Indian River County Research Articles

First Report of a Leaf Spot Disease of Wild Rocket (Diplotaxis tenuifolia) in Florida Caused by Xanthomonas campestris pv. raphani.

Wild rocket, also known as wall rocket or sand rocket (Diplotaxis tenuifolia (L.) DC, family Brassicaceae), is grown in Florida as a salad green and herb, especially for addition to "spring mix" and other bagged salad blends. It is similar in texture and flavor to the more widely known garden arugula (Eruca vesicatoria (L.) Cav. subsp. sativa). During the winter vegetable season of 2006-2007, a leaf spot disease causing severe economic loss was seen in commercial fields of wild rocket near the town of Sebastian in Indian River County, FL. Discrete water-soaked to greasy appearing spots were observed on leaf blades that rarely exceeded 1 mm in diameter with some surrounded by a narrow, yellow halo. There was no evidence of marginal V-shaped lesions suggestive of vascular black rot disease caused by Xanthomonas campestris pv. campestris. A bacterium that formed yellow colonies on nutrient agar was consistently isolated from these lesions. Four strains were isolated, purified, and characterized. All strains were strictly aerobic, gram-negative rods. Strains were positive for esculin hydrolysis and gelatin liquefaction and negative for oxidase, nitrate reduction, urease production, fluorescence on King's B medium, and utilization of asparagine as a sole source of carbon and nitrogen. Proteolysis and an alkaline reaction were observed in inoculated tubes of litmus milk. Colonies were bright yellow and mucoid on plates of yeast extract-glucose-calcium carbonate agar. Carbon source utilization, as revealed by the Biolog system, indicated a match to X. campestris. Fatty acid methyl ester analysis indicated a match with Florida library strains of X. campestris pv. raphani (similarity indices of 0.737 to 0.779). Suspensions (2 × 107 CFU/ml in sterile phosphate-buffered saline) of the four wild rocket strains and a strain isolated in 2003 as a cause of a discrete leaf spot disease of cabbage in southern Florida (1) were sprayed onto plants until runoff with a hand-held plastic mist bottle. Pathogenicity of strains was tested in the greenhouse on seven replicate plants of green cabbage cv. Copenhagen Market, salad arugula cv. Rocket, and wild rocket (an unnamed selection propagated from seed provided by a Florida grower). Symptoms appeared within 6 to 7 days. The wild rocket strains and the cabbage strain were pathogenic on all wild rocket and cabbage test plants, producing small, nonvascular leaf spots. No symptoms were seen on salad arugula or on control plants of wild rocket, cabbage, or arugula sprayed with phosphate-buffered saline. The bacterium was reisolated from infected plants and identified as X. campestris pv. raphani, thus completing Koch's postulates. We have classified the bacterial leaf spot pathogen of wild rocket as X. campestris pv. raphani using the nomenclature of Vincente et al. (2) for X. campestris strains producing nonvascular leaf spots on brassicas. This disease problem seems to be related to widespread use of overhead irrigation in the fields where the disease is prevalent. We have not observed the disease in seepage-irrigated fields of wild rocket.

An Ensemble Seasonal Forecast of Human Cases of St. Louis Encephalitis in Florida Based on Seasonal Hydrologic Forecasts

We present a method for the ensemble seasonal prediction of human St. Louis encephalitis (SLE) incidence and SLE virus transmission in Florida. We combine empirical relationships between modeled land surface wetness and the incidence of human clinical cases of SLE and modeled land surface wetness and the occurrence of SLE virus transmission throughout south Florida with a previously developed method for generating ensemble, seasonal hydrologic forecasts. Retrospective seasonal forecasts of human SLE incidence are made for Indian River County, Florida, and forecast skill is demonstrated for 2–4 months. A sample seasonal forecast of human SLE incidence is presented. This study establishes the skill of a potential component of an operational SLE forecast system in south Florida, one that provides information well in advance of transmission and may enable early interventions that reduce transmission. Future development of this method and operational application of these forecasts are discussed. The methodology also will be applied to West Nile virus monitoring and forecasting.

