George F. O'Meara

Differential Survivorship of Invasive Mosquito Species in South Florida Cemeteries: Do Site-Specific Microclimates Explain Patterns of Coexistence and Exclusion?

ABSTRACT Within 2 yr of the arrival of the invasive container mosquito Aedes albopictus (Skuse), the previously dominant invasive mosquito Aedes aegypti (L.) disappeared from many Florida cemeteries. At some cemeteries, however, Ae. aegypti populations seem stable despite Ae. albopictus invasion. We sought to understand this variation in the outcome (exclusion, coexistence) of this invasion, given that previous experiments show that Ae. albopictus is the superior larval competitor. We tested experimentally the hypothesis that climate-dependent egg survivorship differs between exclusion and coexistence cemeteries and that differences in invasion outcome are associated with microclimate. Viability of eggs oviposited in the laboratory and suspended in vases at six cemeteries was significantly greater for Ae. aegypti than for Ae. albopictus, and greater in 2001 than in 2006. Cemeteries differed significantly in egg survivorship of Ae. albopictus, but not of Ae. aegypti, which is consistent with the hypothesis that Ae. albopictus suffers site-specific, climate-driven egg mortality that mitigates the competitive superiority of larval Ae. albopictus. Principal component (PC) analysis of microclimate records from vases during the experiments yielded three PCs accounting for >96% of the variance in both years of experiments. Multivariate analysis of variance of the three PCs revealed significant microclimate differences among the six cemeteries and between exclusion versus coexistence cemeteries. Stepwise logistic regression of egg survivorship versus microclimate PCs yielded significant fits for both species, and twice as much variance explained for Ae. albopictus as for Ae. aegypti in both years, Higher mortalities in 2006 were associated with high average daily maximum temperatures in vases, with lethal thresholds for both species at ≈40°C. From 1990 to 2007, vase occupancy by Ae. albopictus increased and that by Ae. aegypti decreased, with increasing seasonal precipitation at one well-sampled cemetery. Results support the hypothesis that locally variable climate-driven mortality of Ae. albopictus eggs contributes to patterns of exclusion of, or coexistence with, Ae. aegypti.

Factors affecting mosquito production from stormwater drains and catch basins in two Florida cities

ABSTRACT Mosquito production from drains and catch basins in the cities of Vero Beach and Key West, FL were monitored from May 2004 through August 2005. A total of 48,787 mosquitoes were captured during the study. Of these, over 99% belonged to two species, Culex nigripalpus Theobald (2,630) and Culex quinquefasciatus Say (45,946). Other species collected included Culex restuans Theobald, Culex salinarius Coquillett, Aedes aegypti (L.), Aedes albopictus (Skuse), and Uranotaenia lowii Theobald. Significantly greater numbers of Cx. nigripalpus were collected at Vero Beach than at Key West, but no significant differences in numbers of Cx. quinquefasciatus and in total numbers of mosquitoes between the two cities were evident. Rainfall, salinity, type of structure, structure setting, and presence or absence of predators or competitors influenced the numbers of mosquitoes collected and/or the frequency of positive, negative, dry, or flooded samples.

Interpopulation divergence in competitive interactions of the mosquito Aedes albopictus

Geographic variation in species interactions can have major effects on distributions. Effects of such variation can be particularly evident for invasive species, in which variation in competitive ability can influence invasive success and impacts. We tested the hypothesis that coexistence or exclusion of the resident mosquito Aedes aegypti results from variation among local populations of the invasive Aedes albopictus in competitive interactions with A. aegypti. We also examined the role of variation in fecundity-size relationships in these competitive interactions. We compared competitive abilities of nine North American populations of A. albopictus, three populations from each of three site types: extinction of A. aegypti following A. albopictus invasion, coexistence following A. albopictus invasion, and A. albopictus allopatric to A. aegypti. Competition among larvae from each A. albopictus population and a single A. aegypti population was tested in laboratory microcosms in a response surface design. We found interpopulation differences in competitive ability of A. albopictus, but no strong patterns among site types. Extinction sites had steeper average fecundity-size relationships than coexistence sites and allopatric sites, but this did not translate into superior population performance. Certain individual A. albopictus populations had exceptionally large competitive effects on A. aegypti or poor competitive responses to competition from A. aegypti, but competitive effect and response were not correlated. These results suggest that interpopulation variation in the competitive ability of A. albopictus may only partly explain the geographic pattern of coexistence with or extinction of A. aegypti. Environmental differences among regions may affect the competitive ability of A. albopictus and influence its invasion success and impact.

