Risk of control failure to insecticides malathion, profenophos + cypermethrin mixture, and fipronil in boll weevil (Coleoptera: Curculionidae) populations from Bahia, Brazil

Background To control the boll weevil Anthonomus grandis grandis (Coleoptera: Curculionidae), a key pest of cotton in the Americas, insecticides have been intensively used to manage their populations, increasing selection pressure for resistant populations. Thus, this study aimed to detect insecticide resistance and assess insecticide control failure likelihood of boll weevil populations exposed to malathion, profenophos + cypermethrin, and fipronil insecticides. Results Twelve populations of the boll weevil were collected from commercial cotton fileds of the state of Bahia, northeastern Brazil. These populations were exposed to malathion, profenophos + cypermethrin mixture, and fipronil, at their respective maximum label dose for field applications. Three replicates of 10 adult beetles were exposed to the insecticides and mortality was recorded after 24 h treatment. The control failure likelihood was determined after 48 h. Highest median lethal times ( LT 50 ) were observed for malathion and the profenophos + cypermethrin mixture. Resistance to at least one insecticide was detected in 11 populations; three populations were resistant to malathion and profenophos + cypermethrin; seven were resistant to all insecticides tested. The resistance levels were low (< 10-fold) for the three insecticides. Among 12 populations tested, 58% of them exhibited significant risk of control failure for the insecticides malathion and profenophos + cypermethrin. The insecticide fipronil was efficient for the control of the boll weevil in 83% of the populations. Conclusions The results confirm the significant risk of insecticide control failure in the boll weevil populations to the main compounds used in the region. Thus, proper insecticide resistance management plans are necessary for the boll weevil in the region, particularly for malathion and profenophos + cypermethrin insecticides.