St. Louis Encephalitis Virus in Wild Birds During the 1990 South Florida Epidemic: The Importance of Drought, Wetting Conditions, and the Emergence ofCulex nigripalpus(Diptera: Culicidae) to Arboviral Amplification and Transmission

We analyzed the prevalence of hemagglutination inhibition (HI) antibodies to St. Louis encephalitis (SLE) virus in wild birds during the 1990 SLE epidemic in Indian River County. The initial presence of SLE HI antibody was associated significantly with modeled drought 15 wk prior, wetting conditions 1 wk prior, and the emergence of the Florida SLE virus vector, Culex nigripalpus, 5 wk prior. Our findings indicated that three factors conspired to create the 1990 epidemic: (1) a large population of susceptible wild birds; (2) severe springtime drought, which facilitated amplification of the SLE virus among the Cx. nigripalpus and a portion of the wild bird population; and (3) continued rainfall and wetting of the land surface in the summer and early fall, which sustained a large, host-seeking Cx. nigripalpus population. The continued biting and reproductive activity of Cx. nigripalpus maintained epizootic transmission throughout the summer and early fall in Indian River County. The high level of SLE virus amplification resulted in spillover transmission to humans. We hypothesize that without the continued reproductive activity of the vector mosquito, brought about by excessive summer and fall wetness, the unprecedented SLE virus amplification and consequent transmission to humans would not have been realized in 1990.

Drought-induced amplification of Saint Louis encephalitis virus, Florida.

We used a dynamic hydrology model to simulate water table depth (WTD) and quantify the relationship between Saint Louis encephalitis virus (SLEV) transmission and hydrologic conditions in Indian River County, Florida, from 1986 through 1991, a period with an SLEV epidemic. Virus transmission followed periods of modeled drought (specifically low WTDs 12 to 17 weeks before virus transmission, followed by a rising of the water table 1 to 2 weeks before virus transmission). Further evidence from collections of Culex nigripalpus (the major mosquito vector of SLEV in Florida) suggests that during extended spring droughts vector mosquitoes and nestling, juvenile, and adult wild birds congregate in selected refuges, facilitating epizootic amplification of SLEV. When the drought ends and habitat availability increases, the SLEV-infected Cx. nigripalpus and wild birds disperse, initiating an SLEV transmission cycle. These findings demonstrate a mechanism by which drought facilitates the amplification of SLEV and its subsequent transmission to humans.

ENVIRONMENTAL JUSTICE: A CASE STUDY OF FARM WORKERS IN SOUTH FLORIDA

ABSTRACT One purpose of this study is to examine the complex government infrastructure that implements and enforces laws that were created to protect farm workers from environmental hazards. The second purpose is to present a case study on farm workers in South Florida to determine whether the federal and state laws are protecting this occupational group from environmental hazards related to pesticide exposure. A survey based on questions that pertain to various laws was used to gather data on farm workers in two South Florida counties. Face-to-face interviews were conducted with farm workers at several migrant farm worker day care centers in Palm Beach and Indian River County, Florida. The findings of the study reveal that federal and state laws which are currently in place to protect the workers from pesticide exposure do not adequately protect the workers from exposure to harmful pesticides and farm workers are uninformed of the laws which exist to protect them from possible pesticide exposure. The study concludes with policy recommendations that will improve the implementation and enforcement of the current laws designed to protect farm workers from pesticide exposure.

Mosquito Hosts of Arboviruses from Indian River County, Florida, during 1998

Adult mosquitoes were collected for virus isolation from two sites in Indian River County, FL, from May 5 through August 13, 1998 using dry ice-baited CDC light traps (81 trap-nights) and CDC gravid traps (254 trap-nights). A total of 46,150 female mosquitoes (923 mosquito-pools, 50 females/pool) were processed for virus isolation. These females represented 18 species of mosquitoes, with Culex nigripalpus comprising 77.4% of all mosquitoes collected, followed by Aedes infirmatus (4.9%), Ae. vexans (4.0%) and Cx. erraticus (2.4%). No St. Louis encephalitis (SLE) and eastern equine encephalitis (EEE) virus isolates were obtained. Keystone (KEY) and Tensaw (TEN) viruses were isolated from Ae. albopictus (one isolate of KEY); Anopheles crucians (two isolates of TEN); Cx. nigripalpus (one isolate of TEN and 2 isolates of KEY); Coquilletidia perturbans (two isolates of TEN); and Wyeomyia vanduzeei (one isolate of TEN). All isolates were obtained from mosquitoes collected in CDC light traps, except for the KEY virus isolate from Ae. albopictus, which was collected in a CDC gravid trap. The isolation of TEN virus from Wy. vanduzeei is a first record for Florida.

