Abstract. The availability of tools to control mosquito (Diptera:Culicidae) vectors that transmit disease is often limited by a variety of economic, environmental and social issues. In emergency conditions (epidemics, hurricanes, floods etc.), the application of pesticides as space sprays (either by ground or air) is the common method of choice in order to rapidly limit adult local mosquito production in the affected area. Space spray application now employs ultra-low-volume technology for the control of adult mosquitoes. However, the use of space sprays often raises social and environmental concerns by the general public that is served. This review will define and illustrate modern ultra-low-volume technology for the purpose of application as a space spray, as well as describing the engineering controls that have been developed to minimize the environmental impact. The primary social concern is validity and efficacy of application. To address this point, the review will attempt to synthesize the global literature to address the effectiveness of space sprays to significantly impact mosquito vectors in relation to human disease.
In order to explore the spatial pesticide spraying deposition distribution, the downwash flow field characteristics for unmanned aerial vehicle (UAV) pesticide application with accurate flight height and velocity and the relationship of these two aspects, a novel measurement method was proposed in this paper. A model '3WQF80-10' single-rotor diesel UAV was tested using this method in wheat field and the effects of flight direction, flight parameters and crosswind on the distribution of spatial spraying deposition quality balance (SSDQB) and the downwash flow field distribution were researched. A cuboid aluminum sampling frame of spatial spraying deposition quality balance (SFSSDQB) with monofilament wires was made for collecting the droplets in four directions, and a set of multi-channel micro-meteorology measurement system (MMMS) was applied for measuring the downwash wind speed in three directions. Besides, BeiDou Navigation Satellite System (BNSS) was used for controlling and recording the working height, velocity and track of this model of single-rotor UAV. The results showed the distribution of the spatial spray deposition and the downwash flow field of UAV could be measured effectively at exact flight height and velocity via this method. When the average wind speed was 0.9 m/s, the average temperature was 31.5°C and the average relative humidity was 34.1%, and the average distribution ratios of spraying deposition for model '3WQF80-10' UAV on the upwind part, the top part, the downwind part and the bottom part were 4.4%, 2.3%, 50.4% and 43.7%, respectively. The flight directions of forward and backward had an impact on droplet deposition distribution and the working effect of flying backwards, with 60% of deposition ratio of the bottom part of the SFSSDQB, was better than flying forward. There was a linear negative correlation between the coefficient of variation (CV) of the bottom part and the flight height and the coefficient of determination was 0.9178, which means that the deposition distribution becomes more uniform with the increase of height. Additionally, there was a linear positive correlation between weighted mean deposition rate and crosswind speed and the coefficient of determination was 0.9684, which shows the deposition distribution gets more concentrated towards the downwind part with the rise of crosswind speed. Therefore, according to the results of tests of downwash airflow speed, it is shown that regardless of the flight direction and height and the crosswind, all these factors influence the droplet deposition distribution via weakening the intensity of the downwash airflow field in the direction perpendicular to the ground. The results can provide valuable information for the research of UAV pesticide application techniques and the establishment of the standard of spraying deposition and drift tests of UAV in crop field.
We assessed the efficacy of ultra-low volume aerial adulticiding with 2 new water-based, unsynergized formulations of Aqua-K-Othrin (2% deltamethrin) and Pesguard S102 (10% d-phenothrin) against the riceland mosquitoes of Greece. A helicopter with Global Positioning System (GPS) navigation, real-time weather recording, and spray dispersal modeling (AgDISP) was utilized to accurately treat the experimental blocks by adjusting spray line positions to changing meteorological conditions. Two application rates were applied per formulation that corresponded to 0.75 and 1.00 g AI/ha of deltamethrin and 7.50 and 10.00 g AI/ha of d-phenothrin. The mosquitoes used for the trials were the main nuisance species found in rice field areas of Thessaloniki, which were primarily Aedes caspius, followed by Culex modestus and Anopheles sacharovi. Overall mean mortality of caged mosquitoes was 69.2% and 64.8% for deltamethrin and d-phenothrin, respectively. Mean population decrease in wild mosquito populations within the treatment areas was 76.5% and 78% for deltamethrin and d-phenothrin, respectively. The AgDISP dispersal model, coupled with GPS navigation and real-time weather recording, enabled accurate placement of the spray cloud such that the majority of the treatment area received sufficiently high droplet densities to result in uniform caged-mosquito mortality across all sampling sites.
