Inheritance Mode Of Malathion Resistance And Biochemical Mechanism In Bactrocera Dorsalis (Hendel)

This dissertation regards Bactrocera dorsalis (Hendel) as the study target. On the bases of malathion resistance selection of B. dorsalis in laboratory, the developmental dynamics of resistance has been identified. The heritability and risk assessment of resistance to malathion has been analysed. Meanwhile, reciprocal crosses and backcross were performed between susceptible strain and resistant strain. The inheritance mode of resistance to malathion in B. dorsalis has been made clearly, including the dominancy, cytoplasmic or chromosomal inheritance and the detection of genetic factors number. In addition, the differences of detoxification enzyme activity in the susceptible and resistant strain, the changes of detoxification enzyme activity after treatment by sub lethal doses of malathion were measured by 96-well microplate reader. It is designed to provide the scientific basis for the use of malathion in the field and the resistance management of B. dorsalis, and it also provide strong theoretical basis for the thorough analytical of metabolic resistance of B. dorsalis to malathion.The main findings are as follows:1 Resistance selection of B. dorsalis to malathion and resistance risk assessmentThe resistance selection to malathion of B. dorsalis was conducted in the laboratory environment. After 22 generations continuous selection, LD50 to malathion increased from 114.62 ng/fly to 2096.83 ng/fly, the resistance folds rose from 1.86 folds to 34.02 folds, reaching a middle level. The realized heritability that B. dorsalis to malathion was 0.1621, it showed that the development of resistance was relatively slow. In addition, the realized heritability in the earlier process was higher than that in the later process. Evolving 10 fold resistance to malathion need 10.9 to 24.0 generations under selection pressure of 50% to 90% and h2 of 0.1621.2 The inheritance mode of resistance that B. dorsalis to malathionThe reciprocal crosses and backcross were performed between susceptible strain and resistant strain to investigate the inheritance of resistance to malathion in B. dorsalis. Results showed that the inheritance mode of resistance to malathion in B. dorsalis was autosomal, polygenic and incomplete dominant.3 The activitiesof P450s, GSTs and CarEs in different strains of B. dorsalisThe activity of P450s, GSTs and CarEs in whole body and the midgut from both susceptible and resistant strains were measured with 96-well microplate reader. The results showed that the activities of P450s, GSTs and CarEs in resistant strain were significantly higher than those of the susceptible strain in whole body or the midgut. Besides, the activity of three detoxification enzymes was higher in the midgut than in whole body in two strains. These suggested that the development of resistance to malathion might be related to the raised activities of P450s, GSTs and CarEs. Whether in whole body or midgut, the P450s activity showed highest differences among the three detected detoxification enzymes, indicating that P450s plays a major role in the metabolic resistance of B. dorsalis to malathion.4 Influences of sublethal doses of malathion on the activity of detoxification enzyme indifferent strains of B. dorsalisThe corresponding LD10 and LD30 of susceptible and resistant strain were obtained based on the bioassay results. The body and the midgut tissue of individual survival were collected after treated with sublethal doses of malathion at different treatment times to both susceptible and resistant strain, then the activity of the corresponding GSTs and CarEs were measured. The results showed that the GSTs and CarEs activity were shown a dynamic process within 24 h after different treatment times with sublethal doses of malathion, and their activitives of resistant strains were higher than that of susceptible strain at different times and doses. For whole body, the sublethal doses of malathion induced the GSTs activity in the susceptible strains. LD10 induced the GS Ts activity, however LD30 inhibited the activities in the resistant strains. The affect of sublethal doses of malathion to the activities of CarEs in two strains was not obvious. In the midgut, different sublethal doses induced the activities of GSTs at 4 h in the susceptible strain, and inhibited the activities of GSTs in the resistant strain. The change of CarEs activities was the same with that of GSTs. It suggested that GSTs and CarEs participated in the metabolic resistance of B. dorsalis to malathion.