Mortality Patterns of Simulium vittatum Larvae (Diptera: Simuliidae) Following Exposure to Insecticidal Proteins Produced by Bacillus thuringiensis var. israelensis.

Products containing insecticidal crystalline proteins (ICPs) produced by Bacillus thuringiensis var. israelensis (Bti ICPs) are used to suppress vector and nuisance populations of black flies. The efficacy of an application of these products is often determined by a posttreatment evaluation of larval mortality. Larvae are typically removed from the substrate at some point in time after application of the product and mortality is determined. The time necessary for the effects of Bti ICPs to cause morality in exposed larvae can vary, and there is little consensus on how long operators should wait before evaluating larval mortality. This study was conducted to provide more information to larvicide applicators when performing posttreatment evaluations. Simulium vittatum larvae were exposed to Bti ICPs under controlled conditions and the mortality was monitored over time. Larvae exposed to operational concentrations of ICPs exhibited maximum mortality, approximately 87%, after 4 h. Exposure of larvae to 1/3 of that concentration resulted in similar mortality; however, the maximum mortality was not reached until 8 h postexposure. Additional experiments revealed that maximum mortality and time to maximum mortality can also be affected by components in the larval medium. Larval mortality was compared between larvae exposed to Bti ICPs in moderately hard water, medium containing 50 parts per million (ppm) of kaolinite, and medium containing 50 ppm of cellulose. The clay material had no significant effect on larval mortality or time to achieve maximum mortality. When cellulose was present in the medium, the time to maximum mortality was increased 50% and overall mortality was reduced by more than 40%.

Host predilection and transmissibility of vesicular stomatitis New Jersey virus strains in domestic cattle (Bos taurus) and swine (Sus scrofa).

BACKGROUND: Epidemiologic data collected during epidemics in the western United States combined with limited experimental studies involving swine and cattle suggest that host predilection of epidemic vesicular stomatitis New Jersey virus (VSNJV) strains results in variations in clinical response, extent and duration of virus shedding and transmissibility following infection in different hosts. Laboratory challenge of livestock with heterologous VSNJV strains to investigate potential viral predilections for these hosts has not been thoroughly investigated. In separate trials, homologous VSNJV strains (NJ82COB and NJ82AZB), and heterologous strains (NJ06WYE and NJOSF [Ossabaw Island, sand fly]) were inoculated into cattle via infected black fly bite. NJ82AZB and NJ06WYE were similarly inoculated into swine. RESULTS: Clinical scores among viruses infecting cattle were significantly different and indicated that infection with a homologous virus resulted in more severe clinical presentation and greater extent and duration of viral shedding. No differences in clinical severity or extent and duration of viral shedding were detected in swine. CONCLUSIONS: Differences in clinical presentation and extent and duration of viral shedding may have direct impacts on viral spread during epidemics. Viral transmission via animal-to-animal contact and insect vectored transmission are likely to occur at higher rates when affected animals are presenting severe clinical signs and shedding high concentrations of virus. More virulent viral strains resulting in more severe disease in livestock hosts are expected to spread more rapidly and greater distances during epidemics than those causing mild or inapparent signs.

Mechanical transmission of vesicular stomatitis New Jersey virus by Simulium vittatum (Diptera: Simuliidae) to domestic swine (Sus scrofa).

Biting flies have been suggested as mechanical vectors of vesicular stomatitis New Jersey Virus (family Rhabdoviridae, genus Vesiculovirus, VSNJV) in livestock populations during epidemic outbreaks in the western United States. We conducted a proof-of-concept study to determine whether biting flies could mechanically transmit VSNJV to livestock by using a black fly, Simulium vittatum Zetterstedt (Diptera: Simuliidae), domestic swine, Sus scrofa L., model. Black flies mechanically transmitted VSNJV to a naive host after interrupted feeding on a vesicular lesion on a previously infected host. Transmission resulted in clinical disease in the naïve host. This is the first demonstration of mechanical transmission of VSNJV to livestock by insects.

Impacts of lawn-care pesticides on aquatic ecosystems in relation to property value.

