Lethal and sublethal effects of the chitin synthesis inhibitor chlorfluazuron on Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae)

Abstract

Bradysia odoriphaga Yang and Zhang is the primary insect pest that affects Chinese chive in northern China. Nevertheless, very few studies have been conducted on the use of chitin synthesis inhibitors (CSIs) for the control of B. odoriphaga. Here, lethal and sublethal effects of the CSI chlorfluazuron on B. odoriphaga were studied to explore the use for integrated pest management (IPM) of B. odoriphaga. A contact and ingestion toxicity bioassay showed that chlorfluazuron was more active against B. odoriphaga than three other CSIs, with a 72h LC₅₀ of 0.1593mg/L. Treatment with the LC₅₀ dose of chlorfluazuron decreased both the intrinsic and finite rates of increase of B. odoriphaga, in addition to reproduction rate, survival rate, and fecundity, and the mean generation time, total preovipositional period and larval development duration were shortened, compared with those of the control and LC₁₀ groups. The mean generation time, total preovipositional period and larval development duration were all also markedly decreased by treatment with chlorfluazuron at the LC₁₀. Furthermore, chlorfluazuron inhibited the feeding of the final instar larvae for a short period. Glutathione S-transferase and microsomal mixed function oxidase activities increased after exposure to the chemical. These results showed that chlorfluazuron at the sublethal LC₅₀ treatment inhibited B. odoriphaga population growth, whereas the danger of causing rapid population growth by using a lower sublethal concentration was demonstrated with the sublethal LC₁₀ treatment. Therefore, chlorfluazuron should be used with caution in an IPM program for B. odoriphaga.

Keywords: Bradysia odoriphaga Yang and Zhang; Chlorfluazuron; Glutathione S-transferase; Microsomal mixed function oxidase; Population dynamics; Two-sex life table.