Settling on leaves or flowers: herbivore feeding site determines the outcome of indirect interactions between herbivores and pollinators

Herbivore attack can alter plant interactions with pollinators, ranging from reduced to enhanced pollinator visitation. The direction and strength of effects of herbivory on pollinator visitation could be contingent on the type of plant tissue or organ attacked by herbivores, but this has seldom been tested experimentally. We investigated the effect of variation in feeding site of herbivorous insects on the visitation by insect pollinators on flowering Brassica nigra plants. We placed herbivores on either leaves or flowers, and recorded the responses of two pollinator species when visiting flowers. Our results show that variation in herbivore feeding site has profound impact on the outcome of herbivore–pollinator interactions. Herbivores feeding on flowers had consistent positive effects on pollinator visitation, whereas herbivores feeding on leaves did not. Herbivores themselves preferred to feed on flowers, and mostly performed best on flowers. We conclude that herbivore feeding site choice can profoundly affect herbivore–pollinator interactions and feeding site thereby makes for an important herbivore trait that can determine the linkage between antagonistic and mutualistic networks.</p

Editorial: Mechanisms underlying plant-pollinator-herbivore interactions

not applicabl

Die Hysterie um Pestizide ist kein Furz im Wasserglas

Pestizid-Rückstände werden mittlerweile in allen Ökosystemen gefunden - mit weitreichenden Folgen für Mensch, Tier und Umwelt

Competition matters: using in vitro community models to study the impact of human skin bacteria on mosquito attraction

The human skin bacteria play an important role in the production of volatiles that attract mosquitoes. Using some of the most abundant human skin bacterial species, we created in vitro community models to assess whether increased microbial biodiversity could reduce human attractiveness to females of the dengue fever mosquito Aedes aegypti and whether co-culturing bacterial commensals affects overall attraction. More complex bacterial models were less attractive to female mosquitoes than the simplest models. For instance, the triple bacterial community model was approximately three times less attractive than Staphylococcus epidermidis alone. Our data show, for instance, that an in vitro community model mimicking the skin composition of a highly attractive individual to the anthropophilic Anopheles gambiae was also more attractive to anthropophilic Ae. aegypti than a community model mimicking the skin composition of a poorly attractive individual to An. gambiae. In line with these results, volatile analyses of the blends emitted by the different in vitro community models showed that the more complex models had lower emission overall. Effects on mosquito responses differed sharply when the different bacteria species were sharing the same resources used for growth, showing that either competition or commensalism may influence their relative growth, and that this consequently can influence mosquito responses. We conclude that studies on mosquito responses to skin volatiles need to take the microbial community into account

Integrating Studies on Plant-Pollinator and Plant-Herbivore Interactions

Research on herbivore-induced plant defence and research on pollination ecology have had a long history of separation. Plant reproduction of most angiosperm species is mediated by pollinators, and the effects of herbivore-induced plant defences on pollinator behaviour have been largely neglected. Moreover, there is expected to be a trade-off between plant reproductive strategies and defence mechanisms. To investigate this trade-off, it is essential to study herbivore-induced plant resistance and allocation of resources by plants, within the same system, and to test if indirect plant resistance can conflict with pollinator attraction. Here, I review the key literature highlighting connection between plant defence and reproduction, and propose to exploit natural variation among plant species to assess the ecological costs of plant responses to herbivores and pollinators. It is crucial to study herbivore-induced resistance and resource allocation by plants within the same study system.There is a need to link the study of herbivore-induced responses with that of plant-pollinator associations, and ultimately to plant fitness.Focussing on the underlying mechanisms of plant responses to herbivory and pollination will help to understand if and how the attraction of carnivores can conflict with the attraction of pollinators.The use of natural variation in plant species will allow the assessment of the ecological costs associated with plant responses to herbivores and pollinators.</p

Editorial: Flower Metabolism and Pollinators

ISSN:1664-462

No evidence of flowering synchronization upon floral volatiles for a short lived annual plant species: Revisiting an appealing hypothesis

Background: Self-incompatible plants require simultaneous flowering mates for crosspollination and reproduction. Though the presence of flowering conspecifics and pollination agents are important for reproductive success, so far no cues that signal the flowering state of potential mates have been identified. Here, we empirically tested the hypothesis that plant floral volatiles induce flowering synchrony among self-incompatible conspecifics by acceleration of flowering and flower opening rate of non-flowering conspecifics. We exposed Brassica rapa Maarssen, a self-incompatible, in rather dense patches growing annual, to (1) flowering or non-flowering conspecifics or to (2) floral volatiles of conspecifics by isolating plants in separate containers with a directional airflow. In the latter, odors emitted by non-flowering conspecifics were used as control. Results: Date of first bud, duration of first flower bud, date of first flower, maximum number of open flowers and flower opening rate were not affected by the presence of conspecific flowering neighbors nor by floral volatiles directly. Conclusions: This study presents a compelling approach to empirically test the role of flower synchronization by floral volatiles and challenges the premises that are underlying this hypothesis. We argue that the life history of the plant as well as its interaction with pollinators and insect herbivores, as well as the distance over which volatiles may serve as synchronization cue, set constraints on the fitness benefits of synchronized flowering which needs to be taken into account when testing the role of floral volatiles in synchronized flowering.</p