[Cross resistance to pyrethroids in Aedes aegypti from Cuba induced by the selection with organophosphate malathion].

A strain from Aedes aegypti (L) collected in the municipality of Santiago de Cuba with low levels of resistance to malathion (1.79x) was subjected to selection pressure aimed at evaluating the evolution of the resistance to this organophosphate and its usefulness for control. After 5 generations of selection (SAN-F5) with malathion, it was not possible to increase the resistance and it was obtained a value of resistance factor (FR50) of 2.22x. None or little cross resistance to the following organophosphate insecticides was observed: fenthion, temephos and fenitrotion; however, it was found an elevated cross resistance to deltamethrin pyrethroid, with a value of 287.5x in the third generation of selection. It was also observed cross resistance to other pyrethroids (lambda-cyhalothrin, cypermethrin and ciflutrine). The mechansim of elevated esterases did not generate resistance to pyrethroids, which was corroborated through inhibition gel studies and through the calculation of the frequency in microtitering plaques. Nevertheless, there was an increase in the frequency of the glutathione-s-transferase mechanism from 0.049 in Santiago de Cuba to 0.42 in SAN-F5, which may be associated with the resistance to pyrethroids. The cross resistance to pyrethroids, mainly to deltamethrin, resulting from the selection with malathion may limit the use of these insecticides in the control unless a good strategy for their use is laid down.