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The biochemical basis of tolerance to malathion in Rhodnius prolixus
M I Picollo de Villar1, A Fontan, E Wood
1Centro de Investigaciones de Plagas e Insecticidas, CIPEIN, (CITEFA-CONICET), Pcia. de Buenos Aires, Argentina.
Abstract:
1. LC50 of malathion, fenitrothion and lindane were determined in R. prolixus and T. infestans. R. prolixus was shown to be tolerant to malathion. 2. The penetration rate of (14C)-malathion into R. prolixus and T. infestans was similar. 3. Acetylcholinesterase from R. prolixus heads was 3.3-fold less sensitive to inhibition by malaoxon than the similar enzyme of T. infestans. 4. R. prolixus showed more activity of GSH-S-transferases against DCNB than T. infestans. 5. The in vitro degradation of (14C)-malathion demonstrated that R. prolixus is more active than T. infestans in carboxyester splitting to give alpha and beta monoacids. 6. The synergism of TPP and TOCP on malathion toxicity was higher in R. prolixus than in T. infestans. 7. Esterase activity against alpha and beta naphthyl acetates proved to be much lower in R. prolixus homogenates than in T. infestans homogenates. An inverse result was observed when PTA was the substrate.
Insights
Rhodnius prolixus exhibits tolerance to malathion due to less sensitive acetylcholinesterase and higher degradation activity compared to Triatoma infestans. These factors contribute to differential insecticide susceptibility.
Area of Science:
- Vector biology
- Insect toxicology
- Biochemistry
Background:
- Triatomine insects like Rhodnius prolixus and Triatoma infestans are vectors for Chagas disease.
- Understanding insecticide resistance mechanisms is crucial for vector control strategies.
Purpose of the Study:
- To investigate the differential susceptibility of R. prolixus and T. infestans to insecticides, focusing on malathion.
- To elucidate the biochemical basis for malathion tolerance in R. prolixus.
Main Methods:
- Determination of lethal concentrations (LC50) for malathion, fenitrothion, and lindane.
- Measurement of (14C)-malathion penetration rates.
- Enzyme inhibition assays for acetylcholinesterase sensitivity to malaoxon.
- Assays for glutathione S-transferases (GSH-S-transferases) and carboxylesterase activities.
- In vitro degradation studies of (14C)-malathion.
Main Results:
- R. prolixus showed significantly higher tolerance to malathion compared to T. infestans.
- R. prolixus acetylcholinesterase was less sensitive to malaoxon inhibition, and R. prolixus exhibited higher in vitro malathion degradation via carboxylesterases.
- Higher activity of GSH-S-transferases was observed in R. prolixus.
- Synergism of malathion toxicity by TPP and TOCP was more pronounced in R. prolixus.
Conclusions:
- Differential activity of detoxification enzymes, particularly carboxylesterases and potentially GSH-S-transferases, contributes to malathion tolerance in R. prolixus.
- Reduced sensitivity of acetylcholinesterase is another key factor in R. prolixus malathion tolerance.
- These findings provide insights into insecticide resistance mechanisms in triatomine vectors.