<i>Tyrosine\nHydroxylase</i> Is Required\nfor the Larval–Pupal Transformation and Immunity of Plutella xylostella: Potential for Pest Management

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