Chemical conspicuousness, ant organs, and specificity in myrmecophilous caterpillars partitioning ant-plant systems

Resource partitioning among sympatric species is crucial for assembling ecological communities, such as caterpillar-ant assemblages in tropical forests. Myrmecophilous caterpillars use behavioral and chemical strategies to coexist with ants, avoiding attacks. While these strategies are well-understood in single pair of interacting species, such as those involving myrmecophiles and ants, their role in complex multitrophic interactions that include several species of plants, herbivores and ants remains unclear. We aimed to identify the role of cuticular hydrocarbons and specialized morphological structures that caterpillars use to interact with ants (called ant organs) in the recognition process between two riodinid caterpillar species and their respective ant-plant systems. We hypothesized that caterpillars' cuticular profiles would be conspicuous, possessing cues of rewards to ants, allowing specific ants to recognize and not attack them on plants. We performed experiments exposing caterpillars to ants to assess the role of larval ant organs and the specificity of caterpillar-ant interactions on plants. We analyzed cuticular hydrocarbons of caterpillars, ant workers and plants using gas chromatography/mass spectrometry. Our experiments showed that larval ant organs were activated according to each treatment and caterpillars were consistently accepted by their associated ants when transferred to host plants occupied by the same ant species. However, caterpillars transferred to plants with a non-associated ant species that do not tend them were often killed. This highlights the specificity of these interactions. Caterpillar cuticular hydrocarbon profiles, while present in far lower amounts than those of ant workers and plants, were distinctive, suggesting a strategy of chemical conspicuousness that helps caterpillars to be recognized by ants and prevents attacks in specific ant-plant systems. Our results indicate that ants recognize conspicuous cuticular hydrocarbons, while caterpillars convey multimodal signals from ant organs during interactions, which are essential for caterpillar survival in these specific interactions.