Some insectivorous birds orient towards insect‐defoliated trees even when they do not see the foliar damage or the herbivores. There are, however, only a few studies that have examined the mechanisms behind this foraging behaviour. Previous studies suggest that birds can use olfactory foraging cues (e.g. volatile organic compounds (VOCs) emitted by defoliated plants), indirect visual cues or a combination of the two sensory cues. VOCs from insect‐defoliated plants are known to attract natural enemies of herbivores, and researchers have hypothesized that VOCs could also act as olfactory foraging cues for birds. We conducted three experiments across a range of spatial scales to test this hypothesis. In each experiment, birds were presented with olfactory cues and their behavioural responses or foraging outcomes were observed. In the first experiment, two different VOC blends, designed to simulate the volatile emissions of mountain birch (Betula pubescens ssp. czerepanovii) after defoliation by autumnal moth (Epirrita autumnata) larvae, were used in behavioural experiments in aviaries with pied flycatchers (Ficedula hypoleuca). The second experiment was a field‐based trial of bird foraging efficiency; the same VOC blends were applied to mountain birches, silver birches (B. pendula) and European white birches (B. pubescens) with plasticine larvae attached to the trees to serve as artificial prey for birds and provide a means to monitor predation rate. In the third experiment, the attractiveness of silver birch saplings defoliated by autumnal moth larvae versus intact controls was tested with great tits (Parus major) and blue tits (Cyanistes caeruleus) in an aviary. Birds did not orient towards either artificial or real trees with VOC supplements or towards herbivore‐damaged saplings when these saplings and undamaged alternatives were hidden from view. These findings do not support the hypothesis that olfactory foraging cues are necessary in the attraction of birds to herbivore‐damaged trees.

One of the first observations that plants might utilize cues released by damaged neighbors under natural conditions was made in birch forests in 1985. However, the mechanisms underlying the observations were not determined, and birch (Betula spp.) has been neglected as a study system for inter-plant interaction ever since. Volatiles released by vegetative plant parts in response to herbivore damage play important roles as signals in plant-to-plant interactions in a range of woody and herbaceous plant species, and also have been shown to mediate signaling between branches of the same plant that have limited vascular connection. We established greenhouse experiments to assess: 1) whether exposure to plant volatiles from herbivore-damaged birches primes defense responses in undamaged neighbors; and 2) whether defenses also are primed in undamaged parts of the same plants with limited vascular connection. We observed a priming of defense responses, which were manifested in an augmented emission of terpenes and aromatic compounds in undamaged conspecific neighbors, and also an augmented emission of green leaf volatiles in systemic branches. Our work provides strong evidence of inter-plant signaling by volatiles, and an intra-plant systemic response in birch. However, the responses are specific, with emissions of different groups of plant volatiles typifying the primed response. This work complements and extends the previous work conducted with a natural population of birches.

Semiochemical-based management strategies are important for controlling bark beetles, such as invasive Red Turpentine Beetle (Denroctonus valens), the causal agent for mass mortality of pine trees (Pinus spp.) in China. It has been previously shown that the pheromone verbenone regulates the attack density of this beetle in a dosedependent manner and that the gut bacteria of D. valens are involved in verbenone production. However, molecular functional verification of the role of gut bacteria in the pheromone production of D. valens is still lacking. To better understand the molecular function of gut bacterial verbenone production, we chose a facultative anaerobic gut bacterium (Enterobacter xiangfangensis) of D. valens based on its strong ability to convert cis-verbenol to verbenone, as shown in our previous study, and investigated its transcriptomics in the presence or absence of cis-verbenol under anaerobic conditions (simulating the anoxic environment in the beetle's gut). Based on this transcriptome analysis, aldehyde dehydrogenase (ALDH1) was identified as a putative key gene responsible for verbenone production and was knocked-down by homologous recombination to obtain a mutant E. xiangfangensis strain. Our results show that these mutants had significantly decreased the ability to convert the monoterpene precursor to verbenone compared with the wildtype bacteria, indicating that ALDH1 is primarily responsible for verbenone conversion for this bacterium species. These findings provide further mechanistic evidence of bacterially mediated pheromone production by D. valens, add new perspective for functional studies of gut bacteria in general, and may aid the development of new gene silencing-based pest management strategies.

