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Introduction: Since the methodologies used to calculate Stegomyia indices have been shown to be inadequate for assessing the risk of dengue virus transmission and targeting Aedes aegypti control strategies, new surveillance methods are needed., Objective: To evaluate the water-surface sweeping method in combination with calibration factors to estimate the total number of Ae. aegypti late larval stages (L3/L4) in large water-storage containers at different temperatures at which transmission of dengue virus occurs., Materials and Methods: Calibration factors were derived based on the proportion of L3/L4 recovered from a predetermined number of larvae using a net of specific dimensions and water-storage containers of different capacities and water levels in semi-field conditions and at four different altitudes (14, 358, 998 and 1,630 meters above sea level). The calibration factors obtained at 14 masl were then fully validated in a field study site at this altitude., Results: Four calibration factors were derived at 14 masl (28-30°C) that were used to estimate the total L3/L4 numbers in large water storage containers greater than 20 L (n=478) at 1/3, 2/3 and full water-levels. This methodology was accurate and robust within and between the 10 pairs of field workers who applied it. Different calibration factors were, however, derived to accurately estimate the total L3/L4 numbers at each of the study sites located at 358, 998 and 1,630 masl, where average temperatures were 19°C, 24°C, and 26°C respectively., Conclusions: The accurate estimates of L3/L4 numbers calculated using the water surface sweeping method can be useful for evaluating intervention strategies directed against the larval stages.

Aedes aegypti (L.) density indices obtained in a dengue fever (DF) endemic area were compared. One hundred and twenty premises, in an urban area of Colombia where dengue type-1 and type-2 virus cocirculated, were randomly selected and sampled for 7 months. The geometric mean monthly numbers (density index, DI) of Ae. aegypti eggs (ODI), 4th instar larvae (LDI), pupae (PDI), and adults (ADI) were calculated based on the use of ovitraps, nets, and manual aspirators, respectively. A negative temporal correlation was observed between the LDI and the ODI (r = -0.83, df = 5, and P < 0.01). Positive temporal correlations were only observed between the LDI and the PDI (r = 0.90, df = 5, and P < 00.5) and the Breteau and House indices (r = 0.86, df = 5, and P < 0.01). No other correlations were found between these indices and any of the other density indices or the incidence of suspected DF cases in residents, the temperature, the rainfall, or seasonal fluctuations. Our results were, therefore, probably due to the most productive Ae. aegypti breeding sites (large water containers) being located indoors within this study area. The number of adult female Ae. aegypti/person (n = 0.5) and pupae/person (n = 11) in our study area were lower and dramatically higher than the transmission thresholds previously reported for adult and pupae, respectively. Because there were confirmed DF cases during the study period, the transmission threshold based on the Ae. aegypti pupae was clearly more reliable. We found that the mean ovitrap premise index (OPI) was 98.2% during this study and that the mean larval (L-4th instars) premise index (LPI) was 59.2%, and therefore we suggest that the OPI and LPI would be more sensitive methods to gauge the effectiveness of A. aegypti control programs.

A sampling method coupled with statistical calibration factors was developed to accurately assess the numbers of larvae and pupae of Aedes aegypti in large water-storage containers of variable capacities and water levels. Aedes aegypti productivity in different types of breeding sites found in an urban study area in central Colombia was assessed and compared. In this study, water-storage tanks and drums were found to comprise 79% of the containers positive for larval Ae. aegypti, which contributed to 93 and 92% of the total production of populations of 4th-stage larvae and pupae, respectively. These main breeding sites of Ae. aegypti were found at an indoor to outdoor ratio of 2.4:1 and no correlation was found between temporal fluctuation of populations of larval Ae. aegypti and monthly rainfall. Netted lids that used inexpensive local materials were designed to prevent oviposition by Ae. aegypti. During a 6-month trial period, 56% of inspected containers had netted lids correctly in place. Of these, 78% had no mosquito larvae. Because only 37% of uncovered containers were free of mosquito larvae, a significant difference was demonstrated when these inexpensive mechanical barriers were used (chi2 = 138.7; P < 0.001). These netted lids and the improved methods described to assess the productivity of larval and pupal Ae. aegypti in this study are now being used in combination with other strategies to assess and control these populations of dengue virus vectors in the main port city on the Atlantic Coast of Colombia.