Opposing female responses to body and fecal odors of nylon-implanted male Tenebrio molitor

Abstract Terminal investment is a reproductive strategy in which individuals increase reproductive effort when future survival is reduced. Here, we investigated whether male mealworm beetles (Tenebrio molitor) subjected to a standard nylon implantation treatment alter chemical signals used by females during mate choice. Females were offered a simultaneous choice between body odors, fecal odors, or combined body + fecal odors from implanted and control males. We also compared male survival between treatments. Females were more attracted to the body odors of implanted males but less attracted to their fecal odors. When body and fecal odors were presented together, no significant preference was detected. The combination of increased body-odor attractiveness and reduced survival is consistent with, but does not demonstrate, terminal investment, while the contrasting response to fecal odors indicates that the effects of implantation on chemical attractiveness depend strongly on odor source. The findings are compatible with, but do not directly test, the fermentation hypothesis of chemical communication, because the microbial origin of the fecal odors was not determined. More broadly, our results show that body and fecal odors can provide contrasting information during mate assessment, although the present design cannot determine whether the response to combined odors reflects signal integration, odor masking, or another interaction between odor cues.