Tachykinin-related peptide signalling is important for the immune response of the mealworm beetle Tenebrio molitor L.

Insects possess a well-developed innate immune system, which encompasses both cellular and humoral mechanisms. On the basis of the similarities in neuropeptide actions between insects and vertebrates, we assume that neuropeptides such as tachykinin-related peptides (TRPs) regulate insect immune responses and are themselves modulated following infection. In this study, we examined how immune activation affects the expression of genes encoding TRP precursors and receptors (TRP and TRPR) and whether TRPs directly modulates selected immune mechanisms in the pest species Tenebrio molitor. Our results revealed two important insights. First, after activation of the immune system, TRP and TRPR genes were significantly downregulated in the nervous system and immune-related cells. These changes are closely correlated with the changes of the expression level of immune genes. We then show using Spantide II, a potent antagonist of TRPR, and RNAi knock-down of TRP and TRPR the modulation of key processes of the T. molitor humoral response. This includes the over-expression of genes encoding antimicrobial peptides and the important arthropod immune effector phenoloxidase activity. Our findings highlight a compelling association between the TRP and immune regulation in Tenebrio and provide insights into the hormonal regulation of physiological processes in insects. Our research also provides novel insights that can contribute to the development of sustainable pest control strategies amid increasing insecticide resistance.