Silencing Chitinase Genes Increases Susceptibility of<i>Tetranychus cinnabarinus</i>(Boisduval) to Scopoletin

Abstract

The carmine spider mite Tetranychus cinnabarinus is a major pest of crop and vegetable plants worldwide. Previous studies have shown that scopoletin is a promising acaricidal compound against Tetranychus cinnabarinus. However, the acaricidal mechanism of scopoletin remains unclear. In the present study, 12 full-length cDNAs of chitinase (CHIT) genes from Tetranychus cinnabarinus (designated TcCHITs ) were cloned and characterized. Although TcCHITs were expressed throughout all life stages, their expression levels were significantly upregulated during the larval and nymphal stages. TcCHITs were downregulated 24 h after treatment with scopoletin and upregulated 24 h after treatment with diflubenzuron (DFB, a chitin synthesis inhibitor). Feeding double-stranded RNA effectively silenced TcCHIT transcription in Tetranychus cinnabarinus , thus increasing its susceptibility to scopoletin but reducing that to DFB. Meanwhile, TcCHIT silencing in larvae and adult resulted in an extremely low molting rate (7.3%) and high mortality rate (53.3%), respectively, compared with those in the control group. CHIT genes are closely related to arthropod survival, molting, and development in Tetranychus cinnabarinus , suggesting that acaricidal mechanisms of scopoletin and DFB may occur by inhibition and activation of CHIT gene expression, respectively. TcCHIT constitutes a possible target of scopoletin and DFB in Tetranychus cinnabarinus .