Maternal food provisioning in relation to condition-dependent offspring odours in burrower bugs (Sehirus cinctus).

The sensory modalities used for communication among family members have at least partly evolved within an organism's pre-existing sensory context. Given the well-known general importance of chemical communication in insects, we hypothesized in sub-social insects with parental care that chemical signals emitted by larvae to influence parental care (i.e. solicitation pheromones) would have evolved. To test this hypothesis, we performed an experiment in the burrower bug Sehirus cinctus (Hemiptera: Cydnidae) where nymphs were hand-reared under high- or low-food conditions. These hand-reared clutches were used as a source of volatiles. The volatiles were collected for chemical analysis and delivered to caring mothers to quantify their behavioural response. As predicted, mothers exposed to volatiles from nymphs in poor condition provisioned significantly more food than those exposed to air (controls) or volatiles from high-condition nymphs. Chemical analysis revealed that nymphs emitted a blend of eight compounds of which alpha-pinene and camphene showed the strongest relationship with food treatment. Exposure to pure synthetic alpha-pinene and camphene did not affect maternal provisioning, however, suggesting that the functional significance of alpha-pinene and/or camphene may occur in a blend with other compounds. This study shows a clear effect of condition-dependent offspring odours on maternal food provisioning and identifies, for the first time, candidate compounds for a potential chemical offspring begging signal.