Azadirachtin ingestion is lethal and inhibits expression of ferritin and thioredoxin peroxidase genes of the sweetpotato whitefly Bemisia tabaci

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 10 ppm azadirachtin using a two-layered parafilm feeding chamber. Mortality gradually increased with time and increased dosage, with all individuals dead at 72 and 48 h at 5 and 10 ppm, 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 5 ppm azadirachtin for 12 h 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.