Generalist Aphid Research Articles

Transgenerational effects and the cost of ant tending in aphids.

In mutualistic interactions, partners obtain a net benefit, but there may also be costs associated with the provision of benefits for a partner. The question of whether aphids suffer such costs when attended by ants has been raised in previous work. Transgenerational effects, where offspring phenotypes are adjusted based on maternal influences, could be important in the mutualistic interaction between aphids and ants, in particular because aphids have telescoping generations where two offspring generations can be present in a mature aphid. We investigated the immediate and transgenerational influence of ant tending on aphid life history and reproduction by observing the interaction between the facultative myrmecophile Aphis fabae and the ant Lasius niger over 13 aphid generations in the laboratory. We found that the effect of ant tending changes dynamically over successive aphid generations after the start of tending. Initially, total aphid colony weight, aphid adult weight and aphid embryo size decreased compared with untended aphids, consistent with a cost of ant association, but these differences disappeared within four generations of interaction. We conclude that transgenerational effects are important in the aphid–ant interactions and that the costs for aphids of being tended by ants can vary over generations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-013-2659-y) contains supplementary material, which is available to authorized users.

Toxic and deterrent effects of phytohemagglutinin on the grain aphid Sitobion avenae

The toxicity and deterrent effects of phytoheamagglutinin (Phaseolus vulgaris agglutinin, PHA) to the grain aphid (Sitobion avenae F.) was investigated in the laboratory by use of liquid diets or gels containing various PHA concentrations. The addition of PHA to the liquid diet increased the aphid pre-reproductive period, mortality, and generation time and decreased aphid fecundity and intrinsic rate of natural increase. Aphids fed on sucrose-agarose gels with higher concentrations of PHA exhibited no phloem-feeding behavior. The number of gel penetrations was reduced and duration of the pathway phase was increased as PHA concentration increased. These results indicate that PHA is detrimental to S. avenae and that the effect of PHA is at least partially explained by suppression of feeding behaviour. PHA could be useful for managing S. avenae.

Aphid-host plant interaction

Black bean aphid, Aphis fabae (Homoptera; Aphididae) is a serious pest causing crop loss. Plant-aphid interaction is a dynamic system subjected to continual variation and changes. Host plants induce various biochemical and physical defense mechanisms due to aphid feeding. Aphids can overcome plant defenses by enzymatic adaptations and sequestering secondary metabolites produced by the plant within their bodies as a defense against their enemies. Many strategies were developed and evolved by aphids in order to overcome plant defense barriers which allowed them to feed, grow and reproduce on their host plants. This study aimed to aid in better understanding of the effect of altering host plant on specialist and generalist aphid fitness.The influence of plant defense on population development of Aphis fabae was also investigated. Analyses for insect enzymes were also demonstrated in addition to further biochemical studies on host plant defences. Generalists showed different ecological and enzymatic adaptations towards host plants than specialist Aphis fabae. The results were fully discussed in details.

The Biology And Ecology Of Brachycaudus Divaricatae Shaposhnikov (Hemiptera, Aphidoidea) On Prunus Cerasifera Ehrhart In Western Poland

Abstract Brachycaudus divaricatae - was described by Shaposhnikov in the Middle East as a heteroecious aphid species migrating between Prunus divaricata and Melandrium album. The research conducted in Poland proved that this species can be described as holocyclic and monoecious. A significantly shortened development cycle with a summer-winter diapause characterizes this species in Poland. The aim of our studies was a detailed research of the species biology conducted to explain this phenomenon. Elements of the biology and ecology of the new fauna species Brachycaudus divaricatae Shap., were studied in Poland during the 2008-2010 time period. The term of spring hatching, number of generations per season, development length of particular generations, lifespan of specimen, and fecundity of particular generations were all defined. The three-year study proved that 6 to 8 aphid generations can develop on P. cerasifera in Poland. The emergence of sexuales (amphigonic females and males) of B. divaricatae occurred very early in the season: in mid-May, and the first eggs were laid in June.

