Frequency and intensity of pyrethroid resistance through the CDC bottle bioassay and their association with the frequency of kdr mutations in Aedes aegypti (Diptera: Culicidae) from Mexico

BACKGROUND

The control of Aedes aegypti (L.), the main urban vector that causes arboviral diseases such as dengue, Chikungunya and Zika, has proved to be a challenge because of a rapid increase in insecticide resistance. Therefore, adequate monitoring of insecticide resistance is an essential element in the control of Ae. aegypti and the diseases it transmits. We estimated the frequency and intensity (Resistance Frequency Rapid Diagnostic Test [F-RDT] and Resistance Intensity Rapid Diagnostic Test [I-RDT]) of pyrethroid resistance in populations of Ae. aegypti from Mexico using the bottle bioassay and results were related to the frequencies of knockdown resistance (kdr) mutations V1016I and F1534C.

RESULTS

All populations under study were resistant to the pyrethroids: bifenthrin (99%), d-(cis-trans)-phenothrin (6.3% cis, 91.7% trans) and permethrin (99.5%) according to F-RDT, and showed moderate to high-intensity resistance at 10× the diagnostic dose (DD) in I-RDT. Frequencies of the kdr mutation V1016I in Ae. aegypti populations were correlated with moderate permethrin resistance at 10× DD, whereas F1534C mutation frequencies were correlated with high bifenthrin resistance at 5× DD. Both I1016 and C1535 were highly correlated with high-intensity phenothrin resistance at 1× to 10× DD.

CONCLUSIONS

This study showed that high frequencies of kdr mutations V1016I and F1534C are reflected in the results of F-RDT and I-RDT tests. Bioassays in conjunction with the characterization of genetic resistance mechanisms are indispensable in the strategic and rational management of resistance in mosquitoes. © 2018 Society of Chemical Industry.

Frequency of V1016I and F1534C mutations in the voltage-gated sodium channel gene in Aedes aegypti in Venezuela

BACKGROUND

The V1016I and F1534C mutations in the voltage-gated sodium channel gene have been associated with resistance to pyrethroids and DDT in Aedes aegypti mosquitoes. A study was carried out to determine the frequency of I1016 and C1534 by real-time PCR in five natural populations of Ae. aegypti in Venezuela during 2008, 2010 and 2012, as well as in a strain selected with 0.14 µg of deltamethrin for 15 generations.

RESULTS

In natural populations, frequencies of I1016 varied between 0.01 and 0.37, and frequencies of C1534 between 0.35 and 1.0. In the Pampanito strain, the frequency of I1016 increased from 0.02 in F1 up to 0.5 in F15 and from 0.35 up to fixation for C1534 after selection with deltamethrin.

CONCLUSION

The results showed that C1534 frequencies are higher than I1016 frequencies in natural populations of Ae. aegypti in Venezuela, and that deltamethrin selected the C1534 more rapidly than I1016.

Susceptibility status of Aedes aegypti (L.) (Diptera: Culicidae) to temephos in Venezuela

BACKGROUND

Temephos is an insecticide widely used in Venezuela to control the proliferation of the larvae of Aedes aegypti (L.), the principal vector of dengue virus. The aim of this study was to identify the susceptibility to temephos of Ae. aegypti in four locations in western Venezuela: Lara, Tres Esquinas, Ureña and Pampanito. Larval bioassays were conducted on samples collected in 2008 and 2010, and the levels of α- and β-esterases, mixed-function oxidases, glutathione-S-transferase and insensitive acethyl cholinesterase were determined.

RESULTS

Larval populations from western Venezuela obtained during 2008 and 2010 were found to be susceptible to temephos, with low resistance ratios and without overexpression of enzymes.

CONCLUSIONS

The low RR values reveal the effectiveness of temephos in controlling the larval populations of Ae. aegypti. Control strategies must be vigorously monitored to maintain the susceptibility to temephos of these populations of Ae. aegypti.

Resistance to malathion and deltamethrin in Aedes aegypti (Diptera: Culicidae) from western Venezuela

Resistance to the insecticides deltamethrin and malathion and the enzymes associated with metabolic resistance mechanisms were determined in four field populations of Aedes aegypti (L.) from western Venezuela during 2008 and 2010 using the bottle assay and the microplate biochemical techniques. For deltamethrin, mortality rates after 1 h exposure and after a 24-h recovery period were determined to calculate the 50% knock-downconcentration (KC50) and the lethal concentration (LC50), respectively. For malathion, mortality was recorded at 24 h to determine the LC50. For deltamethrin, resistance ratios of knock-down resistance and postrecovery were determined by calculating the RRKC50 and RRLC50, comparing the KC50 and LC50 values of the field populations and those of the susceptible New Orleans strain. Knock-down resistance to deltamethrin was moderate in the majority of the populations in 2008 (RRKC50 values were between 5- and 10-fold), and only one population showed high resistance in 2010 (RRKC50 > 10-fold). Moderate and high postrecovery resistance to deltamethrin was observed in the majority of the populations for 2008 and 2010, respectively. There was significantly increased expression of glutathione-S-tranferases and mixed-function oxidases. All populations showed low resistance to malathion in 2008 and 2010 with significantly higher levels of alpha-esterases for 2008 and 2010 and beta-esterases for 2008.

Resistance to symptomatic insulin reactions after fasting

This study was carried out to determine if, in fasting, an adaptation to utilization of ketones could prevent cerebral dysfunction during periods of acute, insulin-induced glucopenia. In the course of standard insulin tolerance tests (0.1-0.2 U/kg), nine obese subjects manifested frank hypoglycemic reactions resulting in an increase in urinary catecholamine excretion from 61 to 113 mug/24 hr (P < 0.01). After fasting 2 months, administration of weight-adjusted doses of insulin produced identical maximum insulin concentrations and disappearance curves. However, no insulin reactions nor significant rises in catecholamine excretion occurred despite equal extent and rate of glucose fall. Glucose concentrations as low as 0.5 mmoles/liter (9 mg/100 ml) failed to precipitate hypoglycemic reactions. During the postfast insulin tolerance tests, mean plasma 2-hydroxybutyrate (beta-OHB) decreased from 8.02 to 6.69 mmoles/liter (P < 0.01). In another five fasting subjects tested, the A-V difference for beta-OHB across brain increased progressively from 0.21 to 0.70 mmoles/liter whereas across the forearm no consistent uptake could be demonstrated. Simultaneously, the A-V difference across the brain for glucose decreased from 0.24 to 0.07 mmoles/liter of plasma. In addition to insulin-induced suppression of hepatic ketogenesis, the augmented cerebral ketone uptake during insulin hypoglycemia contributes to the net fall in plasma beta-OHB. Ketoacids, extracted by the fast-adapted brain, supplant glucose as a metabolic substrate preventing overt hypoglycemic reactions during acute glucopenia.