes

Abstract The olfactory responses of Aphidius gifuensis to odors from two host plants (Nicotiana tabacum and Brassica napus ssp.) and their complexes with different infestation levels of two host aphids (Myzus persicae and Lipaphis erysimi) were respectively examined in an olfactometer. The results showed that female A. gifuensis did not respond to odors of undamaged or mechanically damaged host plants, but significantly responded to odors of aphid/plant complexes. Moreover, A. gifuensis responded significantly to odors of both M. persicae and L. erysimi/plant complexes when host plants were infested by high levels of aphids, suggesting that quantity of aphid‐induced volatiles could be important for attracting A. gifuensis. When tested between aphid/plant complexes, A. gifuensis did not show its preference for either complex. The efficiency of A. gifuensis against aphids in open fields potentially could be improved by using its olfactory response to aphid/plant complexes.     

Comparative analysis of Solanum stoloniferum responses to probing by the green peach aphid Myzus persicae and the potato aphid Macrosiphum euphorbiae

Abstract Plants protect themselves against aphid attacks by species‐specific defense mechanisms. Previously, we have shown that Solanum stoloniferum Schlechtd has resistance factors to Myzus persicae Sulzer (Homoptera: Aphididae) at the epidermal/mesophyll level that are not effective against Macrosiphum euphorbiae Thomas (Homoptera: Aphididae). Here, we compare the nymphal mortality, the pre‐reproductive development time, and the probing behavior of M. persicae and M. euphorbiae on S. stoloniferum and Solanum tuberosum L. Furthermore, we analyze the changes in gene expression in S. stoloniferum 96 hours post infestation by either aphid species. Although the M. euphorbiae probing behavior shows that aphids encounter more probing constrains on phloem activities–longer probing and salivation time– on S. stoloniferum than on S. tuberosum, the aphids succeeded in reaching a sustained ingestion of phloem sap on both plants. Probing by M. persicae on S. stoloniferum plants resulted in limited feeding only. Survival of M. euphorbiae and M. persicae was affected on young leaves, but not on senescent leaves of S. stoloniferum. Infestation by M. euphorbiae changed the expression of more genes than M. persicae did. At the systemic level both aphids elicited a weak response. Infestation of S. stoloniferum plants with a large number of M. persicae induced morphological changes in the leaves, leading to the development of pustules that were caused by disrupted vascular parenchyma and surrounding tissue. In contrast, an infestation by M. euphorbiae had no morphological effects. Both plant species can be regarded as good host for M. euphorbiae, whereas only S. tuberosum is a good host for M. persicae and S. stoloniferum is not. Infestation of S. stoloniferum by M. persicae or M. euphorbiae changed the expression of a set of plant genes specific for each of the aphids as well as a set of common genes.     

Aphid responses to volatile cues from turnip plants (Brassica rapa) infested with phloem-feeding and chewing herbivores

Herbivore-induced plant volatiles provide foraging cues for herbivores and for herbivores’ natural enemies. Aphids induce plant volatile emissions and also utilize plant-derived olfactory volatile cues, but the chemical ecology of aphids and other phloem-feeding insects is less extensively documented than that of chewing insects. Here, we characterize the volatile cues emitted by turnip plants (Brassica rapa) under attack by an aphid (Myzus persicae) or by the chewing lepidopteran larva Heliothis virescens. We also tested the behavioral responses of M. persicae individuals to the odors of undamaged and herbivore-damaged plants presented singly or in combination, as well as to the odor of crushed conspecifics (simulating predation). Gas chromatographic analysis of the volatile blend of infested turnips revealed distinct profiles for both aphid- and caterpillar-induced plants, with induced compounds including green-leaf alcohols, esters, and isothiocyanates. In behavioral trials, aphids exhibited increased activity in the presence of plant odors and positive attraction to undamaged turnip plants. However, aphids exhibited a strong preference for the odors of healthy versus plants subjected to herbivore damage, and neither aphid- or caterpillar-damaged plants were attractive compared to clean-air controls. Reduced aphid attraction to herbivore-infested plants may be mediated by changes in the volatile blend constituent composition, including large amounts of isothiocyanates and green-leaf volatiles or, in the case of aphid-infested plants, of the aphid alarm pheromone, (E)-β-farnesene.     