Effect ofIsaria fumosorosea(Hypocreales: Cordycipitaceae) andLysiphlebus testaceipes, (Hymenoptera: Braconidae) on the Brown Citrus Aphid: Preliminary Assessment of a Compatibility Study

Recently, a strain of Isaria fumosorosea Wize (.Ifr) (= Paecilomyces fumosoroseus [Luangsa-ard et al. 2005]), (Hypocreales: Cordycipitaceae) was discovered in a Florida citrus grove infecting the Asian citrus psyllid, Diaphorina citri Kuwayama (Meyer et al. 2008). Also, laboratory studies have demonstrated that Ifr may be effective against several commercially important pests of citrus (Poprawski et al. 1999; Avery et al. 2009; Hoy et al. 2010; Hunter et al. 2011). Therefore, the use of Ifr (PFR 97TM 20% WDG, Certis USA, Columbia, Maryland), approved in 2011 by EPA for use in commercial citrus, may offer a potential tool for balancing citrus pest management with consum er demands for organic citrus produce. The brown citrus aphid (BCA), Toxoptera citri cidus Kirkaldy (=T. citricida [Nieto Nafria et al. 2005]), (Hemiptera: Aphididae) was discovered in Florida in 1995 and is recognized as a serious pest of citrus capable of vectoring citrus triseza virus (Halbert & Brown 1996; Michaud 1998; Roy & Brlansky 2009). Under optimal conditions, na tive natural enemies provide good management of BCA, although these are easily disrupted by insecticide applications (Michaud 1998; 2002). Presently, the aphid's population is managed in part by the parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae) (Evans & Strange 1997). This generalist aphid parasitoid Lysiphlebus testaceipes, native to Florida and the Americas, is an effective biocontrol agent of BCA (Evans & Strange 1997). The objectives of our study were to assess the impact of Ifr on the mor tality of BCA populations as well as the parasit ism and emergence rates of L. testaceipes. BCA and Carrizo citrus (a trifoliate hybrid: Washington navel x trifoliate orange) were ob tained from the Sub-Tropical Insect Research Unit, USDA Horticulture Research Laboratory in Fort Pierce, Florida. For the experiment, 5 car rizo citrus seedlings (25-30 cm tall) were placed in each of four separate nylon mesh-covered cages (35 x 35 x 35 cm) and each infested with 4 alate BCA (20 per cage). A second infestation was made after 9 days. Cages were maintained in a growth room at 24.0 ± 1 °C, 45.0 ± 1 % RH and 16:8 h (L:D) photoperiod. Two weeks later, 10 L. testa ceipes adults were added to two of the cages. After an additional 4 days, one cage with and without L. testaceipes was treated with Isaria fumosoro sea (Ifr) suspension (PFR 97TM 20% WDG) at 107 CFU/ml using Nalgene® (Nalge Nunc Interna tional, Rochester, NY) aerosol sprayer. The ger mination of PFR 97TM blastospores was 96% using the technique of Avery et al. 2009. The remaining 2 cages were sprayed with an equal volume of wa ter. Parasitoids were temporarily removed from all cages prior to spraying to eliminate potential drowning and were replaced with an additional 5 to compensate for handling stress. Two replicates of the same study were conducted on different dates.

‘Myrosin cells’ are not a prerequisite for aphid feeding on oilseed rape (Brassica napus) but affect host plant preferences

