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.

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.

Historical applications of induced sterilisation in field populations of mosquitoes.

Research on sterile mosquito technology from 1955 to the 1980s provided a substantial body of knowledge on propagation and release of sterile mosquitoes. Radiation sterilisation and chemosterilisation have been used effectively to induce dominant lethality and thereby sterilise important mosquito vectors in the laboratory. Experimental releases of chemosterilised males provided complete control of Anopheles albimanus in a small breeding population (14-15 sq km) in El Salvador. Releases of radiation sterilised males failed to control either Aedes aegypti or Anopheles quadrimaculatus in the USA. Releases of radiation-sterilised and chemosterilised male Culex quinquefasciatus in the USA and India were successful in some instances. Development of genetic sexing systems for Anopheles and improved physical separation methods for Culex have made it possible to rear and release males almost exclusively (> 99%) minimizing the release of potential vectors, the females. Factors that affected efficacy in some field programmes included reduction of competitiveness by radiation, immigration of fertilized females from outside the release zones, and inability of laboratory-bred males to perform in the wild. Despite significant progress, institutional commitments to carry the process further were generally lacking in the late 1970s and until recently. Now, with renewed interest and support for further assessment of this technology, this paper summarizes the current knowledge base, prioritizes some areas of investigation, and challenges scientists and administrators to maintain an awareness of progress, remain realistic about the interpretation of new findings, and make decisions about the sterile insect technique on the basis of informed scientific documentation. Areas recommended for priority research status include the establishment of genetic sexing mechanisms that can be transferred to other mosquito species, re-examination of radiation sterilisation, aerial release technology and mass rearing.

Comparison of dilute and neat formulations of Anvil by ultra-low volume ground application against Anopheles quadrimaculatus in Arkansas.

Neat (undiluted) and diluted ground-applied ultra-low volume (ULV) cold aerosol formulations of sumithrin (Anvil) were evaluated against Anopheles quadrimaculatus adults. Both formulations were applied at 1.938 g/AI/ha (0.00173 lb/AI/acre). Caged sentinel mosquitoes were placed on 1.5-m stakes 30.4, 60.9, and 91.0 m downwind and perpendicular to the line of spray. Mortality was observed at 1, 12, and 24 h posttreatment. Except for 1-h readings at 30.4 and 91.0 m the neat formulation was significantly more effective than the dilute. Droplet size and density averaged 13.6 microm and 422/cm2 for dilute formulation and 14.3 microm and 251/cm2 for the neat. There was no apparent relationship between droplet size and density when compared with mosquito mortality.

Impact of low aerial application rates of Dibrom 14 on potential vectors.

Aerial applications designed to assess the impact of low application rates of naled (Dibrom 14) on potential vector species were conducted in 2003 with caged adult Anopheles quadrimaculatus in open grassland at Cecil Airfield in Jacksonville, FL. Offset flight paths of 2,000-6,000 (calculated by the AgDisp aerial application model) and 1,000-ft swath widths were conducted with a Micronair AU4000 rotary atomizer, which provides a several-fold increase in droplets between 7 and 22 microm. Mean volume median diameters of 8.0, 7.8, and 9.4 microm and 290, 506, and 192 droplets per sq cm were observed in the target area with application rates of 0.125, 0.25, and 0.5 fl oz per acre, respectively. The observed mean mortality of caged mosquitoes 12 h posttreatment, corrected for mortality in untreated controls, was 14%, 80%, and 99% at 0.125, 0.25, and 0.5 fl oz per acre, respectively. These results indicate that applications at 0.25 fl oz per acre or less should be avoided and rates greater than 0.5 fl oz may be required for adequate control in canopied habitats and less-than-optimum terrains.

Ground ultra-low volume assessment of Aqua-Kontrol.

Against caged field-collected Anopheles quadrimaculatus Say adults, ultra-low volume (ULV) applications of 3.175 g a.i./0.40 ha (0.007 lb a.i.lac) of synergized permethrin (4% Aqua-Kontrol) gave excellent control (mean: 90%). Droplet collections on magnesium-oxide-coated (MGO) glass slides from 3 applications revealed mean deposition rate of 216 droplets/cm2 and 11-micron volume median diameter (VMD) (based on Aqua-Kontrol label spread factor of 0.61).

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.

Sterile-insect methods for control of mosquito-borne diseases: an analysis.

Effective vector control, and more specifically mosquito control, is a complex and difficult problem, as illustrated by the continuing prevalence (and spread) of mosquito-transmitted diseases. The sterile insect technique and similar methods control certain agricultural insect pest populations in a species-specific, environmentally sound, and effective manner; there is increased interest in applying this approach to vector control. Such an approach, like all others in use and development, is not a one-size-fits-all solution, and will be more appropriate in some situations than others. In addition, the proposed release of pest insects, and more so genetically modified pest insects, is bound to raise questions in the general public and the scientific community as to such a method's efficacy, safety, and sustainability. This article attempts to address these concerns and indicate where sterile-insect methods are likely to be useful for vector control.