Pesticide has made a great contribu tion on controlling plant diseases and insect pests,however it also contaminated ecological environment and threatened the secu rity of birds.

• 农药曾经为人类控制生物病虫害作出过巨大贡献，但是农药污染也破坏了生态环境，对野生鸟类的生存造成了严重威胁。