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

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.

Descriptions of two new species of Eimeria (Apicomplexa: Eimeriidae) and of Eimeria chinchillae-like oocysts from the plains vizcacha Lagostomus maximus (Desmarest, 1817) (Rodentia: Chinchillidae) from Argentina.

Of 163 fecal samples collected between March 1997 and February 1999 from the plains vizcacha, Lagostomus maximus (Rodentia: Chinchillidae), 19 (12%) were found to be positive for coccidia. All species are from the genus Eimeria and 2 are described here as new. The third species is consistent with the description of Eimeria chinchillae De Vos and Van der Westhuizen, 1968. Sporulated oocysts of Eimeria lagostomi n. sp. are ellipsoidal to subspheroidal, 35.7 x 30.9 (26-36 x 30-41), with a length:width (L/W) ratio of 1.2 (1.0-1.3), without a micropyle (M) or polar granule (PG), but with an oocyst residuum (OR) comprised of a round, compact mass of many small granules. The sporocysts are lemon-shaped, 14.2 x 10.2 (9-11 x 11-16), with an L/W ratio of 1.4 (1.2-1.7) and have a Stieda body (SB) and sporocyst residuum (SR). Eimeria vizcacho n. sp. has sporulated oocysts that are subspheroidal, 26.4 x 23.4 (21-27 x 23-31), with an L/W ratio of 1.1 (1.1-1.2), lack an M and OR, but have 1-2 PGs. Sporocysts are elongate-ellipsoidal, 14.3-9.0 (8-10 x 13-15), with an L/W ratio of 1.6 (1.4-1.8), lack an SB, but have 2 SR; the first a small mass of granules lying between the sporozoites in the middle or at 1 end, and the second also of many small granules, always at the opposite end. Sporulated oocysts of the E. chinchillae-like organism are ellipsoidal to subspheroidal, 20.7 x 17.5 (15-22 x 17-24) with an L/W ratio of 1.2 (1.0-1.3), lack an M and OR, but have 0-3 PGs. Sporocysts are ellipsoidal, 10.7-6.9 (6-8 x 8-13) with an L/W ratio of 1.55 (1.3-1.8) and have an SB and SR.