Influence of cabbage proteinase inhibitors in situ on the growth of larval Trichoplusia ni and Pieris rapae

Trypsin and chymotrypsin inhibitors are proteins that are developmentally regulated in foliage of cabbage plants, appearing at high concentrations in young foliage on mature plants. This temporal and spacial regulation of foliar proteinase inhibitors is synchronized with the appearance and distribution of foliar feeding Lepidoptera. When insects were allowed to select their feeding sites, larval Pieris rapae fed on the young foliage of cabbage plants, while larval Trichoplusia ni fed on the mature foliage on cabbage plants. Larval P. rapae that fed on mature plants were significantly smaller than larvae feeding on young plants, while there was no significant difference between larval T. ni feeding on mature plants and those feeding on young plants. Thus, there was a significant inverse correlation between the level of proteinase inhibitory activity in cabbage foliage and larval growth. When P. rapae and T. ni were provided with an artificial diet containing total protein (including significant levels of proteinase inhibitors) that was extracted from cabbage foliage, them was a significant reduction in growth and development of both species of Lepidoptera