Host immune activation is common under a pathogen invasion. This physiological response can promote changes in the body surface compounds, thus providing chemical cues related to health that might be useful to conspecifics. By recognizing the current immunological status of social partners, individuals can modulate their behavior to minimize the risk of infection. Tegument wounding, an immune elicitor, is a required step for many parasites to become established in a host. By using the neotropical eusocial paper wasp Mischocyttarus metathoracicus as a model organism, we first performed a lure presentation experiment in the field to test if wasps discriminate conspecific immunological status (experimentally manipulated by wounding) during on nest social interactions. Then, we performed gas chromatography–mass spectrometry analyses to test if immunostimulation by wounding alters the wasps’ cuticular hydrocarbon profile. We found that wasps reduce the duration of aggressive physical contact when interacting with wounded lures, despite displaying a similar frequency of inspective and aggressive behaviors toward both the wounded and the control lures. Besides, we found a subtle increase in a single cuticular hydrocarbon in the wounded wasps. Thus, wasps recognize conspecific immunological status, likely by chemical cues, and modulate their behavior in order to defend the colony against intruders while minimizing the personal risk of infection.

Microplastics (MPs) are widespread pollutants of emerging concern, and the risks associated with their ingestion have been reported in many organisms. Terrestrial environments can be contaminated with MPs, and terrestrial organisms, including arthropods, are predisposed to the risk of ingesting MPs. In the current study, the larvae of the paper wasp Polistes satan were fed two different doses (6 mg or 16 mg at once) of polystyrene MPs (1.43 mm maximum length), and the effects of these treatments on immature development and survival till adult emergence were studied. Ingestion of the two doses resulted in mortality due to impaired defecation prior to pupation. The survival of larvae that ingested 16 mg of MPs was significantly lower than that of the control. The ingestion of 16 mg of MPs also reduced the adult emergence (11.4%) in comparison to the control (44.4%). MPs were not transferred from the larvae to the adults that survived. These findings demonstrate that MP ingestion can be detrimental to P. satan, e.g. larval mortality can decrease colony productivity and thus the worker force, and that MPs can potentially affect natural enemies that occur in crops, such as predatory social wasps.

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Spermatozoa vary in quantity, quality and design across species and individuals. Here, we reported the first detailed analysis of sperm traits in two primitively eusocial paper wasps, Polistes dominula and Polistes gallicus, which differ in their nuptial strategies and body size as follows: lek-territoriality of the large P. dominula males, defending exclusive territories at landmarks; scramble competition of the small P. gallicus, where serial mating may occur because males interfere with rivals and replace them during copulation. We compared the number, viability, and length of sperm, and its coefficient of variation, between these sympatric paper wasps patrolling and marking the same landmarks during the same summer: a good opportunity to analyse sperm across species while controlling for environmental variables. Spermatozoa were more numerous and longer in P. dominula than in P. gallicus males. Viability was similar in both species and positively covaried with male body size. Intra-male variation in sperm length was significantly reduced in P. gallicus, as predicted in the case of selection for an optimal sperm design. We hypothesized that precopulatory sexual selection (lek-territoriality vs. scramble competition) may affect sperm traits.