[Resistance to the organophosphate insecticides temephos and malathion in Culex pipiens L. (Diptera, Culicidae) from the Adriatic coast near Friuli].

Susceptibility to organophosphorus insecticides Temephos and Malathion was tested in Culex pipiens L. larvae from Friuli Adriatic coast (North-East of Italy). The samples were collected in various sites of three zones with different intensity of insecticidal treatments. Tests were made following the W.H.O. recommendations. The tests were made on larval samples which were exposed for 24 hours to ascending concentrations of each insecticide. From the observed percentage mortalities the LC50 and LC90 values were calculated. The resistance ratio was obtained comparing the CL50 values with reference CL50 values provided by the W.H.O. The obtained data suggest the existence of Cx. pipiens populations resistant to the tested chemicals in the most intensively treated touristic zone (Lignano Sabbiadoro). The samples collected in an agricultural zone with no mosquito control treatments showed a slight reduced susceptibility to the tested compounds.