Domingo Montada Dorta,1 Juan Bisset Lazcano,2 María M. Rodríguez Coto3
1. Biologist, M.Sc. Researcher, Head of Chemical Control Laboratory, IPK (Instituto de Medicina Tropical “Pedro Kourí” [“Pedro Kourí” Trpoical Medicine Institute])
2. Biologist, PhD, Researcher, Head of Vector Control Department, IPK
3. Biochemist, PhD, Researcher, Head of Toxicology and Genetics Laboratory
Resistance to chemical insecticides is an obstacle in the path of the success of vector control programs of medical importance. Approximately 40% of the 506 of these species have developed resistance (WHO). Around 50% of these species are mosquitoes that are vectors of malaria, dengue, yellow fever and filariasis (Fonseca, 2005). At present, Aedes aegypti (L.) (Diptera: Culicidae) is the main vector of dengue, Zika and chikungunya in Cuba, the Caribbean and Latin America, making it the species subjected to the most selection pressure with insecticides used in programs aimed at controlling this mosquito species. As a result, the issue of insecticide resistance has been widely studied in this species.
It is crucial to improve community participation and mobilization for sustained vector control.
In Latin America, several types of insecticides have been used for vector control. These include pyrethroids, which have been the most frequently used since the 90s until the present. Ae. aegypti has developed resistance to the molecules of insecticides in the different groups: organochlorines, organophosphates, pyrethroids and carbamates in countries across the region (Maestre-Serrano, 2013). In Cuba in October 1981, at the end of the dengue epidemic, a campaign to eradicate the was carried out, and the most widely-used insecticide was organophosphate malathion. As a result, the species was almost completely eradicated, although, due to the high selection pressure, the density of the Culex quinquefasciatus mosquito (S) (Diptera: Culicidae) population began to increase as it developed resistance to malathion (Bisset et al., 1991), which led to the start of the use of cypermethrin in 1986, the first insecticide formulated using pyrethroid (Rodríguez et al., 1993).
Pyrethroid Resistance in Larvae and Adult Mosquitoes
With the prolonged use of organophosphorus larvicide temephos, which has been in use since it was created in October 1981 in the campaign to eradicate the Ae. aegypti to date, it has been proven that the mosquito Ae. aegypti has developed resistance to this insecticide in most Caribbean countries (Rawlins, 1998, Paeporn et al., 2003, Rodríguez et al., 2004, Bisset et al., 2004, Braga et al., 2004, Saelim et al., 2005, Rodríguez et al., 2007, 2010; Bisset et al., 2009, 2013). In recent years, pyrethroids have been used as adulticides during periods in which the mosquito population is heavy and/or during dengue epidemics. Pyrethroid resistance has been diagnosed in Ae. aegypti from Puerto Rico (Hemingway et al., 1989), the Dominican Republic (Mekuria, 1991), Venezuela (Mazarri and Georghiou, 1995) and Cuba (Rodríguez et al., 2002, 2003, 2004, 2005, 2007, 2011 and Bisset et al., 2017). In Mexico, research carried out in Mérida, Yucatán, found that populations of Ae. aegypti larvae showed high levels of resistance to temephos and permethrin, which is due to the constant use of temephos for over 30 years and of permethrin for over 10 years (González et al., 2013).
A study carried out on Ae. aegypti from Jamaica, Costa Rica, Panama, Nicaragua, Peru, Venezuela and Cuba showed that all larvae were resistant to temephos, except for the Nicaraguan strain, which showed only moderate resistance. All strains were found to be susceptible to malathion, with similar results for fenthion and fenitrothion, except for the Peruvian strain, which showed moderate resistance to fenthion, and the Havana strain, which showed high resistance to fenthion and moderate resistance to fenitrothion. A high level of resistance to methyl pirimiphos was found in the strains from Panama, Costa Rica and Venezuela; however, the strains from Santiago de Cuba, Jamaica and Peru showed only moderate resistance to this chemical. The Santiago de Cuba strain was the one with the highest level of resistance to chlorpyrifos, followed by Costa Rica and Jamaica, with Havana, Panama, Nicaragua and Peru showing susceptibility to chlorpyrifos. The Venezuelan strain showed moderate resistance to chlorpyrifos. Findings with insecticides deltamethrin, lambda-cyhalothrin, betacypermethrin and cyfluthrin showed that the Havana strain was resistant to all pyrethroids, and the Santiago de Cuba, Peruvian and Venezuelan strains all showed high levels of resistance to deltamethrin, which can be attributed to the high level of resistance to temephos in these countries. Moderate resistance to lambda-cyhalothrin, betacypermethrin and cyfluthrin was observed in the Santiago de Cuba strain. Larvae in the strains from Nicaragua, Peru and Venezuela showed complete susceptibility to lambda-cyhalothrin, betacypermethrin and cyfluthrin (Rodriguez et al., 2007).
|Active monitoring and surveillance of vectors should be carried out to determine effectiveness of control interventions.|
|It is necessary to emphasize on the rotation of formulations based on insecticide molecules that do not have cross-resistance. Consequently, we can delay the emergence of resistance as well as reduce breeding areas.|
|Stagnant water can become a hot spot for mosquitoes. Therefore, is it necessary to apply appropriate insecticides in the surroundings of houses and in gardens and thus reduce the rate of vector-transmitted diseases.|
In adult mosquitoes (Rodriguez et al., 2007), the findings showed that half of the strains evaluated were susceptible to lambda-cyhalothrin and betacypermethrin. The strains of Santiago de Cuba, Jamaica, Panama, Nicaragua and Venezuela were found to be susceptible to lambda-cyhalothrin; however, the Havana strain was found to be resistant to this insecticide, and the rest of the strains (Jamaica, Costa Rica and Peru) were categorized as “under monitoring for resistance.” The strains from Havana, Costa Rica and Venezuela were susceptible to cypermethrin, and the rest of the strains were placed in the resistance monitoring category as defined by WHO. Only one of the strains tested was found to be susceptible to deltamethrin (Panama). Three strains were susceptible to cyfluthrin (Santiago de Cuba, Costa Rica and Venezuela), two of them were found to be resistant to this insecticide (Havana and Peru). Meanwhile, the rest (Jamaica, Panama and Nicaragua) were categorized as being under monitoring for resistance. The Santiago de Cuba, Nicaraguan and Venezuelan strains were susceptible to chlorpyrifos; however, the Havana, Jamaican and Peruvian stains were resistant to this organophosphate, and the Panamanian and Costa Rican strains were placed in the monitoring for resistance category.
How to Continue Vector Control
It has been proven that Ae. aegypti has developed resistance against organophosphorus insecticides and pyrethroids in several Latin American countries. The main programs for controlling Ae. aegypti in Latin America, including the Ae. aegypti control campaign in Cuba, still use temephos as larvicide and pyrethroids as adulticides during epidemics or when faced with high-density populations of vectors. However, in light of the prevalence of insecticide resistance that is developing in the Latin American countries discussed here, it is also necessary to place greater emphasis on the rotation of formulations based on insecticide molecules that do not have cross-resistance, in order to delay the emergence of resistance, as well as to focus on reducing breeding areas and improve environmental sanitation, in order to reduce the frequency of the application of insecticides, thus achieving effective and sustainable control over the vector.