First report of the lethal activity and synergism between deltamethrin, amitraz and piperonyl butoxide against susceptible and pyrethroid-resistant nymphs of Triatoma infestans

• Published in: Experimental parasitology Vol. 218; p. 107986
• Main Authors: Dadé, M.M., Daniele, M.R., Machicote, M., Errecalde, J.O., Rodriguez-Vivas, R.I.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.11.2020
• Subjects: Amitraz; Deltamethrin; Synergistic effect; Triatoma infestans; Triatomicidal activity; Vector control; Triatoma infestans; Synergistic effect; Vector control; Deltamethrin; Triatomicidal activity; Amitraz
• ISSN: 0014-4894; 1090-2449
• DOI: 10.1016/j.exppara.2020.107986

In South America, Triatoma infestans (Hemiptera: Reduviidae) is the main vector of the parasite Trypanosoma cruzi, etiological agent of Chagas disease. The main strategy for vector control is to spray domestic structures with pyrethroids. Reports of populations of T. infestans with varying degrees of resistance to pyrethroids have made the search for alternative molecules for vector control necessary. In the first stage of this work we investigated the lethal activity of amitraz and deltamethrin against susceptible and pyrethroid-resistant nymphs of Triatoma infestans. Lethal dose at 50% (LD50) of susceptible nymphs were compared with those recorded in pyrethroid-resistant nymphs and the resistance ratio (RR50) was obtained. The RR50 of deltamethrin was approximately 300. In the case of amitraz, we observed similar triatomicidal activity in the two nymph populations (RR50: 0.7). In a second stage of the work, we determined the synergistic effect of amitraz and piperonyl butoxide (PBO) on the lethal activity of deltamethrin. The strong synergistic effect of PBO on the lethal activity of deltamethrin in resistant nymphs produced a decrease in RR50 to almost one third of the RR50 reported in absence of the synergist. Amitraz plus PBO lethal activity was similarly increased in pyrethroid susceptible and resistant nymphs. Our data indicate that deltamethrin synergism by amitraz was higher against resistant than to susceptible nymphs (Synergist ratio (SR50) of: 7.2- and 4.1-fold, respectively). In pyrethroid resistant nymphs, the highest level of synergism was obtained combining deltamethrin with amitraz and PBO (SR50: 26.7-fold). These results indicate that this combination could be considered an effective alternative for the control of T. infestans. [Display omitted] •Topical application of deltamethrin and amitraz was lethal against nymphs of Triatoma infestans.•Salvador Mazza colony of T. infestans showed high levels of resistance to deltamethrin.•Lethal activity of amitraz was similar against susceptible and pyrethroid-resistant nymphs.•Synergism of deltamethrin by amitraz alone or PBO alone was similar against pyrethroid-resistant nymphs.•The highest level of synergism was obtained combining deltamethrin with amitraz and PBO.