Specialization is an important attribute of a biological control agent. The maritime pine bast scale, Matsucoccus feytaudi Ducasse (Hemiptera Matsucoccidae), is an invasive species in Southeast ...France and the North of Italy. Iberorhyzobius rondensis Eizaguirre (Coleoptera: Coccinellidae), is a recently described ladybird species. Both adults and larvae are predaceous, feeding on egg masses of M. feytaudi, and are strongly attracted to M. feytaudi’s sex pheromone. To evaluate the potential of I. rondensis as a biocontrol agent of the scale, we studied its niche breadth and prey range with emphasis on pine forests and hemipterans as tested prey. In this study, I. rondensis was found to achieve complete development only when fed on M. feytaudi egg masses (92.9% survival) and an artificial prey: eggs of Ephestia kuehniella Zeller (27.6% survival). From the 2nd instar onwards, complete development could be achieved using other prey species, although larvae had significantly higher mortality and slower development. In choice tests, M. feytaudi was the preferred prey. Surveys of the ladybird populations in the Iberian Peninsula revealed that it was found exclusively on Pinus pinaster Aiton, the sole host of M. feytaudi. The unusual specialization of I. rondensis, among other predaceous ladybirds, makes it an appropriate candidate for classical biological control of M. feytaudi.
Aim
Climate is a major driver of large‐scale variability in biodiversity, as a likely result of more intense biotic interactions under warmer conditions. This idea fuelled decades of research on ...plant‐herbivore interactions, but much less is known about higher‐level trophic interactions. We addressed this research gap by characterizing both bird diversity and avian predation along a climatic gradient at the European scale.
Location
Europe.
Taxon
Insectivorous birds and pedunculate oaks.
Methods
We deployed plasticine caterpillars in 138 oak trees in 47 sites along a 19° latitudinal gradient in Europe to quantify bird insectivory through predation attempts. In addition, we used passive acoustic monitoring to (i) characterize the acoustic diversity of surrounding soundscapes; (ii) approximate bird abundance and activity through passive acoustic recordings; and (iii) infer both taxonomic and functional diversity of insectivorous birds from recordings.
Results
The functional diversity of insectivorous birds increased with warmer climates. Bird predation increased with forest cover and bird acoustic activity but decreased with mean annual temperature and functional richness of insectivorous birds. Contrary to our predictions, climatic clines in bird predation attempts were not directly mediated by changes in insectivorous bird diversity or acoustic activity, but climate and habitat still had independent effects on predation attempts.
Main Conclusions
Our study supports the hypothesis of an increase in the diversity of insectivorous birds towards warmer climates but refutes the idea that an increase in diversity would lead to more predation and advocates for better accounting for activity and abundance of insectivorous birds when studying the large‐scale variation in insect‐tree interactions.
Résumé
Objectif
Le climat est l'un des principaux facteur structurant de la variabilité à grande échelle de la biodiversité, possiblement en raison d'interactions biotiques plus intenses dans des conditions de température plus élevées. Cette idée a alimenté des décennies de recherche sur les interactions plantes‐herbivores, mais on en sait beaucoup moins sur les interactions impliquant les niveaux trophiques supérieurs. Nous avons comblé cette lacune en caractérisant à la fois la diversité des oiseaux et leur activité de prédation le long d'un gradient climatique à l'échelle européenne.
Localisation
Europe.
Taxon
Oiseaux insectivores et chênes pédonculés.
Méthodes
Nous avons déployé des leurres en pâte à modeler mimant des chenilles sur 138 chênes dans 47 sites le long d'un gradient latitudinal de 19° en Europe pour quantifier l'insectivorie avienne par le biais de tentatives de prédation. De plus, nous avons utilisé la surveillance acoustique passive pour (i) caractériser la diversité acoustique des paysages sonores environnants; (ii) estimer l'abondance et l'activité des oiseaux à travers des enregistrements acoustiques passifs et (iii) déduire à la fois la diversité taxonomique et fonctionnelle des oiseaux insectivores à partir des enregistrements.
