Pakistan J. Zool., vol. 42(5), pp. 623-630, 2010. Comparative Effects of Cyfluthrin on Intracellular Protease Activities in Insecticide-Resistant and Susceptible Strains of Musca domestics L. Mushtaq A. Saleem, Richard M. Wilkins and A. R. Shakoori Department of Agriculture Entomology, University College of Agriculture, B. Z. University, Multan, Pakistan (MAS), Department of Agriculture and Environmental Science, University of Newcastle upon Tyne, NEI 7RU, England (RMW) and Biological Sciences, Punjab University, New Campus, Lahore, Pakistan (ARS) Abstract.- To elucidate whether insecticide toxicity in insects involves insecticide-induced abnormalities of the intracellular protein catabolic process, we have determined in vivo effect of one of the commonly used synthetic pyrethroid, cyfluthrin on the activities of representative protein catabolising cytoplasmic and lysosomal proteases (responsible for the various stages of the protein degradation cascade and essential for normal cell functioning) in resistant and susceptible strains of Musca domestica. Effect of cyfluthrin was determined at LC50 dose level after 48 hour of treatment in both live and dead adult flies, compared with controls. In susceptible strain, cyfluthrin increased all cytoplasmic proteases in surviving flies (ranging from 16 to 148%) and their elevation was further intensified in dead flies (ranging from 24 to 177%). Of lysosomal proteases only cathepsin H (+18%) and D (-26%) were affected in surviving flies while in dead flies cathepsin B and L were additionally affected. Conversally in resistant flies, cyfluthrin produced mixed responses of increase or decrease in cytoplasmic and lysosomal proteases of surviving flies and this affect was further increased or it adopted the route of readjustment in dead flies. We conclude that cyfluthrin affected almost all proteases and such changes in proteases could play an important role in the development of resistance in M. domestica to insecticides. Key words.- Cufluthrin, Musca domestica, insecticide-resistance, cytoplasmic proteases, lysosomal proteases, aminopeptidases, endopeptidases, cathepsins INTRODUCTION According to the reports of Central Plant Protection Department, Pakistan has been importing a large quantities of synthetic organic insecticides to control insect pests of important crops such as cotton, sugarcane, rice etc. It is estimated that pesticides more than value of Rs. 12.0 billion are imported and used on such crops every year (Saleem and Ashfaq, 2004). This figure is increasing steadily with the rapid growth of population. Of the total import, about 80% is consumed on cotton crop. The extensive and indiscriminate use of insecticides has resulted development of resistance in various insects to insecticides. For instance a high level of resistance has been developed in Helicoverpa armigera and Bemisia tabaci against cypermethrin and methamidophos, respectively (Ahmad et al., 1995). Development of insect resistance to insecticides has emerged as important problem in this country and the world over. Likewise Musca * Corresponding author: mushtaqasaleem@hotmail.com 0030-9923/2010/0005-0623 $ 8.00/0 Copyright 2010 Zoological Society of Pakistan. domestica has also developed resistance to commonly used insecticides such as DDT and malathion etc. Thus it has become imperative to study biochemical resistance mechanisms in various insect pests to the related insecticides (Saleem et al., 1994a,b). It is now well established that insecticide detoxification enzymes such as mixed function oxidases, carboxylesterases and glutathione-S- transferases are mainly responsible for development of resistance in insects to various insecticides. According to review of the literature, these detoxification enzymes are inducible and such increased enzymatic activities may be due to alteration in gene regulation e.g. increased transcription and translation or post-translational modification of protein (Bresnick, 1980; Terriere, 1984; Brown and Brogdon, 1987). Hence extensive research studies have been focused on induction of detoxification enzymes in various insects followed by insecticidal treatments (Terriere, 1984). On the contrary very little attention has been paid regarding possible role of proteolytic enzyme activities in mechanism of resistance development in insects to insecticides, although much work has been