The enzyme myrosinase (EC 3.2.3.1.147) is present in specialised myrosin cells and forms part of the glucosinolate-myrosinase system, also known as 'the mustard oil bomb', which has an important role in the defence system of cruciferous plants against insect pests. Transgenic Brassica napus MINELESS have been produced by transgenic ablation of myrosin cells. This prompted us to investigate the importance of myrosin cells in plant-aphid interactions. In order to study this, we challenged transgenic MINELESS and wild-type cultivar Westar seedlings with the aphids Brevicoryne brassicae (a specialist) and Myzus persicae (a generalist). Our study included aphid free-choice and aphid fecundity experiments. Data from these experiments showed that B. brassicae prefers wild-type seedlings and M. persicae prefers MINELESS. B. brassicae and M. persicae showed significant variation in establishment on plants regardless of whether they were wild type or MINELESS and also differed significantly in affecting plant parts. Myrosinase activity in MINELESS control seedlings was 83.6% lower than the wild-type control seedlings. Infestation with either of the two aphid species induced myrosinase levels in both wild-type and MINELESS seedlings. Infestation with M. persicae reduced the concentration of most glucosinolates while B. brassicae had the opposite effect. B. brassicae enhanced the formation of glucosinolate hydrolysis products both in wild-type and MINELESS seedlings. However, M. persicae decreased All ITC but increased 3,4ETBut NIT in wild-type seedlings. Taken together, the investigation shows that the presence of myrosin cells affects the preference of generalist and specialist aphid species for Brassica napus plants.

The tri-trophic interactions hypothesis: interactive effects of host plant quality, diet breadth and natural enemies on herbivores.

Several influential hypotheses in plant-herbivore and herbivore-predator interactions consider the interactive effects of plant quality, herbivore diet breadth, and predation on herbivore performance. Yet individually and collectively, these hypotheses fail to address the simultaneous influence of all three factors. Here we review existing hypotheses, and propose the tri-trophic interactions (TTI) hypothesis to consolidate and integrate their predictions. The TTI hypothesis predicts that dietary specialist herbivores (as compared to generalists) should escape predators and be competitively dominant due to faster growth rates, and that such differences should be greater on low quality (as compared to high quality) host plants. To provide a preliminary test of these predictions, we conducted an empirical study comparing the effects of plant (Baccharis salicifolia) quality and predators between a specialist (Uroleucon macolai) and a generalist (Aphis gossypii) aphid herbivore. Consistent with predictions, these three factors interactively determine herbivore performance in ways not addressed by existing hypotheses. Compared to the specialist, the generalist was less fecund, competitively inferior, and more sensitive to low plant quality. Correspondingly, predator effects were contingent upon plant quality only for the generalist. Contrary to predictions, predator effects were weaker for the generalist and on low-quality plants, likely due to density-dependent benefits provided to the generalist by mutualist ants. Because the TTI hypothesis predicts the superior performance of specialists, mutualist ants may be critical to A. gossypii persistence under competition from U. macolai. In summary, the integrative nature of the TTI hypothesis offers novel insight into the determinants of plant-herbivore and herbivore-predator interactions and the coexistence of specialist and generalist herbivores.

Biology and ecology of Appendiseta robiniae (Hemiptera: Aphidoidea) — an alien species in Europe

Abstract Elements of the biology and ecology of A. robiniae were studied in Poland during the period of 2008–2009. The term of spring hatching, number of generations per season, developmental time of particular generations, lifespan of specimens and fecundity of particular generations were all defined. The dynamics of the species’ occurrence on its host plant were also determined. The two-year study showed a maximum of 11 aphid generations can develop on Robinia pseudoacacia. Females of the second and third generations were found to be the most fertile. These findings indicate that the species has adapted well in Poland and its biological predispositions have enabled it to rapidly increase in population.

Herbivory by a Phloem-Feeding Insect Inhibits Floral Volatile Production

There is extensive knowledge on the effects of insect herbivory on volatile emission from vegetative tissue, but little is known about its impact on floral volatiles. We show that herbivory by phloem-feeding aphids inhibits floral volatile emission in white mustard Sinapis alba measured by gas chromatographic analysis of headspace volatiles. The effect of the Brassica specialist aphid Lipaphis erysimi was stronger than the generalist aphid Myzus persicae and feeding by chewing larvae of the moth Plutella xylostella caused no reduction in floral volatile emission. Field observations showed no effect of L. erysimi-mediated floral volatile emission on the total number of flower visits by pollinators. Olfactory bioassays suggested that although two aphid natural enemies could detect aphid inhibition of floral volatiles, their olfactory orientation to infested plants was not disrupted. This is the first demonstration that phloem-feeding herbivory can affect floral volatile emission, and that the outcome of interaction between herbivory and floral chemistry may differ depending on the herbivore's feeding mode and degree of specialisation. The findings provide new insights into interactions between insect herbivores and plant chemistry.

