Three cytochrome P450s in Laodelphax striatellus metabolize imidacloprid and nitenpyram through different catalytic reactions.

Nilaparvata lugens (brown planthopper, BPH) and Laodelphax striatellus (small brown planthopper, SBPH) are two planthoppers pests on rice, and can direct metabolize neonicotinoid through detoxification by P450s. Previous studies demonstrated that NlCYP6ER1, NlCYP4CE1, NlCYP6CW1 and NlCYP6AY1 were constitutively overexpressed in neonicotinoid-resistant BPH strains, contributing to neonicotinoid metabolism. However, the homologous genes, LsCYP6ER1, LsCYP4CE1 and LsCYP6CW1, in SBPH were not over-expressed in populations with higher resistance ratios to neonicotinoids. The only exception was LsCYP6AY3, which was confirmed to hydroxylate imidacloprid. Similarly in this study, the expression of LsCYP6ER2, LsCYP4CE2 and LsCYP6CW1 were not significantly different among SBPH field populations. Nevertheless, RNAi against LsCYP6ER2, LsCYP6CW1 and LsCYP4CE2 obviously increased imidacloprid and nitenpyram toxicity to SBPH. The recombinant LsCYP6ER2, LsCYP6CW1 and LsCYP4CE2 all possessed the capability to metabolize imidacloprid and nitenpyram. All three P450s metabolized imidacloprid into a major metabolite, 4/5-OH imidacloprid. Recombinant LsCYP6ER2 and LsCYP6CW1 metabolized nitenpyram into one major metabolite (N-desmethyl nitenpyram), while LsCYP4CE2 metabolism got two major metabolites, hydroxy nitenpyram and N-desmethyl nitenpyram. The results demonstrated that LsCYP6ER2, LsCYP4CE2 and LsCYP6CW1 metabolized neonicotinoids to achieve a basal tolerance. That means the conservation of catalytic function in homologous P450s among species was not directly related to its role in insecticide resistance, whose gene overexpression in resistant insects is an essential. Taken together, the work provides new insights into mechanisms of metabolic function of insect P450s, especially in two closely related insect species.