Epidemiological features of and public health response to a St. Louis encephalitis epidemic in Florida, 1990-1.

A St. Louis encephalitis (SLE) epidemic in Florida during 25 weeks in 1990-1, resulted in 222 laboratory-diagnosed cases, an attack rate in the 28 affected counties of 2.25/100,000. Disease risk rose with advanced age, to 17.14/100,000 in persons over 80 years, and all 14 fatal cases were in persons over 55 years (median, 70 years). Community serosurveys in Indian River County, the epicenter of the outbreak (attack rate 21/100,000), showed acute asymptomatic infections in 3.6% of the persons surveyed, with higher rates in persons with outdoor occupational exposure (7.4%) and in clients of a shelter for the indigent (13.3%). A matched case-control study found that evening outdoor exposure for more than 2 h was associated with an increased risk for acquiring illness (odds ratio [OR] 4.33, 95% CI 1.23-15.21) while a number of recommended personal protective measures were protective. Four SLE patients were dually infected with Highlands J virus, the first reported cases of acute infection with this alphavirus. The case-control study provided the first evidence that a public education campaign to reduce exposure had a protective effect against acquiring the disease.

Avian serology in a St. Louis encephalitis epicenter before, during, and after a widespread epidemic in south Florida, USA.

Blood and serum from 3,915 wild and domestic birds (2,590 resident, 139 migrant, and 1,186 captive), representing 56 species collected in central Florida from 1989 through 1997, were analyzed for evidence of St. Louis encephalitis (SLE) virus transmission. All sera were tested for SLE hemagglutination inhibition (HI) antibody. Selected sera and bloods were tested for SLE neutralizing (NT) antibody and virus. The reproductive success of resident birds was highest from 1990-1992 and lowest from 1994-1997. Transmission of SLE to resident birds, especially mourning doves (Zenaida macroura), peaked during the summer of 1990, a year during which a widespread SLE epidemic was recorded in central Florida. The SLE antibody-positive resident birds 1st appeared during September of the epidemic year. Some SLE, HI antibody-positive resident birds were captured throughout 1991, but only 5% were yearlings, compared with 36% in 1990. By 1993, wild resident birds expressing HI and NT antibodies to SLE had nearly disappeared. None of the migrant birds tested were SLE-positive. Sentinel chickens maintained in Indian River County during the epidemic year seroconverted to SLE starting in early July with peak seroconversion rates in August, September, and October. High (> or = 50%) SLE seroconversion rates in sentinel chickens preceded those in wild birds by 10 wk and preceded peak human SLE transmission by at least 8 wk. Major SLE epidemics in south Florida depend on abundant wild bird populations, especially during the amplification phase of the transmission cycle. We propose that hard winter freezes along the temperature-subtropical climatic zone interface in central Florida, at approximately 27 degrees 30' North Latitude, opens foraging and nesting habitats for ground-feeding birds, resulting in high reproductive success and an abundance of seronegative individuals that rapidly amplify the SLE later in the year.

Snuffing Out H2S in Water and Air

Dealing effectively with hydrogen sulfide in groundwater presented a major challenge for the coastal Indian River County Utilities Department in Florida. Stripping the odorous substance from the water was only half the solution; keeping the smell from drifting through the air in the neighborhood was the other half. This article describes three different odor control systems that IRCUD field‐tested: the catalytic carbon unit; a conventional two‐stage wet scrubber system; and, a conventional in‐line oxidation with chlorine‐air injection and mixing. Results indicated that the catalytic/adsorptive carbon unit was the most cost effective and resulted in producing finished water quality that will meet future Safe Drinking Water Act trihalomethane information levels for Phase 2 disinfection.

