| The oriental fruit fly, Bactrocera dorsalis (Hendel) is distributed in tropical and subtropical regions including southern area of Changjiang river of China, due to its polyphagous and well adaptation to various climates. It is also one of the most damaging fruit pest in the world and have caused severe economic damage. Insecticides are applied as the primary method of controlling this fruit fly species. However, different resistance levels to various types of traditional insecticides have been observed in this pest in many areas, including mainland China and Taiwan. Anthranilic diamide insecticides exhibit a novel mode of action, targeting the ryanodine receptors in insect muscle cells. As a second-generation commercialized ryanodine receptor insecticide, cyantraniliprole has been shown to be safe for non-target vertebrates based on structural differences between insect and mammalian ryanodine receptors, while conserving beneficial arthropods.This paper clarified the baseline susceptibility of B. dorsalis to cyantraniliprole in the south China, established a cyantraniliprole-resistant strain as well and clarified the development pattern of resistance, also studied the cross-resistance, the effects on biological characteristics and the metabolic resistance mechanism of this resistant strain. At the same time, this paper discussed the sublethal effects of cyantraniliprole in B. dorsalis, and laid a solid foundation for the wise use of cyantraniliprole as well as providing help for the understanding of periodic outbreaks of pests in the field. The specific findings are as follows:1. The susceptibility of field-collected populations of B. dorsalis to cyantraniliprole was assessed via a diet incorporation bioassay in adults. Based on the obtained LC50values (ranging from3.29μg/g to15.83μg/g), all the testing populations were susceptible to cyantraniliprole, with the samples of WH (Hubei province) being the most tolerant (by4.80-fold). Two (SY, Hainan province, CS, Hunan province) of the nine field-collected populations of B. dorsalis showed a similar susceptibility to cyantraniliprole, while the remaining populations displayed narrow variations in tolerance compared to the laboratory strain.2. The susceptible strain was used for the selection of cyantraniliprole-resistance strain and about80%of the adults were killed one and a half days after feeding of cyantraniliprole in the selection. After14generations of selection, the resistance of the selected strain increased19.44-fold compared with the laboratory susceptible colony. The resistance development was slow till generation Hand exponential increase of resistance was found at generation12. By estimated, the realized resistance heritability was0.124. Assuming that the h2of field B. dorsalis was half of that of the established resistance strain, it required64.5-35.8generations for B. dorsalis to obtain10-fold increase in resistance under the selective pressure of50%-90%. If the h2of field B. dorsalis was0.124, it required17.8-9.9generations for B. dorsalis to obtain10-fold increase in resistance under the selective pressure of50%-99%.3. The results of the cross-resistance bioassay revealed that this cyantraniliprole-resistance strain appeared no cross-resistance to other9insecticides. Negative cross-resistance was found in the cyantraniliprole-resistance strain with chlorpyrifos, cypermethrin and trichlorfon and emamectin. This strain showed very low level of cross-resistance to cypermethrin with2.41fold. The cross-resistance to other insecticide was between1.38-1.68fold.4. Synergist assays were performed to determine the potential detoxification mechanisms. PBO, DEM and DEF showed significant synergism effects in resistant strain with PBO being the highest,6.81fold. PBO also showed significant synergism effects in lab and CS strain.Compared with the susceptible strain, the enzyme activity of superoxide of last instar laval of the resistant strain was significantly declined with0.681fold. Catalase activity was also reduced to a certain extent, but did not reach a significant level; and there was no significant effect on the activity of peroxidase.The activity of esterases (AchE and CarEs) of cyantraniliprole-resistance strain showed obvious increase with1.267fold while comparing with the susceptible strain. However, other detoxification enzymes did not show any obvious increase in the activity.5. The larval development duration and the first mating time of the cyantraniliprole-resistance strain were significantly prolonged with respect to control and the weight of pupae was also increased. However, the duration of pupae of the cyantraniliprole-resistance strain was significantly shortened, while the pupation rate showed no effect. The fecundity and male longevity of the cyantraniliprole-resistance strain were decreased sharply, while the egg hatch and the female longevity showed nonsignificant nagtive impacts. The cyantraniliprole resistance also showed some effects on the mating behavior of the cyantraniliprole-resistance strain. The remating ratio of the female that mated with the treated male was significantly improved. However, there was no effects on the total mating times and mating competitiveness.6. An ingestion toxicity bioassay showed that cyantraniliprole was active against B. dorsails, and the72h feeding LC50was3.22μg/g in adult diet for a susceptible strain. Sublethal does of cyantraniliprole (1.30μg/g adult diet) induced a hormesis effect on B. dorsal is. The mating competitiveness of B. dor salis treated with3.27μg/g adult diet of cyantraniliprole was significantly lower than controls. The lower dose (1.30μg/g adult diet) of cyantraniliprole improved the total mating times of both mating pairs in treated groups and also the mating competitiveness of the treated males when compared with the higher dose and controls. Cyantraniliprole-treated females of the mated pairs with the lower dose laid more eggs.In all, all of the nine field-collected populations of B. dorsalis showed a similar susceptibility to cyantraniliprole and there was resistance risk in the B. dorsalis strain and the metabolic resistance mechanism was related with esterases and mixed function oxidase, and the fitness cost of the resistance strain was also affected, and there was an induced hormesis effect on at least some behaviors associated with adult mating. |
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