Hongjian Ding

Volatiles from potato plants infected with potato leafroll virus attract and arrest the virus vector, Myzus persicae (Homoptera: Aphididae)

The influence of viral disease symptoms on the behaviour of virus vectors has implications for disease epidemiology. Here we show that previously reported preferential colonization of potatoes infected by potato leafroll virus (genus Polerovirus) (luteovirus) (PLRV) by alatae of Myzus persicae, the principal aphid vector of PLRV, is influenced by volatile emissions from PLRV–infected plants. First, in our bioassays both differential immigration and emigration were involved in preferential colonization by aphids of PLRV–infected plants. Second, M. persicae apterae aggregated preferentially, on screening above leaflets of PLRV–infected potatoes as compared with leaflets from uninfected plants, or from plants infected with potato virus X (PVX) or potato virus Y (PVY). Third, the aphids aggregated preferentially on screening over leaflet models treated with volatiles collected from PLRV–infected plants as compared with those collected from uninfected plants. The specific cues eliciting the aphid responses were not determined, but differences between headspace volatiles of infected and uninfected plants suggest possible ones.

Volatile Cues Influence the Response of Rhopalosiphum padi (Homoptera: Aphididae) to Barley Yellow Dwarf Virus–Infected Transgenic and Untransformed Wheat

Abstract The attractiveness of Barley yellow dwarf luteovirus (BYDV)–infected wheat plants to Rhopalosiphum padi L. was evaluated under laboratory conditions. Two untransformed wheat varieties, virus-susceptible Lambert and virus-tolerant Caldwell, and one transgenic wheat genotype (103.1J) derived from Lambert and expressing the BYDV coat protein gene, were tested in three bioassays. First, R. padi responses to BYDV-infected or noninfected Lambert and Caldwell were evaluated. Significantly more aphids settled onto virus-infected than noninfected plants when aphids were able to contact the leaves. Second, aphid responses to headspace from virus-infected or noninfected Lambert and Caldwell were tested. Significantly more aphids congregated on screens above headspace of BYDV-infected plants than above headspace of noninfected plants of both varieties. Third, aphid responses to headspace from virus-infected or noninfected and sham-inoculated (exposed to nonviruliferous aphids) Lambert and 103.1J plants were examined. Significantly more aphids congregated on screens above BYDV-infected than above noninfected or sham-inoculated Lambert. No significant differences in R. padi preferences for headspace above BYDV-infected compared with noninfected or sham-inoculated 103.1J plants were observed. The concentration of volatiles extractable from whole plant headspace was greater on BYDV-infected Lambert than on BYDV-infected 103.1J, noninfected, or sham-inoculated plants of either genotype. This is the first report of volatile cues associated with BYDV infection in wheat plants influencing the behavior of the vector R. padi. Additionally, these findings show for the first time that transgenic virus resistance in wheat can indirectly influence the production of volatiles making virus-infected plants less attractive or arrestant to aphids than are infected untransformed plants.

Changes in green peach aphid responses to potato leafroll virus-induced volatiles emitted during disease progression.

ABSTRACT Previous research has shown that green peach aphids, Myzus persicae (Sulzer), preferentially settle on leaflets of potato plants (Solanum tuberosum L.) infected with potato leafroll virus (PLRV) compared with sham-inoculated controls, at least in part because of aphid responses to volatile cues from the plants. The prior work used plants 4 wk after inoculation. In this study, aphid emigration from the vicinity of leaflets of PLRV-infected plants at 2, 4, 6, 8, and 10 wk after inoculation was compared with emigration from leaflets of sham-inoculated control plants. For the bioassay, 30 aphids were placed directly above a test leaflet on screening to exclude gustatory and tactile cues and in darkness to exclude visual cues. The numbers emigrating were recorded every 10 min for 1 h. Volatile organic compounds (VOCs) were collected from the headspace of the test plants, quantified, and compared among treatments. In bioasssays with leaflets of upper nodes of the plants, aphid immigration rates were significantly lower from leaflets of PLRV-infected plants than from sham-inoculated plants at 4 and 6 wk after inoculation, but not at 2, 8, and 10 wk after inoculation. In bioassays with leaflets from lower nodes, emigration did not differ between PLRV-infected plants and shaminoculated plants at any stage in the infection. Volatile compounds detectable in the headspace of intact plants at 2, 4, and 8 wk after inoculation (or sham inoculation) changed with plant age and with disease progression, potentially explaining behavioral responses of the aphids.

Induced chemical defenses in invasive plants: a case study with Cynoglossum officinale L.

