Towards the biocontrol of dengue: copepods as predators of Aedes larvae in Sri Lanka
With the expansion of the disease-transmitting Aedes mosquitoes worldwide, researchers have been exploring control strategies to enhance and complement traditional chemical and mechanical vector control methods. The biocontrol of Aedes larvae by natural predators such as copepods or guppy fish has been increasingly studied and evaluated. Recent research conducted in Sri Lanka has assessed the potential for the biocontrol of Aedes larvae by five locally available copepods. In this Infectious Thoughts interview, we speak to Pr. Menaka D. Hapugoda, professor in Molecular Medicine at the University of Kelaniya in Ragama, Sri Lanka, about current challenges in vector-borne diseases faced by Sri Lanka and the potential for a biocontrol approach to vector control.
Given the gaps in the chemical and mechanical control of vectors of disease, many countries are facing challenges in controlling these vectors. What have been some of the main challenges faced specifically by Sri Lanka, in terms of specific vectors and diseases?
Malaria and lymphatic filariasis have been eliminated in Sri Lanka a few years back. Dengue is an important emerging and re-emerging infectious disease in Sri Lanka at present. The disease has a significant effect on livelihoods of people living in the endemic areas of the country.
Integrated vector control methods including residual insecticide spraying use of space spray application, use of chemical larvicides, health education of the community and community participation are conducted during the epidemic seasons by the Health Authorities. Insecticides are sprayed during international flights to avoid introduction of the Aedes species. Still the disease causes massive outbreaks with introduction of new strains of dengue viruses together with herd immunity of people, densities of human and mosquito populations and other environmental factors such as intermittent rainfall etc.
Which alternative bio-control method does your research focus on?
Our research has been focusing on the following biological control agents: carnivorous copepods (operational level), larvivorous fish (operational level), dragon flies (operational level), Aedes mosquitoes infected with Wolbachia (laboratory level).
In addition, we also work on modified vectors including: sterile male Aedes mosquitoes (we are currently waiting to get official approval to conduct field trails) and transgenic Aedes aegypti mosquitoes with dengue viral RNA replication interference (semi-field trials have been successfully completed).
Collection of copepods from water bodies. https://doi.org/10.1371/journal.pone.0216140.g001
What would be the main advantages in developing biocontrol approaches?
Carnivorous copepods are available in numerous water bodies in Sri Lanka, and they can be easily collected and cultured at a small laboratory. Then they can be released to permanent water holding containers. Once they are released they can easily breed in water bodies. Another advantage is that they do not cause any harm to the natural environment.
Do all copepods offer the same result in terms of reducing the number of Aedes larvae? Can your results be easily applied to different habitats across areas or even countries?
There are a few carnivorous copepod species which give good results - they tend to have a big body size. The advantage of these species is that they can be applied to different habitats across areas. As water quality can affect the survival of these copepod species, it is important to ensure that fresh water is applied in containers. But interestingly, fresh water containers and bodies are also the preferred water conditions for mosquitoes in which dengue vectors also breed. So copepods and Aedes larvae prefer the same types of environments, and will flourish in similar conditions.
Which partnerships or innovations would you like to see developed in order to scale up this strategy? How can this be effectively combined into a broader vector control programme for Sri Lanka, for example given that the use of chemical control interventions could mitigate the presence of copepods themselves?
We work together with the National Dengue Control Programme in Sri Lanka. Therefore, we will strengthen our collaboration to work with them to use this control method in the future. It is difficult to mitigate chemical control methods on the presence of copepods, so we will work to facilitate the use of this approach together with other control approaches.
Link to further information on this work:
Lahiru Udayanga, Tharaka Ranathunge, M. C. M. Iqbal, W. Abeyewickreme, Menaka Hapugoda
Lahiru Udayanga (Department of Biosystems Engineering, Faculty of Agriculture & Plantation Management, Wayamba University of Sri Lanka, Sri Lanka, Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Sri Lanka)
Tharaka Ranathunge (Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Sri Lanka
M. C. M. Iqbal (National Institute of Fundamental Studies, Kandy, Sri Lanka)
W. Abeyewickreme (Department of Paraclinical Science, Faculty of Medicine, Sir John Kotelawala Defense University, Ratmalana, Sri Lanka)