Rhizobacteria modify plant–aphid interactions: a case of induced systemic susceptibility

Beneficial microbes, such as plant growth-promoting rhizobacteria and mycorrhizal fungi, may have a plant-mediated effect on insects aboveground. The plant growth-promoting rhizobacterium Pseudomonas fluorescens can induce systemic resistance in Arabidopsis thaliana against several microbial pathogens and chewing insects. However, the plant-mediated effect of these beneficial microbes on phloem-feeding insects is not well understood. Using Arabidopsis as a model, we here report that P. fluorescens has a positive effect on the performance (weight gain and intrinsic rate of increase) of the generalist aphid Myzus persicae, while no effect was recorded on the crucifer specialist aphid Brevicoryne brassicae. Additionally, transcriptional analyses of selected marker genes revealed that in the plant-microbe interaction with M. persicae, rhizobacteria (i) prime the plant for enhanced expression of LOX2, a gene involved in the jasmonic acid (JA)-regulated defence pathway, and (ii) suppress the expression of ABA1, a gene involved in the abscisic acid (ABA) signalling pathway, at several time points. In contrast, almost no effect of the plant-microbe interaction with B. brassicae was found at the transcriptional level. This study presents the first data on rhizobacteria-induced systemic susceptibility to an herbivorous insect, supporting the pattern proposed for other belowground beneficial microbes and aboveground phloem feeders. Moreover, we provide further evidence that at the transcript level, soil-borne microbes modify plant-aphid interactions.

Plant neighborhood influences colonization of Brassicaceae by specialist and generalist aphids

A plant's own characteristics, but also those of its neighbors, might have an impact on its probability of being colonized by herbivorous insects. A plant might be less colonized and experience associational resistance when it grows near repellent neighbors. In contrast, it might be more colonized and experience associational susceptibility near attractive neighbors. To date, mechanisms that drive associational defense are not really understood. In order to gain insights into the occurrence of associational resistance versus associational susceptibility under field conditions, we conducted an experiment to determine the influence of neighboring plants on the colonization of a focal plant by aphids. The focal plant was always Brassica oleracea. The neighbors were B. oleracea (control), B. napus, B. nigra, or Solanum lycopersicum, which represent contrasting levels of physical and chemical defenses. The focal plant, B. oleracea, was more colonized by the specialist aphid Brevicoryne brassicae, and experienced associational susceptibility when it was surrounded by B. nigra or B. napus. In contrast, B. oleracea was less colonized by the generalist aphid Myzus persicae, and experienced associational resistance when it was surrounded by S. lycopersicum, B. nigra or B. napus. Neighboring plants had no significant impact on host plant choice by the generalist aphid Macrosiphum euphorbiae. In conclusion, attraction or repulsion of the specialist aphid B. brassicae and the generalist aphid M. persicae by B. nigra, B. napus, and S. lycopersicum resulted in associational susceptibility or associational resistance for B. oleracea.

Prey-mediated effects of glucosinolates on aphid predators

1. Plant resistance against herbivores can act directly (e.g. by producing toxins) and indirectly (e.g. by attracting natural enemies of herbivores). If plant secondary metabolites that cause direct resistance against herbivores, such as glucosinolates, negatively influence natural enemies, this may result in a conflict between direct and indirect plant resistance. 2. Our objectives were (i) to test herbivore-mediated effects of glucosinolates on the performance of two generalist predators, the marmalade hoverfly (Episyrphus balteatus) and the common green lacewing (Chrysoperla carnea) and (ii) to test whether intraspecific plant variation affects predator performance. 3. Predators were fed either Brevicoryne brassicae, a glucosinolate-sequestering specialist aphid that contains aphid-specific myrosinases, or Myzus persicae, a non-sequestering generalist aphid that excretes glucosinolates in the honeydew, reared on four different white cabbage cultivars. Predator performance and glucosinolate concentrations and profiles in B. brassicae and host-plant phloem were measured, a novel approach as previous studies often measured glucosinolate concentrations only in total leaf material. 4. Interestingly, the specialist aphid B. brassicae selectively sequestered glucosinolates from its host plant. The performance of predators fed this aphid species was lower than when fed M. persicae. When fed B. brassicae reared on different cultivars, differences in predator performance matched differences in glucosinolate profiles among the aphids. 5. We show that not only the prey species, but also the plant cultivar can have an effect on the performance of predators. Our results suggest that in the tritrophic system tested, there might be a conflict between direct and indirect plant resistance.

