Yellow Fever Mosquito: Container Emptying Alone May Not Be Enough

The yellow fever mosquito, Aedes aegypti, is an important vector of dengue, Zika, and chikungunya. Females prefer to lay eggs on the inner walls of small, water containers such as vases, buckets, and pet food containers, just above the waterline. Those eggs adhere to the surface and can withstand drying and heat for months, even up to a year, waiting to hatch the next time the container is refilled. Because of this phenomenon, dumping water out of containers alone is not enough as the "egg bank" will still remain glued to the walls.

A field study conducted in temperate Argentina (Rubio et al., 2025) investigated whether adding basic mechanical egg removal to routine container emptying improves mosquito control. Researchers worked in a public cemetery in Tigre (Buenos Aires Province), an environment with thousands of plastic flower vases, an ideal habitat for container-breeding insects. Across nine plots, they labeled 855 black plastic vases (both cone and box styles) and compared three approaches: (1) emptying only (EM), (2) emptying plus brushing with a toilet brush (BR), and (3) emptying plus scrubbing with a cellulose cloth (SC). They also tracked two non-target dipterans that share similar oviposition on container walls: a drain fly species (Clogmia albipunctata) and a biting midge (Dasyhelea necrophila).

Figure 1: Freshly emerged adult yellow fever mosquito (Aedes aegypti)

Before intervention, 89% (765/855) of containers held water, and nearly half of those (351) contained immature stages of at least one species. Yellow fever mosquito was the most common (251 containers), followed by C. albipunctata (104) and D. necrophila (51). Post-intervention assessments took place five days after treatment, when any viable eggs left on the walls would have hatched into first- or second-instar larvae, assuming the vases were refilled to the brim.

Mechanical egg removal clearly outperformed emptying alone for the yellow fever mosquito. Relative to their pre-intervention levels, emptying water reduced the proportion of positive containers by roughly 11.8–18.5%, while scrubbing achieved 16.7–43.4% and brushing 20.8–48.1%. Both brushing and scrubbing worked best in cone-shaped vases, though benefits were still detectable in box-shaped ones. The takeaway was that simpler shapes are easier to clean thoroughly, while larger, boxy containers with edges and corners are harder to clean of eggs, unless you spend significantly more time cleaning them.

Figure 2: Eggs of Aedes triseriatus

Mechanical removal of eggs also reduced viable C. albipunctata eggs, suggesting these methods can suppress some nuisance species that share the same wall-laying habit. In contrast, container wall cleaning had no effect on D. necrophila. A biological explanation is that Dasyhelea lays egg masses coated in a sticky protective substance, which may shield them from being dislodged by simple brushing or scrubbing.

Even those containers assigned to the "empty only" group show some reduced mosquito activity, largely because refilling them to the brim right after intervention temporarily discouraged fresh oviposition and disposed of existing larvae. However, the main insight holds: if you don’t physically remove or disrupt the egg bank on the walls, you leave behind some ready-to-hatch mosquito eggs that will repopulate the container as soon as it gets wet again. That’s why the authors argue mechanical ovicidal steps should be a standard part of community source-reduction campaigns, especially for containers that cannot be discarded (e.g., vases, pet dishes).

Authors argue that cleaning container walls is simple, low-cost, and non-chemical. The process involves cleaning the containers by vigorous horizontal passes with a brush or a disposable scrub cloth and rinsing the cleaning tools between containers to avoid cross-contamination. Nevertheless, cleaning hundreds of containers manually is labor-intensive when compared to simple spraying with insect growth regulators. The authors acknowledge that these steps won’t address “cryptic” containers that remain unseen. But for the many containers that public health teams and residents already empty routinely, adding mechanical egg removal is a practical upgrade with significant gains.

The study also highlights the need to consider other small insects that share the same breeding habitats as Aedes aegypti. Some of these species, like drain flies or biting midges, are harmless or even useful because their larvae help break down organic material in standing water. Others can occasionally become nuisances in homes or urban areas. Understanding how mosquito control measures affect these non-target species is important for maintaining ecological balance. Overall, the research shows that physically removing mosquito eggs should become a standard part of community-based control programs.

References

• Rubio, A., Melgarejo-Colmenares, K., Kliger, M., Cardo, M. V., & Vezzani, D. (2025). Container emptying alone falls short: Mechanical egg removal enhances Aedes aegypti management. Pest Management Science, 81(7), 3474–3481. https://doi.org/10.1002/ps.8715