Mosquitoes in Belnem on the island of Bonaire: Sources and management implications

Student Report 

The people of Bonaire are affected by diseases that are transferred by mosquitoes. The problems are related to specifically the Aedes aegypti mosquito. It was unknown if these mosquitoes originate from the residential areas themselves or from a natural mangrove area close by. The general perception of the residents is that the mangrove area is a possible source for the mosquitoes in residential areas. In order to decide on the best management approach to deal with human health risks connected to mosquitoes, the origin of the mosquitoes in the residential areas was examined as well as the current mosquito control methods.

In order to find out what an effective way is to deal with the mosquitoes that are posing a risk to the residents of Belnem a field study was performed. In the field, mosquitoes and abiotic factors were measured across a transect of study sites from the residential area to the natural area. Five main study sites were selected, and for each study site 3 areas were selected (approximately 50 meters apart) to conduct measurements (15 locations in total). For 13 weeks, data was collected on all study sites. During each measurement, the human landing catch (HCL) method was applied for 10 minutes and all mosquitoes during that time were caught with an aspirator. Furthermore, data about various abiotic variables was collected in order to understand the fluctuations of mosquito abundance over time and location. (6 locations were added later because more insight about the range of the mosquitoes was desired). 

Four species of mosquitoes have been found during 219 HCL sessions of 10 minutes on 21 different locations. A total of 208 mosquitoes were caught. The species were the Culex quinquefasciatus, Aedes taeniorhynchus and the RTU 3 mosquito (until species is identified the term Recognizable Taxonomic Unit is applied). On the additional study sites near the residential areas A. aegypti was found. The pattern shows that the population of C. quinquefasciatus is only present in the residential area of Belnem. It also shows that the A. taeniorhynchus and the RTU 3 mosquito population are located only in the salt marsh mangrove area of Lac Bay. No mosquitoes were caught between Belnem and Lac Bay. This indicates that there are two separate sources of mosquitoes, Lac Bay and Belnem, each with their own species.

In the first two weeks no mosquitoes were caught. In week 7 a peak in abundance took place and then declined again after one week. This could be explained by a positive and significant correlation between the number of mosquitoes and the quantity of rain. Relative humidity also had a positive significant relation with mosquito abundance. Furthermore, the species found in the residential area, A. aegypti and C. quinquefasciatus, cannot survive the hypersaline environment found in Lac Bay (>40‰). This may explain why those species were not found in the mangroves in dry conditions. 

The A. aegypti acts as a vector for dengue, chikungunya and zika, this mosquito cannot survive the saline environment and is not found in the mangroves it can be concluded that the mosquitoes in the mangroves of Lac Bay do not pose a risk to the residents of Belnem in the current dry conditions. An effective way to deal with the mosquito issue in Belnem is to keep using the current strategy of eliminating habitat and in addition start monitoring the quantity of rain. After heavy rainfall breeding places can be checked immediately and high  mosquito abundance’s can potentially be prevented. Another addition is to instigate more participation of the residents by using a door-to-door strategy. This way, mosquito abundance can potentially also be controlled effectively in a wet year. 

However, the results of this project are based on data that were collected during a very dry fieldwork period, so the results and recommendations should be viewed in that light. In order to have a more accurate idea of the mosquito distribution in wet conditions, more research should be performed in a wet year.

For more information, contact Dolfi Debrot (dolfi.debrot@wur.nl)