Efecto de las arañas (Arachnida: Araneae) como depredadoras de insectos plaga en cultivos de alfalfa (Medicago sativa) (Fabaceae) en Argentina

Spiders are predators that reduce insect pest populations in agroecosystems. Trials were conducted to measure the selectivity against different insect preys, the daily consumption, effect of predators alone and together with a known number of preys, and the indirect effect of predators on vegetation. For this, experimental units (1 x 1m) were used covered with a fine plastic mesh. Misumenops pallidus, Oxyopes salticus and Araneus sp. were used as generalist predators, and aphids, weevils, locusts, chrysomelids and Lepidoptera larvae as their potential preys. Among the preys offered, the spiders preferred Lepidoptera larvae compared to the other two pests groups (weevils and aphids). The maximum consumption rate was of 93.33% for Lepidoptera larvae, 25.33% for aphids and 11.67% for weevils. The Q Index values for the three species of spiders showed a positive selectivity only for defoliating larvae. O. salticus showed the highest values of consumption rates while Rachiplusia nu was the most consumed. The maximum value of consumption in 24 hours was showed by O. salticus on R. nu (C) = 2.8. The association of several species of predatory spiders increased the total number of insects captured, and also showed that the addition of spiders caused a decrease in the number of leaves damaged by the effect of lepidopterous larvae.

Quantifying aphid predation: the mealy plum aphid Hyalopterus pruni in California as a case study

Summary 1. Generalist insect predators provide an important ecosystem service in the regulation of agricultural pests. However, the role of predation in the dynamics of aphid populations has been difficult to quantify as any change in aphid density results from a balance between two opposing processes, aphid recruitment through reproduction and aphid mortality through predation. 2. Our goal in this study was to determine the degree to which aphid consumption by naturally occurring densities of aphidophagous predators is responsible for observed seasonal changes in aphid densities. We quantified consumptive predation using a mechanistic approach that incorporates the balance between aphid recruitment and mortality. We used the mealy plum aphid Hyalopterus pruni in Prunus domestica plum orchards as a model system. 3. Our approach was to compare two quantities: a demographic‐based estimate of predation and an observation‐based estimate of predation. The demographic‐based estimate used a simple model of aphid population growth and predation. It estimates the mortality that must have occurred to give rise to observed changes in aphid densities between sample dates. The model uses independent estimates of aphid population growth rate in the absence of predation. The observation‐based estimate combined field data on predator densities in plum orchards with stage‐ and species‐specific per capita predation rates estimated from field observation. 4. Predation may have reduced the rate at which mealy plum aphid populations increased early in the season and rebounded from mid‐season declines, but was not sufficient to prevent high aphid densities or to accelerate rates of decline later in the season. Moreover, predation at naturally occurring densities did not appear sufficient to drive the directional changes in mealy plum aphid densities at any point through the season. 5. Synthesis and applications. Our study shows that natural densities of generalist predators can be too low to provide effective biological control services for an aphid pest. Generalist aphid predators could provide more effective control if early‐season densities were increased through augmentative releases or encouragement of crop colonization, but the commercial viability of these options remains to be tested.