Cucurbit aphid‐borne yellows virus (CABYV) modifies the alighting,settling and probing behaviour of its vector Aphis gossypii favouring its own spread

Plant pathogens are able to influence the behaviour and fitness of their vectors in such a way that changes in plant–pathogen–vector interactions can affect their transmission. Such influence can be direct or indirect, depending on whether it is mediated by the presence of the pathogen in the vector's body or by host changes as a consequence of pathogen infection. We report the effect that the persistently aphid‐transmitted Cucurbit aphid‐borne yellows virus (CABYV, Polerovirus) can induce on the alighting, settling and probing behaviour activities of its vector, the cotton aphid Aphis gossypii. Only minor direct changes on aphid feeding behaviour were observed when viruliferous aphids fed on non‐infected plants. However, the feeding behaviour of non‐viruliferous aphids was very different on CABYV‐infected than on non‐infected plants. Non‐viruliferous aphids spent longer time feeding from the phloem in CABYV‐infected plants compared to non‐infected plants, suggesting that CABYV indirectly manipulates aphid feeding behaviour through its shared host plant in order to favour viral acquisition. Viruliferous aphids showed a clear preference for non‐infected over CABYV‐infected plants at short and long time, while such behaviour was not observed for non‐viruliferous aphids. Overall, our results indicate that CABYV induces changes in its host plant that modifies aphid feeding behaviour in a way that virus acquisition from infected plants is enhanced. Once the aphids become viruliferous they prefer to settle on healthy plants, leading to optimise the transmission and spread of this phloem‐limited virus.     

Aphid-host plant interactions: does aphid honeydew exactly reflect the host plant amino acid composition?

Plants provide aphids with unbalanced and low concentrations of amino acids. Likely, intracellular symbionts improve the aphid nutrition by participating to the synthesis of essential amino acids. To compare the aphid amino acid uptakes from the host plant and the aphids amino acid excretion into the honeydew, host plant exudates (phloem + xylem) from infested and uninfested Vicia faba L. plants were compared to the honeydew produced by two aphid species (Acyrthosiphon pisum Harris and Megoura viciae Buckton) feeding on V. faba. Our results show that an aphid infestation modifies the amino acid composition of the infested broad bean plant since the global concentration of amino acids significantly increased in the host plant in response to aphid infestations. Specifically, the concentrations of the two amino acids glutamine and asparagine were strongly enhanced. The amino acid profiles from honeydews were similar for the two aphid species, but the concentrations found in the honeydews were generally lower than those measured in the exudates of infested plants (aphids uptakes). This work also highlights that aphids take large amounts of amino acids from the host plant, especially glutamine and asparagine, which are converted into glutamic and aspartic acids but also into other essential amino acids. The amino acid profiles differed between the host plant exudates and the aphid excretion product. Finally, this study highlights that the pea aphid, a “specialist” for the V. faba host plant, induced more important modifications into the host plant amino acid composition than the “generalist” aphid M. viciae.     

Influence of adult experience on host microhabitat location by the generalist parasitoid,Campoletis sonorensis (Hymenoptera: Ichneumonidae)

The effect of adult experience on microhabitat location behavior of the generalist parasitoid Campoletis sonorensis (Cameron)was examined in a wind tunnel bioassay. Responses were tested to the odors of two host plants (cotton and sesame) of Heliothis virescens (F.) or a nonhost plant (potato), either damaged and infested with host larvae and host products (host/plant complex) or intact, clean and uninfested. Parasitoid females remained naive or were allowed one oviposition experience on either of the plants, 1 min, 2 h, or 24 h prior their introduction into the wind tunnel. In a no-choice test, parasitoids experienced 1 min prior to bioassay completed significantly more flights to sesame and potato host/plant complexes than did naive parasitoids. However, 24 h after experience, only females experienced on potato completed more flights to the host/ plant complex than did naive females. Parasitoids experienced 1 min prior to flight to undamaged plants showed a slight increase in flight response (significant only for potato) but, after 24 h, completed only as many flights as naive parasitoids. In a dual-choice situation, parasitoids did not show a preference for either of the two host plants but did prefer a host to a nonhost plant. This innate plant preference was not changed by a single oviposition experience. The potential significance of these results to the microhabitat location behavior of C. sonorensisin the field is discussed.