Fecundity, autogeny, and the larval environment of the pitcher-plant mosquito, Wyeomyia smithii

SummaryPupae and fourth instar larvae of a southern (30°N, Alabama, USA) population of Wyeomyia smithii Coq. (Diptera: Culicidae) were collected from pitcher plants. Adults which emerged were maintained without food then dissected to determine their egg clutch size. Among females which matured eggs, fecundities were negatively correlated with larval densities in individual pitchers. The mean autogenous fecundity of the overwintering generation did not differ from a summer sample. Adults unable to mature eggs comprised 6–39% of samples, depending on whether collected as pupae or fourth instar larvae. Fecundity was negatively correlated with time to adult eclosion among larvae maintained on unrenewed pitcher contents in the laboratory.Cohorts from this population were reared in artificial containers from egg hatch to adulthood at a single density and a superior or inferior diet. On the superior larval diet, all females survived to reproductive age, and all but one (>99%) produced eggs autogenously. On the inferior diet, survivorship to adult eclosion was significantly less, a high proportion of females died before reaching reproductive age, and only 19% of survivors matured eggs without blood. Protracted larval development induced by the inferior diet did not influence the probability of autogeny among females that survived to reproductive maturity.The relationship between larval environment and reproductive strategies is contrasted across the geographic range of W. smithii. Bloodfeeding occurs among southern populations where density dependent constraints on preimaginal growth are constantly severe. The loss of hematophagy among northern populations may have been facilitated by periods of density independent larval growth.

SEASONAL VARIATION IN THE ABUNDANCE OF CULEX NIGRIPALPUS AND CULEX QUINQUEFASCIATUS IN WASTEWATER PONDS AT TWO FLORIDA DAIRIES

Abstract Patterns of seasonal variation in the relative abundance of immature Culex mosquitoes in wastewater ponds at dairies located in 2 different regions of peninsular Florida were compared. Culex nigripalpus and Cx. quinquefasciatus were by far the most common mosquitoes collected during the study (99,344 and 106,225 individuals, respectively). Within-station differences in abundance of Cx. nigripalpus and Cx. quinquefasciatus were evident depending upon time of year. There were also between-station differences in the abundances of the 2 species depending upon time of year and station. Environmental and behavioral factors are implicated in some of the observed differences. We discuss mosquito control options for dairy ponds as well as possible impacts of mosquito production from these areas to humans and to animal health and production.

Mosquito production from four constructed treatment wetlands in peninsular Florida.

ABSTRACT Several techniques were used to sample adult and immature mosquitoes in 4 constructed treatment wetlands in Florida. Adults of 19 species (7 genera) of mosquitoes were collected, and immatures of the most abundant species and of 60% of all species also were collected. Few significant differences between sites and stations in the numbers of mosquitoes collected were discovered. Culex nigripalpus Theobald was the most abundant mosquito found in adult (carbon dioxide-baited suction traps) and ovitrap collections, whereas Mansonia spp. and Uranotaenia spp. were most common in pump-dip-grab samples. The roles of rooted and floating vegetation and of water quality in determining mosquito production from these areas are discussed.

Facultative blood-feeding in the crabhole mosquito, Deinocerites cancer.

ABSTRACT. 1. Most of the female crabhole mosquitoes Deinocerites cancer Theobald entering bait traps had undeveloped ovaries.

The Spread of Culex coronator (Diptera: Culicidae) Throughout Florida

Since 2005, there have been numerous reports of Culex coronator Dyar and Knab well outside of small geographic areas in Arizona, New Mexico and Texas, the range reported by Darsie and Ward (2005). Debboun et al. (2005) collected Cx. coronator in southwestern Louisiana at Fort Polk from several sites from spring to fall of 2004. Culex coronator was reported to be well-established in ten central and southern Mississippi counties (Varnado et al. 2005, Goddard et al. 2006). Smith et al. (2006) reported the species from four Florida counties and two additional Florida counties in 2008 (Smith 2008). McNelly et al. (2007) and Gray et al. (2008) reported collections of this species from south Alabama. Moulis et al. (2008) found this species in South Carolina and Georgia in 2007 and additional sites in three Georgia counties were reported in 2008 (Kelly et al. 2008). Carpenter and LaCasse (1955) reported that Cx. coronator larvae occur in rain-filled pools and artificial containers. Recent collections of Cx. coronator larvae have been reported from a variety of habitats including roadside ditches, spring-fed and rainfilled pools (Goddard et al. 2006), containers (Gray et al. 2008), a seepage pool near brackish marshland in South Carolina (Moulis et al. 2008), storm sewers (Manrique-Saide et al. 2012), and tires (Yee et al. 2012). The most recently published taxonomic keys used in Florida do not show Cx. coronator as occurring in the state (Darsie and Morris 2003, Darsie and Ward 2005) and Darsie and Morris (2003) do not include Cx. coronator in the Keys to the Adult Females and Fourth Instar Larvae of the Mosquitoes of Florida. Working with specimens of Cx. coronator, and following the current version of Darsie and Morris (2003), one would be faced with a choice between Culex tarsalis Coquillett and Culex bahamensis Dyar and Knab. Both species in the key and Cx. coronator have hind tarsomeres with basal and apical rings of pale scales, so Cx. coronator might be misidentified as either Cx. bahamensis or Cx. tarsalis. The extent of misidentification of Cx. coronator in Florida is unknown. Once it was recognized that this species was being misidentified, O’Meara and Connelly provided a list of characters and a comparison chart for distinguishing Cx. tarsalis from Cx. coronator for anyone attempting to identify Florida mosquitoes. Host-feeding patterns suggest that Cx. coronator feeds primarily on mammals but birds may also be a source for blood (reviewed by Mackay et al. 2010). To our knowledge, Cx. coronator has not yet been incriminated as a vector of arthropod-borne viruses in Florida, but West Nile virus (WNV) has been detected in this species in nature from Louisiana (Mackay et al. 2008, Unlu et al. 2010), underscoring the importance of properly identifying this species and its distribution. Also, Cx. coronator has been found to be naturally infected with St. Louis encephalitis virus (Anderson et al. 1957) and Venezuelan equine encephalitis virus (Scherer et al. 1971, Sudia and Newhouse 1975). During an investigation of the vector potential of Cx. coronator in Florida, Alto et al. (2014) reported Cx. coronator to be a competent vector of WNV under some conditions. An assessment of vector competence was made by exposing adult females to WNV-infected blood with viral titers comparable to viremia profiles in avian hosts (Komar et al. 2003, GuerreroSánchez et al. 2011). This species was highly susceptible to infection and dissemination of WNV. At 28° C, the transmission rate was 28 – 67%; and up to 17% at 25° C. Post-blood feeding, this species can delay oviposition for weeks and will lay more eggs when the source of blood is from birds, factors that may facilitate its role as a vector of WNV (Shaman et al. 2005) and St. Louis encephalitis virus (Day and Curtis 1999, Shaman et al. 2002). The geographic expansion of the range of Cx. coronator in Florida is reported here.

