Resistance Risk Assessment Of Spodoptera Litura To Flubendiamide And It’s Mixture

The common cutworm, Spodoptera litura (Fabricius), is a worldwide distributed polyphagous agricultural pest, which has led to a dramatically increasing damage to crops in China in recent years. The pest was usually controlled with synthetic pesticides and had developed resistance to most commonly used pesticides. As a novel insecticide with special action mechanism, flubendiamide has a good efficient effect on the pest. The development of resistance is of concern with the use of any new pesticide. An understanding of the resistance phenomenon can lead to better strategies to manage resistance. In this paper, the resistance levels of the field populations of S. litura from different regions in Guangxi to four insecticides were detectded, the resistance risk of S. litura to flubendiamide and its mixture were assessed, and the metabolic resistance mechanisms of the pest on flubendiamide were preliminarily studied. The main results were as follows:1. The toxicity of four insecticides, including flubendiamide, chlorantraniliprole, avermectins, and the mixture of flubendiamide and avermectins on the sensitive population of S. litura were measured with leaf dipping method. The results showed that the LC50values were0.26813mg/L,0.12183mg/L,7.9853mg/L and0.1163mg/L, respectively. The toxicity in sequence was:the mixture of flubendiamide and avermectins> chlorantraniliprole> flubendiamide>avermectins.2. The resistance levels of the field populations S. litura from different areas in Guangxi, to four insecticides were measured by leaf dipping method. The resistance ratios of the populations tested to flubendiamide, chlorantraniliprole, avermectins, and the mixture of flubendiamide and avermectins were1.39to2.26folds,1.10to2.79folds, 13.95to34.37folds, and7.61to12.11folds, respectively, suggesting that the populations tested to flubendiamide and chlorantraniliprole be still in sensitive stages, while to avermectins and the mixture of flubendiamide and avermectins be in low to medium resistance stages.3. The susceptible strain of S.litura was continuously selected for12generation with flubendiamide under selective pressure of30%to70%mortality for each selective generation in laboratory. The resistance to flubendiamide of the resisant strain which was selected for12generation had increased by8.94-fold compared with the susceptible strain. The resistance realized heritability and resistance risk of S.litura to flubendiamide were evaluated with threshold trait analysis method. The realized heritability (h2) of resistance to flubendiamide was0.3038. Theoretically, to obtain5-fold and10-fold increase in resistance to flubendiamide, the pest required4generations and6generations under selective pressure of90%mortality for each generation, respectively.4. The susceptible strain of S.litura was continuously selected for11generation with the mixture of flubendiamide and avermectins during the12-generation rearing process under selective pressure of30%to70%mortality for each selective generation in laboratory. The resistance to the mixture of the resisant strain which was selected for11generation had increased by5.56-fold compared with the susceptible strain. The realized heritability (h2) of resistance to the mixture was0.1858. Theoretically, to obtain5-fold and10-fold increase in resistance to the mixture, the pest required6generations and8generations under selective pressure of90%mortality for each generation.5. Based on the above results, the pest required4generations and6generations to obtain5-fold and10-fold increase in resistance to flubendiamide under selective pressure of90%mortality for each generation, while the pest required6generations and8generations to obtain5-fold and10-fold increase in resistance to the mixture of flubendiamide and avermectins under the same selective pressure, suggesting that the development of resistance to flubendiamide in S.litura could be postponed by application with the mixture of flubendiamide and avermectins.6. The enzyme activity of glutathione S-transferase, esterase and multi-function oxidase in the susceptible and resistant strain of Spodoptera litura were tested with enzyme dynamic method. The results indicated that there were significant difference in the activities of esterase and multi-function oxidase between the resistant strain and the susceptible strain, with the activity ratio of2.32and2.77, while there was no difference in the activity of glutathione S-transferase between the two strains, with the activity ratio of1.01. It suggested that the esterase and multi-function oxidase could most likely be involved in the mechanisms for flubendiamide resistance in S. litura, but glutathione S-transferase was no relevant to the resistance.7. The synergism of PBO, TPP and DEM on flubendiamide in resistance strain was determined with leaf dipping method. The result revealed that PBO and TPP had significant synergistic effects on flubendiamide, with the synergistic rate of21.55and15.85, respectively, while DEM had no apparent synergistic effect, with the synergistic rate of1.01. The inference that the resistance of S. litura to flubendiamide was related to esterase and multi-function oxidase, but irrelevant to glutathione S-transferase was further documented.