Diversity and Genetic Reassortment of Keystone Virus in Mosquito Populations in Florida

Keystone orthobunyavirus (KEYV), a member of the genus Orthobunyavirus, was first isolated in 1964 from mosquitoes in Keystone, Florida. Although data on human infections are limited, the virus has been linked to a fever/rash syndrome and, possibly, encephalitis, with early studies suggesting that 20% of persons in the Tampa, Florida, region had antibodies to KEYV. To assess the distribution and diversity of KEYV in other regions of Florida, we collected > 6,000 mosquitoes from 43 sampling sites in St. Johns County between June 2019 and April 2020. Mosquitoes were separated into pools by species and collection date and site. All pools with Aedes spp. (293 pools, 2,171 mosquitoes) were screened with a real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay that identifies KEYV and other closely related virus species of what was previously designated as the California encephalitis serogroup. In 2020, screening for KEYV was expanded to include 211 pools of Culex mosquitoes from sites where KEYV-positive Aedes spp. had been identified. rRT-PCR-positive samples were inoculated into cell cultures, and five KEYV isolates from Aedes atlanticus pools were isolated and sequenced. Analyses of the KEYV large genome segment sequences revealed two distinct KEYV clades, whereas analyses of the medium and small genome segments uncovered past reassortment events. Our data documented the ongoing seasonal circulation of multiple KEYV clades within Ae. atlanticus mosquito populations along the east coast of Florida, highlighting the need for further studies of the impact of this virus on human health.

Efficacy Evaluation of Medium-Chain Fatty Acids as Skin and Spatial Repellents Against Aedes aegypti (Diptera:Culicidae) Mosquitoes

Fatty acids derived from natural oils are considered as perspective products for adoption as repellents. Fatty acids derived from coconut oil have shown promise as repellents. This study consisted of an olfactometer evaluation of new formulations containing medium-chain fatty acids for spatial repellency and an in laboratory arm-in cage study for contact repellency against Aedes aegypti L. mosquitoes. Six formulations each of capric acid and lauric acid were evaluated for spatial repellency. These formulations contained 0.28-10% of either capric acid or lauric acid as the active ingredients in a consumer friendly skin care formulation. Base formula without fatty acids was evaluated as control in spatial repellency evaluation. For the arm-in cage evaluations, six formulations of capric acid, one base formulation, and a 7% N,N-diethyl-m-toluamide (DEET) product were tested for contact repellency. For contact repellency, United States Department of Agriculture (USDA) standard repellent test cages were used to determine the complete protection time (CPT) of the different formulated repellents. Among all capric acid formulations tested, the concentration of 2.25% (wt) indicated the best level of spatial repellency, but not significantly different from other concentrations. None of the lauric acid concentrations showed any level of spatial repellency. In the arm-in-cage evaluations, the highest contact repellency resulted from 4.5% capric acid, which was significantly higher than 7% DEET and base formula.

Evaluation of Essential Oils as Spatial Repellents Against Aedes aegypti in an Olfactometer

Spatial repellents are becoming an integral part of the integrated mosquito management and are considered another tool to prevent mosquito-borne diseases. They are also gaining attention as a potential disease transmission breaking strategy. Current vector control practices are losing their viability due to resistance development in arthropods to synthetic pesticides. Economic feasibility of developing natural products is driving towards search for natural products as spatial repellents evidenced by increase in number of their studies. Different volumes (0.0625, 0.125, 0.25, 0.5 ml) of clove oil, eucalyptus oil, geraniol, Immortelle oil, lemongrass oil, and RepelCare (mixture of turmeric oil and eucalyptus oil) were evaluated for their repellency against Aedes aegypti, replicating each test 5 times. Biogents lure and fresh air were used as control. The evaluations were conducted in a True Choice olfactometer by passing air carrying 2 vapors from 2 different products, i.e., an attractant, repellent, or clean air, through 2 chambers and providing mosquitoes an option to move to the chamber of their choice. For each run, 24-h-starved 15-20 female Ae. aegypti were released into the mosquito release chamber and number of mosquitoes in the 2-choice chambers and the mosquito release chamber were counted after 15 min and recorded. The difference in mosquitoes between 2 chambers indicated presence or absence of repellency. All the natural oils and RepelCare provided ≥70% repellency, except for Immortelle oil which had no repellency. All repellents tested except Immortelle and lemongrass oils showed increase in repellency with increase in application volume. However, minimum application volume to be effective was different for each oil. Lemongrass is the only oil which showed a peak at 0.125-ml volume.

Laboratory Evaluation of Bigshot Maxim Against Three Species of Larval and Adult Mosquitoes, Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus

The use of synthetic insecticides has been the main approach in mosquito control programs (MCPs) to prevent or reduce mosquito populations. The global problem of insecticide resistance and the concern of environmental impacts of synthetic insecticides have resulted in the interest of botanicals as an alternative. In this study, the botanical product BigShot Maxim, which contains cedarwood oil (14%), thyme oil (0.53%), and cinnamon oil (0.23%) as active ingredients, was examined in adulticide and larvicide bioassays against Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus. In the adulticide bioassay, 100% mortality was reached at a dilution of 1:10 after 4 h of exposure for all 3 species. In the larvicide bioassay, at the highest tested concentration (30 ppm by volume) the greatest mortality was 96.44 ± 1.44% SE for Ae. aegypti, 92.44 ± 2.07% SE for Cx. quinquefasciatus, and 33.33 ± 3.61% for An. quadrimaculatus, respectively. Insecticidal properties presented in all the experiments indicate that BigShot Maxim could be a viable alternative to some synthetic insecticides used in MCPs.