Changes in gluconasturtiin concentration in Chinese cabbage with increasing cabbage looper density

Changes in the levels of gluconasturtiin (2-phenylethyl glucosinolate), an aromatic glucosinolate, was used to evaluate the response of 'Green Rocket' Chinese cabbage (Brassica campestris ssp. pekinensis L.) to the feeding of three and five cabbage looper (Trichoplusia ni Hubner) larvae per plant. Plants were harvested 0, 10, and 17 days after infestation. The change in gluconasturtiin concentration resulting from decreased light capture from diminished leaf area was also studied. All samples were assayed for gluconasturtiin concentration using high-performance liquid chromatography. The gluconasturtiin concentration of plants subjected to five larvae per plant showed a 59% increase 10 days after infestation compared with noninfested plants. Difference in gluconasturtiin concentration between three and five larvae per plant was nonsignificant. Seventeen days after initial infestation and 7 days after larvae were removed (final harvest), gluconasturtiin concentration did not decrease compared with the previous harvest. Reduced light or leaf area removal did not significantly affect gluconasturtiin concentration.