Immune Stimulation via Wounding Alters Chemical Profiles of Adult Tribolium castaneum

Group-living individuals experience immerse risk of disease transmission and parasite infection. Especially in social, but also in some non-social insects, disease control with immunomodulation takes place not only via individual immune defenses, but also via infochemicals such as contact cues and (defensive) volatiles to mount a group level immunity. However, little is known about whether an activation of the immune system leads to changes in chemical phenotypes, which may mediate these responses. We here asked whether individual immune experience resulting from wounding or injection of heat-killed Bacillus thuringiensis leads to changes in the chemical profiles of female and male adult red flour beetles (Tribolium castaneum), which are non-social but gregarious. We analyzed insect extracts using GC-FID to study the chemical composition of (1) cuticular hydrocarbons (CHCs) as candidates for the transfer of immunity-related information between individuals via contact, and (2) stink gland secretions, with target analysis of benzoquinones as main active compounds regulating external immunity. Despite a pronounced sexual dimorphism in CHC profiles, wounding stimulation led to similar profile changes in males and females with increases in the proportion of methyl-branched alkanes compared to naive beetles. While changes in the overall secretion profiles were less pronounced, absolute amounts of benzoquinones were transiently elevated in wounded compared to naive females. We suggest that the changes in different infochemicals may mediate immune status signaling in the context of both internal and external immune responses in groups of this non-social insect, thus showing parallels to social immunity.