Spatial Repellents Protect Small Perimeters from Riceland Mosquitoes in a Warm-Humid Environment.

Recent experiments suggest spatial repellents may significantly reduce biting pressure from host-seeking riceland mosquitoes, such as Anopheles quadrimaculatus, in a warm-humid open-field habitat. However, little is known regarding efficacy of these formulations in partially enclosed spaces where US military personnel may be sheltered or concealed in an operational environment. In this study we investigated the capability of 3 spatial repellents-metofluthrin, linalool, and d-cis/trans allethrin-to reduce mosquito incursion into small open-top enclosures of US military camouflage netting. We found that metofluthrin was more effective in partially enclosed spaces compared with the open field, whereas both linalool and d-cis/trans allethrin provided superior protection in the open. These findings support strategic selection of spatial repellents depending on the environment immediately surrounding the host.

Field evaluation of four spatial repellent devices against Arkansas rice-land mosquitoes.

Four commercially available spatial repellent devices were tested in a rice-land habitat near Stuttgart, AR, after semi-field level assessments had been made at the Center for Medical, Agricultural, and Veterinary Entomology, Agricultural Research Service, US Department of Agriculture in Gainesville, FL. OFF! Clip-On(metofluthrin), Mosquito Cognito (linalool), No-Pest Strip (dichlorvos), and ThermaCELL (d-cisltrans allethrin) were selected for this study from >20 candidate products. The units based on metofluthrin, linalool, or d-cisltrans allethrin significantly reduced captures of 1 or more of the mosquito species at surrogate human sites (unlit Centers for Disease Control and Prevention traps with CO2 and octenol). Among the mosquito species analyzed statistically (Anopheles quadrimaculatus, Culex erraticus, and Psorophora columbiae), there were significantly different responses (up to 84% reduction) to individual products, suggesting that combinations of certain spatial repellents might provide significantly greater protection.

Optimized aerial applications of two resmethrin formulations against caged Anopheles quadrimaculatus.

Optimized aerial applications were conducted to assess the efficacy of 2 formulations of resmethrin (Scourge 18-54, Aqua-Scourge 10-30) for control of caged adult Anopheles quadrimaculatus. Micronair AU4000 rotary atomizers were employed to apply the chemical. Both compounds were applied at 0.0035 lb AI/acre (3.92 g AI/ha) with the use of the AGDISP computer model to predict appropriate flight offsets (up to 1,219.2 m). Efficacy was based on bioassays with caged An. quadrimaculatus adults and assessment of impinger-collected droplets. Both compounds provided effective mosquito control. Mean mortality at 24 h posttreatment averaged 80.4% for Scourge, and 80.7% for Aqua-Scourge. Mean droplet sizes, Dv0.5 = 26 microm and 38 microm, and mean density, 74 droplets/cm2 and 41 droplets/cm2, for Scourge and Aqua-Scourge, respectively, were consistent with the bioassay results. Analysis of droplet deposition and mortality failed to reveal a statistical correlation between mortality and deposit volume.

Aerial ultra-low-volume assessment of ANVIL 10+10 against Anopheles quadrimaculatus.

Against caged field-collected adults of Anopheles quadrimaculatus, optimized aerial applications of ANVIL 10+10 at 18.4 ml (1.63 g active ingredient)/0.4 ha produced a mean mortality of 92% at 1, 12, and 24 h after treatment. These trials were conducted with 7 stacked passes applied 1,067 m upwind of the target site when wind velocity was 18-21 km/h at an application altitude of 46 m and 5-10 km/h at groundlevel. When the wind velocity aloft was greater than might be operationally acceptable (27 km/h), reduced efficacy (64% mortality) was observed in the bioassay site (1,524 m downwind from 11 stacked passes) in an unreplicated application. Droplets from the 2 tail-mounted Beecomist 360-A-12-V rotary atomizers (fitted with wire sleeve cages of size 40 mesh) collected on spinning Teflon-coated slides in the target area averaged a volume mean diameter (VMD) of 29 microm and a droplet density of 39 droplets/cm2 in 18- to 21-km/h winds. With 27-km/h winds aloft and a greater application offset, the VMD and droplet density dropped to 23 microm and 18 droplets/cm2, respectively. Coupled with unreplicated results from a nonoptimized application, these tests provide further documentation of the efficacy of ANVIL 10+10 for wide-area adult mosquito control and for optimization technology.

Distribution and seasonal abundance of Cnephia pecuarum (Diptera: Simuliidae) in Arkansas.

