Divergent responses of two cereal aphids to previous infestation of their host plant

The role of pollen odour in resource location by the pollen beetle, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a pollen-feeding insect regarded as a pest of oilseed rape, Brassica napus L., (Brassicaceae) crops, was investigated in a linear track olfactometer. Both male and female beetles were attracted to the odour of whole oilseed rape flowers, indicating that these insects can locate their host plants using floral odours as cues. The attractive odour of flowers was found to emanate from all floral parts tested: the petals/sepals, the anthers, and from pollen itself. Therefore, at least part of the attractive odour of oilseed rape flowers emanates from pollen. Beetles were more attracted to floral samples containing anthers than those without anthers when these odours were directly compared in a choice-test, and this indicates that there were detectable differences between them. Anthers and pollen may therefore release distinctive odours that are quantitatively and/or qualitatively different from the odour of the rest of the flower. These experiments support the hypothesis that pollen-seeking insects use pollen odour cues to locate this food source.     

Influence of host log age and refuge from natural enemies on colonization and survival of Phoracantha semipunctata

The pine cone weevil, Pissodes validirostris Gyll. (Coleoptera: Curculionidae), attacks seed cones of most Eurasian pine species, except these of Swiss stone pine (Pinus cembra L.). Behavioural responses of adult weevils to cone volatile emissions of Swiss stone pine and to those of a common host, mountain pine (Pinus uncinata Ram.), were compared in an olfactometer. Weevils were significantly attracted by the volatile blend emitted by mountain pine, but Swiss stone pine volatiles elicited an inverse response, with most weevils moving in the opposite direction to the odour source. However, the majority of second instar weevil larvae that were extracted from mountain pine cones and transferred into Swiss stone pine cones were capable of developing to the adult stage. This suggests that Swiss stone pine cones do not contain strong feeding deterrents that could prevent larval development. The possible factors involved in the absence of colonization of Swiss stone pine cones by cone weevils are discussed.     

The influence of host plant species on parasitism of pollen beetles (Meligethes spp.) by Phradis morionellus

We investigated the response of the specialist insect predator Oligota kashmirica benefica (Coleoptera: Staphylinidae) to volatiles from lima bean leaves infested with the spider mite Tetranychus urticae (Acari: Tetranychidae), both in a Y-tube olfactometer and in a field in Kyoto, Japan. Adult male and female predators were significantly more attracted to T. urticae-infested leaves than to clean air. Adult male and female predators were not more attracted to uninfested leaves, artificially damaged leaves, or the spider mites and their visible products when compared to clean air. In a field trap experiment, 12 adult predators were caught in three traps containing T. urticae-infested lima bean plants over 13 days, whereas no adult predators were trapped in three traps containing uninfested lima bean plants during the same period. These results showed that O. kashmirica benefica adults responded to herbivore-induced plant volatiles from T. urticae-infested lima bean leaves under both laboratory and field conditions.     

Learning of host-infested plant volatiles in the larval parasitoid Cotesia kariyai

The ability to learn plant volatiles in Cotesia kariyai females was examined by wind tunnel bioassays. Searching experience on a host-infested corn plant increased subsequent flight responses of females to the infested plant. Females experiencing host by-products together with the volatiles extracted from infested leaves one time showed an increased response. However, such behavioral changes were not observed in females which experienced only the host by-products or the volatiles. Thus, the increased response is considered to be preference learning. Multiple experiences of C. kariyai with host by-products together with the volatiles did not increase their flight response to the volatiles. Furthermore, this learned response gradually decreased within 2 days. These behavioral modifications based on experience would be advantageous for C. kariyai to locate their polyphagous hosts efficiently.     

Diurnal changes in the concentrations of 2-phenylethyl β-D-glucopyranoside and the corresponding volatile aglycone in the tissue and headspace of Trifolium repens L. florets

Distinct synchronous diurnal rhythms were detected in the concentrations of phenethyl alcohol and phenethyl acetate in the tissue of blooming Trifolium repens florets. Corresponding rhythmic oscillations were observed for the same two compounds in the floral headspace. Maximum content of the volatiles in the tissue and headspace was observed 3–9 h after initiation of the photophase. The concentrations of phenethyl alcohol and phenethyl acetate in the tissue increased significantly during floral development. At full bloom the tissue contained amounts sufficient to support 2–3 h of emission. Several observations suggested that esterification of phenethyl alcohol was the source for phenethyl acetate. Trimethylsilyl derivatization and enzymatic hydrolysis of fractionated flower extracts identified 2‐phenylethyl β‐d ‐glucopyranoside as the major glucoside in the florets. The pool of glucosides increased significantly during floral development and at full bloom 97% of the phenethyl alcohol was bound as glucoside. The concentration of 2‐phenylethyl β‐d ‐glucopyranoside did not vary in a rhythmic diurnal manner. The dynamics among the diurnal rhythmic phenomena in the tissue and headspace and the fraction of volatiles bound as glucosides is discussed.     

