Potential for exploitative competition, not intraguild predation, between invasive harlequin ladybirds and flowerbugs in urban parks

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Abstract In aphidophagous insect communities invaded by the harlequin ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae), intraguild predation (IGP) is widely implicated in the displacement of native predators, however, indirect trophic interactions are rarely assessed. Using molecular gut-content analysis, we investigated the relative frequencies of IGP by H. axyridis on the predatory flower bug Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) and prey overlap for a shared prey, the lime aphid Eucallipterus tiliae L. (Hemiptera: Aphididae), in Tilia 9 europaea crowns in urban parks. The frequency of IGP by H. axyridis was low: 2.7 % of larvae and 3.4 % of adults tested positive for A. nemoralis DNA. The presence of lime aphid DNA in predators was higher: 56.5 and 47.9 % of H. axyridis larvae and adults, respectively, contained E. tiliae DNA, whereas 60.8 % of adult A. nemoralis tested positive for aphid DNA. Incorporating insect densities revealed that the density of H. axyridis larvae had a strong negative effect on the likelihood of detecting aphid DNA in A. nemoralis. Prey overlap for E. tiliae was widespread in space (2–13 m height in tree crowns) and time (May–October 2011) which suggests that interspecific exploitative competition, mediated by predator life-stage, more so than IGP, is an important indirect trophic interaction between cooccurring H. axyridis and A. nemoralis. Whether exploitative competition equates to displacement of A. nemoralis populations requires further investigation. Our results emphasize the need to incorporate indirect interactions in studies of insect communities following invasion, not least because they potentially affect more species than direct interactions alone.

Keywords: Indirect effects, Molecular gut content, Anthocoris nemoralis, Harmonia axyridisEucallipterus tiliae, Predator–prey interactions

Howe AG, Ravn HP, Bressen Pipper C and Aebi A (2016) Potential for exploitative competition, not intraguild predation, between invasive harlequin ladybirds and flowerbugs in urban parks. Biological Invasions 18:517-532 (doi:10.1007/s10530-015-1024-y)

Pister la pyrale: un projet de sciences citoyennes

La pyrale du buis fait des ravages dans les jardins privés et publics de la ville de Neuchâtel. Un groupe interdisciplinaire de chercheurs collabore avec des citoyens pour suivre sa trace et pour réfléchir à des solutions innovantes à ce problème.

Pour en savoir plus, visiter la page du projet.

Chenille de pyrale du buis. Photo: A. Aebi

Chenille de pyrale du buis.
Photo: A. Aebi

Quarantine arthropod invasions in Europe: the role of climate, hosts and propagule pressure

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Aim To quantify the relative importance of propagule pressure, climatematching and host availability for the invasion of agricultural pest arthropods in Europe and to forecast newly emerging pest species and European areas with the highest risk of arthropod invasion under current climate and a future climate scenario (A1F1).

Location Europe.

Methods We quantified propagule pressure, climate-matching and host availability by aggregating large global databases for trade, European arthropod interceptions, KoeppenGeiger world climate classification (including the A1F1 climate change scenario until 2100) and host plant distributions for 118 quarantine arthropod species.

Results As expected, all the three factors, propagule pressure, climate suitability and host availability, significantly explained quarantine arthropod invasions in Europe, but the propagule pressure only had a positive effect on invasion success when considered together with climate suitability and host availability. Climate change according to the A1F1 scenario generally increased the climate suitability of north-eastern European countries and reduced the climate suitability of central European countries for pest arthropod invasions.

Main conclusions To our knowledge, this is the first demonstration that propagule pressure interacts with other factors to drive invasions and is not alone sufficient to explain arthropod establishment patterns. European countries with more suitable climate and large agricultural areas of suitable host plants for pest arthropods should thus be more vigilant about introduction pathways. Moreover, efforts to reduce the propagule pressure, such as preventing pests from entering pathways and strengthening border controls, will become more important in north-eastern Europe in the future as the climate becomes more favourable to arthropod invasions.

PDF available here

Outreach (clic on the images!)

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Distribution of Endosymbiotic Reproductive Manipulators Reflects Invasion Process and Not Reproductive System Polymorphism in the Little Fire Ant Wasmannia auropunctata

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Endosymbiotic reproductive manipulators may have drastic effects on the ecological and evolutionary dynamics of their hosts. The prevalence of these endosymbionts reflects both their ability to manipulate their hosts and the history of the host populations. The little fire ant Wasmannia auropunctata displays a polymorphism in both its reproductive system (sexual versus clonal populations) and the invasive status of its populations (associated to a habitat shift). We first screened for the presence of a diverse array of reproductive parasites in sexual and clonal populations of W. auropunctata, as a means to investigate the role of endosymbionts in reproductive phenotypes. Wolbachia was the only symbiont found and we then focused on its worldwide distribution and diversity in natural populations of W. auropunctata. Using a multilocus scheme, we further characterized the Wolbachia strains present in these populations. We found that almost all the native sexual populations and only a few clonal populations are infected by Wolbachia. The presence of similar Wolbachia strains in both sexual and clonal populations indicates that they are probably not the cause of the reproductive system polymorphism. The observed pattern seems rather associated to the invasion process of W. auropunctata. In particular, the observed loss of Wolbachia in clonal populations, that recurrently emerged from sexual populations, likely resulted from natural heat treatment and/or relaxed selection during the shift in habitat associated to the invasion process. PDF

Gaps in Border Controls Are Related to Quarantine Alien Insect Invasions in Europe

Alien insects are increasingly being dispersed around the world through international trade, causing a multitude of negative environmental impacts and billions of dollars in economic losses annually. Border controls form the last line of defense against invasions, whereby inspectors aim to intercept and stop consignments that are contaminated with harmful alien insects. In Europe, member states depend on one another to prevent insect introductions by operating a first point of entry rule – controlling goods only when they initially enter the continent. However, ensuring consistency between border control points is difficult because there exists no optimal inspection strategy. For the first time, we developed a method to quantify the volume of agricultural trade that should be inspected for quarantine insects at border control points in Europe, based on global agricultural trade of over 100 million distinct origin-commodity-species-destination pathways. This metric was then used to evaluate the performance of existing border controls, as measured by border interception results in Europe between 2003 and 2007. Alarmingly, we found significant gaps between the trade pathways that should be inspected and actual number of interceptions. Moreover, many of the most likely introduction pathways yielded none or very few insect interceptions, because regular interceptions are only made on only a narrow range of pathways. European countries with gaps in border controls have been invaded by higher numbers of quarantine alien insect species, indicating the importance of proper inspections to prevent insect invasions. Equipped with an optimal inspection strategy based on the underlying risks of trade, authorities globally will be able to implement more effective and consistent border controls.

Bacon SJ, Bacher S, Aebi A (2012) Gaps in Border Controls Are Related to Quarantine Alien Insect Invasions in Europe. PLoS ONE 7(10): e47689. doi:10.1371/journal.pone.0047689  PDF

“Voyage, voyage” un article d’Atlant Bieri paru dans Vivai


Des mouvements de quelques millimètres de certaines amibes aux mouvements spatio-temporels d’un palmier dattier… en passant par les transports involontaires d’insectes à travers le monde. Un article sur la mobilité écrit par Atlant Bieri, paru dans le magazine Vivai de Septembre 2012.

En français PDF

En allemand PDF

En italien PDF