Résultats
Nous avons montré une augmentation de la diversité fonctionnelle des oiseaux insectivores avec la température moyenne. La prédation avienne augmentait avec la couverture forestière et l'activité acoustique des oiseaux, mais diminuait avec la température annuelle moyenne et la richesse fonctionnelle des oiseaux insectivores. Contrairement à nos prédictions, la variation de la diversité des oiseaux n'était pas le lien mécaniste entre le climat et la variation des tentatives de prédation sur les leurres, laquelle était directement influencée par le climat et la couverture forestière.
Conclusions Principales
Notre étude confirme l'hypothèse d'une augmentation de la diversité des oiseaux insectivores vers des climats plus chauds, mais ne corrobore pas l'idée qu'une augmentation de la diversité conduirait à davantage de predation. Elle plaide en faveur d'une meilleure prise en compte de l'activité et de l'abondance des oiseaux insectivores lors de l'étude de la variation à grande échelle des interactions entre insectes et arbres.
CONTEXT: In heterogeneous landscapes, habitat complementation is a key process underlying the distribution of mobile species able to exploit non-substitutable resources over large home ranges. For ...instance, insectivorous bats need to forage in a diversity of habitat patches offering varied compositions and structures within forest landscape mosaics to fulfill their life cycle requirements. OBJECTIVES: We aimed at analyzing the effects of forest structure and composition measured at the stand and landscape scales on bat species richness, abundance and community composition in pine plantation forests of south-western France. METHODS: We sampled bat communities at different periods of the summer season using automatic ultrasound recorders along a tree composition gradient from pine monocultures to pure oak stands. We analyzed bat species activity (as a proxy for bat abundance) and species richness with linear mixed models. Distance-based constrained ordinations were used to partition the spatio-temporal variation in bat communities. RESULTS: Deciduous tree cover increased bat activity and modified community composition at both stand and landscape scales. Changes in bat communities were mostly driven by landscape-scale variables while bat activity responded more to stand-scale predictors. CONCLUSIONS: The maintenance of deciduous trees at both stand and landscape scales is likely critical for bat communities living in fast-growing conifer plantations, by increasing the availability and diversity of prey and roosting sites. Our study suggests that bats respond to forest composition at both stand and landscape scales in mosaic plantation landscapes, mainly through a resource complementation process.
Bark beetles are notorious pests of natural and planted forests causing extensive damage. These insects depend on dead or weakened trees but can switch to healthy trees during an outbreak as ...mass-attacks allow the beetle to overwhelm tree defences. Climatic events like windstorms are known to favour bark beetle outbreaks because they create a large number of breeding sites, i.e., weakened trees and for this reason, windthrown timber is generally preventively harvested and removed. In December 1999, the southwest of France was struck by a devastating windstorm that felled more that 27
million
m
3of timber. This event offered the opportunity to study large-scale spatial pattern of trees attacked by the bark beetle
Ips sexdentatus and its relationship with the spatial location of pine logs that were temporally stored in piles along stand edges during the post-storm process of fallen tree removal. The study was undertaken in a pure maritime pine forest of 1300
ha in 2001 and 2002. We developed a landscape approach based on a GIS and a complete inventory of attacked trees. During this study more than 70% of the investigated stands had at least one tree attacked by
I. sexdentatus. Spatial aggregation prevailed in stands with
n
≥
15
attacked trees. Patches of attacked trees were identified using a kernel estimation procedure coupled with randomization tests. Attacked trees formed patches of 500–700
m
2 on average which displayed a clumped spatial distribution. Log piles stemming from the sanitation removals were mainly distributed along the large access roads and showed an aggregated spatial pattern as well. The spatial relationship between patches of attacked trees and log pile storage areas was analyzed by means of the Ripley’s statistic that revealed a strong association at the scale of the studied forest. Our results indicated that bark beetle attacks were facilitated in the vicinity of areas where pine logs were stored. The spatial extent of this relationship was >1000
m. Similar results were obtained in 2001 and 2002 despite differences in the number and spatial distribution of attacked trees. The presence of a strong “facilitation effect” suggests that log piles should be removed quickly in order to prevent outbreaks of bark beetles.
