Wide Spread Cross Resistance to Pyrethroids in <I>Aedes aegypti</I> (Diptera: Culicidae) From Veracruz State Mexico

Abstract

Seven F1 strains of Aedes aegypti (L.) were evaluated by bottle bioassay for resistance to the pyrethroids d-phenothrin, permethrin, deltamethrin, λ-cyalothrin, bifenthrin, cypermethrin, α-cypermethrin and z-cypermethrin. The New Orleans strain was used as a susceptible control. Mortality rates after a 1h exposure and following a 24h recovery period were determined. The resistance ratio between the 50% knockdown values (RRKC50) of the F1 and New Orleans strains indicated high levels of knockdown resistance (kdr). The RRKC50 with α-cypermethrin varied from 10–100 among strains indicating high levels of kdr. Most of the strains had moderate resistance to d-phenothrin. Significant but much lower levels of resistance were detected for λ–cyalothrin, permethrin and cypermethrin. For z-cypermethrin and bifenthrin, only one strain exhibited resistance with RRKC50 values of 10- and 21-fold, respectively. None of the strains showed RRKC50 >10 with deltamethrin, and moderate resistance was seen in three strains, while the rest were susceptible. Mosquitoes from all strains exhibited some recovery from all pyrethroids except d-phenothrin. Regression analysis was used to analyze the relationship between RRLC50 and RRKC50. Both were highly correlated (R2 = 0.84 – 0.97) so that the slope could be used to determine how much additional pyrethroid was needed to insure lethality. Slopes ranged from 0.875 for d-phenothrin (RRLC50 ≃ RRKC50) to 8.67 for λ–cyalothrin (~8.5 fold more insecticide needed to kill). Both RRLC50 and RRKC50 values were highly correlated for all pyrethroids except bifenthrin indicating strong cross resistance. Bifenthrin appears to be an alternative pyrethroid without strong cross resistance that could be used as an alternative to the current widespread use of permethrin in Mexico.

Susceptibility to insecticides and resistance mechanisms in Aedes aegypti from the Colombian Caribbean Region

“…The resistance to DDT recorded in all the populations evaluated concurs with the findings of other earlier studies, in which general resistance to this agent was observed [15,29,34,35]. In some of these studies, it was suggested that this resistance came from a population of Ae.…”

“…They would also explain the results obtained in this and other studies carried out in Colombia where there is resistance to pyrethroids such as permethrin and cyfluthrin, even those these have not been used or minimally used in public health [5]. The presence of the I1,016 mutation in Colombia provides the first evidence of another mechanism of resistance to pyrethroids, in addition to the enzymatic alteration previously described in different populations of other regions of Colombia [5,15,29]. We found relatively low I1,016 homozygote frequencies as compared to other pyrethroid resistant populations from other countries [28,[39][40][41][42].…”

“…In the case of pyrethroids, the exposure time was 1 h during which observations were made every 10 min to record the numbers of knocked down mosquitoes up to 1 h. All mosquitoes were gently transferred to a recovery container without insecticide and were offered a cotton ball soaked in a sugar solution. Mortality was recorded at 24 h. Both the bottles and recovery containers were kept at 24 ± 2°C and 70% RH following Flores et al [15]. The monitored mortality 24 h after a 1 h insecticide exposure provides a means of implicating other, possibly metabolic, forms of resistance based on the observation that many of the mosquitoes that were knocked down following pyrethroid exposure in the bottle bioassay recovered when removed from the pesticide.…”

“…A slope~1 suggests LC50~KC50 or that most knocked down mosquitoes are dead 24 hours later. A slope > 1 suggests LC50 > KC50 or that recovery occurs and more insecticide is required to kill knocked down mosquitoes [15].…”

Local Evolution of Pyrethroid Resistance Offsets Gene Flow Among Aedes aegypti Collections in Yucatan State, Mexico

“…This situation is beneficial for insecticide resistance management; providing critical "islands" of pyrethroid susceptibility that provide a source for susceptibility alleles. Because wide cross resistance to pyrethroids has been reported among mosquito populations across Mexico, 31,32 the use of nonpyrethroid molecules listed in the new Official Mexican policy for the surveillance and control of vectors 6 will help to maintain the sink of pyrethroid-susceptible Ae. aegypti in Yucatan State.…”