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 reproduction and survival.

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.

Phase I (2021-2023)

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 study landscapes in space and time. Preliminary evidence also indicated significant variation between sites; information that may be critical for the ATSBs to succeed in local mosquito control interventions.

Phase II (2024)

Due to differences in the performance of ATSBs across the three countries, research was continued to understand the efficacy of the ATSBs with respect to human population density and local vegetation:

• 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.

Initial work involved 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 identified potential areas for trial sites with high and low levels of sugar and high and low density of housing. We then confirmed 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.

Research also aimed to quantify the natural sugar availability in the clusters where ATSBs were deployed in epidemiological trials in Mali, Zambia and Kenya. In addition to those sites outlined above, we mapped the availability of sugar nectar in additional areas where ATSB deployments also include entomological assessments (mosquito captures). Again, this required botanical surveys and plant trait collection to create the sugar maps in the different study sites.

Phase III (2024/25)

Addressing Key Biological Knowledge Gaps Related to the ATSB Vector Control Paradigm Background

A series of semi-field and field experiments are being conducted to measure mosquito bait station feeding rates in various ecological settings in Benin and Kenya. A key component of these experiments is assessing the natural botanical ecology and local sugar availability in each study location. Ultimately, understanding vector sugar feeding dynamics is essential for characterising how environmental factors influence mosquito behaviour and the efficacy of ATSBs.

Phase IV (2025) 

Addressing Key Biological Knowledge Gaps in the ATSB Vector Control Paradigm

To improve our understanding of different types of ATSBs, additional laboratory trials are needed to determine which volatile organic compounds are emitted by these baits, how long the baits produce a volatile profile, and how far the volatiles can disperse. This work will help assess bait efficacy in controlled conditions and provide insights into their potential performance in the field.

Image credit: Angela Harris (IVCC)