To determine the potential impacts of lawn-care pesticides on aquatic ecosystems, the macroinvertebrate communities of six streams were assessed using a multimetric approach. Four streams flowed through residential neighborhoods of Peachtree City, GA, USA, with differing mean property values and two reference streams were outside the city limits. A series of correlation analyses were conducted comparing stream rank from water quality and physical stream parameters, habitat assessments, benthic macroinvertebrate metric, pesticide toxicity and metal toxicity data to determine relationships among these parameters. Significant correlations were detected between individual analyses of stream rank for pesticide toxicity, specific conductance, turbidity, temperature and dissolved oxygen with benthic macroinvertebrate metrics.

Identification of communal oviposition pheromones from the black fly Simulium vittatum.

The suite of pheromones that promote communal oviposition by Simulium vittatum, a North American black fly species, was identified and characterized using gas chromatography-mass spectrometry, electrophysiological, and behavioral bioassays. Behavioral assays demonstrated that communal oviposition was induced by egg-derived compounds that were active at short range and whose effect was enhanced through direct contact. Three compounds (cis-9-tetradecen-1-ol, 1-pentadecene, and 1-tridecene) were identified in a non-polar solvent extract of freshly deposited S. vittatum eggs that were capable of inducing the oviposition response. Electroantennography demonstrated that two of these three compounds (1-pentadecene and 1-tridecene) actively stimulated antennal neurons. Identification of the oviposition pheromones of this family may be helpful in developing control measures for nuisance black flies and for medically-important species such as Simulium damnosum sensu lato.

Identification of human semiochemicals attractive to the major vectors of onchocerciasis.

BACKGROUND: Entomological indicators are considered key metrics to document the interruption of transmission of Onchocerca volvulus, the etiological agent of human onchocerciasis. Human landing collection is the standard employed for collection of the vectors for this parasite. Recent studies reported the development of traps that have the potential for replacing humans for surveillance of O. volvulus in the vector population. However, the key chemical components of human odor that are attractive to vector black flies have not been identified. METHODOLOGY/PRINCIPAL FINDINGS: Human sweat compounds were analyzed using GC-MS analysis and compounds common to three individuals identified. These common compounds, with others previously identified as attractive to other hematophagous arthropods were evaluated for their ability to stimulate and attract the major onchocerciasis vectors in Africa (Simulium damnosum sensu lato) and Latin America (Simulium ochraceum s. l.) using electroantennography and a Y tube binary choice assay. Medium chain length carboxylic acids and aldehydes were neurostimulatory for S. damnosum s.l. while S. ochraceum s.l. was stimulated by short chain aliphatic alcohols and aldehydes. Both species were attracted to ammonium bicarbonate and acetophenone. The compounds were shown to be attractive to the relevant vector species in field studies, when incorporated into a formulation that permitted a continuous release of the compound over time and used in concert with previously developed trap platforms. CONCLUSIONS/SIGNIFICANCE: The identification of compounds attractive to the major vectors of O. volvulus will permit the development of optimized traps. Such traps may replace the use of human vector collectors for monitoring the effectiveness of onchocerciasis elimination programs and could find use as a contributing component in an integrated vector control/drug program aimed at eliminating river blindness in Africa.

Black fly involvement in the epidemic transmission of vesicular stomatitis New Jersey virus (Rhabdoviridae: Vesiculovirus).

The transmission routes of Vesicular stomatitis New Jersey virus (VSNJV), a causative agent of vesicular stomatitis, an Office International des Epizooties List-A disease, are not completely understood. Epidemiological and entomological studies conducted during the sporadic epidemics in the western United States have identified potential virus transmission routes involving insect vectors and animal-to-animal contact. In the present study we experimentally tested the previously proposed transmission routes which were primarily based on field observations. Results obtained provide strong evidence for the following: (1) hematophagous insects acquire VSNJV by unconventional routes while blood feeding on livestock, (2) clinical course of VSNJV infection in livestock following transmission by an infected insect is related to insect bite site, (3) infection of livestock via insect bite can result in multiple transmission possibilities, including animal-to-animal contact. Taken together, these data significantly add to our understanding of the transmission routes of a causative agent of one of the oldest known infectious diseases of livestock, for which the details have remained largely unknown despite decades of research.

