Compromised minds: cognitive decline in a social insect correlates with parasitism status.

Parasites can influence host physiology and behavior, often impairing cognition. We investigated how infection and parasite load affect olfactory learning and memory in the paper wasp Polistes dominula workers parasitized by the insect parasite Xenos vesparum (Strepsiptera). We adapted a Pavlovian conditioning assay based on the proboscis extension reflex protocol. We tested three groups: unparasitized workers, singly parasitized workers, and superparasitized workers. Wasps were conditioned to associate a floral odorant with sucrose and later assessed in a memory assay. Unparasitized workers outperformed superparasitized workers in both assays, while single parasitized individuals showed intermediate performance. Superparasitized workers were less responsive during the conditioning and exhibited greater generalization during the memory test. Our results revealed that not only parasitization, but also parasite load correlates negatively with host cognition. These findings highlight the cognitive costs of parasitism in social insects and align with previously observed behavioral patterns in this complex host-parasite system.