The use of bioassay cages in the efficacy assessment of pesticides, application techniques, and technologies is common practice using numerous cage designs, which vary in both shape and size as well as type of mesh. The objective of this work was to examine various cage shapes and mesh types for their filtration effects on air speed, spray droplet size, and spray volume. Reductions in wind speed and droplet size seen inside the cages were measured by placing cages in a low-speed wind tunnel at air speeds of 0.5 m/sec, 1 m/sec, 2 m/sec, and 4 m/sec and cage face orientations (relative to the air stream) of 0 degrees, 10 degrees, 22.5 degrees, and 45 degrees. Reduction in spray volume inside a select number of cages was also evaluated under similar conditions. Generally, greater air speed reductions were seen at lower external air speeds with overall reductions ranging from 30% to 88%, depending on cage type and tunnel air speed. Cages constructed with screens of lower porosities and smaller cylindrical-shaped cages tended to provide greater resistance to air flow and spray volume. Overall, spray droplet size inside the cages was minimally reduced by 0-10%. There was a 32-100% reduction in concentration of the spray volume applied relative to that recovered inside the bioassay cages, depending on the cage geometry and screening material used. In general, concentration reductions were greatest at lower air speeds and for cages with lower porosity screens. As a result of this work, field researchers involved in assessing the efficacy of vector control applications will have a better understanding of the air speed and spray volume entering insect bioassay cages, relative to the amount applied, resulting in better recommended application techniques and dosage levels.
This article compares the collection characteristics of a new rotating impactor Florida Latham Bonds (FLB) sampler for ultrafine aerosols with a mimic of the industry standard (Hock-type). The volume and droplet-size distribution collected by the rotating impactors were measured via spectroscopy and microscopy. The rotary impactors were colocated with an isokinetic air sampler for a total volume flux measurement and a laser diffraction instrument for droplet-size distribution measurement. The measured volumetric flux and droplet-size distribution collection efficiencies were compared across 3 wind speeds (1, 1.8, and 3.5 m/sec). The FLB sampler had higher flux collection efficiencies than the Hock-type sampler. The FLB sampler collected 89%, 87%, and 98% of the total volume available per unit area at 1, 1.8, and 3.5 m/sec, respectively, whereas the Hock-type sampler collected 68%, 19%, and 21% of across the same wind speeds. Changes in wind speed had less impact and resulted in less data variability for the FLB sampler.
A supporting stand to suspend rotating impactors and mosquito cages is a requirement for field tests during pesticide efficacy trials. We present schematics for a collection device and associated support system for sampling droplets of ultra-low-volume (ULV) sprays during mosquito adulticide applications. This system offers the advantages of cost efficiency, increased ease of deployment, off-season storage, visibility, stability, and ULV collection efficacy. Use of this system ensures that droplet collection and meteorological equipment is at appropriate and consistent heights between trials. The 2 arms of the support allow for placement of multiple cages, light-emitting or reflecting devices, and wind-indicating ribbons to be attached to the station. The support described makes possible deployment of stations over a wider variety of terrains, increasing the extent of field trials. Presentation of the simple design and fabrication of the rotating collection device (impactor), T-station, and its support is provided.
Measurements of spray volume and droplet size are critical to evaluating the movement and transport of applied sprays associated with both crop production and protection practices and vector control applications for public health. Any sampling device used for this purpose will have an efficiency of collection that is a function of the sampling device itself, the droplet size of the spray being sampled, and the airspeeds under which the sampling is conducted. This study focuses on two rotary impaction devices, the Hock and the FLB samplers, that were evaluated under two droplet sized sprays and four airspeeds. The collected spray concentrations were compared to standard passive samplers whose theoretical collection efficiency was calculated and used to estimate the actual spray volume sampled. Additionally, droplet sizing information derived from image analysis of droplet deposits on the rotary impactor collection surfaces was compared to actual measurements of droplet size of the sampled spray cloud. Generally, overall collection efficiencies ranged from 2.5% to 20%, with the FLB being more efficient than the Hock and with lower efficiencies at higher airspeeds for both samplers. Comparison of the droplet sizing data showed that the FLB sampler tended to underpredict the D V10 and D V50 data, while the Hock tended to overpredict the D V50 and D V90 data.
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