The role of predator-prey naïveté for the invasion success of lady beetles - A comparison of species interactions across two continents

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Invasive species pose a major threat to global biodiversity. Despite the growing scientific literature on detrimental effects of invasive species, we often lack a mechanistic understanding why some species become invasive while others remain benign. Insect predators, in particular, represent a significant portion of the non-native fauna. Possibly, invasive predators might remain undetected by native top-predators and thus suffer less intraguild interference (naïve predator hypothesis). In addition, invasive predators might benefit from the lack of predator avoidance by native prey (naïve prey hypothesis). The ability to recognize non-native predators and consequently the strength of intraguild interference and predator avoidance is expected to depend on cue similarity with native predators. Non-native predators bearing a unique set of cues might have the double advantage of naïve prey and naïve predators and thus outcompete native predators.Lady beetles have been intentionally redistributed across continents as biocontrol agents against aphids, with one species being invasive in two continents. Some aphid species are protected by ants, while others have evolved a characteristic antipredator behavior against lady beetles (e.g. dropping from plants). Due to the strong trophic interdependence and the availability of similar (congeneric species in the invaded range) and novel (no congeneric species in the invaded range) non-native lady beetle species, the ant-lady beetle-aphid system is particularly well suited to test for predator-prey naïveté. Here, we will compare the aggression of ants towards lady beetles, the avoidance behavior of aphids, and the consumption of aphids by lady beetles currently occurring in Europe and in North America. The comparison of interactions with European lady beetles in their native and in the invaded range will reveal whether differences in these interactions contribute to the invasion success. In addition, we will analyze lady beetle cues to quantify cue similarity between native and non-native species. The combination of behavioral experiments with chemical analyses enables us to test the predator-prey naïveté hypothesis.The intercontinental approach is crucial to evaluate the importance of predator-prey naiveté for the invasion success of a non-native species. The proposed project will further contribute to a general mechanistic understanding of biological invasions by relating species interactions to the cue similarity between native and non-native species. This joint approach will not only shed light on the semiochemicals that mediate these interactions but also improve our ability to explain and predict high-impact invasions of insect predators.