Recent findings from Singapore suggest the effective control of the Aedes aegypti mosquito may not lead to an increase in populations of the Aedes albopictus mosquito, another known vector of dengue and other arboviruses. This unexpected conclusion emerges from two years of entomological surveillance, aimed at assessing the ecological impacts of suppression programs based on the Wolbachia-infected Aedes aegypti approach.
The global rise of dengue fever linked to Aedes aegypti has prompted researchers and public health officials to investigate alternative control measures. The sterile insect technique (SIT) and incompatible insect technique (IIT) represent two promising strategies. They involve releasing infected males capable of suppressing wild mosquito populations through various biological mechanisms. Singapore has been conducting extensive trials using these techniques to manage its local mosquito populations.
Despite concerns about Aedes albopictus potentially filling ecological gaps left by suppressed Aedes aegypti populations, the latest study reveals no significant correlation between the two species post-suppression. Analysis of mosquito populations collected from over 70,000 Gravitraps showed Aedes albopictus numbers fluctuated but did not consistently increase alongside the reductions of Aedes aegypti. Notably, researchers found evidence of improved disease management, as dengue virus prevalence remained significantly lower within Ae. albopictus compared to Ae. aegypti.
According to the study, "Together, these results indicate suppression of Aedes aegypti in the community may not be directly associated with any increase of Aedes albopictus population or capacity." This statement reflects the findings of the comprehensive assessment completed between 2020 and 2022 across multiple urban sites, including high-rise residential apartments. Surveillance data indicated no reliable surge of Aedes albopictus after Aedes aegypti population reductions.
Beyond simply monitoring populations, the study also focused on the vertical distribution of Aedes albopictus within high-rise apartments. The methodology employed examined how the two mosquito species occupied trajectories within built environments. Interestingly, the analysis revealed little change—indicating Ae. albopictus remained less inclined to occupy territories associated with human proximity.
Dr. Wong and colleagues found, "The suppression of Aedes aegypti using a hybrid SIT-IIT approach appears to have limited impact on the abundance and vertical distribution of Aedes albopictus.” This points to distinct habitat preferences and minimal competition between the two species, highlighting how urban ecological dynamics may affect vector competency.
One of the more reassuring findings was the year-on-year monitoring of dengue prevalence. A total of 47,294 Aedes aegypti and 17,850 Aedes albopictus were screened for dengue viruses. Results revealed the average dengue prevalence for Ae. albopictus was approximately 18 times lower than for Ae. aegypti. The researchers emphasized: "Dengue prevalence in field Ae. albopictus was approximately 18 times lower than field Ae. aegypti." This statistic supports the notion of Aedes albopictus as less competent at transmitting the dengue virus, which is advantageous for public health strategies focused on reduction.
Though the initial results appear hopeful, the study raises concerns about potential future risks. The researchers warned about the danger of decreased vigilance if Aedes aegypti populations significantly dwindle, which could lead communities to neglect aggressive source reduction efforts necessary for controlling Aedes albopictus populations. Experts agree it is pivotal to maintain strong environmental management practices, even with lowered infection transmission rates.
Overall, these results contribute significant insights to the fields of entomology and public health. The findings reinforce the concept of managing mosquito populations through integrated vector management approaches and highlight the variable population dynamics possible among competing species. Continued surveillance programs and research are necessary to navigate future challenges presented by global climate change and urbanization's influence on mosquito prevalence.