Biological activity of capsaicin and its effects on development and fecundity in Bemisia tabaci were tested in the laboratory. The results showed that capsaicin induced direct mortality in different developmental stages of B. tabaci, and the mortality of whiteflies were significantly dosage-dependent. The toxicity of capsaicin to different developmental stages of B. tabaci by either leaf-dip or egg/larval-dip bioassays (the LC50 for adult, egg and nymph were 3525.79, 1603.29 and 1526.27 mg x L(-1), respectively) was higher than that by systemic bioassay (the LC50 for adult, egg and nymph were 5360.04, 2359.19 and 5897.43 mg x L(-1), respectively), and toxicity of capsaicin to eggs was higher than to adults in both bioassay methods. 2000 and 4000 mg x L(-1) concentrations of capsaicin had strong antifeedant effect on B. tabaci, as exemplified by reduced honeydew excretion of adults feeding on leaves treated with capsaicin compared with untreated leaf discs. Capsaicin also had strong oviposition deterrence against B. tabaci, with 94. 2% of selective oviposition deterrence rate and 83. 0% of nonselective oviposition deterrence rate when exposed to 4000 mg x L(-1) concentration for 24 h. We did not find effect on development time of B. tabaci eggs and nymphs, and on molting rate of adults when exposed to capsaicin at 500, 1000 and 2000 mg x L(-1) concentrations, however, exposure to 4000 mg x L(-1) concentration of capsaicin significantly affected development time of B. tabaci nymphs and molting rate of adults. Exposure to capsaicin also significantly reduced fecundity of B. tabaci adults, and this reduction was significantly dosage-dependent.
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