Blood feeding and oviposition by Culex nigripalpus (Diptera: Culicidae) before, during, and after a widespread St. Louis encephalitis virus epidemic in Florida.

A widespread epidemic of St. Louis encephalitis (SLE) virus was reported from central Florida from late July through December 1990 with 226 clinical cases and 11 deaths in humans. The abundance of blood-fed and gravid Culex nigripalpus Theobald females, the vector of SLE in Florida, was monitored at a resting site in Indian River County, FL, for the 3 yr before the epidemic, the epidemic year, and for 1 yr following the epidemic. Each study year was divided into four 3-mo periods that depict the subtropical SLE transmission cycle; a January-March maintenance phase, an April-June amplification phase, a July-September early transmission phase, and an October-December late transmission phase. The abundance of blood-fed and gravid females was significantly greater during the amplification, early transmission, and late transmission phases of the 1990 SLE epidemic when compared with the 3 pre-epidemic years. Throughout the study, Cx. nigripalpus blood feeding and oviposition was driven by epic (> 50 mm) rainfall events. The abundance of gravid females decreased, whereas the number of blood-fed females increased following heavy rainfalls. Epizootic and epidemic transmission of SLE to sentinel chickens and humans in Indian River County was greatest immediately following heavy rainfalls that synchronized Cx. nigripalpus oviposition and blood feeding.

Reclaimed Wastewater Irrigation and Fertilization of Mature `Redblush' Grapefruit Trees on Spodosols in Florida

An experiment was designed to determine the effects of canal water and reclaimed wastewater on growth, yield, and fruit quality of mature (25-year-old) `Redblush' grapefruit (Citrus paradisi Macf.) trees on sour orange (C. aurantium L.) rootstock. The study was conducted from 1 Oct. 1990 to 18 Apr. 1994 at a site adjacent to the Indian River County municipal wastewater treatment facility located near Vero Beach, Fla. Treatments included canal water applied based on one-third or two-thirds soil water depletion and reclaimed wastewater applied using microsprinklers at 23.1 mm/week (low), 30.7 mm/week (moderate) and 38.6 mm/week (high). Trees receiving low and moderate levels of reclaimed wastewater had the largest canopies and trunk diameters and highest yields, even though the amount of fertilizer applied was less than that of canal water plots. Leaf nutrient levels were generally within acceptable ranges for N, P, K, Ca, Mg, and Na except in 1991 when levels were deficient due to excessive rainfall and leaching. Leaf B levels were similar for all reclaimed wastewater treatments but were lower for the canal water treatment in 1992 and 1993. Fruit growth rate, fruit and juice weight, total soluble solids (TSS), titratable acidity (TA), and TSS: TA ratio were similar for all treatments in 2 of 3 years. Peel thickness was similar for all treatments. Heavy metal concentration in the reclaimed wastewater was at low or nondetectable levels. Similarly, enteric viruses in the effluent were always <0.003 plaque forming units/liter. Reclaimed wastewater irrigation significantly increased weed growth compared to the canal water treatment.

Factors Influencing the Distribution of Blackchin Tilapia Sarotherodon melanotherodon (Osteichthyes: Cichlidae) in the Indian River System, Florida

The blackchin tilapia, Sarotherodon melanotheron, was first collected from the Indian River system, in Brevard County, Florida, in 1980. Since its introduction, this species has expanded its range northward along the coast approximately 37 km, to just north of Whites Point, Brevard County, and southward about 68 km to Vero Beach, Indian River County. Laboratory studies on salinity tolerance indicate an ability of this species to tolerate hypersaline concentrations of at least 100 ppt, and to reproduce in salinities of up to 35 ppt. The northern distribution of blackchin tilapia is almost certainly limited by cold temperature; however, the potential exists for extensive coastal, and possibly inland, invasion south of Its present limits.