Host‐associated differentiation and evidence for sexual reproduction in Iranian populations of the cotton aphid, Aphis gossypii

AbstractPhytophagous insects with wide host ranges often exhibit host‐associated genetic structure. We used microsatellite analysis to assess the population structure of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), a serious pest on many economically important crops worldwide. We sampled aphids from five host plant species in Iran and detected strong population subdivision, with an overall multilocus FST of 0.191. The matrix of pairwise FST values indicated that differentiation between populations collected from different hosts was significantly stronger than between populations from the same hosts. Host‐associated differentiation was further supported by Bayesian clustering analyses, which grouped all samples from cotton together with aubergine, and all samples from cucumber together with pumpkin and hibiscus. This adds to the growing body of evidence that many seemingly generalist aphids are in fact an assemblage of host‐specialized lineages. Although we detected a clear genetic signature of clonal reproduction, the genotypic diversity of A. gossypii in Iran is much higher than in other parts of the world. Particularly samples from cotton exhibited a surprisingly high genotypic diversity, suggesting that many lineages on this host are cyclical parthenogens that engage in regular bouts of sexual reproduction.

Parasitoid control of aphids in organic and conventional farming systems

Organic farmers cannot use most commonly available synthetic insecticides to control crop pests and reduce economic losses due to pest outbreaks. Instead, they rely heavily on the activities of naturally occurring predators and parasitoids, particularly in broad-acre crops such as cereals. It is still unclear whether organic farms which typically support greater levels of biodiversity also experience greater levels of pest control services. We assess whether organic farming systems were better able to control cereal aphids due to a greater diversity and activity of naturally occurring parasitoid species. We anticipated greater parasitism rate of aphids in organic arable fields due to closer proximity to plants that provide resources for adult parasitoids and places that are suitable for overwintering, and the presence of alternate aphid hosts when cereals are absent. Aphids were collected from organic and conventional cereal crops, and screened for parasitoid DNA using diagnostic polymerase chain reaction (PCR). Aphid abundance was low across the season, however organic cereal fields had significantly greater aphid abundance. From the 1446 aphids screened we detected 12 parasitoid taxa. There was no difference in parasitism rate between the farming systems (org. mean mortality 20.9 ± 3.3% s.e., con. 29.8 ± 4.9%). Furthermore, there was no difference between farming systems in hyperparasitoid attack and multiparasitism rates, parasitoid richness and parasitoid community diversity. The most abundant species recorded on organic and conventional farms was the generalist aphid primary parasitoid Ephedrus plagiator. It appears that the extra plant diversity and greater area of semi-natural habitats on organic farms offer no advantage for increasing cereal aphid parasitoid diversity, at least at the aphid abundances encountered during the sampling period.

Influence of presence and spatial arrangement of belowground insects on host‐plant selection of aboveground insects: a field study

Abstract 1. Several studies have shown that above‐ and belowground insects can interact by influencing each others growth, development, and survival when they feed on the same host‐plant. In natural systems, however, insects can make choices on which plants to oviposit and feed. A field experiment was carried out to determine if root‐feeding insects can influence feeding and oviposition preferences and decisions of naturally colonising foliar‐feeding insects.2. Using the wild cruciferous plant Brassica nigra and larvae of the cabbage root fly Delia radicum as the belowground root‐feeding insect, naturally colonising populations of foliar‐feeding insects were monitored over the course of a summer season.3. Groups of root‐infested and root‐uninfested B. nigra plants were placed in a meadow during June, July, and August of 2006 for periods of 3 days. The root‐infested and the root‐uninfested plants were either dispersed evenly or placed in clusters. Once daily, all leaves of each plant were carefully inspected and insects were removed and collected for identification.4. The flea beetles Phyllotreta spp. and the aphid Brevicoryne brassicae were significantly more abundant on root‐uninfested (control) than on root‐infested plants. However, for B. brassicae this was only apparent when the plants were placed in clusters. Host‐plant selection by the generalist aphid M. persicae and oviposition preference by the specialist butterfly P. rapae, however, were not significantly influenced by root herbivory.5. The results of this study show that the presence of root‐feeding insects can affect feeding and oviposition preferences of foliar‐feeding insects, even under natural conditions where many other interactions occur simultaneously. The results suggest that root‐feeding insects play a role in the structuring of aboveground communities of insects, but these effects depend on the insect species as well as on the spatial distribution of the root‐feeding insects.

