Appeasing their hosts: a novel strategy for parasite brood

Brood and social parasites exploit the parental care of their host and often integrate into host colonies using different strategies at different moments during their life cycle. In social wasps, the obligate social parasite Polistes atrimandibularis , using chemical mimicry and chemical insignificance, avoids detection by its host, Polistes biglumis , which has an efficient nestmate recognition system. Enslaved host foundresses accept and care for parasite brood as if it were their own. This observation raises the following question: how exactly do parasite brood escape detection and increase host acceptance? Here, we compared the cuticular chemical signatures of parasite brood and host brood. Their signatures differed in composition: parasite larvae and pupae had particularly high levels of alkenes (notably 9-nonacosene), which were absent in host larvae and pupae. Given this result, we tested the effect of 9-nonacosene on host foundresses, and documented that they reduced their aggression. Our findings address a novel integration strategy for social parasite brood as they suggest that the hydrocarbon serves as an appeasement substance and promotes host tolerance of parasite larvae and pupae, which are chemically disparate from host larvae and pupae.