Evaluation of a rapid water-surface sweeping method to accurately estimate numbers of Aedes aegypti (Diptera: Culicidae) late larval stages in large water-storage containers: comparison with pupal estimates.
BACKGROUND
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.


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.
Romero
Claudia M E
CM
Grupo de Investigaciones en Enfermedades Tropicales, Departamento de Medicina, Universidad del Norte, Barranquilla, Colombia. clromero@uninorte.edu.co
Llinás
Humberto
H
Falconar
Andrew K I
AK
D000330:Aedes / Q000254:growth & development; D000818:Animals; D004772:Entomology / Q000379:methods; D007814:Larva; D011679:Pupa; D015203:Reproducibility of Results; D013997:Time Factors; D014867:Water
D014867:Water