Estimation of population age structure, daily survival rates, and potential to support dengue virus transmission for Florida Keys Aedes aegypti via transcriptional profiling.

Aedes aegypti is an important vector of dengue virus and other arboviruses that affect human health. After being ingested in an infectious bloodmeal, but before being transmitted from mosquito to human, dengue virus must disseminate from the vector midgut into the hemocoel and then the salivary glands. This process, the extrinsic incubation period, typically takes 6-14 days. Since older mosquitoes are responsible for transmission, understanding the age structure of vector populations is important. Transcriptional profiling can facilitate predictions of the age structures of mosquito populations, critical for estimating their potential for pathogen transmission. In this study, we utilized a two-gene transcript model to assess the age structure and daily survival rates of three populations (Key West, Marathon, and Key Largo) of Ae. aegypti from the Florida Keys, United States, where repeated outbreaks of autochthonous dengue transmission have recently occurred. We found that Key Largo had the youngest Ae. aegypti population with the lowest daily survival rate, while Key West had the oldest population and highest survival rate. Across sites, 22.67% of Ae. aegypti females were likely old enough to transmit dengue virus (at least 15 days post emergence). Computed estimates of the daily survival rate (0.8364 using loglinear and 0.8660 using non-linear regression), indicate that dengue vectors in the region experienced relatively low daily mortality. Collectively, our data suggest that Ae. aegypti populations across the Florida Keys harbor large numbers of older individuals, which likely contributes to the high risk of dengue transmission in the area.

Dataset for aedes aegypti (diptera: Culicidae) and culex quinquefasciatus (diptera: Culicidae) collections from key West, Florida, USA, 2010-2020.

The Florida Keys Mosquito Control District began deploying Biogents® BG Sentinel traps to monitor Aedes aegypti (Diptera: Culicidae) populations in Key West during a small autochthonous dengue outbreak that began in November 2009. This paper provides weekly data for twelve collection points from January 2010 through December 2020. BG Sentinel traps were baited with dry ice and proprietary BG Lure and were set in the afternoon and retrieved the following morning totalling 19 collection hours. Trap collections also included Culex quinquefasciatus and thus data for that species is also included. The collection data could provide insight into dengue transmission in a small sub-tropical US city.

Mosquito Surveillance and Insecticide Resistance Monitoring Conducted by the Florida Keys Mosquito Control District, Monroe County, Florida, USA.

Mosquito control programs in the State of Florida are charged with protecting human and animal health, fostering economic development of the State, permitting enjoyment of the natural attractions in Florida, and improving the quality of life of citizens. Mosquito control programs must accomplish these tasks in such a manner as will protect the environment and terrestrial, marine, and freshwater ecosystems. The Florida Keys Mosquito Control District provides a science-based Integrated Pest Management mosquito control program to the residents of the Florida Keys, Monroe County, Florida. Operational decisions are based on surveillance of adult and immature mosquitoes. Mosquito populations are monitored by means of carbon dioxide-baited light traps BG Sentinel traps, truck traps, gravid traps, oviposition traps, and human landing rate counts. Larvae and pupae are monitored by inspections of natural and human-made immature habitats. Due to past and current reliance on chemical pesticides for control of mosquitoes, the District maintains a pesticide resistance detection program consisting of CDC bottle bioassays and larval bioassays, challenging local mosquito species with currently used adulticides and larvicides.

Ground Applications of Vectobac® WDG with A1 Super-Duty Mist Sprayer® and Micronair® AU5000 Atomizer for Suppression of Aedes aegypti Populations in the Florida Keys.

Since 2011, the Florida Keys Mosquito Control District (FKMCD) has used the WALS® application strategy with VectoBac® WDG containing Bacillus thuringiensis israelensis via helicopter in Key West for the control of Aedes aegypti larval populations. In 2018, FKMCD conducted a study to determine the effectiveness of using a trailer-mounted A1 Super Duty Mist Sprayer® (A1 Mist Sprayers) with a Micronair® AU5000 (Micron Group) atomizer to apply VectoBac WDG by ground at the rate of 0.5 lb/acre (0.56 kg/ha). Bioassay cups were placed in a residential area encompassing open, moderate, and heavy cover scenarios between 0 and 300 ft (0-91.44 m) perpendicular to the spray line. An application rate of 0.5 lbs/acre (0.56 kg/ha) was used. Bioassay cups were collected after application and returned to the laboratory where 100 ml of distilled water and 10 F1 generation Ae. aegypti larvae were added. Laval mortality was monitored at 2, 4, and 24 h. Three separate runs were completed during the summer of 2018. Average larval mortality at 24 h was >90%. The field trial demonstrated sufficient efficacy to introduce this method of larviciding into operational use.

Human Blood Feeding by Aedes aegypti (Diptera: Culicidae) in the Florida Keys and a Review of the Literature.

