Aphid acceptance of Hordeum genotypes is affected by plant volatile exposure and is correlated with aphid growth

Nineteen genotypes of Hordeum vulgare were characterized as partially resistant or susceptible regarding growth of the bird cherry - oat aphid (Rhopalosiphum padi L.). These genotypes were treated with volatiles from undamaged plants of barley cultivar Alva. Aphid host acceptance (AHA) was significantly affected in seven genotypes, and the magnitude of the effect was positively correlated with aphid growth (AG) in a resistance screening test. Changes in AHA induced by volatiles from the same genotype were also positively correlated with AG. All genotypes were tested as inducers with cultivar Kara as the receiver of volatiles. Five genotypes induced significant reductions in AHA of Kara. The results show that aphids are able to detect changes in responding plants induced by volatiles from another cultivar. Plant volatile interactions may thus be a component of induced resistance to aphids. These interactions could influence the results of experiments used to select for insect-resistant plants in plant breeding programmes

Communication between undamaged plants can elicit changes in volatile emissions from neighbouring plants, thereby altering their susceptibility to aphids

Plant volatiles play an important role in intra- and interspecific plant communication, inducing direct and indirect defenses against insect pests. However, it remains unknown whether volatile interactions between undamaged cultivars alter host plant volatile emissions and their perception by insect pests. Here, we tested the effects of exposure of a spring barley, Hordeum vulgare L., cultivar, Salome, to volatiles from other cultivars: Fairytale and Anakin. We found that exposing Salome to Fairytale induced a significantly higher emission of trans-beta-ocimene and two unidentified compounds compared when exposed to Anakin. Aphids were repelled at a higher concentration of trans-beta-ocimene. Salome exposure to Fairytale had significant repulsive effects on aphid olfactory preference, yet not when Salome was exposed to Anakin. We demonstrate that volatile interactions between specific undamaged plants can induce changes in volatile emission by receiver plants enhancing certain compounds, which can disrupt aphid olfactory preferences. Our results highlight the significant roles of volatiles in plant-plant interactions, affecting plant-insect interactions in suppressing insect pests. This has important implications for crop protection and sustainable agriculture.The airborne interactions between certain undamaged spring barley (Hordeum vulgare L.) cultivars induce changes in volatile emission in receiving plants by enhancing the production of certain ideal volatile organic compounds. These changes trigger strong repellent effects on aphids (Rhopalosiphum padi L.), suggesting the significant roles of volatile-mediated plant-plant interactions in the development of integrated pest management for sustainable agriculture practices

Changed host plant volatile emissions induced by chemical interaction between unattacked plants reduce aphid plant acceptance with intermorph variation

Olfactory orientation by aphids is guided by specific volatile blends released from their hosts. Host plants that co-exist with other plants may be less attractive for aphids due to volatile interactions between neighboring plants which can lead to changes in their volatile emissions. These changes in host plant volatile profiles induced by interactions between undamaged plants could be used to manage aphid populations in crops. When potato plants are exposed to volatiles from onion plants, the volatile profile of potato changes in relation to that of unexposed plants with consistently greater quantities of two terpenoids released. We examined the host plant searching behavior of aphids and showed that induced changes in plant volatile emissions affect aphid behavior. We assessed olfactory responses of winged and wingless aphids, Myzus persicae Sulzer (Hemiptera: Aphididae) to the changed volatile emissions. Both morphs were significantly less attracted to odors of potato plants that had been exposed to volatiles from onion than to odors of unexposed potato plants. Further, both morphs were significantly less attracted to synthetic blends mimicking volatiles emitted by onion-exposed potato plants than to blends mimicking non-exposed controls, and to single compounds emitted in greater quantities by exposed potato. Aphid morphs were repelled differently depending on the concentration of odor sources; winged aphids responded to higher doses than did wingless aphids. The aphid responses to changes in plant volatile profiles induced by neighboring plants may facilitate refinement of habitat manipulation strategies (e.g., intercropping) for integrated pest management to reduce aphid occurrence in crops

Sustainable plant protection for increased food security in a changing climate

The global climate is changing. Rising temperatures in temperate regions are making headlines, but there are a host of changes that may have even greater impact on a global scale, particularly in regions where food security is already delicately balanced. Rising sea levels, changing patterns of rainfall, availability of water and increasing concentration of carbon dioxide in the atmosphere are all likely to affect the biotic environment upon which we depend

Great Tits Learn Odors and Colors Equally Well, and Show No Predisposition for Herbivore-Induced Plant Volatiles

Ability to efficiently localize productive foraging habitat is crucial for nesting success of insectivorous birds. Some bird species can use olfaction to identify caterpillar-infested trees by detection of herbivore induced plant volatiles (HIPVs), but these cues probably need to be learned. So far, we know very little about the process of olfactory learning in birds, whether insectivorous species have a predisposition for detecting and learning HIPVs, due to the high ecological significance of these odors, and how olfaction is integrated with vision in making foraging decisions. In a standardized setup, we tested whether 35 wild-caught great tits (Parus major) show any preference for widely abundant HIPVs compared to neutral (non-induced) plant odors, how fast they learn to associate olfactory, visual and multimodal foraging cues with food, and whether the olfactory preferences and learning speed were influenced by bird sex or habitat (urban or rural). We also tested how fast birds switch to a new cue of the same modality. Great tits showed no initial preference for HIPVs compared to neutral odors, and they learned all olfactory cues at a similar pace, except for methyl salicylate (MeSA), which they learned more slowly. We also found no differences in learning speeds between visual, olfactory and multimodal foraging cues, but birds learned the second cue they were offered faster than the first one. Bird sex or habitat had no effect on learning speed or olfactory preference, but urban birds tended to learn visual cues more slowly. We conclude that insectivorous birds utilize olfactory and visual cues with similar efficiency in foraging, and that they probably don't have any special predisposition toward the tested HIPVs. These results confirm that great tits are flexible foragers with good learning abilities

