The current Zika virus outbreak in the Americas offers a stark reminder of how urbanization and ease of travel can magnify exposure to container mosquitoes and the viruses they transmit. Debilitating and sometimes deadly diseases such as dengue, Zika, chikungunya and yellow fever can proliferate quickly in concentrated urban areas, areas that also serve as natural hubs for international travel.
By 2050, it’s expected that 2/3 of all people on Earth will reside in urban areas. Along with close interpersonal proximity comes proximity to a host of man-made vessels (storm drains, toys, pots, refuse, etc.) that serve as prime container-mosquito breeding sites. As people travel between those urban areas, diseases travel with them. In its 2015 travel forecast, the U.S. Department of Commerce (DOC) predicted that the number of visitors traveling to the U.S. from abroad will increase as much as 20% by the year 2020. Outbound travel originating from the U.S. increased by about 10% in 2014.
DESIGNING A CONTAINER MOSQUITO CONTROL PROGRAM
Despite Zika’s introduction in the Americas and the troubling effects of the disease, public health officials have gotten a clear head start on effective means to battle container mosquitoes in densely populated areas. Since Zika is vectored by the same Aedes aegypti and albopictus species that vector dengue and chikungunya, the success of recent trials aimed at controlling these species across multiple geographies and habitats bodes well for programs challenged with mitigating exposure to these threats.
As with any disease vector control challenge, the starting point for container mosquito control should be an integrated approach that utilizes source reduction, larviciding and adulticiding. At the root of program design is a clear understanding of container mosquito biology and their preferred habitats, and how those factors combine to represent a unique and yet well-defined target for intervention. Habitat and species determine application method, which in turn drives selection of a product solution (when applicable) that addresses those specific needs.
THE SPECIES CHALLENGE
Target Species
Aedes aegypti and Aedes albopictus (container mosquitoes)
- Day Biters
- Highly aggressive
- Extremely adaptable
- Success at colonizing both artificial man-made and natural containers
- It takes very little water for container mosquito larvae to survive to become blood seeking adults
THE HABITAT CHALLENGE
- Container mosquitoes prefer man-made habitats such as roof gutters, water-holding refuse, plastic toys, and flower pots, as well as natural, plant-based phytotelmata such as leaf axls, tree holes, and fallen leaves
- These habitats are in abundance in urban/semi-urban areas
- In many situations, people need to store water on their property to survive
- While many of these sites are obvious and water can either be removed or treated with larvicides, other sites can be small and cryptic
THE PRODUCT/APPLICATION CHALLENGE
Given the unique biology + habitat complex that exists for container species relative to other complexes, custom integrated approaches are needed to combat these disease vectors. For many mosquito species, a traditional, integrated approach to source reduction, larviciding, and adulticiding provides a robust, sustainable mosquito control program. For container mosquitoes such as Aedes aegypti which prefers to thrive close to human proximity, the traditional approach presents some significant challenges.
Source Reduction Intervention
Source Reduction is considered the most permanent form of mosquito control because it eliminates or reduces habitats where mosquitoes develop. Since many mosquito species lay their eggs in standing water, source reduction often includes the removal of debris or other vessels in which water collects — items such as buckets or discarded tires.
The Challenge: For this strategy, “reduction” is the operative word since it is often impossible to eliminate all sources of standing water in an affected area. And since container mosquitoes often lay their eggs in sites that are extremely small and difficult to find, complete source reduction is impossible on a large-scale. The cost of source reduction, in person-hours, can also be substantial.
Larviciding Intervention
Larviciding is widely considered the most effective form of mosquito control. Applied using ground or aerial treatments, larvicides kill mosquito larvae before they become adults and become airborne. Larviciding as a base-line intervention is gaining widespread acceptance because itefficiently suppress mosquito populations in their most vulnerable stages of development, and improves the efficiency of adulticides when needed.
The Challenge: Similar to the challenges highlighted for source reduction, traditional larviciding application methods require full knowledge of where the water source is. Since container mosquito larval habitats are often cryptic, historically it has been difficult to find and address all habitats within a given area.
Adulticiding Intervention
Ultimately, it is adult mosquitoes that are responsible for disease transmission. It follows that any program actively combating vector-borne disease will include an important adulticiding component. While the mobility of flying adults renders adulticiding less efficient than other forms of control, adulticides serve as a necessary last line of defense – often the go-to approach when disease outbreaks occur via container mosquito vectors. Ground applications are usually employed to control container mosquito species.
The Challenge: While many common mosquitoes are active at dusk, aggressive, container breeding mosquito species such as Aedes aegypti and Aedes albopictus look for blood sources during the day. Limiting container breeding interventions to adulticides becomes complicated since the atmospheric conditions for spraying adulticides outdoors are not optimal during daylight hours – the time when these species are most active.