Tyrosine Hydroxylase Is Required for the Larval-Pupal Transformation and Immunity of Plutella xylostella: Potential for Pest Management

Abstract

Plutella xylostella has developed high levels of resistance to many commonly used insecticides. Tyrosine hydroxylase (TH) is essential for insect survival; thus, we evaluated whether TH could be a potential target for controlling P. xylostella. In this study, PxTH was identified; further qPCR analysis showed that PxTH increased its expression during larval pupation and was highly expressed in the head and epidermis of prepupa in P. xylostella. Subsequently, we found a significant decrease in insect pupation and eclosion rates after injection of dsPxTH or a feeding diet supplemented with 3-iodo-tyrosine (3-IT) as a TH inhibitor in P. xylostella. Moreover, this study suggested that PxTH enzyme activity and dopamine concentrations were significantly decreased, agreeing with the blockage of larval-pupal cuticle tanning, with thinner puparium and less melanization after feeding 3-IT. In addition, expression levels of four antimicrobial peptide genes were significantly inhibited after P. xylostella feeding with 3-IT, and injection of Escherichia coli resulted in 73.3% mortality, indicating that PxTH was required for immune responses. In summary, these results confirmed that PxTH was involved in the development and immunity of P. xylostella, suggesting a critical potential novel insecticide target for RNAi-based pest control.

Keywords: Plutella xylostella; cuticle tanning; immune; larval pupation; responses; tyrosine hydroxylase.