LAUSR

Abstract The predacious mite Neoseiulus cucumeris (Oudemans) is an effective natural enemy of pest insects and mites. To identify the relative fitness of the avermectin-resistant strain of N. cucumeris, the life history parameters of avermectin resistant (R) and susceptible (S) strains of N. cucumeris were observed under experimental conditions (25 ± 1°C, 90 ± 5% RH and L: D = 14:10 h) feeding upon Tetranychus truncatus (Ehara). Fertility, net reproductive rates (R0 /female), intrinsic rates of increase (r/day) and development durations of the two strains were compared. The abamectin resistant strain of N. cucumeris had significantly shorter developmental duration and longevity than the sensitive stain. However, the mean fecundity of the resistant strain was significantly higher than that of the susceptible strain. The net reproductive rate (R0=30.3833 offspring), the intrinsic rate of increase (r=0.2231 d-1) and the finite rate of increase (λ=1.2499 d-1) of the resistant strain were only slightly higher than those of the susceptible strain (R0=29.5333 offspring, r=0.2130 d-1, λ=1.2373 d-1); the differences were not significant. However, the mean generation time (T=15.1768 d) of the resistant strain was significantly shorter than that of the susceptible strain (T=16.0314 d).