The Fluorescent Particle Spray Droplet Tracer Method1

Abstract

The fluorescent particle (FP) spray droplet tracer method makes it possible to identify pesticide spray droplets by size and by number directly on insects, foliage, and other solid substrates. All of the insects and the foliage act as impingement substrates for the spray droplets traced by use of fluorescent particles. Spray droplets larger than the range of 10-20-µ, diameter can be detected for the first time in the field on target (and nontarget) insects and foliage. The FP method makes data available on the transport, distribution, and impingement of pesticide sprays. Such data have not been readily available in the past. The FP method is based on the uniform suspension of a known number of solid, insoluble, micron-size, fluorescent (Zn-Cd sulfide) particles in a known volume of nonvolatile pesticide liquid. The spray droplets formed from such a fluid suspension contain a predictable number of fluorescent particles as a function of the diameter of the droplets at their moment of formation. When a spray droplet containing these insoluble fluorescent particles impinges on target (or nontarget) insects or foliage, the FP’s, being insoluble, are filtered out on the surface where they remain with excellent adhesion in a discrete, recognizable droplet grouping. The FP’s in each droplet grouping can be counted under a microscope when the substrate is illuminated with long-wavelength UV light. The lower limit of detect ability of spray droplets by size is a function of the number of FP’s per unit volume which can be suspended in the original spray liquid while retaining its viscosity and flow characteristics within operational limits. FP methodology can be independent of use of insecticides and therefore is a new method for large or small area tests on arthropod migration.