Local fruit orchards have incurred heavy losses due to invasive insects, including the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), in Guizhou Province, China. In our efforts to manage this invasive pest, a laboratory study was conducted to evaluate the response of adult B. dorsalis to an extract of Ageratina adenophora (Spreng.) R.M. King & H. Rob (Gunneridae: Asteraceae). We evaluated the contact toxicity and oviposition-deterrent activity of the extract on adult B. dorsalis, as well as the sublethal effects on survival and reproduction. We found that the A. adenophora extract has significant insecticidal activity, with the 24-h median lethal concentration (LC₅₀) for adults being 26.014 mg/ml. The extract of A. adenophora also showed oviposition inhibition. A residual deterrent effect (28.16%) was evident up to 5 d after treatment. Exposure to the LC₂₅ concentration of the A. adenophora extract caused significant differences in preoviposition and fecundity, decreased adult longevity in the F₀ generation, and decreased egg and pupa survival in the F₁ generation. The levels of carboxylesterase enzyme activity in adults treated with the extract were significantly lower than those in the untreated controls at 12 h and 24 h. This latter phenomenon could perhaps be an adaptive response to the extract that might reduce its toxic effects in B. dorsalis.