Effects of zinc exposure on the reproduction of Spodoptera litura Fabricius (Lepidoptera: Noctuidae).

Reproductive toxicity of Zn to insects was investigated in this study. By exposing phytophagous insect Spodoptera litura Fabricius to Zn in artificial diets of larvae, we investigated the effects of Zn on reproduction at ecological and molecular levels. A significantly shorter period of laying eggs was observed in S. litura exposed to 300-750mg Zn/kg. The oviposition rate, fecundity and hatchability of female adults treated with 750mg Zn/kg were significantly lower than those of the controls (31.43%, 20.95% and 52%, respectively, compared to the control). The Zn accumulation and vitellin (Vn) content in eggs were tested by inductively coupled plasma-atomic emission spectrometry and Bradford combining Western-blot, respectively. The results showed that Zn accumulated in the eggs, which has affected the weight and Vn content of eggs with significant negative correlations. The down-regulated expression levels of vitellogenin (Vg) mRNA were detected by real-time polymerase chain reaction (RT-PCR): the relative quantity of Vg mRNA was less than half of the controls at higher than 450mg Zn/kg wet weight. These results indicated that excess Zn made expression of Vg gene down-regulated and caused poor accumulation of egg yolk, which led to a reduction in egg numbers and failure of eggs to hatch.