Studies On The Susceptibility Of Striped Flea Beetle(SFB), Phyllotreta Striolata (Fabricius), To Insecticides In The Vegetable Field

As a major crucifer-specific pest, the striped flea beetle (SFB), Phyllotreta striolata (Fabricius), spreads widely across the world. The beetles infest many crucifers like mustard, turnip, radish, and related weeds, and with the planting area of crucifers larger than ever, the problem of its continuous damages to the vegetables by SFB is becoming more serious in the south of China, from which a heavy economic loss results every year. At present, chemical treatments play a significant role in the control and management of SFB. However, with the mass application of insecticides, some problems have emerged, e.g. the decline of the control effect of SFB with insecticides. Thus this paper focused on the study on the insecticide susceptibility of SFB to provide the control and management of the beetle with necessary theories.1 Techniques for monitoring the susceptibility of SFB to insecticidesThe susceptibility of SFB to insecticides was examined with three kinds of monitoring techniques including leaf-dipping, dropping and filming methods, among which dropping method, with a value of 6.42% of coefficient of variation (CV), was considered best due to its high reproducibility. Also, the susceptibility of SFB from 4 regions was tested to chlorpyrifos, carbosulfan and cypermethrin via dropping and leaf-dipping method, both of which could be applied to produce reliable results.Diagnostic dose method was employed to evaluate the dose values of four insecticides for susceptible and non-susceptible individuals of SFB. The results placed the dose value of chlorpyrifos at 40 mg/L and 600 mg/L, dichlovos at 250 mg/L and 1000 mg/L, carbosulfan at 50 mg/L and 800 mg/L, and cypermethrin at 63 mg/L and 1000 mg/L, respectively. And as the results of the test of frequency of resistant genotypes of SFB collected from 4 areas using dropping method, leaf-dipping and diagnostic dose method showed, diagnostic dose methodcould be considered as an alternative to the other 2 methods for monitoring the susceptibility of SFB to insecticides.The frequency distributions of the total esterase and acetylcholinesterase in SFB from 4 regions were detected with enzymatic kinetics method in a microplate reader. The results were compared with those through other methods like dropping and leaf-dipping methods to demonstrate that enzymatic kinetics method was a quick one to determine the frequency distributions of resistant-related enzymes, such as acetylcholinesterase and the total esterase, in their different regions of activity. Thus a fast determination of the susceptibility of the field population of SFB could be made according to the total of the individuals with esterase with an activity of more than 1.6 D(450nm) min-1 insect-1.2 Occurrence of the SFB population and regional diversity of susceptibility of SFB to insecticidesThe susceptibility diversity of SFB collected from different sites in Fujian Province was tested with leaf-dipping, filming and enzymatic kinetics methods and the results indicated that the beetles from most sites had generally developed a low-level resistance to chlorpyrifos, dichlorvos, and carbosulfan, while some middle-level resistant populations of SFB also existed. There were significant differences among the different geographical populations in their susceptibility to cypermethrin, with some populations showing a middle-level or high-level resistance to the insecticide. In general, the SFB populations in the southeast of Fujian Province were lower in the susceptibility to insecticides than those in the northwest.With the analysis of the SFB populations by random amplified polymorphic DNA (RAPD) marker, the results showed that the populations in Fujian Province could be divided into three groups, which were a southeastern group, a northwestern group, and a relatively independent group consisting of Quanzhou and Dongshan populations. This SFB population differentiation could be caused not only by the difference of the geography and distance, but also by the different susceptibility to insecticides of in diff...