Developing a new methodology to identify and predict competition of local flora with ATSBs in Africa

Assessing competition for nectar availability between ATSBs and natural resources

Nectar feeding is a critical source of food for adult mosquitoes of both sexes. Mosquitoes also obtain sugar from other parts and fluids of the plant such as fruits, honeydew, and plant tissue, though floral nectar is their preferred food. For males, plant sugar is the only source of food and is required for their survival. Energy extracted from plants’ sugar is needed to fly and copulate, and if sugar-deprived, mosquitoes do not achieve reproductive success.

Understanding the importance of nectar feeding during the life of mosquitoes along with the increasing presence of pyrethroid resistance and changes on mosquito biting behaviour led to the development of new mosquito control methods such as Attractive Targeted Sugar Baits (ATSBs). This approach incorporates sugars from flowers and fruits that are attractive to mosquitoes together with an insecticidal compound that kills them. However, further studies are needed to understand how nectar availability in time (phenology) and space (abundance) affect the efficacy of this type of mosquito control tool.

To help to fill these gaps, we have collaborated with Innovative Vector Control Consortium (IVCC) to develop a new methodology to estimate the spatial distribution of sugar resource provided by naturally occurring nectar across different landscapes in three study regions in Kenya, Zambia and Mali. The methodology developed involved determining the plant traits of the most abundant species in the study sites (number of flowers per plant, concentration, and volume of sugar in each flower, months of flowering etc.) and combining this information with satellite remote sensing imagery to calculate a first approximation of nectar resource across the landscapes of interest in space and time. The results provided an understanding of the spatial arrangement of the amount and availability of nectar and its timing in the three study sites. Preliminary evidence also indicated significant variation between sites; information that may be critical for the ATSBs to succeed in local mosquito control interventions.

Due to differences in the ATSBs performance in the three countries, IVCC proposed to continue this research to understand the efficacy of the ATSBs depending on density of human population and local vegetation.

This new project has the following objectives and work packages:

Project objectives

• To map the identified traits and species.
• To create online maps of the times/seasons of high natural nectar availability in areas with high and low levels of sugar nectar.
• To demonstrate times and areas of high competition between ATSBs with natural resources.

WP 1: Mapping suitable areas to locate field trials of ASBs in malaria transmission zones in Zambia and Mali

In collaboration with the Zambia and Mali teams, we will identify the following potential areas for trial sites as follows:

• Two clusters with high levels of sugar (+ high density of housing)
• Two clusters with high levels of sugar (+ low density of housing)
• Two clusters of low levels of sugar (+ high density of housing)
• Two clusters of low levels of sugar (+ low density of housing)

We will then confirm the actual differences in nectar resource availability for each site using our previous methodology and involving the measurement of the availability of sugar nectar using botanical surveys, plant traits collection, GIS, and modelling.

WP 2: Quantification of the natural sugar availability in the clusters where ATSBs are deployed in epidemiological trials in Mali, Zambia and Kenya

In addition to those clusters outlined in WP1, we will map the availability of sugar nectar in additional cluster where ATSB deployments also include entomological assessments (mosquito captures). Again, this will require botanical surveys and plant trait collection to create the sugar maps in the different study sites.

Image credit: Angela Harris (IVCC)