Intermediate derivatisation method in the discovery of new acaricide candidates: synthesis of N-substituted piperazine derivatives and their activity against phytophagous mites.

BACKGROUND: To discover and exploit novel acaricidal compounds, a series of novel N-substituted piperazine derivatives were designed and synthesised using a tert-butyl piperazine-1-carboxylate as the starting material by intermediate derivatisation methods, and their acaricidal activities were evaluated. RESULTS: Compounds 11 and 12 exhibited significant acaricidal activity against adults of Tetranychus cinnabarinus in greenhouse tests. Compound 12, in particular, was found to be the best potential candidate acaricide and proved to be more active than the commercial positive controls spirodiclofen and pyridaben, with an LC50 of 0.8977 mg L-1 . Results concerning acaricidal activity against larvae and eggs of T. cinnabarinus indicated that compound 12 possessed equivalent larvicidal activity to spirodiclofen and higher larvicidal activity than pyridaben. Meanwhile, compound 12 showed less ovicidal activity than pyridaben, but higher activity than spirodiclofen. Furthermore, the results of the field trial demonstrated that compound 12 could effectively control Panonychus citri and P. ulmi with long-lasting persistence and rapid action. CONCLUSIONS: The present work indicates that compound 12 could be a novel acaricide candidate for spider mite control. © 2016 Society of Chemical Industry.

Susceptibility of Sogatella furcifera and Laodelphax striatellus (Hemiptera: Delphacidae) to Six Insecticides in China.

The whitebacked planthopper, Sogatella furcifera (Horváth), and small brown planthopper, Laodelphax striatellus (Fallén), both are important crop pests throughout China, especially in rice. Application of chemical insecticides is the major control practice. Consequently, insecticide resistance has become an urgent issue. In this study, resistance levels to six conventional insecticides were evaluated for these two species collected from major occurring areas of China. Additionally, imidacloprid- (resistance ratio [RR] = 10.4-fold) and buprofezin (RR = 15.1-fold)-resistant strains of whitebacked planthopper were obtained through laboratory selections for cross-resistance profiling and synergism assessment to understand resistance mechanisms. The results showed that all tested populations of both species exhibited low to high levels of resistance to chlorpyrifos, while remaining susceptible to thiamethoxam. Three of the 14 whitebacked planthopper populations showed low to moderate resistance to imidacloprid, while all small brown planthopper populations reminded susceptible. All small brown planthopper and whitebacked planthopper (except one) populations showed at least moderate resistance (RR = 10.1-271.1) to buprofezin. All small brown planthopper populations remained susceptible to pymetrozine and nitenpyram, and all whitebacked planthopper populations remained susceptible to isoprocarb. The imidacloprid-resistant whitebacked planthopper strain showed no significant cross-resistance to other tested insecticides. However, the buprofezin-resistant strain exhibited a low-level cross-resistance (CR = 3.1) to imidacloprid. Piperonyl butoxide, triphenyl phosphate, and diethylmaleate displayed no synergism effect on the resistant whitebacked planthopper strains.

Resistance monitoring and assessment of resistance risk to pymetrozine in Laodelphax striatellus (Hemiptera: Delphacidae).

Laodelphax striatellus (Fallén) is a major pest of cultivated rice. Pymetrozine, a pyridine azomethine compound, represents a novel insecticide with a selective activity against sucking pests. The resistance of L. striatellus to thiamethoxam, nitenpyram, chlorpyrifos, and pymetrozine in five field populations, collected from Jiangsu, Anhui, and Zhejiang in China, was monitored from 2009 to 2011 in laboratory. All the populations kept susceptible to minor resistance to thiamethoxam and nitenpyram in the 3 yr (0.6- to 2.2-fold and 0.8- to 3.8-fold, respectively), while the insects developed low to high level resistance to chlorpyrifos (9.7- to 76.1-fold). Three populations were all susceptible to pymetrozine (1.1- to 2.1-fold) in 2009, but the Wuxi and Yancheng populations developed low level resistance to pymetrozine (5.5-fold and 5.3-fold, respectively) in 2011. Meanwhile, the resistance level of the selected strain reared in laboratory increased by 1.0-fold after 12-generation selection with pymetrozine. The realized heritability (h2) of resistance at different selection stages was estimated as 0.0470 (F1 to F13) and 0.2070 (F5 to F13) by using threshold trait analysis. It suggested that L. striatellus had the definite risk of resistance to pymetrozine.