No abstract

Pine wilt disease (PWD) has caused extensive mortality in pine forests worldwide. This disease is a result of a multi-species interaction among an invasive pinewood nematode (PWN) Bursaphelenchus xylophilus, its vector Monochamus sp. beetle, and the host pine tree (Pinus sp.). In other systems, microbes have been shown to attenuate negative impacts on invasive species after the invasion has reached a certain time point. Despite that the role of PWD associated microbes involved in the PWD system has been widely studied, it is not known whether similar antagonistic “hidden microbial players” exist in this system due to the lack of knowledge about the potential temporal changes in the composition of associated microbiota. In this study, we investigated the bacteria-to-fungi ratio and isolated culturable bacterial isolates from pupal chambers and vector beetle tracheae across five sampling sites in China differing in the duration of PWN invasion. We also tested the pathogenicity of two candidate bacteria strains against the PWN-vector beetle complex. A total of 118 bacterial species belonging to 4 phyla, 30 families, and 54 genera were classified based on 16S sequencing. The relative abundance of the genus Serratia was lower in pupal chambers and tracheae in newly PWN invaded sites (<10 years) compared to the sites that had been invaded for more than 20 years. Serratia marcescens strain AHPC29 was widely distributed across all sites and showed nematicidal activity against PWN. The insecticidal activity of this strain was dependent on the life stage of the vector beetle Monochamus alternatus: no insecticidal activity was observed against final-instar larvae, whereas S. marcescens was highly virulent against pupae. Our findings improved the understanding of the temporal variation in the microbial community associated with the PWN-vector beetle complex and the progress of PWD and can therefore facilitate the development of biological control agents against PWN and its vector beetle.

The transition toward more sustainable plant protection with reduced pesticide use is difficult, because there is no “silver bullet” available among nonchemical tools. Integrating several plant protection approaches may thus be needed for efficient pest management. Recently, increasing the genetic diversity of plantations via cultivar mixing has been proposed as a possible method to reduce pest damage. However, previous studies have not addressed either the relative efficiency of exploiting cultivar mixing and intrinsic plant herbivore resistance or the potential utility of combining these approaches to increase cropping security. Here, using a full factorial experiment with 60 woodland strawberry plots, we tested for the relative and combined effect of cultivar mixing and intrinsic plant resistance on herbivore damage and yield. The experiment comprised two levels of diversity (“high” with 10 varieties and “low” with two varieties) and three levels of resistance (“resistant” comprising only varieties intrinsically resistant against strawberry leaf beetle Galerucella tenella; “susceptible” with susceptible varieties only; and “resistance mixtures” with 50:50 mixtures of resistant and susceptible varieties). The experiment was carried out over two growing seasons. Use of resistant varieties either alone or intermixed with susceptible varieties in “resistance mixtures” reduced insect herbivory. Interestingly, resistant varieties not only reduced the mean damage in “resistance mixtures” by themselves being less damaged, but also protected intermixed susceptible varieties via associational resistance. The effect of higher genetic diversity was less evident, reducing herbivory only at the highest level of herbivore damage. In general, herbivory was lowest in plots with high diversity that included at least some resistant varieties and highest in low diversity plots consisting only of susceptible varieties. Despite this, no significant difference in yield (fruit biomass) was found, indicating that strawberry may be relatively tolerant. Our results demonstrate that combined use of high genetic diversity and resistant varieties can help reduce pest damage and provide a useful tool for sustainable food production. “Resistance mixtures” may be particularly useful for sensitive food crops where susceptible varieties are high yielding that could not be completely replaced by resistant ones.

Food availability sets the stage for incubation behaviour of a female bird and thereby indirectly determines the nest temperature, which in turn affects development and metabolism of avian embryos. Changes in development and metabolism in turn are known to influence offspring's ability to adjust to environmental changes later in life. However, few studies have investigated the role of interspecific differences in incubation behaviour in relation to niche separation between competing sibling species. We studied the effects of habitat quality (in terms of caterpillar availability) on incubation behaviour of two ecologically similar and closely related species, collared and pied flycatchers (Ficedula albicollis and F. hypoleuca), in their hybrid zone on the island of Öland, Sweden. Even though both species prefer caterpillar-rich deciduous forests as nesting sites, collared flycatchers, whose nestlings have higher energetic demands, are able to nest only in deciduous forests, whereas pied flycatchers have more flexible habitat requirements. Overall, higher food availability was associated with increased nest attendance, higher incubation temperature and a lower number of foraging trips across species. In addition, collared flycatchers had more frequent and shorter foraging trips across habitat types, allocated more heat to eggs and therefore maintained higher nest temperatures compared to pied flycatchers. We argue that the higher heat allocation or the need to maintain a higher nest temperature for embryo development may constrain collared flycatchers to focus on relatively more profitable prey. Our results highlight the importance of considering incubation behaviour in the context of understanding species differences in niche use. Significance statement Niche separation plays an important role in mitigating effects of competition between closely related species. Whether species differences in incubation behaviour relate to differences in niche use remains unknown. We compared incubation behaviour of two sympatric flycatcher species that differ in sensitivity to food availability. The competitively more dominant and larger species, the collared flycatcher, whose nestlings are more sensitive to food shortages, made more frequent foraging trips but allocated more heat to eggs, leading to higher nest temperature despite lower nest attendance, compared to pied flycatchers. These interspecific differences may be a result of differences in embryo sensitivity or female physiology and contribute to the niche separation between the species, which in turn can facilitate coexistence.

Our understanding of animal microbiota acquisition and dispersal-mediated variation has rapidly increased. In this study, using the model of host pine-pinewood nematode-vector beetle ( Monochamus sp.) complex, we disentangled the routes of microbial community assembly and transmission mechanisms among these different participants responsible for highly destructive pine wilt disease.