Florida Medical Entomology Laboratory

A compartmental, deterministic model was used to explore the effects of temperature dependency in mosquito mortality on the likelihood of epidemics and the size of outbreaks of Chikungunya virus under Florida temperature conditions. Two known vectors, Aedes albopictus and Ae. aegypti, were included, with similar structure but allowing mortality and abundance parameters to vary between them. The mortality relationship with temperature had a central optimal survival region, with increasing mortality outside these regions. The central temperature and the annual mean temperature were most influential in the likelihood of an epidemic, although the variance explained was low. The central temperature, annual mean temperature and day of virus infection influenced the size of the outbreaks. Regression models including two-way interactions explained more of the variance in outcomes than the main effects models, but there was still substantial variance left unexplained. Given the model structure, higher order interactions would be required to explain most of the variance.

Culicoides biting midges (Diptera: Ceratopogonidae) and mosquitoes (Diptera: Culicidae) are important vectors of pathogens affecting ruminants. On deer farms, Culicoides species transmit bluetongue virus and epizootic hemorrhagic disease virus, while mosquitoes can cause chronic stress and even exsanguination. We evaluated the effectiveness of the insecticide ­InsectGuard (0.5% permethrin), applied as a barrier treatment and pour-on, to reduce mosquito and biting midge landings on deer in Martin County, Florida. Deer simulators baited with carbon dioxide and fitted with sticky cards were used to trap landing insects. A polyethylene fence barrier treated with InsectGuard (1.34 fl oz/m2) and an untreated fence were tested against a no-barrier control. Separately, InsectGuard pour-on (1 fl oz per deer) was compared to an untreated control. The ­InsectGuard-treated barrier and pour-on applications reduced landings of three Culicoides species, including Culicoides insignis Lutz, a key bluetongue virus vector, by 175-fold and 7-fold, respectively. The InsectGuard-treated barrier also reduced mosquito landings: Culex spp. (15-fold), and Psorophora spp. (6-fold). While the InsectGuard pour-on caused a dramatic reduction of C. insignis, it had no measurable effect on Culex spp., Psorophora spp., or Culicoides floridensis Beck and appeared to attract Culicoides pusillus Lutz (8-fold increase). Our findings demonstrate that permethrin-treated barriers and pour-on applications can reduce the landing and, therefore, potential infectious bites of mosquitoes and biting midges. These interventions can be incorporated as part of an integrated vector management program for deer farms to enhance control outcomes, in combination with other strategies such as adulticide sprays, habitat management, and vaccination.

The recent emergence of Oropouche virus (OROV) highlights the importance of understanding insecticide susceptibility in the genus Culicoides (Diptera: Ceratopogonidae). In addition to the vector of OROV, this genus contains many other species that are biting nuisances and vectors of pathogens that affect humans, livestock, and wildlife. With adulticides as the primary method of Culicoides control, there is growing concern about insecticide resistance, compounded by the lack of tools to monitor Culicoides susceptibility. We adapted the Centers for Disease Control and Prevention (CDC) bottle bioassay and field cage trial methods, typically used to monitor insecticide susceptibility in mosquitoes and formulated adulticide efficacy, to evaluate permethrin susceptibility in the widely distributed coastal nuisance species, Culicoides furens. Permethrin caused 100% mortality in C. furens in field and laboratory assays. We identified a diagnostic dose (10.75 µg) and time (30 min) that resulted in 100% mortality in CDC bottle bioassays. Additionally, we determined that no-see-um netting is an effective mesh for field cage trials, allowing for the accurate assessment of Culicoides susceptibility to ultra-low volume applications of formulated adulticides like Permanone 30–30, a widely used adulticide. These methodologies offer essential tools for assessing Culicoides susceptibility, which is crucial for managing populations of Culicoides and preventing the spread of OROV and other pathogens.

Article Review: Harbach, R.E. 2024. The Composition and Nature of the Culicidae (Mosquitoes). Centre for Agriculture and Bioscience International and the Royal Entomological Society, United Kingdom. ISBN 9781800627994 was published on January 1, 2025 in the journal Florida Entomologist (volume 108, issue 1).

