Toxicity and kinetic studies of H+, K+-ATPase sensitivity to cyfluthrin and fenpropathrin in Egyptian field populations of Spodoptera littoralis

Abstract

Toxicity of two pyrethroids (cyfluthrin and fenpropathrin) against cotton leafworm, Spodoptera littoralis, larvae werecollected from heavily sprayed fields in different areas in Dakahlia and El-Beheira Governorate. H+, K+-ATPase (protonpump)activity was measured in laboratory (lab.) strain and compared with enzyme activities for other collected strains. Thesensitivity of H+, K+-ATPase activity was measured by I50 values. The I50 values of cyfluthrin were 0.24; 0.46; 0.54; 0.65, and0.68 μM for lab; Abo-Hommos; Shobrakheet; Aga, and El-Senbellaween strains respectively, while I50 values offenpropathrin were 0.44; 0.58; 0.66; 0.84, and 0.87 μM for lab and four field strains respectively. Also, proton-pump enzymekinetic parameters, Km (Michaelis-Menten kinetics, constant) and Vmax (maximum velocity) values and the inhibitionconstant (Ki) were determined. The obtained data proved that cyfluthrin and fenpropathrin compounds were competitiveinhibitors of proton-pump activity. Results indicated that, the pyrethroid have shown potentiality against larvae of S.littoralis, so, these pyrethroids may be effect of a novel mechanism of action for inhibition of proton-pump activity, theserecommended for S. littoralis larvae control. It could be concluded that the use of pyrethroid, may avoid increasing ofresistance by effect of new mode of action where they disrupt the development of target pest, Therefor proton-pump may playan important role the mode of action of these pesticides in future.