Target verification of allyl isothiocyanate on the core subunits of cytochrome c oxidase in Sitophilus zeamais by RNAi

Abstract

Allyl isothiocyanate (AITC) is a volatile organic compound with a potent insecticidal activity to the stored-grain pest Sitophilus zeamais Motschulsky, which severely damages grain storage and container transport worldwide. Our previous study showed that mitochondrial complex IV was the primary target of AITC in adult Sitophilus zeamais. To further verify the targets of AITC, we employed RNA interference (RNAi) by using double-stranded RNA (dsRNA) to knockdown three core subunits of cytochrome c oxidase (COX)-I, -II and -III in 18-day-old larvae prior to their exposure to AITC to detect susceptibility changes. The susceptibility of dsRNACOX-I and -II injection treatments to AITC significantly increased at 72 h while the mortality reached up to 85.56% and 67.78%, respectively, and dsRNACOX-I and dsRNACOX-II injection showed the same subcellular structural characteristics showing vacuolization and vague mitochondrial cristae and decrease of COX activity during AITC fumigation treatment, suggesting the potential of COX-I and COX-II as the targets of AITC. High mortality reached up to 75.55%, 71.88% and 82.22%, respectively, and the phenotype of larvae turning from milky white to dark brown in the thorax and death eventually was confirmed after dsRNACOX-I, -II and -III injection. COX-I and -II were elucidated as the potential targets of AITC and dsRNACOX-I, -II and -III have the potential to be developed into nucleic acid pesticides for their robust lethal effects and are worth pursuing for improving AITC fumigation activity in Sitophilus zeamais control. © 2020 Society of Chemical Industry.