This study investigated the volatile emission from apple (Malus x domestica Borkh., cv. Golden Delicious) foliage that was either intact, mechanically-damaged, or exposed to larval feeding by Pandemis heparana (Denis and Schiffermüller) (Lepidoptera: Tortricidae). Volatiles were collected by closed-loop-stripping-analysis and characterized by gas chromatography-mass spectrometry in three time periods: after 1 h and again 24 and 48 h later. Volatiles for all treatments also were monitored continuously over a 72-h period by the use of proton transfer reaction - time of flight-mass spectrometry (PTR-ToF-MS). In addition, the volatile samples were analyzed by gas chromatography-electroantennographic detection (GC-EAD) using male and female antennae of P. heparana. Twelve compounds were detected from intact foliage compared with 23 from mechanically-damaged, and 30 from P. heparana-infested foliage. Interestingly, six compounds were released only by P. heparana-infested foliage. The emission dynamics of many compounds measured by PTR-ToF-MS showed striking differences according to the timing of herbivory and the circadian cycle. For example, the emission of green leaf volatiles began shortly after the start of herbivory, and increased over time independently from the light-dark cycle. Conversely, the emission of terpenes and aromatic compounds showed a several-hour delay in response to herbivory, and followed a diurnal rhythm. Methanol was the only identified volatile showing a nocturnal rhythm. Consistent GC-EAD responses were found for sixteen compounds, including five aromatic ones. A field trial in Sweden demonstrated that benzyl alcohol, 2-phenylethanol, phenylacetonitrile, and indole lures placed in traps were not attractive to Pandemis spp. adults, but 2-phenylethanol and phenylacetonitrile when used in combination with acetic acid were attractive to both sexes.

Honeybees are well recognised for their key role in plant reproduction as pollinators. On the other hand, their activity may vector some pathogens, such as the bacterium Erwinia amylovora, the causative agent of fire blight disease in pomaceous plants. In this research, we evaluated whether honeybees are able to discriminate between healthy and E. amylovora-infected flowers, thus altering the dispersal of the pathogen. For this reason, honeybees were previously trained to forage either on inoculated or healthy (control) apple flower. After the training, the two honeybee groups were equally exposed to inoculated and control flowering apple plants. To assess their preference, three independent methods were used: (1) direct count of visiting bees per time frame; (2) incidence on apple flowers of a marker bacterium (Pantoea agglomerans, strain P10c) carried by foragers; (3) quantification of E. amylovora populations in the collected pollen loads, proportional to the number of visits to infected flowers. The results show that both honeybee groups preferred control flowers over inoculated ones. The characterisation of volatile compounds released by flowers revealed a different emission of several bioactive compounds, providing an explanation for honeybee preference. As an unexpected ecological consequence, the influence of infection on floral scent increasing the visit rate on healthy flowers may promote a secondary bacterial spread.

Root activities in terms of respiration and non-structural carbohydrates (NSC) storage and mobilization have been suggested as major physiological roles in fine root lifespan. As more frequent heat waves and drought periods within the next decades are expected, to what extent does thermal acclimation in fine roots represent a mechanism to cope with such upcoming climatic conditions? In this study, the possible changes in very fine (diameter < 0.5 mm) and fine (0.5-1 mm) root morphology and physiology in terms of respiration rate and NSC [soluble sugars (SS) and starch] concentrations, were investigated on 2-year-old Fagus sylvatica saplings subjected to a simulated long-lasting heat wave event and to co-occurring soil drying. For both very fine and fine roots, soil temperature (ST) resulted inversely correlated with specific root length, respiration rates and SSs concentration, but directly correlated with root mass, root tissue density and starch concentration. In particular, starch concentration increased under 28 °C for successively decreasing under 21 °C ST. These findings showed that thermal acclimation in very fine and fine roots due to 24 days exposure to high ST (∼ 28 °C), induced starch accumulation. Such 'carbon-savings strategy' should bear the maintenance costs associated to the recovery process in case of restored favorable environmental conditions, such as those occurring at the end of a heat wave event. Drought condition seems to affect the fine root vitality much more under moderate than high temperature condition, making the temporary exposure to high ST less threatening to root vitality than expected.

No abstract

These data show that herbivore injury does not create a unique chemical signal for adults to locate oviposition or rendezvous sites. Instead, moths may cue to the aromatic-acetic acid combination as a nutritional cue to locate sugary resources. © 2017 Society of Chemical Industry.

Volatile organic compounds (VOCs) mediate communication between plants and insects. Plants under insect herbivore attack release VOCs either at the site of attack or systemically, indicating within-plant communication. Some of these VOCs, which may be induced only upon herbivore attack, recruit parasitoids and predatory insects to feed on the attacking insects. Moreover, some plants are able to 'eavesdrop' on herbivore-induced plant volatiles (HIPVs) to prime themselves against impending attack; such eavesdropping exemplifies plant-plant communication. In apple orchards, the beetle Melolontha melolontha L. (Coleoptera: Scarabaeidae) is an important insect pest whose larvae live and feed on roots for about 4 years. In this study, we investigated whether the feeding activity of M. melolontha larvae (1) alters the volatile profile of apple roots, (2) induces the release of HIPVs systemically in the leaves, and (3) whether infested plants communicate to neighbouring non-infested conspecifics through HIPVs. To answer these questions, we collected constitutive VOCs from intact M9 roots as well as M. melolontha larvae-damaged roots using a newly designed 'rhizobox', to collect root-released volatiles in situ, without damaging the plant root system. We also collected VOCs from the leaf-bearing shoots of M9 whose roots were under attack by M. melolontha larvae and from shoots of neighbouring non-infested conspecifics. Gas chromatography-mass spectrometry analysis showed that feeding activity of M. melolontha larvae induces the release of specific HIPVs; for instance, camphor was found in the roots only after larvae caused root damage. Melolontha melolontha also induced the systemic release of methyl salicylate and (E,E)-a-farnesene from the leaf-bearing shoots. Methyl salicylate and (E,E)-a-farnesene were also released by the shoots of noninfested neighbouring conspecifics. These phenomena indicate the induction of specific VOCs below-and above-ground upon M. melolontha larvae feeding on apple roots as well as plant-plant communication in apple plants.

No abstract