Biological transmission of vesicular stomatitis virus (New Jersey serotype) by Simulium vittatum (Diptera: Simuliidae) to domestic swine (Sus scrofa).

The role of hematophagous arthropods in vesicular stomatitis virus (New Jersey serotype; VSV-NJ) transmission during epizootics has remained unclear for decades in part because it has never been shown that clinical or subclinical disease in a livestock host results from the bite of an infected insect. In this study, we investigated the ability of VSV-NJ-infected black flies (Simulium vittatum Zetterstedt) to transmit the virus to domestic swine, Sus scrofa L. Experimental evidence presented here clearly demonstrates that VSV-NJ was transmitted from black flies to the swine. Transmission was confirmed by seroconversion or by the presence of clinical vesicular stomatitis followed by seroconversion. Our results represent the first report of clinical vesicular stomatitis in a livestock host after virus transmission by an insect.

The effect of seston on mortality of Simulium vittatum (Diptera: Simuliidae) from insecticidal proteins produced by Bacillus thuringiensis subsp. israelensis.

Water was collected from a site on the Susquehanna River in eastern Pennsylvania, where less-than-optimal black fly larval mortality had been occasionally observed after treatment with Bacillus thuringiensis subsp. israelensis de Barjac insecticidal crystalline proteins (Bti ICPs). A series of experiments was conducted with Simulium vittatum Zetterstedt larvae to determine the water related factors responsible for the impaired response to Bti ICPs (Vectobac 12S, strain AM 65-52). Seston in the water impaired the effectiveness of the ICPs, whereas the dissolved substances had no impact on larval mortality. Individual components of the seston then were exposed to the larvae followed by exposure to Bti ICPs. Exposure of larvae to selected minerals and nutritive organic material before ICP exposure resulted in no significant decrease in mortality. Exposure of larvae to silicon dioxide, cellulose, viable diatoms, and purified diatom frustules before Bti ICP exposure resulted in significant reductions in mortality. Exposure of larvae to purified diatom frustules from Cyclotella meneghiniana Kützing resulted in the most severe impairment of mortality after Bti ICP exposure. It is postulated that frustule-induced impairment of feeding behavior is responsible for the impairment of larval mortality.

Influence of selected antibiotics on the response of black fly (Simulium vittatum) larvae to insecticidal proteins produced by Bacillus thuringiensis subsp. israelensis.

A controlled current toxicity test (CCTT) was developed to evaluate the response of black fly (Simulium vittatum) larvae to insecticidal proteins following exposure to various antibiotics. The bacterium, Bacillus thuringiensis subsp. israelensis (Bti), produces proteins that are toxic to Nemotoceran Diptera, such as black flies and mosquitoes, when ingested. These insecticidal crystalline proteins (ICPs) are highly efficacious in controlling black flies; however, speculation has arisen regarding the potential for antibiotic contamination of waterways to mitigate the toxicity of these proteins. A series of experiments was conducted with the CCTT in which black fly larvae were exposed to enrofloxacin, tylosin, sulfamethoxazole, and trimethoprim followed by exposure to Bti ICPs. These antibiotics were selected based on their use in agricultural and documented anthropogenic contamination of rivers. Anthropogenic concentrations of a mixture of these four antibiotics did not affect the response of the larvae to Bti ICPs. Subsequent experiments were conducted with antibiotic concentrations 10,000 to 80,000 times higher than those found in contaminated rivers. Exposure of black fly larvae to high levels of enrofloxacin (0.5 mg/L) had no effect upon the susceptibility to Bti ICPs; however, exposure to high levels of tylosin (8 mg/L) resulted in a significant increase in the susceptibility of the larvae to Bti ICPs at 72 h of exposure, but not at 48 h. Exposure of black fly larvae to high concentrations of a mixture of sulfamethoxazole and trimethoprim resulted in a significant increase in the efficacy of the larvicide after 48 and 72 h of exposure. These results suggest that impairment of the efficacy of Bti ICPs to black fly larvae is not due to antibiotic contamination of the larval environment.