Seasonal Occurrence of Anastrepha suspense (Diptera: Tephritidae) in Indian River County, Florida, 1984-1987

The seasonal occurrence of Anastrepha suspense (Loew) was studied in Indian River County, Fla., in 1984-1987. Thousands of A. suspense were trapped yearround in urban areas where loquat, Eriobotrya japonica (Thunb.) Lindl.; Cattley guava, Psidium littorale Raddi var. longipes (O. Berg) Fosb.; Surinam cherry, Eugenia uniflora L.; calamondin, xCitrofortunella mitis (Blanco) J. Ingram & H. E. Moore; and kumquat, Fortunella japonica (Thunb.) Swingle occurred continuously. A. suspense bred on loquat during December-April, then on Surinam cherry in the spring, and Cattley guava in July-September. Meanwhile, a low level of movement of A. suspense from urban areas into adjacent commercial citrus groves was detected. Only 14 A. suspense adults were found in semiurban areas and 12 adults in the commercial citrus groves. Host fruit were also examined in the study and showed that orange and grapefruit were minor hosts of A. suspensa .

Demographic indicators of the relative need for artificial reefs in Florida

Abstract Artificial reef development involves pfonning from a number of perspectives including biological, oceanographie, engineering, and social. This article reviews previous studies and identifies demographic variables that affect the use of artificial reefs by recreational anglers. An index of relative demand was created employing eight components: number of coastal county resident boat anglers, nonresident boat anglers, tourist boat anglers, nonboat anglers, number of fishing clubs, number of charter/party boats, number of registered pleasure boats, and the rate of county population growth. By comparing the magnitude of the index to the number of existing artificial reefs off of Florida's 35 coastal counties, an estimate of relative need was graphically portrayed on a state map. Indian River county on the Atlantic coast and Hernando, Hillsborough, Pasco, Citrus, Levy, Lee, and Charlotte counties on the central Gulf coast are the areas with the greatest demand relative to existing reef supply.

Rainfall-Directed Oviposition Behavior of Culex nigripalpus (Diptera: Culicidae) and Its Influence on St. Louis Encephalitis Virus Transmission in Indian River County, Florida

Resting Culex nigripalpus Theobald were collected with a ground aspirator three times a week in Indian River County, Fla., from January 1985 through December 1987. The number of green (newly emerged), empty, blood-fed, and gravid females in each collection was counted; up to 100 empty females were dissected to estimate the abundance of empty, parous females in the population. In general, this species was uncommon during the dry season from January through June but increased during the wet season in July and remained abundant through early winter. During the wet season, green, parous, and gravid females were periodically abundant. Time series analysis demonstrated that green and parous mosquitoes were positively associated through time and that gravid females were associated negatively with daily rainfall. The strongest correlations were recorded in 1985, a year during which St. Louis encephalitis virus was detected with increased frequency in Indian River County. Laboratory experiments in a large outdoor wind tunnel confirmed that high relative humidity was important for the initiation and successful completion of oviposition by gravid, field-collected Cx. nigripalpus mosquitoes. Thus, intermittent rainfall during autumn may serve to delay oviposition, increase longevity, synchronize blood feeding, and enhance transmission of St. Louis encephalitis virus by infected mosquitoes in the field.

Influence of Rainfall on Culex nigripalpus (Diptera: Culicidae) Blood-Feeding Behavior in Indian River County, Florida

Culex nigripalpus Theobald abundance was monitored by ground aspirator collections taken three times a week at a site in Indian River County, Fla. from January 1985 through December 1987. Aspirator collections allowed daily surveillance of fluctuations in mosquito abundance and changes in blood-feeding behavior. A Time Series Analysis of the 3-yr period revealed a significant cross correlation between C. nigripalpus engorgement and daily rainfall. This was especially pronounced in 1985, when St. Louis encephalitis virus was common in Indian River County, but was much less pronounced in 1987, when no virus activity was recorded. Rainfall in July, August, and September strongly influenced mosquito abundance during the autumn and early winter when virus transmission was most common. Dry conditions during July and August 1987 reduced mosquito abundance drastically during the following autumn.

