Abstract
Azadirachtin is a plant-derived triterpenoid compound, which has adverse effects on growth, feeding, and reproduction of insects. However, its action is not well understood at the molecular level. The effects of oral ingestion of azadirachtin in whiteflies, Bemisia tabaci, a serious pest of various agriculturally important plants, were determined by assessing their mortality and changes in gene expression. Whiteflies (0-day-old) were allowed to ingest 20% sugar solution containing 0, 1, 5, or 10ppm azadirachtin using a two-layered parafilm feeding chamber. Mortality gradually increased with time and increased dosage, with all individuals dead at 72 and 48h at 5 and 10ppm, respectively. Furthermore, the mRNA levels of 15 genes, which are associated with development, metabolism, defenses, and stresses, were compared between whiteflies which ingest either 0 or 5ppm azadirachtin for 12h by quantitative real-time RT-PCR. Most genes changed mRNA levels at less than 2 folds. However, the expression of thioredoxin peroxidase 1 and two ferritin genes which have protective roles against oxidative stress was inhibited up to 3–6 folds more than that in untreated whiteflies. These results suggest that lethal toxicity of azadirachtin may be due to increased cellular oxidative stress of B. tabaci.
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