On November 7, 2023, 3 female specimens of Aedeomyia squamipennis were captured in Collier County, Florida, for the first time during routine adult mosquito surveillance in Collier Seminole State Park. This species was first found in the USA in Miami-Dade County in 2016 and has since expanded into multiple counties throughout South Florida. The presence of Ad. squamipennis has implications for arbovirus transmission as it is a vector for the Venezuelan equine encephalitis virus group. The detection of this mosquito species also highlights the importance of a robust and consistent mosquito surveillance program.

Despite the increasing burden of dengue, the regional emergence of the virus in Kenya has not been examined. This study investigates the genetic structure and regional spread of dengue virus-2 in Kenya. Viral RNA from acutely ill patients in Kenya was enriched and sequenced. Six new dengue-2 genomes were combined with 349 publicly available genomes and phylogenies used to infer gene flow between Kenya and other countries. Analyses indicate two dengue-2 Cosmopolitan genotype lineages circulating in Kenya, linked to recent outbreaks in coastal Kenya and Burkina Faso. Lineages circulating in Western, Southern, and Eastern Africa exhibiting similar evolutionary features are also reported. Phylogeography suggests importation of dengue-2 into Kenya from East and Southeast Asia and bidirectional geneflow. Additional lineages circulating in Africa are also imported from East and Southeast Asia. These findings underscore how intermittent importations from East and Southeast Asia drive dengue-2 circulation in Kenya and Africa more broadly.

In the last 2 decades, there has been an increase in the geographic range and frequency of vector-borne diseases. Management of mosquito populations has become challenging due to increasing rates of resistance to existing insecticidal products and formulations. Several alternative tools have emerged to suppress or replace mosquito populations. One of these tools is the In2Care Mosquito Station (In2Care station). This dual-action station contains the insect growth regulator pyriproxyfen which disrupts the development of immatures and the entomopathogenic fungus Beauveria bassiana (B. bassiana) strain GHA which kills exposed adult mosquitoes. The In2Care stations have previously been shown to effectively control Aedes aegypti in field settings at a density of 6 stations/acre rather than the label-recommended 10 stations/acre. To further test the efficacy of low station density deployment, we deployed In2Care stations in the Pleasant Street Historic District of Gainesville, Florida, at a density of 3 stations/acre over a period of 2 years in the presence or absence of ground larvicidal applications. The deployment of stations resulted in no measurable impact on Ae. aegypti and Culex quinquefasciatus adult or immature abundance suggesting that the low-density deployment of In2Care stations is insufficient to reduce Ae. aegypti and Cu. quinquefasciatus abundance within treatment areas.

Insects often exhibit irruptive population dynamics determined by environmental conditions. We examine if populations of the Culex tarsalis mosquito, a West Nile virus (WNV) vector, fluctuate synchronously over broad spatial extents and multiple timescales and whether climate drives synchrony in Cx. tarsalis, especially at annual timescales, due to the synchronous influence of temperature, precipitation, and/or humidity. We leveraged mosquito collections across 9 National Ecological Observatory Network (NEON) sites distributed in the interior West and Great Plains region USA over a 45-month period, and associated gridMET climate data. We utilized wavelet phasor mean fields and wavelet linear models to quantify spatial synchrony for mosquitoes and climate and to calculate the importance of climate in explaining Cx. tarsalis synchrony. We also tested whether the strength of spatial synchrony may vary directionally across years. We found significant annual synchrony in Cx. tarsalis, and short-term synchrony during a single period in 2018. Mean minimum temperature was a significant predictor of annual Cx. tarsalis spatial synchrony, and we found a marginally significant decrease in annual Cx. tarsalis synchrony. Significant Cx. tarsalis synchrony during 2018 coincided with an anomalous increase in precipitation. This work provides a valuable step toward understanding broadscale synchrony in a WNV vector.