Resistance Of Aphis Gossypii Glover (Homoptera: Aphididae) To Imidacloprid And Biological Effects And Biochemical Mechanisms Of Pymetrozine To Imidacloprid-resistant Population Of Aphis Gossypii

In order to prove resistance risk and clear the control effects of pymetrozine to imidacloprid-resisitant population of Aphis gossypii, to propose the management strategies to control the imidacloprid-resistant population. The test used the wingless adult aphids of the imidacloprid-resistant population (RF27), the Xiajin population (XJ) and the susceptible population (SS) by using the dipping method, microspot method, biochemical method and systematic observation method, respectively, to study on biochemical mechanisms and biological characteristics of Aphis gossypii to imidacloprid, as well as measure the cross-resistance of the imidacloprid-resistant population of Aphis gossypii Glover (Homoptera: Aphididae) to pymetrozine and other ten pesticides and the effects of pesticide application on its biological characteristics and biochemical mechanisms. The results as follows:1.The results in laboratory selected populations showed: the test made a imidacloprid selection to susceptible population in the laboratory, after 27 generations, the resistance ratio increased to 24.96, and it reached to moderate level of resistance. During the resistance selection, the resistance of Aphis gossypii to imidacloprid developed slowly in the initial stage of resistance selection, however, the resistance developed quickly after 9 generations. If the resistance was selected in the laboratory, the resistance level maybe keep rising. The test indicated although the resistance of Aphis gossypii to imidacloprid developed slowly, compared to other pesticides, it still had the potential and risk to develop high level of resistance to imidacloprid.2.The results of cross-resistance showed: The LC50 of pymetrozine to RF27 and SS was 0.2677 and 1.3072μg/mL, respectively, the ratio of cross-resistance was 0.20, there was significant negative cross-resistance phenomenons of RF27 to pymetrozine, so pymetrozine could be as high efficiency pesticide to control Aphis gossypii; Carbosulfan, diafenthiuron, acetamiprid, nitenpyram, buprofezin, avermectins, cyhalothrin, omethoate, methomyl and chlorphrifos could be only as rotation pesticides to control Aphis gossypii.3. The synergisms of synergists to pesticide showed: SV1 and DEM didn't represent obvious synergisms in RF27 and SS, however, TPP and PBO showed obvious synergisms, the synergisms in RF27 was higher than that in SS, especially the synergism ratio of TPP had exceeded 2. So CarE and MFO played an important role in RF27, AChE and GST only played subordinate role in RF27.4.The biochemical results showed : The specific activities of CarE, AChE and GST in RF27 were higher than those in SS, especially the specific activities of CarE in RF27 much higher than that in SS. The results indicated CarE played an important role in RF27, AChE and GST played subordinate role in RF27.5.The fitness results showed: The honeydew secretions and bodyweights in SS, RF27 and XJ treated by imidacloprid lower than those in control (SS, RF27 and XJ treated by water), the inhibitory rate was 80.6%, 12.8%, 23.3% and 58.2%, 48.6%, 51.5%, respectively at 72 h.There were obvious developmental disadvantages in RF27, compared to SS, including the lower nymphal survival rate, the lower net reproductive rate and the longer mean generation time, the lower intrinsic rate of natural and the finite rate of increase, and the lower relative fitness (0.73). There were significant biological fitness disadvantages in RF27.6.The results showed by microspot method: The LD50 was 1.2130×10-5 and 8.5063×10-5μg/aphid in RF27 and SS treated by pymetrozine, respectively, toxicity ratio was only 0.24 and 1.57, respectively, however the toxicity ratio was 38.9 and 34.6 in RF27 and SS treated by imidacloprid. So pymetrozine could control RF27 and XJ (field population) effectively.The specific activities of CarE, AChE and GST in RF27 treated by pymetrozine were lower than those in RF27, the results showed CarE, AChE and GST were the major reasons of negative cross-resistance phenomenon. The honeydew secretions and bodyweights in RF27 treated by pymetrozine were lower than those in RF27, which showed that pymetrozine could effect feeding and growth of Aphis gossypii. RF27 treated by pymetrozine showed developmental disadventages, including the lower nymphal survival rate (only 64.60%), the lower net reproductive rate(10.39), the longer mean generation time(10.87d), the lower intrinsic rate of natural increase and the finite rate of increase(0.21and1.23, respectively), and the lower relative fitness ( only 0.70). These results indicated that pymetrozine has high application value in controlling A.gossypii.