Olfactory learning of plant genotypes by a polyphagous insect predator

Olfactory learning may allow insects to forage optimally by more efficiently finding and using favourable food sources. Although olfactory learning has been shown in bees, insect herbivores and parasitoids, there are fewer examples from polyphagous predators. In this study, olfactory learning by a predatory coccinellid beetle is reported for the first time. In laboratory trials, adults of the aphidophagous ladybird Coccinella septempunctata did not prefer the odour of one aphid-infested barley cultivar over another. However, after feeding on aphids for 24 h on a cultivar, they preferred the odour of that particular cultivar. The mechanism appeared to be associative learning rather than sensitisation. Although inexperienced ladybirds preferred the odour of an aphid-infested barley cultivar over uninfested plants of the same cultivar, after feeding experience on a different cultivar this preference disappeared. This may indicate the acquisition and replacement of olfactory templates. The odour blends of the different aphid-infested barley cultivars varied qualitatively and quantitatively, providing a potential basis for olfactory discrimination by the ladybird. The results show that predatory coccinellids can learn to associate the odour of aphid-infested plants with the presence of prey, and that this olfactory learning ability is sensitive enough to discriminate variability between different genotypes of the same plant

Diel behaviour and time budget of the adult pine weevil, Hylobius abietis

The pine weevil (Hylobius abietis (L.); Coleoptera: Curculionidae) has a high economic impact on forest regeneration in Europe. The general biology of the pine weevil has received considerable attention, but there is insufficient knowledge about its diel behaviour and time budget. Therefore, the feeding and locomotion behaviour of individual adult weevils on Norway spruce (Picea abies (L.) Karst.) seedlings is observed for 24 hour-periods in the laboratory. Both girdled and non-girdled seedlings are used to assess how the weevils’ behaviour is influenced by the plants physiological response to the girdling. The locomotion pattern shows a distinct maximum during the beginning of the dark phase whereas most feeding occurs during the second half of the dark phase and the first hours of the subsequent light phase. The girdling treatment increase the time that weevils spend on the seedlings during the first part of an observation session, but has no effect on their feeding pattern. The weevils’ time budgets on girdled and non-girdled seedlings are similar. On average, they spend 34 % of their time in locomotion and 6 % on feeding. Females spend more time feeding than males (7.1 % vs. 4.2 %), possibly because they have higher food requirements, e.g. for egg production. Females also spend more time in total on the seedlings than males (26.3 % vs. 7.0 %). This study reveals, in high temporal resolution, the diel feeding and locomotion behaviour and time budget of male and female pine weevils

The structure of feeding behavior in a phytophagous insect (Hylobius abietis)

Analysis of the feeding behavior of animals using such a high temporal resolution that meals can be defined may improve our understanding of the mechanisms regulating feeding. Meals can be distinguished in an ethologically meaningful manner by using the ‘meal criterion’, the shortest non-feeding interval between feeding bouts recognized as meals. However, such a criterion has only been determined for a few insect species. Applying a recent method developed for assessing meal criteria for vertebrates, we determined the meal criterion for Hylobius abietis (L.) (Coleoptera: Curculionidae) based on data from video recordings of single individuals feeding on seedlings of Norway spruce, Picea abies (L.) Karst. (Pinaceae). The pine weevil is an economically important pest insect because it feeds on the stem bark of planted conifer seedlings. Weevils had 4-5 meals per day. Each meal lasted about 24 min during which about 13 mm2 of bark per meal were removed. Females had longer total meal durations and longer non-feeding intervals within meals than males. Girdling seedlings did not affect the weevils’ feeding properties. The size of meals was significantly correlated to the duration of non-feeding intervals before and after them. This study is one of few describing the feeding behavior of an insect at a temporal resolution that allows individual meals to be distinguished. With more meal-related data from insects available, differences in meal properties may be interpreted based on phylogeny, ecology, and physiology. Our results may also assist in the setup and interpretation of studies of plant-insect interactions, and facilitate the evaluation and development of methods to protect plants against herbivores

Decoding neighbour volatiles in preparation for future competition and implications for tritrophic interactions

Plant volatile signals can provide important information about the physiological status and genetic identity of the emitter, and nearby plants can use this information to detect competitive neighbours. The novelty of these signals is that plants eavesdropping to volatiles of undamaged neighbours respond with typical competition responses, even before competition takes place, initiating specific growth responses that can increase their competitive capacity. This preparing for future competition mechanism affects the behaviour and abundance of herbivore pests and their natural enemies. Previously, such responses were only known to occur in response to volatiles released by damaged plants. However, volatile interactions occur only in specific combination of species/genotypes, indicating that plants use volatile signals in the detection and adaption only to substantial competitive neighbours. (C) 2016 The Author(s). Published by Elsevier GmbH