A sublethal imidacloprid concentration alters foraging and competition behaviour of ants
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Neonicotinoid pesticides, such as the widely used compound imidacloprid, are suspected to impair cognitive capacity, behaviour, and fitness of a number of non-target species. We tested whether sublethal imidacloprid concentrations alter the foraging and aggression behaviour of two European ant species. Even though the nestmate-recruitment of Lasius niger was not affected by pesticide exposure, these ants required more time to become active and the number of foraging workers was lower than in sub-colonies not exposed to imidacloprid. In interspecific confrontations, imidacloprid increased the aggressiveness of a usually subordinate species (Lasius flavus) enormously (3.7-fold increase in average number of aggressive encounters), whereas they did not affect a subdominant species (L. niger) that severely (1.2-fold increase in average number of aggressive encounters). The high frequency of aggressive encounters of L. flavus vs. non-exposed L. niger workers, reduced their survival probability significantly down to 60 %. The observed behavioural alterations of the two ant species have the potential to impair their viability and co-occurrence with behaviourally dominate species due to a decreased exploitative competition and a reduced chance to locate and use resources before competitors. As competition is considered key in structuring ant communities, changes in aggressiveness are likely to alter established dominance hierarchies and thereby the dynamic and structure of ant communities.
KeywordsNeonicotinoid Neurotoxicity Interspecific confrontation Non-target species Sublethal effects
Analysis of variance
Standard error of log
Cox proportional hazard regression model
Degrees of freedom
Generalized linear model
Linear mixed model
No active ingredient
Standard error of the mean
We thank Bernhard Seifert, Museum of Natural History Senckenberg, for the determination of the ant species. We are also grateful to Katharina Peschke for helpful comments on the manuscript and to Patrick Schulz, Marc Bilton, Simon Schwarz (all Tübingen University), and Margit Einsiedler (Augsburg University) for their support during various stages of this work.
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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