Abstract: Petrobia harti is a very serious worldwide pest mite harming Oxalis corymbosa, and pyridaben as a broad-spectrum, contact-killing acaricide that is highly effective against P. harti. To clarify the sublethal effects of pyridaben on P. harti and provide data for developing comprehensive control strategies for this mite with minimal usage of pyridaben, the toxicity of pyridaben against P. harti was determined by a leaf impregnation method. The sublethal doses used were determined by a regression equation of P. harti death rate on pyridaben concentration, in order to identify concentrations predicted to be lethal to 10% or 20% of a test population of mites (LC₁₀ and LC₂₀, respectively). The effects of the LC₁₀ and LC₂₀ sublethal pyridaben doses on the development, fertility and life-history parameters of P. harti were evaluated by establishing a life table. It was found that the fecundity of P. harti was significantly decreased after treatment with the sublethal doses of pyridaben (P<0.05) with the number of eggs laid per female reduced, respectively, by 53.37% and 55.46% in the F₀ generation and 41.34% and 45.24% in the F₁ generation in the LC₁₀ and LC₂₀ treatments, compared to the controls. Similarly, the oviposition duration was significantly shortened, respectively, by 3.11 and 4.75 days in F₀ generation and 3.47 and 2.81 days in the F₁ generation. The average adult longevity was also significantly shortened, respectively, by 1.45 and 2.04 days in the F₀ generation and 3.24 and 4.00 days in the F₁ generation. Compared to the control, after treatment with sublethal pyridaben doses, the net reproductive rate (R₀), intrinsic rate of increase (r_m) and finite rate of increase (λ) of P. harti were all significantly decreased in the LC₁₀ and LC₂₀ treatments (the R₀ from 28.54 to 16.91 and 15.48; the r_m from 0.1650 to 0.1276 and 0.1249; the λ from 1.17941 to 1.1435 and 1.1330; P<0.05), while the mean generation time (T) and the population doubling time (Dt) were both significantly prolonged (the T from 20.31 to 22.17 and 21.94 days; the Dt from 4.20 to 5.43 and 5.55 days, respectively; P<0.05). The results indicated that the sublethal doses of pyridaben at LC₁₀ and LC₂₀ decreased the development rate and fecundity of laboratory populations of P. harti.

Key words: Petrobia harti, pyridaben, sublethal effect, life-table parameters