The ‘evolution of increased competitive ability’ (EICA) hypothesis is an extension of optimal defense theory and predicts that reduced pressure from insect herbivores in the introduced range results in evolution of reduced defenses in invading plant populations, allowing greater allocation of resources to competitive traits such as growth rate and reproduction. The EICA hypothesis considered levels of defensive chemistry to be fixed within a particular genotype. In this paper, we propose that if herbivory is reduced in the introduced range, but chemical defenses are inducible in response to herbivory, evolution of reduced defenses and any associated increase competitive ability should not occur. Rather, mean induced and constitutive levels of induced defenses should be similar in introduced and native ranges, but the variance about mean induced levels should be greater in the introduced range. This is predicted because induced levels will occur less frequently in the introduced range where herbivory is reduced, thereby insulating these levels from the stabilizing selection expected in the native range where induced levels occur more frequently. We conducted a preliminary study to examine this by comparing constitutive and induced concentrations of total pyrrolizidine alkaloids (PAs) from native (European) and introduced (western North America) populations of Cynoglossum officinale L. The mean constitutive and induced concentrations of PAs did not differ between continents, but the variability of the induced concentrations was significantly greater for plants from the introduced range. Although our study with C. officinale is provisional due to a small sample size, it supports our predictions for evolution of inducible defenses in introduced ranges where herbivore pressure is reduced. Most chemical defenses in plants have been found to be inducible, so similar patterns may occur widely. If so, this weakens the generality of EICA’s predictions concerning chemical defenses. The effects of inducible defenses should be considered in cross-continent comparisons of other invasive plant species.

Oviposition Responses by Hessian Fly, Mayetiola destructor, to Wheats Varying in Surfaces Waxes

Leaf waxes are known to contain oviposition stimulants for Hessian fly. In dual-choice tests comparing seedlings of each of three nonglaucous lines of wheat with its corresponding glaucous line, Hessian flies laid similar numbers of eggs on each genotype. However, when plants from these genotypes were tested at the flag-leaf stage, Hessian flies deposited 25–100% more eggs on the nonglaucous genotype compared to normal wax genotype in each pair. Leaf waxes extracted from the genotypes in one of these pairs (Avalon and nonglaucous Avalon) at the seedling and the flag-leaf stage and tested on paper leaf models elicited oviposition responses similar to those observed on the intact plants. Scanning electron microscopy showed differences in crystal density on nonglaucous and glaucous genotypes only at the flag-leaf stage. Gas chromatography–mass spectrometry of the leaf wax extracts showed that fly oviposition responses were associated with differences in the chemical composition of the waxes. This is the first report of Hessian fly oviposition responses varying among genotypes of wheat with different surface wax composition.

A plant surface mutation mediates predator interference among ladybird larvae

Abstract 1. We investigated mechanisms causing predator–predator interference between fourth instar Hippodamia convergens larvae foraging for pea aphids on pea plants, Pisum sativum, with a wild‐type wax bloom, and the lack of such interference between larvae foraging on pea plants with a reduced‐wax bloom caused by the single gene mutation wel.

Different Reactions of Potato Varieties to Infection by Potato Leafroll Virus, and Associated Responses by its Vector, Myzus persicae (Sulzer)

Vector-dependent plant pathogens can alter their hosts such that vector behavior and pathogen spread are affected. For example, Potato leafroll virus (PLRV)-induces changes in volatiles emitted by potato plants (Solanum tuberosum L.) that influence settling behavior by Myzus persicae, a principal vector of the virus. Prior work in this pathosystem has utilized a single potato variety, Russet Burbank, but as is true for other plant responses to biotic stresses, responses may differ among plant genotypes. To examine this, PLRV-induced changes in headspace volatile organic compounds (VOCs) and associated aphid responses to these VOCs were compared among four potato varieties (Chipeta, Desiree, IdaRose, and Russet Burbank). Total headspace VOCs differed among the varieties and were differentially induced by PLRV infection such that the effect of variety, infection, and their interaction was significant; two of the varieties had increased concentrations of headspace VOCs, and two did not. MANOVA for the effect of infection and variety on total VOCs and major VOC classes also was significant. A principal component analysis (PCA) partially separated the VOC profiles from the four varieties. Aphid arrestment differed in response to the VOCs of the four varieties, and was greater on those that were more readily infected by PLRV (Desiree and Russet Burbank) as compared with those that were less readily infected (Chipeta and IdaRose). Aphid responses were not clearly related to specific characteristics of blends, such that total VOCs and composition appear to contribute. The four varieties used in this study have distinct pedigrees representative of different cultivated forms of S. tuberosum. Although cultivated potato varieties have been subjected to genetic manipulation by humans, the differences in PLRV induced changes in VOCs nonetheless indicate the potential for complex effects of PLRV infection on host plant VOC emissions, and vector responses in managed, and natural systems.