Diverse Phage-Encoded Toxins in a Protective Insect Endosymbiont

The lysogenic bacteriophage APSE infects "Candidatus Hamiltonella defensa," a facultative endosymbiont of aphids and other sap-feeding insects. This endosymbiont has established a beneficial association with aphids, increasing survivorship following attack by parasitoid wasps. Although APSE and "Ca. Hamiltonella defensa" are effectively maternally transmitted between aphid generations, they can also be horizontally transferred among insect hosts, which results in genetically distinct "Ca. Hamiltonella defensa" strains infecting the same aphid species and sporadic distributions of both APSE and "Ca. Hamiltonella defensa" among hosts. Aphids infected only with "Ca. Hamiltonella defensa" have significantly less protection than those infected with both "Ca. Hamiltonella defensa" and APSE. This protection has been proposed to be connected to eukaryote-targeted toxins previously discovered in the genomes of two characterized APSE strains. In this study, we have sequenced partial genomes from seven additional APSE strains to address the evolution and extent of toxin variation in this phage. The APSE lysis region has been a hot spot for nonhomologous recombination of novel virulence cassettes. We identified four new toxins from three protein families, Shiga-like toxin, cytolethal distending toxin, and YD-repeat toxins. These recombination events have also resulted in reassortment of the downstream lysozyme and holin genes. Analysis of the conserved APSE genes flanking the variable toxin cassettes reveals a close phylogenetic association with phage sequences from two other facultative endosymbionts of insects. Thus, phage may act as a conduit for ongoing gene exchange among heritable endosymbionts.

Evaluation of Artificial Diets for Rearing <I>Aphis glycines</I> (Hemiptera: Aphididae)

Artificial aphid diets have been previously developed for the pea aphid, Acyrthosiphon pisum (Harris), and the green peach aphid, Myzus persicae (Sulzer). The ability to rear aphids on an artificial diet allows for selectively adding or subtracting compounds from an aphid's food source to determine the effect on fecundity and longevity. Five diets previously developed for the green peach aphid and the pea aphid were tested for their suitability for rearing soybean aphid, Aphis glycines Matsumura. The best diet, originally developed for the green peach aphid and based on the amino acid profile of young potato plants, allowed 12 generations of soybean aphids to develop. For all diets tested, aphid fecundity, and longevity were greatly reduced in comparison with aphids reared on soybean, Glycine max (L.) Merr., plants or on detached soybean leaves. In addition, mean developmental time was significantly longer for aphids reared on artificial diets.

Cis -Jasmone induces Arabidopsis genes that affect the chemical ecology of multitrophic interactions with aphids and their parasitoids

It is of adaptive value for a plant to prepare its defenses when a threat is detected, and certain plant volatiles associated with insect damage, such as cis-jasmone (CJ), are known to switch-on defense metabolism. We used aphid and aphid parasitoid responses to Arabidopsis thaliana as a model system for studying gene expression and defense chemistry and its impact at different trophic levels. Differential responses to volatiles of induced Arabidopsis occurred for specialist and generalist insects: the generalist aphid, Myzus persicae, was repelled, whereas the specialist, Lipaphis erysimi, was attracted; the generalist aphid parasitoid Aphidius ervi was attracted, but the specialist parasitoid Diaeretiella rapae was not affected. A. ervi also spent longer foraging on induced plants than on untreated ones. Transcriptomic analyses of CJ-induced Arabidopsis plants revealed that a limited number of genes, including a gene for a cytochrome P450, CYP81D11, were strongly up-regulated in the treated plants. We examined transgenic Arabidopsis lines constitutively overexpressing this gene in bioassays and found insect responses similar to those obtained for wild-type plants induced with CJ, indicating the importance of this gene in the CJ-activated defense response. Genes involved in glucosinolate biosynthesis and catabolism are unaffected by CJ and, because these genes relate to interactions with herbivores and parasitoids specific to this family of plants (Brassicaceae), this finding may explain the differences in behavioral response of specialist and generalist insects.