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

Abstract EN

Toxicity of two pyrethroids (cyfluthrin and fenpropathrin) against cotton leafworm, Spodoptera littoralis, larvae were collected 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.

The sensitivity of H+, K+-ATPase activity was measured by I50 values.

The I50 values of cyfluthrin were 0.24; 0.46; 0.54; 0.65, and 0.68 μM for lab; Abo-Hommos; Shobrakheet; Aga, and El-Senbellaween strains respectively, while I50 values of fenpropathrin were 0.44; 0.58; 0.66; 0.84, and 0.87 μM for lab and four field strains respectively.

Also, proton-pump enzyme kinetic parameters, Km (Michaelis-Menten kinetics, constant) and Vmax (maximum velocity) values and the inhibition constant (Ki) were determined.

The obtained data proved that cyfluthrin and fenpropathrin compounds were competitive inhibitors 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, these recommended for S.

littoralis larvae control.

It could be concluded that the use of pyrethroid, may avoid increasing of resistance by effect of new mode of action where they disrupt the development of target pest, Therefor proton-pump may play an important role the mode of action of these pesticides in future.