Study on residue trends of imidacloprid in pear fruit.

The residue dynamics and terminal residues of imidacloprid in pear fruit and the effect of bagging on pesticide content in fruit were analyzed. The results showed that the degradation half-life of imidacloprid was 9.68 d in peel and 5.39 d in flesh. When the whole tree was sprayed 1 or 2 times with 1 000 times diluted of imidacloprid, the final residues were 0.181 mg·kg-1 and 0.225 mg·kg-1 in peel, respectively. When sprayed with 1 500 times diluted of insecticide, the final residues were 0.022 mg·kg-1 and 0.031 mg·kg-1 in peel. Imidacloprid could not be detected in flesh whatever the application concentration was. The final residues could be controlled to lower than MRL (0.5 mg·kg-1). Results indicated that the residue mostly existed in peel and seldom in flesh. The residue of imidacloprid in peel of bagged fruits was 96.6% lower than that in nonbagged fruits. The difference between two treatments was extremely significant.