Aedes aegypti L. is considered to have a proclivity for feeding on human blood even when other hosts are available. However, few studies have demonstrated host use by this mosquito in the continental United States, where local transmission of dengue, Zika, and chikungunya viruses has been recently documented. This study investigated the bloodmeal sources of female Ae. aegypti in the subtropical city of Key West and the surrounding county in Florida with the goal of identifying preferred hosts. Blood-engorged Ae. aegypti mosquitoes were collected from BG Sentinel traps used as part of a routine surveillance program in the Florida Keys (Monroe County, Florida). Bloodmeal samples were analyzed using PCR assays, sequencing, and comparison with reference sequences in GenBank. Aedes aegypti females from Key West fed predominantly on humans (79.6%) and did not differ statistically from females collected from the rest of the Florida Keys (69.5%). Culex quinquefasciatus Say (Diptera: Culicidae), considered a host generalist, was collected and analyzed from the same sites for comparative purposes. Females of Cx. quinquefasciatus fed predominantly (70.7%) on birds and nonhuman mammals in the Florida Keys, corroborating the validity of molecular assay breadth and demonstrating that given the same group of available hosts Ae. aegypti selects humans. Our results indicated that Ae. aegypti has a high rate of human-biting in a subtropical area within the United States, supporting its role in recent local transmission of dengue and other viruses.

Establishment of Aedes albopictus (Diptera: Culicidae) in the Florida Keys, 2001-2017.

The presence of Aedes albopictus (Skuse) was first reported in the Florida Keys in 1993. Despite extensive surveillance, the Florida Keys Mosquito Control District (FKMCD) only collected specimens occasionally on a few islands, some years finding no evidence of the invasive species. In 2013-2017, FKMCD witnessed a sudden increase in population size and geographic extent of Ae. albopictus. Samples of Ae. albopictus have now been identified on 30 different islands in the Florida Keys. Three islands in particular (Key Largo, Big Pine Key, and Stock Island) have produced multiple positive samples during at least 4 of the last 5 yr, suggesting establishment of the invasive species. FKMCD continues to monitor Ae. albopictus throughout the Keys and make extensive efforts to reduce population abundance and geographic extent of this disease vector.

Effects of Mosquito Control Adulticides on Sterile Cochliomyia hominivorax (Diptera: Calliphoridae).

Effects of mosquito control adulticides on sterile screwworm flies, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), were investigated via bottle bioassays, outdoor cage tests, and exposure to treated vegetation. In bottle bioassays, 43 µg of permethrin via dilution of Evoluer, 474.56 µg of malathion via dilution of Fyfanon, and 25 µg of naled via dilution of Dibrom Concentrate were used to challenge screwworm flies. Permethrin was more toxic to screwworm flies than was malathion, which was more toxic than naled. On succeeding days, permethrin was still lethal to the flies, whereas malathion and naled were less toxic. During outdoor cage trials, screwworm mortality declined as distance from the spray truck increased. Sterile screwworm flies were killed by lower concentrations of permethrin needed to kill black salt marsh mosquitoes, Aedes taeniorhynchus (Wiedemann) (Diptera: Culicidae). Flies exposed to treated vegetation taken from the path of the spray cloud died more quickly than did flies exposed to leaves taken 5 ft inside the canopy. Fly mortality increased as volume mean diameter of droplets increased. In spite of the toxicity of Evoluer to screwworm flies, aspects of their biology make it unlikely that mosquito control operations would affect released flies.

A Large Scale Biorational Approach Using Bacillus thuringiensis israeliensis (Strain AM65-52) for Managing Aedes aegypti Populations to Prevent Dengue, Chikungunya and Zika Transmission.

BACKGROUND: Aedes aegypti is a container-inhabiting mosquito and a vector of dengue, chikungunya, and Zika viruses. In 2009 several cases of autochthonous dengue transmission were reported in Key West, Florida, USA prompting a comprehensive response to control A. aegypti. In Key West, larvae of this mosquito develop in containers around human habitations which can be numerous and labor intensive to find and treat. Aerial applications of larvicide covering large areas in a short time can be an efficient and economical method to control A. aegypti. Bacillus thuringiensis israelensis (Bti) is a bacterial larvicide which is highly target specific and appropriate for wide area spraying over urban areas, but to date, there are no studies that evaluate aerial spraying of Bti to control container mosquitoes like A. aegypti. METHODOLOGY: This paper examines the effectiveness of aerial larvicide applications using VectoBac® WG, a commercially available Bti formulation, for A. aegypti control in an urban setting in the USA. Droplet characteristics and spray drop deposition were evaluated in Key West, Florida, USA. The mortality of A. aegypti in containers placed under canopy in an urban environment was also evaluated. Efficacy of multiple larvicide applications on adult female A. aegypti population reduction was compared between an untreated control and treatment site. CONCLUSIONS: Droplet characteristics showed that small droplets can penetrate through dense canopy to reach small containers. VectoBac WG droplets reached small containers under heavy canopy in sufficient amounts to cause > 55% mortality on all application days and >90% mortality on 3 of 5 application days while controls had <5% mortality. Aerial applications of VectoBac WG caused significant decrease in adult female populations throughout the summer and during the 38th week (last application) the difference in adult female numbers between untreated and treated sites was >50%. Aerial larvicide applications using VectoBac WG can cover wide areas in a short period of time and can be effective in controlling A. aegypti and reducing A. aegypti-borne transmission in urban areas similar to Key West, Florida, USA.