Context
Anthropogenic activities readily result in the fragmentation of habitats such that species persistence increasingly depends on their ability to disperse. However, landscape features that ...enhance or limit individual dispersal are often poorly understood. Landscape genetics has recently provided innovative solutions to evaluate landscape resistance to dispersal.
Objectives
We studied the dispersal of the common meadow brown butterfly,
Maniola jurtina
, in agricultural landscapes, using a replicated study design and rigorous statistical analyses. Based on existing behavioral and life history research, we hypothesized that the meadow brown would preferentially disperse through its preferred grassy habitats (meadows and road verges) and avoid dispersing through woodlands and the agricultural matrix.
Methods
Samples were collected in 18 study landscapes of 5 × 5 km in three contrasting agricultural French regions. Using circuit theory, least cost path and transect-based methods, we analyzed the effect of the landscape on gene flow separately for each sex.
Results
Analysis of 1681 samples with 6 microsatellites loci revealed that landscape features weakly influence meadow brown butterfly gene flow. Gene flow in both sexes appeared to be weakly limited by forests and arable lands, whereas grasslands and grassy linear elements (road verges) were more likely to enhance gene flow.
Conclusion
Our results are consistent with the hypothesis of greater dispersal through landscape elements that are most similar to suitable habitat. Our spatially replicated landscape genetics study allowed us to detect subtle landscape effects on butterfly gene flow, and these findings were reinforced by consistent results across analytical methods.
Conspecific insect herbivores co-occurring on the same host plant interact both directly through interference competition and indirectly through exploitative competition, plant-mediated interactions ...and enemy-mediated interactions. However, the situation is less clear when the interactions between conspecific insect herbivores are separated in time within the same growing season, as it is the case for multivoltine species. We hypothesized that early season herbivory would result in reduced egg laying and reduced performance of the next generation of herbivores on previously attacked plants. We tested this hypothesis in a choice experiment with box tree moth females (Cydalima perspectalis Walker, Lepidoptera: Crambidae). These females were exposed to box trees (Buxus sempervirens L., Buxaceae) that were either undamaged or attacked by conspecific larvae earlier in the season. We then compared the performance of the next generation larvae on previously damaged vs undamaged plants. Previous herbivory had no effect on oviposition behaviour, but the weight of next generation larvae was significantly lower in previously damaged plants. There was a negative correlation between the number of egg clutches laid on plants by the first generation and the performance of the next generation larvae. Overall, our findings reveal that early season herbivory reduces the performance of conspecific individuals on the same host plant later in the growing season, and that this time-lagged intraspecific competition results from a mismatch between the oviposition preference of females and the performance of its offspring.
•Butterfly diversity was driven by forest quality, not by fragmentation.•Forest butterfly richness was higher in riparian forests than in isolated fragments.•Riparian forests host more specialized ...butterfly species than deciduous fragments.
The effects of forest fragmentation on biodiversity can be partitioned into habitat loss and increased isolation of habitat fragments. Habitat quality may however prevail over the effects of fragment area and isolation, especially for mobile animals such as butterflies. To test this hypothesis we surveyed butterfly communities in 36 deciduous forest fragments embedded in a conifer plantation matrix, along two orthogonal gradients of fragment area and isolation. We also sampled eight deciduous riparian forests to compare the complete pool of forest butterflies, expected to be found in riparian forests, to the composition of deciduous fragments. We quantified the effects of deciduous woodland area, isolation and quality on total and forest butterfly richness, community composition and several Community-Weighted Mean traits known to mediate butterfly responses to habitat fragmentation. For the 36 fragments, forest butterfly richness and community composition were not affected by fragment area or isolation but by habitat quality, especially host-plant composition. Riparian forests had higher forest butterfly richness and hosted more habitat specialists, with higher sensitivity to temperature extremes, than deciduous forest remnants. We thus provide new evidence that habitat quality can prevail over fragment area and isolation in shaping the composition of butterfly communities in mosaic landscapes.
