The role of semiochemicals in mediating intraguild interactions between the seven-spot ladybird, Coccinella septempunctata, and the aphid parasitoid, Aphidius ervi, was investigated. Female parasitoids avoided leaves visited by C. septempunctata adults and larvae during the previous 24 hr. Ethanol extracts of C. septempuntata adults and larvae also induced avoidance responses by A. ervi. Two of the hydrocarbons identified by gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS), n-tricosane (C23H48), and n-pentacosane (C25H52), when tested individually at levels found in the adult extract, induced avoidance by A. ervi. Further investigation of the larvae extract, and footprint chemicals deposited by adults in glass Petri dishes, confirmed the presence of the hydrocarbons. Parasitism rates of the pea aphid, Acyrthosiphon pisum, on broad bean plants, Vicia faba, which had been sprayed with a mixture of the chemicals, were lower than those on control plants. The effect, however, was no longer evident if parasitoid foraging was delayed by 24 hr after the plants were treated. The ecological significance of intraguild avoidance behavior and implications for possible use of the semiochemicals involved in future biological control programs are discussed.

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In this paper, we present a hyperbolic Navier-Stokes solver for three-dimensional compressible viscous flows. Hyperbolic Navier-Stokes systems, which have been constructed and demonstrated in two dimensions, are extended here to three dimensions and the eigenstructure of the hyperbolized viscous terms is derived. The system is discretized by the second-order node-centered edge-based method on unstructured grids. The resulting residual equations are solved by an implicit defect-correction solver based on a compact Jacobian derived exactly from a first-order edge-based discretization. Numerical results are presented to examine the practical applicability and potential advantages of the hyperbolic Navier-Stokes method, accurate gradients in particular, through three-dimensional viscous flow problems with unstructured grids.

The avoidance responses of aphid parasitoids with varying host ranges (Aphidius eadyi, Aphidius ervi, and Praon volucre) to chemical trails deposited by intraguild predatory ladybirds, Coccinella septempunctata and Adalia bipunctata, were investigated. Females of all three parasitoid species avoided leaves previously visited by C. septempunctata or A. bipunctata adults. The avoidance responses shown by the two Aphidius species were stronger to trails of C. septempunctata than to those of A. bipunctata. However, P. volucre avoided trails of both ladybird species to a similar degree. Dose responses of these three parasitoid species to the hydrocarbons n-tricosane (C23H48), n-pentacosane (C25H52), and n-heptacosane (C27H56), which are components of the trails of both C. septempunctata and A. bipunctata, were evaluated. Dual-choice bioassays indicated the following: (1) A. eadyi showed more sensitive avoidance responses to n-tricosane than did the other two parasitoid species, (2) all three species showed similar responses to n-pentacosane across a range of doses, and (3) only P. volucre showed avoidance responses to n-heptacosane. Quantitative analyses of each hydrocarbon in the trails of the two ladybird species showed that n-pentacosane and n-heptacosane occur in significantly greater amounts in C. septempunctata trails than in those of A. bipunctata. The trails of the two species also differ qualitatively in the other hydrocarbons present.

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Despite our understanding of chemical defenses and their consequences for plant performance and herbivores, we know little about whether defensive chemicals in plant tissues, such as alkaloids, and their spatial variation within a population play unappreciated and critical roles in plant‐herbivore interactions. Neighboring plants can decrease or increase attractiveness of a plant to herbivores, an example of a neighborhood effect. Chemical defensive traits may contribute to neighborhood effects in plant‐herbivore interactions. We examined the effects of nicotine in leaves (a non‐emitted defense chemical) on plant‐herbivore interactions in a spatial context, using two varieties of Nicotiana tabacum with different nicotine levels. A common garden experiment demonstrated that visits by grasshoppers decreased with increasing density of neighboring plants with a greater nicotine level. In contrast, visits of leaf caterpillars were not affected by neighbors, irrespective of nicotine levels. Thus, our results clearly highlighted that the neighborhood effect caused by the nicotine in leaves depended on the insect identity, and it was mediated by plant‐herbivore interactions, rather than plant‐plant interactions. This study demonstrates that understanding of effects of plant defensive traits on plant‐herbivore interactions requires careful consideration of the spatial distribution of plant defenses, and provides support for the importance of spatial context to accurately capture the ecological and evolutionary consequences of plant‐herbivore interactions.

Seasonal abundance and within-plant distribution of Acyrthosiphon spp. and their natural enemies were investigated on alfalfa in Obihiro, Hokkaido, Japan in 2001. Densities of A. pisum and A. kondoi peaked in early June. Coccinellid and syrphid predators appeared to respond to aphid numbers and were synchronized with aphid populations. Two species of braconid (aphidiine) parasitoids (Aphidius ervi and Praon barbatum) were collected. Parasitism rates for each aphid species were variable through the season, but the estimated number of parasitized aphids reached a peak at the same time as overall aphid densities. After the first harvesting of alfalfa (14 June) aphid densities became very low, and coccinellid and syrphid predators were not found. In contrast to the coccinellid and syrphid predators, the heteropteran predators, Nabis stenoferus and Orius spp. became common during summer. Aphids, immature parasitoids (live parasitized aphids and mummies), Coccinella septempunctata and syrphids occurred more on the upper parts of alfalfa stems than on the lower parts, but this trend was not found for Hippodamia tredecimpunctata. The temporal and spatial distributions of members of the aphidphagous guild are likely to influence natural enemy-aphid relationships and intraguild interactions.