Toxicities Effects Of Several Insecticides And The Characterization Of Detoxification Enzymes In The Oriental Fruit Fly, Bactrocera Dorsalis (Diptera:Tephritidae)

In this study, the susceptibilities of B. dorsalis from four population(KM, GZ, HK and DG) to nine insecticides including malathion, chlorpyrifos, phoxim, triazophos, beta-cypermethrin, deltamethrin, abamectin, imidacloprid and fipronil were evaluated using the micro-drop method. The addition of synergists triphenyl phosphate (TPP), piperonyl butoxide (PBO) and diethyl maleate (DEM) yielded different levels of synergistic effects on different insecticides against each population.Besides, in order to clarify the potential resistant mechanisms of B. dorsalis to beta-cypermethrin, the activity of three kinds of detoxification enzymes of B. dorsalis after treating with different dose (LD20and LD50) of beta-cypermethrin plus three synergists were tested respectively. This research was supported by the the National Basic Research Program of China (2009CB125903and2009CB119200) and the Natural Science Foundation of Chongqing (CSTC,2009BA1042). The main results of the research are as follows:1. The susceptibilities of different populations of B. dorsalis to nine insecticidesThe toxicities of the nine insecticides against the four populations (KM, HK, GZ and DG) of B. dorsalis were measured by using the micro-drop method. The results showed that the sensitivity of the same population of B. dorsalis to different insecticides and the sensitivity of different populations to a same insecticide were all different. Considering the four populations together, fipronil was the most toxic, malathion and imidacloprid were the least toxic compounds against B. dorsalis. For the KM population, the insects were most sensitive to fipronil, followed by phoxim, abamectin, triazophos, beta-cypermethrin, chlorpyrifos, deltamethrin, malathion, and imidacloprid. For the HK population, fipronil was the most toxic compound, followed by deltamethrin, triazophos, abamectin, phoxim, chlorpyrifos, beta-cypermethrin, malathion and imidacloprid. For the DG population, fipronil was also the most toxic compound, followed by triazophos, phoxim, chlorpyrifos, abamectin, deltamethrin, beta-cypermethrin, malathion and imidacloprid. For the GZ population, insects were most sensitive to fipronil, followed by phoxim, triazophos, chlorpyrifos, abamectin, deltamethrin, beta-cypermethrin, malathion and imidacloprid.2. The synergism of synergists to nine kinds of insecticidesIn the study, we found that the same synergist to an insecticide in different populations and a synergist to different insecticides in the same population were all different. The results showed that the addition of PBO, TPP, and DEM significantly increased the toxicity of malathion on the DG population and triazophos against the KM population. PBO and TPP had significant synergistic effects to chlorpyrifos toxicities against the KM population, TPP showed a better synergistic effect against the GZ population. The analysis with pyrethroid insecticides suggested that the three synergists could significantly increase toxicity of both beta-cypermethrin and deltamethrin, with a higher extent against the DG population. In HK population, PBO and DEM had better synergistic effects than toward beta-cypermethrin against the two populations, but the other synergists to pyrethroid insecticides were not showed a good synergistic effect. The three synergists all had better synergistic effects to the two pyrethroid insecticides, and the effect was better to deltamethrin than to beta-cypermethrin. The toxicity of abamectin against the DG population was significantly increased by adding PBO, TPP, and DEM. In the KM population, it was significantly enhanced by PBO and TPP but was not significantly affected by DEM, and synergistic effects of PBO was better than that of TPP and DEM in KM and DG population, DEM was better than PBO and TPP in GZ and HK population. When applied with phoxim and fipronil, the three synergists all showed no significantly synergistic effects against the four populations.3. The effect of synergists to detoxification enzymesIn our study, we found that insecticides and synergist treatments led to dynamic changes in the GSTs, CarEs and P450activities within24h, which may implied that major changes in interior of B. dorsalis caused from changes of activities of GSTs, CarEs and P450were used to adapt and restore external environmental stimuli. TPP inhibited the activity of CarEs, induced the activities of GSTs and P450of B. dorsalis. But higher activity were detected in the fat body, midgut, and Malpighian tubules compared with that of whole body. This suggests that these tissues are important for detoxification. The specific activity of GSTs, CarEs and P450in B. dorsalis which treated with different insecticides all showed different in different tissues. Overall, the highest activity of detoxification enzymes in fat body, midgut and Malpighian tubules was CarEs, GSTs and P450, respectively. Besides, TPP inhibited the activity of CarEs and PBO inhibited the activity of CarEs in the three tissues. These all showed that different tissues of B. dorsalis have different responsibilities in the process of detoxification metabolism of beta-cypermethrin, they may all play the role in beta-cypermethrin detoxification.