ABSTRACT
OBJECTIVE: To establish a baseline of organophosphate susceptibility/resistance in Trinidad and Tobago strains of 4th instar Aedes aegypti. DESIGN AND METHODS: Twenty-one strains of Aedes aegypti (Linneaus) were collected throughout Trinidad and Tobago and 4th instar larvae were bioassayed for sensitivity to five organophosphate insecticides, temephos, malathion, fenthion, fenitrothion and bromophos. The data were computer probit analyzed, resistance ratios [RR] were calculated and statistical analysis was done to determine any incidence of cross-resistance. RESULTS: Low to moderate levels of larval resistance to tenephos [RR 0.8-6.3], malathion [RR 0.8-3.8], fenthion [RR 0.7-6.7], fenitrothion [RR 0.7-3.] and bromophos [RR 0.9-6.4] were observed. Significant levels of cross-resistance were found between pairs of insecticides as follows: temephos/fenthion [rsq = 0.6219]; temephos/fenitrothion [rsq = 0.6117]; fenthion/malathion [rsq = 0.5751]; fenthion/bromophos. [rsq = 0.7255] and fenthion/fenitrothion [rsq = 0.6111]. CONCLUSIONS: The generally low levels of organophosphate insecticide resistance shown in this study indicate that these chemicals can continue to be used in the fight against Ae aegypti and dengue, while we continue to monitor trends in changing resistance patterns.(AU)