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

Capture d_écran 2017-05-11 à 16.19.26

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)

Arthropod symbioses: a neglected parameter in pest- and disease-control programmes

1. Arthropods are important players in biological control as pests, control agents and transmitters of invertebrate diseases. Arthropods are frequently infected with one or several micro-organisms, serving as micro-ecosystems in which multiple interactions can take place. These micro-organisms include disease agents and symbiotic micro-organisms. The latter are usually vertically transmitted and can have a broad spectrum of effects on their hosts, ranging from reproductive manipulations to protection against natural enemies. These interactions may directly or indirectly alter the biology of many arthropods in agriculturally, medically and ecologically relevant ecosystems.

2. Symbiotic micro-organism-induced reproductive manipulations such as cytoplasmic incompatibility and parthenogenesis induction can substantially affect the rearing of biological control agents. Many insects, and recently also mites and nematodes, have been found to be infected, displaying a wide range of effects. We discuss examples of arthropod-micro-organism interactions and effects,
which could have consequences for the practical application of arthropods in biological control.

3. Symbiotic micro-organisms can also be involved in host protection against natural enemies such as parasitoids, pathogenic bacteria, fungi and viruses.

4. Symbiotic bacteria can influence the vectorial capacity of disease-vectoring arthropods and may be very helpful in decreasing the transmission of disease agents.

5. Synthesis and applications. The effect of micro-organisms on the outcome of biological control programmes is usually not considered in risk assessments and failure analyses. This review emphasizes
the importance of endosymbiotic micro-organisms in comprehensive biological control programmes and provides recommendations on how to recognize, avoid or benefit from these influential tenants.

Zindel R, Gottlieb Y, Aebi A. (2011) Arthropod symbiosis, a neglected parameter in pest and disease control programs. Journal of Applied Ecology DOI: 10.1111/j.1365-2664.2011.01984.x