Effect of exposure of Pieris brassicae larvae to 2,4,5-trichlorophenoxyacetic acid on the natural antibacterial activity of serum.

Larvae of the cabbage white butterfly, Pieris brassicae, were reared on a semisynthetic diet with or without 20 ppm of the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and using three assays the sera were subsequently tested for natural antibacterial activity against Bacillus cereus, Escherichia coli K12, and Micrococcus luteus. These assays showed that exposure of larvae to 2,4,5-T lowered the antibacterial activity of the serum against E. coli and M. luteus compared with control animals. Spectrophotometric tests for the presence of a lysozyme-like principle in the serum also revealed similar trends with a significant loss of enzyme activity in 2,4,5-T-treated insects. Overall total serum protein levels of control and 2,4,5-T-treated insects were similar, suggesting a specific effect of the herbicide on certain serum components such as lysozyme. The possible mode of action of the herbicide on production of antibacterial factors is discussed.