The Effects of Plant Infusions on the Collections of Gravid Aedes Aegypti for Arbovirus Surveillance

Abstract

Infusions are commonly used to trap gravid mosquitoes for surveillance and control of arboviral diseases. The nature and plant species can affect attractiveness of infusions likely underpinned by differences in mediating microbe-associated volatile organic compounds. In this study, 4-d old-fermented infusions prepared from leaves of four commonly available plants (mango, banana, cashew, neem) were evaluated on catches of gravid Aedes aegypti using Gravid Aedes Traps. Field experiment was implemented through a Latin square design in urban Ukunda, an endemic area for dengue in coastal Kenya. Of the infusions, mango recorded 2-7-fold increased captures of gravid Ae. aegypti than the other plants; captures decreased in the order banana > cashew > neem. Analysis of the headspace volatiles of the infusions via gas chromatography-mass spectrometry (GC-MS) revealed significant difference in the chemical composition between the plant species (ANOSIM, R = 0.33, p = 0.0003) belonging to the classes ketones (38.4%), terpenes (26.2%), phenolics (24.7%), alcohols (7.4%), hydrocarbons (2.7%), esters (0.18%), indole (0.4%) and carboxylic acids (0.05%). Qualitative and quantitative variation in the volatile constituents of the plant infusions was observed with those in mango and neem being most and least diverse, respectively. Culturing the infusion water in Luria bertani media recovered bacterial isolates which were identified by PCR and sequencing of the16S rRNA gene. The most attractive infusions (were associated with 9 bacterial isolates, where mango had 5 and and banana 4 bacterial isolates, respectively, belonging to the family Bacillaceae and Moraxellaceae (e.g., Acinetobacter sp). Four-three isolates from cashew belong to the family Bacillaceae (2) and Enterobacteriaceae (Klebsiella pneumoniae, Citrobacteri koseri)) similar to neem that in addition exclusively had Pseudomonadaceae (e.g., Pseudomonas mendocina). The findings indicate that gravid Ae. aegypti responded differently to X infusions of the plants whose variation in bacterial composition and volatile emission profiles could account for the observed differential attraction. Identifying the active constituents in most- and least-attractive substrates can be explored in the development of push-pull strategy for controlling this container-breeding mosquito. The potential use of the microbes and associated volatiles in the vector management needs to be explored. The Aedes aegypti mosquito is the primary vector of several viral diseases including dengue and chikungunya which pose a significant threat to human health globally. Outbreaks and inter-epidemic transmissions are associated with the absence of sustainable vector control measures, vaccines and antiviral drugs. Surveillance of this vector for disease risk assessment is an important strategy which is currently being undertaken using the Biogent sentinel traps (BGs) baited with carbon dioxide (CO2. Thus, there is need for development of tools that increase possibility of detecting infected mosquitoes. Gravid Aedes Trap (GAT) is a monitoring tool known to exclusively target blood-fed mosquitoes and whose efficiency can be optimized using lures. This study aimed at elucidating the attractiveness of infusions from leaves of locally available plants including mango, cashew, banana and neem and their associated microbial population, targeting gravid Ae. aegypti for improved arbovirus surveillance. Results: The GAT baited with mango infusion attracted significantly higher number of mosquitoes while the trap baited with neem infusion attracted the least number of mosquitoes (p<0.001). The attraction could be attributed to the volatile organic compounds (VOCs) including phenol, guiacol and spathulenol among others. Similarly, the classes of microbial population including Bacillus, Acinetobacter, Citrobacter identified could be have played a significant role in influencing the attraction of these gravid mosquitoes. X Conclusions/recommendation: This study lays the foundation for the development of potent oviposition lures which will contribute significantly in the improvement of arbovirus surveillance tools and subsequently control of Aedes-borne viral disease. we recommend further laboratory bioassays such as Coupled gas chromatography electroantennographic Detection (GC-EAD) of the individual volatile compounds in order to understand the mosquito antennal response to the distinct chemicals in this identified by GC-MS