Insecticide resistance

During 2000, a control failure after a pyrethroid application for T. infestans control was reported for the region of Salvador Mazza (Salta, Argentina), which was attributed to pyrethroid resistance.54 Subsequent studies have shown the occurrence of other control failure events of T. infestans populations, that were shown resistant to pyrethroids in the interandean valleys and Chaco region of Bolivia54,55 and more recently in several places in the Chaco province in Argentina.10 Studies showed the existence of several mechanisms of insecticide resistance (including penetrability of the insect cuticle, KDR genes,56 suggesting independent development of resistance appearance), and geographical distribution of highly resistant populations (producing pyrethroid-based control failures) limited to the Argentinian-Bolivian border.10 Studies reported so far on the T. infestans populations of the Bolivian Chaco and S. Mazza indicate a resistance rate to deltamethrin higher than 1000 in some places, with some cross-resistance to other pyrethroids and to fipronil, but generally susceptible to organophosphates and carbamates. Organophosphate and carbamate compounds have been sprayed by professional field teams of Argentina and Bolivia to control domestic and peridomestic populations of T. infestans in S. Mazza and various localities in Bolivia. Although postspraying reports indicate a decrease of vector abundance and house infestation, the resistant T. infestans populations are still present in the area.

A recent meta-analysis of insecticide resistance of T. infestans populations showed that although the phenomenon is widespread, control failure due to insecticide resistance is limited to the Argentinian-Bolivian border, it is associated with a particular combination of environmental variables values10 and with the occurrence of the intermediate cytogenetic phenotype (sensu51).

 
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