Effects of sublethal doses of talstar on biochemical components of malathion-resistant and -susceptible adults of rhyzopertha dominica

To evaluate biochemical differences between malathion-resistant and -susceptible adult populations of lesser grain borer,rhyzopertha dominica a sublethal dose (lc20) of talstar,a pyrethroid insecticide,was administered at 1.4ppm to resistant and at 0.22ppm to susceptible population for a period of 48 hours. effects on various biochemical components such as some enzymes e.g.,acid phosphatase (acp),alkaline phosphatase (akp),amylase,cholinesterase (che),glutamic pyruvic transaminase (gpt),glutamic oxaloacetic transaminase (got),and trehalase and among metabolites free amino acids (faa),glucose,glycogen,soluble protein,total protein,total lipids,trehalose,dna and rna contents were studied. acp,amylase,lactate dehydrogenase (ldh) and trehalase activities were increased,whereas,a decrease in akp activity and glycogen and trehalose contents was observed in both populations. inhibition of che activity in resistant but induction in susceptible population indicates non-involvement of this enzyme in resistance of this beetle. among transaminases,both got and gpt activities decreased by 53% and 32% in resistant adults respectively,resulting in accumulation of faa and depletion of total protein contents which can be correlated with increase (52%) in faa level and the reduction (17%) in the total protein contents. the increase in got (23%) and gpt (15%) activities in susceptible adults is an indication of accelerated amino acid catabolism. high activities (43% and 117%) of ldh and isocitrate dehydrogenase (icdh),respectively,in resistant insects indicates that both catabolic pathways (glycolysis and tca cycle) are switched on to cope with the insecticidal stress,thus keeping up its ability to resist the insecticide which is obvious by significant decrease (25%) in glucose level. in susceptible population,ldh activity also elevated (38%) with no change in icdh activity exhibiting its inability to defend the insecticidal stress by complete oxidation of carbohydrates. huge accumulation of lipids (50% and 119%) in resistant and susceptible populations respectively,reveals enhancement of lipid biosynthesis. the higher enzyme activities induced by talstar may be justified by 70% and 76% rise in rna contents in both resistant and susceptible populations,respectively,through a probable increase in transcription rate. conclusively,both populations of r. dominica defended greatly against talstar stress by the induction of the major enzymes under the present experimental conditions. copyright 2011 zoological society of pakistan.