Inhibitional Effects of Metal Zn(2+) on the Reproduction of Aphis medicaginis and Its Predation by Harmonia axyridis

BACKGROUND: Contamination, including metals, can disturb the reproductive processes of many organisms, including both prey and predatory insects. However, there is virtually no information on the effects of high level Zinc (Zn) pollution on aphids and ladybirds. The high concentrations of Zn(2+) or Zn pollution inhibit reproduction in the phytophagous aphid, Aphis medicaginis, and the predatory ladybird Harmonia axyridis could provide important information. RESULTS: It was observed in this study that Zn concentrations in Vicia faba (broad bean) seeds and seedlings in all Zn(2+) treatments were significantly higher than that in the control group, and increased with increasing Zn(2+) concentrations in the solution. The rate of reproduction in A. medicaginis declined significantly (p<0.05) over time in the five groups fed on broad bean seedlings treated with different concentrations of Zn(2+) solution compared with the control group. These results showed that higher concentrations of Zn(2+) significantly inhibited the reproductive capacity of A. medicaginis. We also cloned and identified a gene encoding vitellogenin (Vg) from A. medicaginis, which has an important role in vitellogenesis, and therefore, reproduction was affected by exposure to Zn(2+). Expression of AmVg was reduced with increasing exposure to Zn(2+) and also in the F(1)–F(3) generations of aphids exposed to different Zn(2+) concentrations. Predation by H. axyridis was also reduced in aphids exposed to high-levels of Zn(2+). Similarly, ovipositioning by H. axyridis was also reduced. CONCLUSIONS: Our results suggest that Zn(2+) can significantly affect the reproductive capacity of both A. medicaginis and its predator H. axyridis, the former through effects on the expression of AmVg and the latter through avoidance of aphids containing high levels of Zn(2+).