Surveillance and Control of Potential Mosquito Vectors of Chikungunya, Dengue and Zika Viruses

Stephanie Richards, PhD, Medical Entomologist

Aedes aegypti and Aedes albopictus mosquitoes are responsible for transmitting chikungunya, dengue, and Zika viruses to humans. These mosquito species lay their eggs in water-holding containers in urban and suburban environments, hence regularly dumping out or removing containers can help control these mosquitoes.

Aedes aegypti and Aedes albopictus are primarily active during the daytime. This behavior is different than Culex species of mosquitoes (primarily responsible to transmitting West Nile virus) that are active at dusk and dawn. Differences in activity times mean that we must use different surveillance and control techniques, depending on the mosquito species.

Examples of Commonly Used Mosquito Traps

Carbon-dioxide baited Centers for Disease Control and Prevention light traps are commonly used for collecting adults of several species of mosquitoes. These traps are designed to be set in late afternoon/evening and retrieved the following early morning, hence are not usually effective at collecting day-active mosquitoes such as Aedes aegypti and Aedes albopictus.

The BG Sentinel trap is commonly used to collect adult Aedes aegypti and Aedes albopictus. This trap is set and retrieved during daylight hours and can be baited with lures such as carbon dioxide.

Ovitraps are dark colored (usually plastic) cups filled with water and containing a substrate (e.g., seed germination paper) that attracts mosquitoes ready to lay their eggs. These types of traps are set and retrieved once/week and can be used to determine the occurrence of potential vectors and the numbers of eggs collected on strips can be counted.

Gravid traps can also be used to attract mosquitoes ready to lay their eggs. These types of traps collect the gravid adult females to give an indication of the number of egg-laying adults.

Other Types of Mosquito Surveillance

In addition to setting traps for adult Aedes albopictus and Aedes aegypti, container surveys can be conducted to determine the abundance of mosquito larvae and pupae. For example, in a community, all water-holding containers can be examined for mosquito presence/absence. Where larvae and pupae are found, all or most of the specimens are collected and the species are identified. The abundance of mosquito pupae is a good indicator of adult abundance since this is the life stage right before mosquitoes emerge as adults.

Control Methods for Aedes aegypti and Aedes albopictus

The best way to control Aedes aegypti and Aedes albopictus is to reduce or eliminate water-holding containers (e.g., plant pot receptacles, tarps, buckets, rain barrels) where female mosquitoes lay their eggs. This non-insecticide method of mosquito control can be easily carried out by homeowners. If sources of oviposition are removed, these species of mosquitoes will not be present.

Containers should be removed and/or dumped at least once per week. For containers that cannot be dumped, such as rain barrels, a fine mesh screen can be placed on top to prevent adult mosquitoes from entering to lay their eggs. There are also biological (e.g., Bacillus thuringiensis israelensis) or chemical (e.g., insect growth regulators) larvicides available that can be used to regularly treat water-holding containers. Where there is an abundance of pupae (not impacted by larvicides), monomolecular films can be used to prevent mosquitoes from surfacing to breathe.

Public or private pest control programs can assist in controlling backyard mosquitoes such as Aedes aegypti and Aedes albopictus. Since these species are day-active mosquitoes, traditional truck-mounted ultra-low volume insecticides applied by sprayers at dusk or dawn are generally ineffective. However, there are some products available that have an excitatory component that may encourage these mosquitoes to become active and fly during dusk or dawn when insecticides are applied. Barrier sprays applied to foliage, where mosquitoes rest, are generally effective against Aedes aegypti and Aedes albopictus. That is because there is generally a residual effect of up to three weeks.

Mosquito Surveillance to Determine if Control Measures are Effective

Parity analysis gives information about a mosquito’s age. It involves dissection of mosquito ovaries to determine if mosquitoes have had a blood meal and laid at least one batch of eggs. Parous mosquitoes are older and have laid at least one batch of eggs, while nulliparous mosquitoes are younger and have not yet taken a blood meal or laid eggs. One would expect a mixture of parous and nulliparous mosquitoes in a natural environment pre-treatment; however, if a treatment was effective, post-treatment trapping would show decreased mosquito abundance and more nulliparous (younger, newly emerged) than parous (older) mosquitoes.

Where possible, insecticide resistance monitoring should be done regularly throughout the mosquito season to ensure the most effective insecticides are being used. More information about surveillance and control methods for Aedes aegypti and Aedes albopictus can be found here.


Dr. Stephanie Richards

Dr. Stephanie L. Richards is an Associate Professor of Health Education and Promotion in the Environmental Health Sciences program at East Carolina University. She received a B.S. in Biology and M.S. in Environmental Health from East Carolina University. She completed her Ph.D. in Entomology with a minor in geographic information science at North Carolina State University. She completed her post-doctoral work in Arbovirology at University of Florida, Florida Medical Entomology Laboratory. Learn more.


 

RELATED ARTICLES