Comparative effect of fenitrothion treatment on intracellular protease activities in insecticide-resistant and susceptible strains of Musca domesticaL.

In order to further elucidate the biochemical mechanisms responsible for in secticide resistance in insects, we have determined changes in the activity levels of a comprehensive range of proteolytic enzymes (cytoplasmic and ly sosomal proteinases and peptidases, which play a key role in normal cell fu nctioning) in fenitrothion-resistant (571ab) and susceptible (Cooper) strai ns of Musca domestica following in vivo exposure to the insecticide fenitro thion. Untreated insects of the resistant strain had significantly higher l evels (20-100%) of activity for many protease types compared to the suscept ible strain (whole body analysis). Exposure to fenitrothion resulted in fur ther activity increases for most proteases at some point during the subsequ ent 24 h period in resistant strain insects; susceptible strain insects wer e also capable of similar increases in protease activities. We therefore su ggest that it must be the combination of intrinsically higher protease leve ls (prior to pesticide exposure), together with the capacity to further inc rease protease activities following insecticide exposure, which is importan t in the mechanism by which proteases may confer survival advantages in ins ecticide resistant insects. We further speculate that this mechanism may in volve increased supply of precursor amino acids From proteolytic degradatio n products to the intracellular pool, prior to de novo synthesis of detoxif ying enzymes following insecticide exposure (C) 1999 Elsevier Science Inc. All rights reserved.