RESUMEN
Abstract Triatoma infestans (Klug, 1834), the main vector of Chagas disease in Latin America, is regularly controlled by spraying the pyrethroid deltamethrin, to which some populations have developed resistance. The three main mechanisms of resistance are 1) metabolic resistance by overexpression or increased activity of detoxifying enzymes, 2) target site mutations, and 3) cuticle thickening/modification. We use open-flow respirometry to measure real-time H2O loss rate (VËH2O) and CO2 production rate (VËCO2), on nymphs from susceptible and resistant populations before and after exposure to the insecticide to understand the underlying mechanisms of resistance in live insects. Lack of differences in VËH2O between populations suggested that cuticular thickness/composition is not acting as a relevant resistance mechanism. Similarly, there was no difference in resting VËCO2, suggesting a trade-off between resistance mechanisms and other physiological processes. The increment in VËCO2 after application of deltamethrin was similar in both populations, which suggested that while enhanced enzymatic detoxification may play a role in resistance expression in this population, the main mechanism involved should be a passive one such as target site mutations. Open-flow respirometry provided useful evidence for evaluating the mechanisms involved in deltamethrin resistance. Using this technique could improve efficiency of scientific research in the area of insecticide resistance management, leading to a faster decision making and hence improved control results.
Asunto(s)
Resistencia a los Insecticidas , Insecticidas , Enfermedad , Triatominae , Enfermedad de ChagasRESUMEN
Triatomines are blood-sucking bugs that occur mainly in Latin America. They are vectors of Trypanosoma cruzi, the parasite that causes Chagas disease. Chemical control of Chagas disease´s vectors by using pyrethroid insecticides has been highly successful for the elimination of domestic infestation and consequently the reduction of the vector transmission. However, at the beginning of the 2000s a decrease in the effectiveness of the chemical control of triatomines was detected in several areas from Argentina and Bolivia, particularly in the Gran Chaco eco-region. During the last 15 years, several studies demonstrated the evolution of insecticide resistance in Triatoma infestans and established the presence of different toxicological profiles, the autosomal inherence of resistance, the biological costs of deltamethrin resistance, the expression of deltamethrin resistance thorough the embryonic development, and the main mechanisms of resistance (target-site insensitivity and metabolic detoxification of insecticides). The emergence of pyrethroid resistance coupled with the usual difficulties in sustaining adequate rates of insecticide applications emphasize the need of incorporating other tools for integrated vector and disease control, such as the proposal of the organo-phosphorus insecticide fenitrothion as an alternative chemical strategy for the management of the resistance because it was effective against pyrethroid-resistant populations in laboratory and semi-field trials. New studies on the current situation of presence and spread of resistant populations of triatomines and the acceptance of the use of alternative insecticides are critical requirements in the implementation of strategies for the management of resistance and for the rational design of campaigns oriented to reducing the vector transmission of Chagas' disease.
Asunto(s)
Piretrinas , Triatoma , Resistencia a los Insecticidas , Enfermedad de Chagas , Costos y Análisis de CostoRESUMEN
The status of resistance to cyromazine, 2,2-dichlorovinyl dimethyl phosphate (DDVP), and permethrin relative to field populations of the house fly, Musca domestica L. from Argentinean poultry farms was studied. All the three studied populations (SV, Q, and C) showed resistant ratios (RRs) to cyromazine of 3.9, 10.98, and 62.5, respectively. We observed high levels of resistance toward the organophosphate DDVP and permethrin. The RRs to DDVP ranged from 45.4 to 62.5. No significant differences were found among the studied populations. All the house fly populations were permethrin-resistant, in comparison with the susceptible strain. Two of the analyzed populations (SV and Q) differed significantly in toxicity to the population C. This is the first evidence that house flies from Argentina showed a multi-resistance pattern. The implementation of an insecticide monitoring program on poultry farms of Argentina is needed to prevent field control failures. Furthermore, integrated control strategies are needed to delay detrimental development of insecticide resistance.