We previously reported that a combination of serine and cysteine proteinase inhibitors in bioassays was necessary to reduce the survival of the red flour beetle,
Tribolium castaneum. In a study of the effect of inhibitors on the growth and development of
T. castaneum larvae, survivors were dissected from various inhibitor treatments, and the gut extracts were analyzed for proteinase activity. Zymogram analyses detected major proteinase activities around 20 kDa, and the data suggested that this corresponded to cathepsin-L-like proteinase activity. Larvae surviving treatments with some cysteine proteinase inhibitors (CPI) had decreased 20 kDa proteinase activity and increased activity in various higher molecular mass proteinases. Activity blot analysis with the chymotrypsin substrate n-succinyl-ala-ala-pro-phe para-nitroanilide corresponded to the zymogram results.
In vitro analyses of gut extracts from larvae reared on diet containing CPI demonstrated a loss of inhibition by CPI, with a concomitant increase of inhibition by serine proteinase inhibitors (SPI). Minor changes in inhibition patterns occurred when larvae were fed SPI. These results suggested that T. castaneum larvae compensate for CPI through a stimulation of serine proteinases. Therefore, a successful inhibitor-based control strategy should incorporate inhibitors of both cysteine and serine proteinase subclasses. Supported by USDA-ARS and CPBR-Dow AgroSciences.
Species 1: Coleoptera Tenebrionidae Tribolium castaneum (red flour beetle)
Keywords: insect proteinases, insect digestion
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