| In China, large amounts of chemical insecticides are applied in fields or indoors every year, directly or indirectly bringing selection pressure on insects. In order to explore insect resistant mechanism, we selected cotton aphid Aphis gossypii Glover that is an important pest of cotton and forest trees and mosquito Culex pipiens pallens that acts as an ideal transmitter of a wide variety of human diseases as research objects. Insecticide resistance mechanisms were studied from different aspects. The main research contents and findings are as follows:1. Transcriptomic analysis of Aphis gossypii responding to insecticidesA field population of Aphis gossypii, collected from Shanghai was tested in adult bioassays with frequently applied insecticides, moncrotophos, methom, and imidacloprid. Transcriptome analyses were carried out on insecticide-treated and control aphids, including the quality of transcriptome data and differentially expressed genes. Functional annotation and enrichment analysis of differentially expressed genes were conducted in three databases, KEGG, GO, and IPR. Only the sample of Im (treated by imidacloprid) showed enriched KEGG pathways for differentially expressed genes. In the GO and IPR databases, three treated samples all had enriched differences genes. For the sample of Im (treated by imidacloprid):a total of7951genes were analyzed in the GO database, including343up-regulated genes and13down-regulated genes with enriched GO annotations and participating15and2functions, respectively. A total of3037genes were analyzed in the KEGG database, including7up-regulated genes and4down-regulated genes with enriched KEGG annotations and participating one function, respectively. A total of10007genes were analyzed in the IPR databases, including66up-regulated genes and22down-regulated genes with enriched IPR annotations and participating8and7functions, respectively. For the sample of Me (treated by methom):a total of7951genes were analyzed in the GO databases, including155up-regulated genes were gathered using GO annotatio enrichment analysis, participating4functions. A total of10007genes were analyzed in the IPR databases,30up-regulated genes were gathered using IPR annotatio enrichment analysis, participating5functions. Mo (the Aphis sample stimulated by moncrotophos):a total of7951genes were analyzed in the GO databases,189up-regulated genes were gathered using GO annotatio enrichment analysis, participating16functions. A total of10007genes were analyzed in the IPR databases,26up-regulated genes and22down-regulated genes were gathered using IPR annotatio enrichment analysis, participating7and20functions respectively.Furthermore, some genes related to metabolic resistance were screened and the functions of these genes were similar to those of carboxylesterase, which shed light on the exploration of the molecular mechanism of insecticide resistance in Aphis gossypii. The relationship between these genes and insecticide resistance is required further analysis and study.2. Correlation between carboxylesterase alleles and insecticide resistance in Culex pipiens complexIn order to explore the evolutionary scenario, we analyzed the data from an historical record in2003and a recent investigation on five Culex pipiens pallens populations sampled from north China in2010. Insecticide bioassays showed that these five populations (WHE, YUY, TAA, LPU, BJI) had high resistance to pyrethroids, medium resistance to organophosphates, and low resistance to carbamates. Six types of Ester alleles, EsterB1, Ester2, Ester8, Ester9, Ester810, and Ester11were identified, and the overall pattern of their frequencies in geographic distribution was consistent with the report seven years prior to this study. Statistical correlation analysis indicated that Ester8and Ester9positively correlated with resistance to four insecticides, and EsterB10to one insecticide. The occurrences of these three alleles were positively correlated, while the occurrence of Ester81was negatively correlated with Ester8, indicating an allelic competition.Our analysis suggests that one insecticide can select multiple Ester alleles and one Ester allele can work on multiple insecticides. The evolutionary scenario of carboxylesterases under insecticide selection is possibly"one to many".3. Quick detection of organophosphate resistance in Culex pipiens complex using the coloration of esterases and acetylcholinesterasesBased on the resistance mechanisms of biochemistry and molecular biology, the correlation between the resistance level and the esterase activity was erected and the coloration cards of esterase activity reflecting various resistance levels were produced. According to the inhibitory character of acetylcholinesterase1by different concentrations of propoxur, the correlation between target resistance and coloration reaction was erected. A reaction system to show eye differentiable color was established for the detection of the existence of G119S mutation in the acetylcholinesterase1and its genotypes. These two kits provide convenient and efficient tools for the field work of investigating insecticide resistance and monitoring resistance outbreak in mosquitoes. |
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