Aerobic Metabolism Alterations as an Evidence of Underlying Deltamethrin Resistance Mechanisms in Triatoma infestans (Hemiptera: Reduviidae).

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 (V˙H2O) and CO2 production rate (V˙CO2), 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 V˙H2O between populations suggested that cuticular thickness/composition is not acting as a relevant resistance mechanism. Similarly, there was no difference in resting V˙CO2, suggesting a trade-off between resistance mechanisms and other physiological processes. The increment in V˙CO2 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.

Aerobic Metabolism Alterations as an Evidence of Underlying Deltamethrin Resistance Mechanisms in Triatoma infestans (Hemiptera: Reduviidae) / Alterações do metabolismo aeróbico como evidência de mecanismos subjacentes de resistência à deltametrina em Triatoma infestans (Hemiptera: Reduviidae)

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 (V˙H2O) and CO2 production rate (V˙CO2), 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 V˙H2O between populations suggested that cuticular thickness/composition is not acting as a relevant resistance mechanism. Similarly, there was no difference in resting V˙CO2, suggesting a trade-off between resistance mechanisms and other physiological processes. The increment in V˙CO2 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.

Stage-Dependent Expression of Deltamethrin Toxicity and Resistance in Triatoma infestans (Hemiptera: Reduviidae) From Argentina.

Triatoma infestans Klug (Hemiptera: Reduviidae) is the main vector of Chagas disease in Latin America. This insect has been controlled with pyrethroids since the 1980s, although the emergence of resistance to deltamethrin has decreased control success in some areas of the Gran Chaco ecoregion. The response of T. infestans to deltamethrin was evaluated per developmental stage. In addition, we evaluated the possible stage-dependent expression of deltamethrin resistance. The bioassays were conducted by topical application of the insecticide in acetone. The drop size, age at the time of exposure, and mortality measuring time were standardized per stage. The lethal dose of deltamethrin moderately increased with the developmental stage. The resistance to deltamethrin was expressed in every instar, and was the highest in the fourth- and fifth-instar nymphs. While increasing, weight plays a relevant role in lethal dose stage dependency, a number of contributing factors such as degradative metabolism are probably involved in the variability of insecticide effect and resistance described for different T. infestans developmental stages. Possible explanations for these differences and their implications on resistance management and chemical control are discussed.

Stage-Dependent Expression of Deltamethrin Toxicity and Resistance in Triatoma infestans (Hemiptera: Reduviidae) From Argentina

Triatoma infestans Klug (Hemiptera: Reduviidae) is the main vector of Chagas disease in Latin America. This insect has been controlled with pyrethroids since the 1980s, although the emergence of resistance to deltamethrin has decreased control success in some areas of the Gran Chaco ecoregion. The response of T. infestans to deltamethrin was evaluated per developmental stage. In addition, we evaluated the possible stage-dependent expression of deltamethrin resistance. The bioassays were conducted by topical application of the insecticide in acetone. The drop size, age at the time of exposure, and mortality measuring time were standardized per stage. The lethal dose of deltamethrin moderately increased with the developmental stage. The resistance to deltamethrin was expressed in every instar, and was the highest in the fourth- and fifth-instar nymphs. While increasing, weight plays a relevant role in lethal dose stage dependency, a number of contributing factors such as degradative metabolism are probably involved in the variability of insecticide effect and resistance described for different T. infestans developmental stages. Possible explanations for these differences and their implications on resistance management and chemical control are discussed.

Microgeographical study of insecticide resistance in Triatoma infestans from Argentina.

Chagas disease is a chronic parasitic infection restricted to America where it is currently estimated that 90 million people are at risk of acquiring the infection. Chemical control with pyrethroid insecticides has been effective to reduce disease transmission in several areas of the Southern Cone, although insecticide resistance has evolved and diminished the campaigns' results. Considering previous reports on the different levels of resistance between Triatoma infestans from different geographical areas, the objective of this work was to determine if T. infestans populations are toxicologically structured within localities. Response to the insecticide was measured and compared between houses of two Argentine localities. Different toxicity of deltamethrin was detected between dwellings of Chaco province, accounting for both susceptible and resistant houses within the same locality. However no difference was found among houses of Salta province. The results obtained in this work suggest that geographical structure is present not only at the between localities level, but also at the microgeograhical level.

Autosomal inheritance of deltamethrin resistance in field populations of Triatoma infestans (Heteroptera: Reduviidae) from Argentina.

BACKGROUND: Triatoma infestans (Klug) is the major Chagas disease vector in the Southern Cone area of South America, and its chemical control is based on the use of pyrethroid insecticides. Resistance to deltamethrin in Salta Province, Argentina, has been detected in field populations since 2002, causing the failure of vector control campaigns in this disease-endemic area. The inheritance of deltamethrin resistance in T. infestans was evaluated through reciprocal crosses conducted between resistant and susceptible insects. RESULTS: The response of the reciprocally mated insects' progeny to deltamethrin was intermediate between the highly resistant and the susceptible parent colonies. Lack of significant differences between the LD(50) and resistance ratios of the reciprocally mated insects indicated no sex linkage on this trait. CONCLUSION: Bioassay results, in addition to degree of dominance calculations, suggest that the resistance to deltamethrin in T. infestans is controlled by semi-dominant, autosomally inherited factors.