Development, survival, and reproduction of avermectin-resistant Bryobia praetiosa (Acari: Tetranychidae)

We explored biological fitness variability in avermectin-resistant and -susceptible strains of Bryobia praetiosa. Our study offers a theoretical basis to delay resistance development and resistance management of B. praetiosa. Development and reproduction of the avermectin-resistant strain and the susceptible strain of B. praetiosa were evaluated at 26 ℃. The age-specific life tables of experimental populations of both strains were established. The ecological fitness of the two strains was analyzed by population life-table parameters. Results showed that the development duration of every stage, the average life span, and the number of eggs laid per female of the resistant strain were less than the susceptible strain. The average longevity and eggs laid per female of the resistant strain were 21.89 days and 28.17 eggs, respectively, but the average longevity and eggs laid per female of the susceptible strain were 27.94 days and 40.91 eggs, respectively. The analysis of the life table showed that there was a difference in the population parameters between the two strains. The net reproductive rate (R0) of the resistant strain (28.17) was obviously lower than the R0 of the susceptible strain (45.70) (P<0.05). The finite rate of increase (λ) and population doubling time (p.d.t.) of the resistant strain were 1.267 2 and 2.927 1, respectively. There were significant differences in these parameters between the resistant strain and the susceptible strain (P<0.05). The results indicated that the resistant strain was more disadvantageous in developmental and reproductive characteristics than the susceptible strain. In addition, the relative fitness value of the resistant strain was about half that of the susceptible strain, and there was also a significant degree of fitness defect. The results help to explain the fitness disadvantages of the avermectin-resistant strains of B. praetiosa, and provide reference for the management of avermectin-resistant B. praetiosa.