Effects of Hydrophilic and Hydrophobic Kaolin-Based Particle Films on Pea Aphid (Homoptera: Aphididae) and Its Entomopathogen Pandora neoaphidis (Entomophthorales: Entomophthoraceae)

Abstract Hydrophobic and hydrophilic kaolin-based particle films are effective for control of insect pests in certain agricultural crops. How these products interact with potential biological control agents is not well documented. This study was conducted to evaluate the effects of the hydrophobic (M96-018) and hydrophilic (Surround WP) kaolin-based particle films (Engelhard Corporation, Iselin, NJ) on pea aphid, Acyrthosiphon pisum (Harris), on peas (Pisum spp.), and on the fungal aphid pathogen Pandora neoaphidis (Remaudière and Hennebert) Humber. Over two field seasons (2001 and 2002) in northern Idaho, applications of M96-018 significantly reduced the rate of pea aphid increase on pea, but Surround WP, tested only in 2001, did not reduce aphid population growth rate. Neither particle film treatment was as effective as a standard application of esfenvalerate (DuPont Asana). In the laboratory, particle films suppressed pea aphid populations by up to 30%. M96-018 seemed to have some repellent activity based on aphid distributions after treating plants. When applied along with P. neoaphidis conidia, M96-018 but not Surround WP caused higher percentage of infection mortality of pea aphids by P. neoaphidis than occurred on controls treated only with P. neoaphidis conidia. P. neoaphidis conidia deposited on glass slides coated with M96-018, produced more germ tubes and secondary conidia than those deposited on untreated glass slides or slides treated with Surround WP. This result suggests that greater infection of pea aphids on plants treated with M96-018 is in part a result of a direct enhancement of fungal germination by the particle film.

Behavioral Responses of Green Peach Aphid, Myzus persicae (Sulzer), to the Volatile Organic Compound Emissions from Four Potato Varieties

Green peach aphid Myzus persicae (Sulzer) is a serious pest of potato and causes severe yield loss to potato production worldwide. The volatiles emitted from potato plants influence host selection by M. persicae. A laboratory experiment was conducted to study how these volatile emissions vary among four potato varieties (IdaRose, Desiree, Chipeta and Russet Burbank) having different genetic backgrounds, and to compare the aphid responses to the volatiles emitted by these varieties. Results indicated that headspace volatiles detected, and aphid responses, differed significantly among the varieties. Myzus persicae arrestment was greater in response to Desiree and Chipeta than on Russet Burbank and arrestment on IdaRose was intermediate and did not differ significantly from any of the other varieties, but the arrestment was not related to the total concentration of volatiles released by these varieties. This indicates that the blend of volatiles was important for eliciting arrestment. Eigenvector weightings of principal component 1 were predominantly sesquiterpenes (especially caryophyllene, sesquiphellandrene, α-farnesene and longifolene), whereas those for principal component 2 were predominantly aldehydes and green leaf volatiles (n-hexana1, (Z)-3-hexenol, (E)-2-hexenal and nonanal. The pedigrees of the varieties are not associated with the volatile blends or aphid responses.ResumenEl áfido verde del durazno Myzus persicae (Sulzer) es una plaga seria de la papa y causa severas pérdidas de rendimiento en la producción de papa en todo el mundo. Los compuestos volátiles emitidos de la planta de papa influencian la selección de hospedante por M. persicae. Se condujo un experimento de laboratorio para estudiar cómo éstas emisiones de volátiles varían entre cuatro variedades de papa (IdaRose, Desiree, Chipeta, y Russet Burbank) con contenidos de diferentes antecedentes genéticos, y para comparar las respuestas del áfido a los volátiles emitidos por estas variedades. Los resultados indicaron que los volátiles detectados en espacios libres y la respuesta de los áfidos, diferían significativamente entre las variedades. La permanencia de M. persicae era mayor en respuesta a Desiree y Chipeta que en Russet Burbank y la retención en IdaRose fue intermedia, y no se diferenció significativamente de cualquiera de las otras variedades, pero la retención no estuvo relacionada a la concentración total de volátiles liberados por estas variedades. Esto indica que la mezcla de volátiles era importante para inducir la permanencia. La ponderación del vector propio del componente principal 1 fue predominantemente sesquiterpenos (especialmente cariofileno, sesquifelandreno, α-farneseno y longifoleno), mientras que aquellos para el componente principal 2 fueron predominantemente aldehidos y volátiles de hoja verde (n-hexana1, (Z)-3-hexenol, (E)-2-hexenal y nonanal). No se asocia al pedigrí de las variedades con las mezclas de volátiles o con las respuestas de los áfidos.

Variable Attachment to Plant Surface Waxes by Predatory Insects

In this chapter we will (1) provide an overview of evidence of the influence of habitat characteristics on predation, (2) provide specific evidence for the importance of the plant as habitat, and of variability in plant morphology’s impact on the foraging of insect predators and parasitoids, (3) focus on the role of crystalline waxes on plant surfaces in mediating these types of interactions through their effects on insect attachment, (4) illustrate the implications of the variability of plant surface waxes and insect responses to surface waxes through a case study examining the attachment and performance of five species of predatory beetle on plants differing in surface wax, and (5) discuss implications for ecology of predation along with opportunities for further research.