Studies on the Resistance of Insects to Insecticides. I. Cholinesterase in House Flies (Musca domestica L.) Resistant to DDT

Abstract

The cholinesterase activity in the heads of houseflies resistant to DDT was lower during the first 5 days after emergence than was the activity in the heads of normal flies of the same age. After 5 days there was no consistency in the results. Males, on a wt. basis, in both the resistant and normal colonies, showed more activity than did the females. The activity varied from day to day but no regular pattern was observed. Acetylcholine was hydrolyzed about twice as fast as was acetyl-[beta]-methylcholine and about 7 times as fast as benzoylcholine. The reaction was inhibited by excess substrate and the opt. pH for the enzyme was about 5.75. Little rate change was noted between pH 6.25 and pH 9.0. The dissociation constant, Ks, of the enzyme substrate complex was calculated as 1 x 10-3.