Edge effects are increasing in forest-dominated landscapes worldwide, due to increased fragmentation by other land uses. Understanding how species respond to edges is therefore critical to define ...adequate conservation measures. We compared the relative importance of interior and edge habitats for butterflies in a landscape composed of even-aged pine plantations interspersed with semi-natural habitats. Butterfly assemblages were surveyed simultaneously at the edge and the interior of 68 patches belonging to four main habitat types: herbaceous firebreaks, clearcuts and young pine stands, older pine stands, and deciduous woodlands. Butterfly species richness was higher at edges than in interior habitats, especially for pine stands. Assemblage composition differed significantly between edge and interior habitats, except for firebreaks. Of the 23 most abundant butterfly species, seven were significantly more abundant in one or all edge habitat types, five in interior habitats, and 11 species showed no edge-interior preference. Modelling the presence of individual species in edge habitats revealed the importance of habitat variables such as the abundance of nectar and host-plants, but also of the abundance of the same species in the adjacent interior habitat. Moreover, our results suggest that most species use several, different habitat types to find supplementary or complementary resources, including micro-climatic refuges to escape hot temperatures during summer. The use of adjacent edge and interior habitats by butterflies is probably a key process in such mosaic landscapes and underlines the importance of landscape heterogeneity for butterfly conservation.
During the last decades, an increasing number of predators were found to use specific prey pheromones as chemical cues. Beyond its ecological relevance, this knowledge has practical applications on ...insect conservation and pest control. In this study, we present first evidence that two species of the family Dasytidae (Coleoptera) Aplocnemus brevis Rosenhauer and A. raymondi Sainte-Claire Deville use the sex pheromone of the pine bast scale Matsucoccus feytaudi Ducasse (Hemiptera: Matsucoccidae) as kairomone to locate this prey. The feeding habits and biology of Aplocnemus species are practically unknown. In the laboratory, the adults of Aplocnemus sp. accepted M. feytaudi egg masses as food source as well as other diets. Females represented more than 90% of Aplocnemus sp. attracted to the pheromone lures. We believe that females use this olfactory cue to locate suitable places for oviposition and that larvae are the predators of Matsucoccus. This study further demonstrates that the response to the kairomone elicited short prey searching times, about 23% of the individuals appeared less than 12 min after lure exposure, being consistent with the hypothesis of prey specialization. Habitat and geographical distribution predict an ancestral association of A. brevis with M. feytaudi and of A. raymondi with M. pini. Nevertheless, a recent prey shift of A. raymondi to the invasive M. feytaudi in Corsica is in progress.
Bark beetle infestations are often scattered throughout the forest landscape and therefore difficult to accurately and rapidly assess. We tested a roadside sampling technique in a pure maritime pine ...forest (
Pinus pinaster) of ca. 1300
ha where bark beetle outbreak foci were observed following a windstorm. The sampling method relied on the count along stand edges of all dying or dead trees sighted within a fixed distance from the road. About 2300 trees attacked by
Ips sexdentatus were recorded and located using colour-infrared aerial photography. Accuracy of the infestation map was verified by ground sampling. Piles of cut logs stored along the edge significantly increased the percentage of attacked trees in the neighbouring stand. However, the percentage of attacked trees within the stand edges did not differ with the percentage within the stand interior. It allowed us to use stand edges as sampling units to estimate the mean percentage of attacked trees per stand. At the stand scale, the use of a fixed 10
m wide strip along stand edges maximized the detection of attacked trees and minimized the bias of estimated percent of attacked trees. Based on GIS data, various stratified roadside sampling plans with increasing numbers of edges per stand and increasing numbers of stands per forest were simulated by bootstrap resampling. In a forest without any storage of cut logs, systematic roadside surveys underestimated the level of damage. The sampling accuracy increased with the kilometers of edges surveyed. In a forest with piles of cut logs on which bark beetles can breed, the best option was an adaptive sampling plan where at least two additional consecutive edges were observed in stands close to the pile. As compared to systematic sampling plans, adaptive plans were three times less expensive in terms of sampling effort for the same accuracy. Overall, adaptive sampling plans were also more robust as they provided less biased estimates as the proportion of stands with nearby piles increased in simulated forests.
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