Culex interrogator (Diptera: Culicidae), a Mosquito Species New to Florida

In recent years, two mosquito species, Culex declarator Dyar and Knab and Culex coronator Dyar and Knab, have been detected for the first time in Florida. Single specimens of Cx declarator were collected in 1998 and 2002 in Indian River County and many more Cx. declarator adults were encountered in county surveillance activities during 2003 (Darsie and Shroyer 2004). However, since 2003 this mosquito has been collected infrequently and has been reported from only one additional Florida county, Monroe. Culex coronator is thought to have spread eastward from Texas (Gray et al. 2008) and was initially found in the western panhandle section of Florida in 2005 (Smith et al. 2006). Unlike Cx. declarator, Cx coronator is now found in nearly all Florida counties and is especially common in the southern part of the state (Connelly et al. 2016). Here we report on the finding of yet another Culex spp., Culex interrogator (Dyar and Knab), which is new to Florida. Historically, the northern geographic distribution limit of all three of these Culex (Culex) mosquitoes was southern Texas and other states bordering Mexico (Carpenter and LaCasse 1955, Darsie and Ward 1981). Culex interrogator was initially discovered in Florida in Broward County (Lat. 26°01’10.0”N, Long. 80°07’16.1”W) in August, 2013 when several larvae of this species were collected from a storm water drain that was 53 cm in diameter and contained a considerable amount of grass cuttings. Cooccurring with Cx. interrogator were three other mosquito species: Culex nigripalpus (Theobald), Culex quinquefasciatus (Say), and Culex salinarius (Coquillett). A second Broward County site with Cx. interrogator was found in October, 2014, when immatures of this species were collected from a roadside swale. This site was approximately 26 km west of the first site. In July and August, 2014 at two field study sites in Indian River County, more than 3,000 Culex egg rafts were collected from two types of ovitraps (busboy trays, 56 cm x 44 cm, 8 cm depth) that had been deployed to assess oviposition site preferences of Culex spp. Egg rafts were returned to Florida Medical Entomology Laboratory (FMEL) and held in insectary conditions at 28° C and 80% humidity. After eggs hatched, larvae were identified to species based on larval morphological features. Nine of these egg rafts, all from a single study site, produced Cx. interrogator. Other mosquito species collected with Cx. interrogator in the ovitraps included Cx. nigripalpus, Cx. quinquefasciatus, Cx. coronator, and Cx. salinarius. The ovitraps with Cx. interrogator egg rafts were located in a subdivision with numerous undeveloped lots bordering on agricultural lands. During the summer and autumn of 2014, Cx. interrogator adults were collected at seven other locations in Indian River County, including six of the eight sentinel chicken sites operated by the Indian River Mosquito Control District (IRMCD) where mosquitoes were captured in chicken coop exit traps. In the southern part of the county, near the edge of a pasture, several Cx. interrogator were captured in a dry-ice baited CDC miniature light trap and a passive box trap (Ritchie et al. 2013). Many more were taken in early morning collections of resting adults made with a battery powered aspirator (Table 1). More recently, Cx interrogator has been detected in two other Florida counties. In August, 2015 adults of this mosquito were collected in a CO2-baited light trap near Okeechobee City, Okeechobee County. In January, 2016, immature Cx. interrogator were found in a sample taken from a roadside swale with grass cuttings in Citrus County (Figure 1). Culex interrogator larvae are readily distinguished from