Assessment of mosquito control sprayers performance based on physical deposition and biological efficacy
Résumé
Mosquito Control in France represents about 45 000 ha (domestic and overseas area) and represents a public health concern operated by public authorities. Apart from aerial spraying, mosquito control is mainly achieved by agricultural sprayers (pickup – ATV or manually mounted mist blowers). As spraying applications may lead to variable performance, a specif-ic research program was designed in order to simultaneously assess spray deposition and biological efficacy. This study was a part of the overarching project (Life + Integrated Mosqui-to Control Management - LIFE08/ENV/F/000488). Four mist blowers were tested (Martignani B748 – Tifone City 300 (ATR- TVI nozzles) – Swingtec Mobilstar – knapsack mist blower with AU 8000 rotary nozzle) as used for larvicide application. 22 tests were conducted including 3 repetitions for each equipment setup.BTi (Bacillius Thuringiensis Israelensis) was applied with an application volume of 8 to 12.5 L/ha including 1 to 2.5 L/ha of BTi Vectobac WG® or Aquabac XT® respectively. Each tank mix contained about 1g/L of Brillant SulfloFlavine (BSF) dye tracer. Deposition values at different distances were calculated after tracer content measurement. 3 Petri dishes (f 8 cm) were used to collect ground deposits and placed around a jar including 25 mosquito larvae (Aedes Aegypty L.) for biological control. Alive lar-vae were counted immediately after application, 24h and 48 h after application. Average deposition in 3 Petri dishes was compared with alive larvae at different distances and for each kind of equipment.30 collecting plots placed on a 10m x 10m grid leading to 5 lines of 4 plots located at 20-30-40-50m from the application path. A central line of collectors placed every 5m was used from 55 to 90m. Applications were realized downwind as advised by mosquito control operators at 8 km/h for vehicle mounted sprayers and 4 km/h for hand op-erated sprayer. Individual performance of each sprayer (i.e. efficient spray range) was com-pared to others and to manufacturer indications. A deeper analysis in terms of lethal dosage of Bti was also realized. For example, an application volume of 0.5 L/ha (1/25th of legal appli-cation volume) was found to generate acceptable mortality in some cases. Tentative of ex-planation regarding the global variability obtained after crossing physical deposits and biolog-ical efficacy was conducted. Among all parameters of influence, droplet size and atmospheric conditions were mainly identified. Indeed, best biological efficacy was obtained with lower application volume when small droplet size were produced (Tifone and rotary nozzle).