Proof of concept for eliminating Aedes aegypti production by means of integrated control including turtles, copepods, tilapia, larvicides, and community participation in Monte Verde, Honduras.

Monte Verde, a peri­urban squatter community near San Pedro Sula, virtually eliminated Aedes aegypti production in all known larval habitats: wells; water storage containers including pilas (open concrete water tanks used for laundry), 200-liter drums, 1000-liter plastic "cisterns," buckets; and objects collecting rainwater. The project began in 2016 when Monte Verde was overrun with dengue, Zika, and chikungunya. During more than a year of experimentation, Monte Verde residents crafted an effective, sustainable, and environmentally friendly toolkit that was inexpensive but required full community participation. Biological control with copepods, turtles, and tilapia was at the core of the toolkit, along with a mix of other methods such as getting rid of unnecessary containers, scrubbing them to remove Ae. aegypti eggs, and covering them to exclude mosquitoes or rainwater. Environmentally friendly larvicides also had a limited but crucial role. Key design features: (1) toolkit components known to be nearly 100% effective at preventing Ae. aegypti production when fitted to appropriate larval habitats; (2) using Ae. aegypti larval habitats as a resource by transforming them into "egg sinks" to drive Ae. aegypti population decline; (3) dedicated community volunteers who worked with their neighbors, targeting 100% coverage of all known Ae. aegypti larval habitats with an appropriate control method; (4) monthly monitoring in which the volunteers visited every house to assess progress and improve coverage as an ongoing learning experience for both volunteers and residents. Taking pupae as an indicator of Ae. aegypti production, from September 2018 to the end of the record in December 2021 (except for a brief lapse during COVID lockdown in 2020), the monthly count of pupae fluctuated between zero and 0.6% of the 22,984 pupae counted in the baseline survey at the beginning of the project. Adult Ae. aegypti declined to low numbers but did not disappear completely. There were no recognizable cases of dengue, Zika, or chikungunya after June 2018, though the study design based on a single site did not provide a basis for rigorous confirmation that Monte Verde's Ae. aegypti control program was responsible. Nonetheless, Monte Verde's success at eliminating Ae. aegypti production can serve as a model for extending this approach to other communities. Key ingredients for success were outside stimulation and facilitation to foster shared community awareness and commitment regarding the problem and its solution, enduring commitment of local leadership, compatibility of the toolkit with the local community, overcoming social obstacles, rapid results with "success breeding success," and building resilience.

Using ovitraps to assess the quantity of mosquito larval habitat during local eradication with source reduction and ovitraps.

The quantity of mosquito larval habitat in a specified area was assessed by placing a known number of ovitraps in the same area. The ovitraps competed for oviposition with the unknown quantity of larval habitat, and that quantity was deduced by comparing the number of eggs laid in the ovitraps when the number of ovitraps was changed from one time to another. This method can be used to assess the effectiveness of source reduction. It also provides key information for using ovitraps to eradicate local mosquito populations by competing with existing breeding sites for oviposition. The same ovitraps that are used for control can provide information on how many ovitraps are necessary to ensure eradication.

Larvicidal algae.

Although most algae are nutritious food for mosquito larvae, some species kill the larvae when ingested in large quantities. Cyanobacteria (blue-green algae) that kill larvae do so by virtue of toxicity. While blue-green algae toxins may offer possibilities for delivery as larvicides, the toxicity of live blue-green algae does not seem consistent enough for live algae to be useful for mosquito control. Certain species of green algae in the order Chlorococcales kill larvae primarily because they are indigestible. Where these algae are abundant in nature, larvae consume them to the exclusion of other food and then starve. Under the right circumstances, it is possible to introduce indigestible algae into a breeding habitat so they become abundant enough to render it unsuitable for mosquito production. The algae can persist for years, even if the habitat dries periodically. The main limitation of indigestible algae lies in the fact that, under certain conditions, they may not replace all the nutritious algae in the habitat. More research on techniques to ensure complete replacement will be necessary before indigestible algae can go into operational use for mosquito control.

Cyclopoid copepods.

Cyclopoid copepods have proved more effective for practical mosquito control than any other invertebrate predator of mosquito larvae. Their operational potential is enhanced by the fact that mass production is relatively easy and inexpensive. The exceptional potential of copepods for mosquito control was first realized about 25 years ago. Since then, laboratory experiments with copepods and mosquito larvae around the world have shown: Only the larger copepod species (body length > 1.4 mm) are of practical use for mosquito control. They kill mainly 1st instar mosquitoes. The most effective species have the capacity to kill more than 40 Aedes larvae/copepod/day. They generally kill fewer Anopheles larvae and even fewer Culex larvae. Most field testing of copepods has been in Aedes container-breeding habitats. Field tests have shown that: The most effective copepod species maintain large populations in a container habitat for as long as there is water. They typically reduce Aedes production by 99-100%. They can cause local eradication of container-breeding Aedes mosquitoes if present in a high percentage of breeding sites. Field surveys in Anopheles, floodwater Aedes, and Culex breeding habitats have shown that natural copepod populations can substantially reduce, or even eliminate, mosquito production. Field trials in temporary pools, marshes, and rice fields have demonstrated that introduction of the right copepod species to the right habitat at the right time can eliminate Anopheles or floodwater Aedes larvae. As a rule, copepods cannot eliminate Culex production by themselves, but they can reinforce and augment control by other methods. The only large-scale operational use of copepods to date has been in Vietnam, which has achieved local eradication of Ae. aegypti in hundreds of villages. Conditions in Vietnam are particularly favorable because: Many Ae. aegypti breeding sites are water storage containers that are conspicuous and easily treated. Motivation to maintain copepods in containers for Ae. aegypti control is strong because of the high incidence of dengue hemorrhagic fever. Copepod use is effectively managed by women's associations already experienced with neighborhood health services. Copepods have the potential for local eradication of Ae. aegypti and Ae. albopictus in many other countries besides Vietnam. Professional capacity for copepod management and social institutions for community participation to help with implementation and maintenance are the main factors limiting broader use of copepods for operational mosquito control at the present time.

Turtles.

Juvenile turtles have the capacity to eat more than 500 3rd and 4th instar mosquitos per day. Keeping one turtle in each water-storage tank during field trials for a dengue-control project in Honduras eliminated all mosquito production from the tanks. In Louisiana, keeping turtles in residential roadside ditches polluted by septic-tank effluent reduced Culex quinquefasciatus larvae and pupae by more than 99%. Turtles can serve as alternate hosts for Salmonella when kept in small pet containers, but the available evidence indicates that turtles create no Salmonella hazard in water-storage tanks or other mosquito-breeding habitats. Although turtles would probably not be practical for mosquito control in roadside ditches, they could be effective in storm-water catch basins or holding ponds.