Studies were conducted during 1990-92 to determine the distribution and abundance of the southern buffalo gnat (Cnephia pecuarum) in Arkansas. Field collection of adults near streams throughout Arkansas demonstrated adult occurrence in 24 counties. Abundance studies were conducted by using tent traps baited with dry ice in 3 counties in southeastern Arkansas. In 1990, studies were conducted in Bayou Meto (Ashley County); Seven Devils Swamp (Drew County); and Crocketts Bluff, Bayou Meto, and Little LaGrue Bayou (Arkansas County). During 1991 and 1992, abundance studies were limited to Arkansas County. Results and previous field observations suggest 3 distinct populations in Arkansas (southwestern, southeastern, and central). Seasonal occurrence extended from December to April but varied by location and year. Abundance studies indicated variation in both seasonal occurrence and adult density by year and trap location. Although investigations during 1990-91 showed similar seasonal occurrence trends (peaking in early March), higher adult densities were noted during 1990. In contrast, peak adult density during 1992 occurred in late January. Greatest adult density during the course of these investigations was 7,160 gnats/24 h during 1990 at Crocketts Bluff (Arkansas County). Results suggest that additional studies are warranted to determine the impact of environmental and river factors on seasonal occurrence and abundance of this pest.

Operational note effects of fipronil and lambda-cyhalothrin against larval Anopheles quadrimaculatus and nontarget aquatic mosquito predators in Arkansas small rice plots.

The effects of fipronil and lambda-cyhalothrin, applied at rates labeled for control of the rice water weevil, Lissorhoptrus oryzophilus, on 3 nontarget indigenous insect species in Arkansas rice are described. Three replicates of untreated control checks and fipronil- and lambda-cyhalothrin-treated plots containing 3 sentinel cages each were performed. Ten 4th-stage larvae of Anopheles quadrimaculatus, 10 adult Tropisternus lateralis, or 10 adult Notonecta indica were placed within individual cages in small rice plots treated with ICON 6.2 FS (fipronil) at 0.025 lb active ingredient (AI)/acre (0.028 kg/ha) or KARATEZ 2.08 CS (lambda-cyhalothrin) at 0.03 lb AI/acre (0.033 kg/ha) applied over vegetation and water with a single-boom sprayer. At 24 h after treatment in fipronil plots, significantly higher control of An. quadrimaculatus and T. lateralis (69 and 48% control, respectively) was achieved, compared to N. indica (18%). In lambda-cyhalothrin plots 24 h after treatment, 100% reductions of both T. lateralis and N. indica were highly significant (P < 0.05) from the lower level of control in An. quadrimaculatus (10%). At 48 h after treatment, no significant, differences existed between all species within fipronil plots, with An. quadrimaculatus, T. lateralis, and N. indica obtaining 41, 10, and 7% control, respectively. Significantly higher (P < 0.05) control was obtained in lambda-cyhalothrin plots 48 h after treatment, with 93 and 53% control of T. lateralis and N. indica, respectively, compared to 7% control of An. quadrimaculatus. A marked difference in susceptibility was found between selected nontarget organisms used in this study. When using lambda-cyhalothrin to control adult L. oryzophilus, populations of nontarget beneficial insects, such as T. lateralis and N. indica, could be adversely affected, whereas nontarget pestilent species, such as An. quadrimaculatus, could proliferate. Fipronil achieved higher percentages of control against An. quadrimaculatus, compared to lambda-cyhalothrin, and was less harmful to both nontarget predators.

Initiating arbovirus surveillance in Arkansas, 2001.

Migratory birds could introduce West Nile (WN) virus to Arkansas. The purpose of this study was to establish a cooperative arbovirus surveillance program to monitor mosquitoes and birds in Arkansas for arboviruses. Our objectives were to: 1) perform routine, multicounty collections of mosquitoes and test them for eastern equine encephalitis, St. Louis encephalitis, and WN viruses; and 2) conduct passive surveillance by testing dead wild birds for WN virus. Arbovirus surveillance was organized by the Arkansas Department of Health, University of Arkansas, and Vector Disease Control Incorporated. None of the 14,560 mosquitoes (425 pools) tested were virus positive. Two hundred forty-two dead birds from 62 counties were tested for WN virus. Four blue jays in three counties were positive. These infections are the first reported incidences of WN virus in Arkansas. Sera from five horses with suspected encephalitis all tested negative for WN, eastern equine encephalitis, and western equine encephalitis viruses.