Statistical modelling of insect behavioural responses in relation to the chemical composition of test extracts

Abstract. The use of generalized linear models (GLM) for relating changes in insect behaviour to changes in the chemical composition of a plant extract is presented and applied to data from an experimental study of the olfactory response of Cydia pomonella L. (Lepidoptera: Tortricidae) to apple volatiles. The volatiles were collected from healthy apples, artificially damaged apples or apples infested with C. pomonella larvae (either instar I, IV or V). These treatments produced a blend of 23 major components and the chemical composition of the blends differed substantially amongst the treatments.
A statistically significant relationship was found between the concentration of hexyl hexanoate and 2-methylbutyl acetate in each extract and the number of moths moving upwind. Statistically significant models were developed which suggested that a relationship exists between the concentration of Z , E -α-farnesene, hexyl hexanoate and 2-methylbutyl acetate and the number and duration of movements made by the moths.
Subsequently Y-tube assays were carried out to validate the predictions made with respect to the orientation of mated female C. pomonella . The results of these assays confirm hexyl hexanoate as an attractant. There were indications that 2-methylbutyl acetate acted as a repellent although differences were not statistically significant. Previous bioassays have shown that C. pomonella displays a statistically significant negative linear dose–response to α-farnesene ( Hern & Dorn, 1999 ).
The statistical methods employed are very flexible and fairly easy to implement, offering the potential to screen plant extracts for bioactive compounds with a minimum of biological constraints. Their general applicability has yet to be demonstrated and as such these analyses only offer evidence of statistical relationships; the results must be validated by additional bioassays before conclusions can be drawn.     

植物挥发性物质在蚜虫寄主定位中的作用

本文综述了植物挥发性物质的化学性质、研究方法及其在蚜虫寄主定位中的作用     

Resistance to pathogens in terpene down-regulated orange fruits inversely correlates with the accumulation of D-limonene in peel oil glands

Volatile organic compounds (VOCs) are secondary metabolites acting as a language for the communication of plants with the environment. In orange fruits, the monoterpene D-limonene accumulates at very high levels in oil glands from the peel. Drastic down-regulation of D-limonene synthase gene expression in the peel of transgenic oranges harboring a D-limonene synthase transgene in antisense (AS) configuration altered the monoterpene profile in oil glands, mainly resulting in reduced accumulation of D-limonene. This led to fruit resistance against Penicillium digitatum (Pd), Xanthomonas citri subsp. citri (Xcc) and other specialized pathogens. Here, we analyze resistance to pathogens in independent AS and empty vector (EV) lines, which have low, medium or high D-limonene concentrations and show that the level of resistance is inversely related to the accumulation of D-limonene in orange peels, thus explaining the need of high D-limonene accumulation in mature oranges in nature for the efficient attraction of specialized microorganism frugivores.     

Volatiles from Merino fleece evoke antennal and behavioural responses in the Australian sheep blow fly Lucilia cuprina

To identify flystrike‐related volatile compounds in wool from Merino sheep, the attractiveness of wool to Lucilia cuprina Wiedmann (Diptera: Calliphoridae) was examined. First, a selection of wool samples guided by previous knowledge of sheep lines, predicted to be more susceptible or more resistant to flystrike, was tested. The attractiveness of the 10 samples selected was not associated with field susceptibility: two samples from the more resistant line were identified as most attractive and two samples from the more susceptible line were identified as least attractive, based on the behavioural assays with gravid flies. Comparison of the headspace volatiles of these samples, using solid phase microextraction and gas chromatography‐mass spectrometry‐electroantennographic detection, revealed octanal and nonanal to be present in the attractive wool samples that elicited responses from the fly antenna. Furthermore, the two compounds were not present in wool that was least attractive to L. cuprina. In laboratory bioassays, octanal and nonanal evoked antennal and behavioural responses in gravid L. cuprina, thus confirming their potential role as semiochemicals responsible for attracting L. cuprina to Merino sheep.