Aldicarb Studies in Ground Waters from Florida Citrus Groves and Their Relation to Ground—Water Protection

ABSTRACTThe disappearance of aldicarb [2–methyl–2(methylthio) propionaldehyde 0‐(methylcarbamoyl) oxime] and its two toxic degradation products, aldicarb sulfoxide and aldicarb sulfone, were measured in laboratory studies using ground waters and subsoils collected from citrus groves in Indian River County, Florida, and incubated under controlled conditions which best represented the in situ environment. The half‐life times for the disappearance of aldicarb and its two oxidized sulfur derivatives in ground‐water‐saturated subsoils ranged from 10–26 days. Based on the degradation rates found in this study, hydrologic parameters obtained for Indian River County subsoils, and amounts of total toxic residue reported entering Florida ground waters, it was estimated that toxic residues in aldicarb‐contaminated ground waters in Indian River County would migrate only short distances (0.3–5.2 m) before conversion of toxic residues to nontoxic residues was complete.

Establishment of Aedes vexans in Citrus Groves in Southeastern Florida

Citrus groves in Indian River County in Florida, irrigated by crown-flooding, have provided an extensive new habitat for the mosquito Aedes vexans (Meigen). Eggs are laid mainly under tree canopies at the crowns of citrus grove furrows and require inundation as a hatching stimulus. Normal rainfall provides insufficient water depth in the furrows to hatch many eggs, but crown-flood irrigation hatches large numbers. Therefore, irrigation during periods of drought stimulates mosquito production.

Variable expressions of autogeny in three mosquito species

Patterns of autogeny were compared in 3 mosquito species from a coastal site in Indian River County, Florida. Both autogenous and anautogenous females were found in Aedes taeniorhynchus (Wiedemann) and Wyeomyia vanduzeei Dyar and Knab populations. Mating was a prerequisite for autogeny in certain females of both species (see Tables I and II). All of the Deinocerites cancer Theobald females were autogenous, whether mated or not. The expression of autogeny in A. taeniorhynchus depended upon environmental conditions during the larval stages and the geographical origin of the population. For some A. taeniorhynchus females, mating was needed for autogenous ovarian maturation under all experimental conditions, whereas for others mating became a requirement for autogeny only when the mosquitoes encountered the less favorable larval conditions. In nature, the dominant form of autogeny in A. taeniorhynchus appeared to be the male-induced type. Among W. vanduzeei and A. taeniorhynchus populations, the male-induced form of autogeny was associated with relatively low levels of autogenous fecundity. However, females that possess the capacity for male-induced autogeny have a greater potential for enhancing the size of their initial egg batch by blood-feeding than do females that can express autogeny independent of mating.

Breeding Biology of Five Species of Herons in Coastal Florida

The breeding biology of the Louisiana Heron, Snowy Egret, Cattle Egret, Little Blue Heron, and the Great Egret was studied on Riomar Island, a 2.8-ha mangrove island in Indian River County, Florida from March through May 1973. The Louisiana Heron and Cattle Egret nests were built increasingly more distant from the shoreline as the breeding season advanced. Nests of the Little Blue Heron were not horizontally stratified and the seasonal differences in siting of the Snowy Egret and Great Egret nests were not significant. The Louisiana Heron nests showed vertical stratification and were built significantly higher as the season advanced. Snowy Egret and Great Egret nests were built at lower elevations in midseason, but later nests were at the same height as the earlier nests. The heights of Cattle Egret and Little Blue Heron nests did not change during the season. The Louisiana Heron, Snowy Egret, Cattle Egret, and Great Egret completed clutches the last week of March and the first week of April. Little Blue Herons completed their clutches the second and third weeks in April. The louisiana Heron, Snowy Egret, and Cattle Egret laid eggs on the average at slightly greater than 2-day intervals and the Little Blue Heron and Great Egret at slightly less than 2-day intervals. All five laid replacement clutches when the original clutch was destroyed. Little Blue Heron clutches were significantly larger than Snowy Egret and Great Egret clutches. Louisiana Heron clutches were significantly larger than Great Egret clutches. Incubation began after the first egg was laid in most Snowy Egret, Cattle Egret, and Great Egret nests and was delayed until after the second egg in Louisiana Heron and Little Blue Heron nests. The time interval between hatching of successive eggs in the clutch increased in all species except the Little Blue Heron, which showed a decrease in interval. Nests failures were caused mainly by Brown Pelicans, whose clumsy landings at or near their own nests knocked eggs from nearby heron nests or crushed them. Still nesting success of the Riomar herons was better than any reported in the literature. The Little Blue Herons had the highest nest success because of their relative isolation from the other nesting species.