Plant ants use resistance-related plant odours to assess host quality before colony founding

1. Establishing a horizontally transmitted mutualism is a critical step for many organisms, particularly when an individual can engage with only one partner over its lifetime. Ant foundresses shed their wings before they start to lay eggs, which makes host choice particularly critical for plant-ants that exclusively colonize myrmecophytes. 2. Volatile organic compounds (VOCs) can indicate the identity and physiological condition of an individual and frequently serve as signals or cues that facilitate partner choice. Thus, we hypothesised that obligate plant-ants use VOCs to determine the quality of potential host plants. 3. Indeed, winged females of the plant-ant, Pseudomyrmex ferrugineus, used plant odours to identify high-quality acacia hosts among different species and among individuals of the same species. The VOC blend of a branch was related to reward production and, interestingly, the least attractive blend contained the highest number of compounds. 4. Whereas only seven diff...