The Inhibition of Serine/Threonine Protein Phosphatase Type 5 Mediates Cantharidin Toxicity to Control Periplaneta americana (L.)

SIMPLE SUMMARY: The American cockroach, Periplaneta americana (L.), is a worldwide common sanitary pest. Controlling cockroaches mainly relies on chemical insecticides. However, the irrational and extensive use of insecticides has resulted in increasing resistance in cockroaches. Therefore, alternative agents are urgently needed. Cantharidin (CTD) is an insect defensive toxin that has a significant toxicity against a broad range of pests. In this study, we evaluated the bioactivity of CTD and its derivative Norcantharidin (NCTD) against P. americana to determine their potential for controlling P. americana. CTD showed a significant ingestion toxicity against P. americana (LC(50) = 50.9 μg/mL). To further explore the reason for the toxicity of CTD against P. americana, we cloned and expressed the serine/threonine protein phosphatase type 5 in P. americana (PaPP5) and performed inhibition assays of CTD and NCTD on serine/threonine protein phosphatases (PSPs) and PaPP5. The inhibition assays demonstrated that both CTD and NCTD had inhibitory effects on PSPs and PaPP5. The inhibitory capacity of CTD was superior to that of NCTD in both the PSPs and PP5 inhibition assays. These findings contribute to our understanding of CTD as a biorational pesticide to control P. americana and provide new insights into insecticide development using PP5 as a target. ABSTRACT: The American cockroach, Periplaneta americana (L.), is a notorious urban pest. It has developed insecticidal resistance to commonly used insecticides. Cantharidin (CTD) is a defensive toxin derived from blister beetles. It has been verified to have insecticidal toxicity in a range of pests. In this study, we determined the ingestion toxicity of CTD and norcantharidin (NCTD) to P. americana to test whether they had the potential to be effective against P. americana. Bioassays revealed that CTD produces toxicity against P. americana. The median lethal concentration (LC(50)) value of CTD was 50.92 μg/mL, while NCTD displayed nearly no toxicity against P. americana. The inhibition assays of serine/threonine protein phosphatases (PSPs) in P. americana indicated that CTD and NCTD could inhibit PSPs. The value of the half maximal inhibitory concentration (IC(50)) of CTD was 7.21 ± 0.94 μM, whereas that of NCTD was higher, at 31.65 ± 3.87 μM. Furthermore, the inhibition effect of CTD on the serine/threonine protein phosphatase type 5 of P. americana (PaPP5) was superior to that of NCTD. Specifically, the IC(50) of CTD reached 0.39 ± 0.04 μM, while the IC(50) of NCTD was 1.87 ± 0.23 μM. This study paves the way for insect-derived agents (CTD) to be applied toward controlling P. americana and contributes to the development of novel insecticides based on PP5 as a target.