Impact of pre-seasonal focal treatment on population densities of the mosquito Aedes aegypti in Trinidad, West Indies: a preliminary study.

ABSTRACT

A new pre-seasonal focal treatment strategy against Aedes aegypti L. (Diptera Culicidae) mosquitoes is described for the first time. It was evaluated for 25 weeks using ovitraps, and larval and pupal surveys in the townships of Curepe (treated) and St. Joseph (untreated), Trinidad, West Indies. Both townships were similar with respect to number of houses, size of human populations, the number of Ae. aegypti infested houses and containers. In March 2003, a total of 9403 containers were inspected, of which 1.4 per cent in Curepe (63/4499) and 1.3 per cent in St. Joseph (64/4904) were positive for Ae. aegypti immature stages. Curepe had a lower percentage (12.7 per cent) of the main type of breeding container present (small miscellaneous containers) than St. Joseph (28.1 per cent). Following focal treatment during the month of April (2-3 weeks before the onset of the rainy season), the Ae. aegypti population declined significantly (P>0.01) from a Breteau index (BI; proportion of containers positive for larvae and pupae) of 19.0 to a minimum of 6.0 and a pupae/person index (PI) of 1.23 to a minimum of 0.35 in May, while in the untreated town of St. Joseph, the BI steadily increased from 23 to 38 and the PI rose from 0.96 to 2.00 in August. Similar declines in other measures of population density (the number of positive houses and number of eggs collected in ovitraps) were observed in Curepe, while St. Joseph maintained PI of >1.50 and BI of >28. Furthermore, the Curepe Ae. aegypti population did not return to pre-treatment levels until 9-11 weeks after treatment, far beyond the 6 weeks normally expected during vector suppression campaigns.