Spatial distribution of insecticide resistance in Caribbean populations of Aedes aegypti and its significance

Abstract

To monitor resistance to insecticides, bioassays were performed on 102 strains of the dengue vector Aedes aegypti (L.) from 16 countries ranging from Suriname in South America and through the chain of Caribbean Islands to the Bahamas, where the larvicide temephos and the adulticide malathion have been in use for 15 to 30 years. There was wide variation in the sensitivity to the larvicide in mosquito populations within and among countries. Mosquito strains in some countries such as Antigua, St. Lucia, and Tortola had consistently high resistance ratios (RR) to temephos, ranging from 5.3 to 17.7. In another group of countries--e.g., Anguilla and Curaçao--mosquitoes had mixed levels of resistance to temephos (RR = 2.5-10.6), and in a third group of countries, including St. Kitts, Barbados, Jamaica, and Suriname, mosquitoes had consistently low levels of resistance to temephos (RR = 1-4.6) (P < 0.05). On occasion significantly different levels of resistance were recorded from neighboring A. aegypti communities, which suggests there is little genetic exchange among populations. The impact of larval resistance expressed itself as reduced efficacy of temephos to kill mosquitoes when strains were treated in the laboratory or in the field in large container environments with recommended dosages. Although a sensitive strain continued to be completely controlled for up to 7 weeks, the most resistant strains had 24% survival after the first week. By week 6, 60% to 75% of all resistant strains of larvae were surviving the larval period. Responses to malathion in adult A. aegypti varied from a sensitive population in Suriname (RR = 1.3) to resistant strains in St. Vincent (RR = 4.4), Dominica (RR = 4.2), and Trinidad (RR = 4.0); however, resistance was generally not on the scale of that observed to temephos in the larval stages and had increased only slightly when compared to the levels that existed 3 to 4 years ago. Suggestions are made for a pesticide usage policy for the Caribbean region, with modifications for individual countries. This would be formulated based on each country's insecticide-resistance profile. Use of physical and biological control strategies would play a more critical role than the use of insecticides.

Aedes aegypti resistance to temephos during 2001 in several municipalities in the states of Rio de Janeiro, Sergipe, and Alagoas, Brazil

“…1B), were tested separately, confirming resistance in this municipality. As stated previously by Rawlins (1998), a good correlation was found between RR values and survival after treatment with the diagnostic dose: mosquitoes derived from all three districts that exhibited mortality below 10% with the temephos diagnostic dose (Table II) presented high RR levels (Table IV).…”

Impact of environmental temperatures on resistance to organophosphate insecticides in Aedes aegypti from Trinidad

“…Fenthion is applied perifocally or by space sprays as an adulticide, whereas malathion is applied as an adulticide by thermal fog or ultra-low volume (ULV) spray during a dengue outbreak or in response to complaints of high mosquito densities (6,29). While fenthion and malathion are not routinely used, temephos is the only larvicide applied in potable water for the control of A. aegypti larvae in Trinidad.…”

“…This has been due, in part, to the interaction of several risk factors related to the environment, the virus, the host population, and vector bionomics (3)(4)(5), and to the widespread development of insecticide resistance in the Aedes aegypti mosquito (6,7). Mosquitoes and other poikilothermic vector organisms are sensitive to climatic factors such as temperature, precipitation, and humidity (8).…”

“…The prevention and control of dengue is aimed at the A. aegypti vector, with heavy emphasis on chemical control with insecticides. Organophosphate (OP) insecticides such as fenthion, malathion, and temephos have been used in the Caribbean region to control A. aegypti for the last 40 years (6). However, the continued reliance on these insecticides has resulted in the development of mosquito resistance to the insecticide, which has created a problem for vector control programs (3,6,19).…”

Control of Aedes aegypti with temephos in a Buenos Aires cemetery, Argentina

“…High and moderate resistance to temephos has been described in the Caribbean region 4 and Brazil 3 respectively. In Buenos Aires, where no local transmission of dengue virus has been demonstrated, it is recommended to save insecticides as an efficient tool for preventing potential epidemics only rather than for routine control.…”