Evaluation of flupyradifurone for the management of the Asian citrus psyllid Diaphorina citri via dripping irrigation systems.

BACKGROUND: Chemical control is the most used and effective method to control Diaphorina citri, the vector of the phloem-limited bacteria associated with citrus huanglongbing (HLB) disease. The objectives of this study were to determine the effectiveness of flupyradifurone applied via dripping irrigation systems on D. citri. Bioassays were conducted using leaves harvested on various dates post treatment, and insecticide residue in leaf tissue was quantified. RESULTS: The drip application of flupyradifurone on citrus trees provided high-level and long-term control against D. citri adult, and the median lethal concentration (LC50 ) for ingestion of flupyradifurone in D. citri was 22.22 mg kg-1 (fresh leaf). Flupyradifurone residue was detected in leaf tissue within 3 days after treatment. The measured level of flupyradifurone peaked on day 40 day after application, and then showed a steady decline in subsequent days for all three applied dosages. The amounts of flupyradifurone in upper, middle, and lower leaves were similar, and trends in the change in concentration of flupyradifurone were consistent. CONCLUSIONS: The results demonstrate that flupyradifurone can be a valuable new tool for D. citri management programs, and drip-applied flupyradifurone provides an extended period of control efficacy. This paper could provide a reference to reduce the dependence on foliar-applied insecticides, with associated benefits for non-target exposure to workers and pollinators. © 2021 Society of Chemical Industry.

The linker length of glucose-fipronil conjugates has a major effect on the rate of bioactivation by ß-glucosidase.

BACKGROUND: Endogenous plant ß-glucosidases can be utilized to hydrolyze pro-pesticides and release the bioactive pesticide. Two related glucose-fipronil conjugates with different linkers structure, N-{3-cyano-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl) sulfinyl]-1H-pyrazol-5-yl}-1-(2-triazolethyl-ß-d-glucopyranoside)-1H-1,2,3-triazole-4-methanamine (GOTF) and N-{3-cyano-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl)-sulfinyl]-1H-pyrazol-5-yl}-2-aminoethyl-ß-d-glucopyranoside (GOF), were deglucolysated by ß-glucosidase both in vitro and in vivo at different rates. Here, the basis for these differences was investigated by revealing the kinetics of the reaction and by modeling molecular docking between enzyme and substrate. RESULTS: Results from kinetic study showed that the reaction rate was the main reason for the poorer rate of GOF hydrolysis with respect to GOTF. Modeling of substrate docking indicated that the spacer arm of glucose-fipronil conjugates affects the strength of non-covalent bonds within the active site and the position of fipronil within the pocket. Four glucose-fipronil conjugates and four corresponding aglycones were synthesized, and the hydrolysis data confirmed that the increased tether length between the bulky aglycone and glycone would lead to faster hydrolysis rate. The bioassay results indicated that most glucose-fipronil conjugates displayed moderate to excellent insecticidal activities in vivo against Plutella xylostella larvae. CONCLUSION: This study provides a potential strategy to optimize the substrate structure to enhance hydrolytic specificity in order to design appropriate phloem mobile pro-pesticides. © 2018 Society of Chemical Industry.