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  Why a New Spore Trap?

Raymond W. Schneider
, one of the inventors of the new Ionic Spore Trap, is a plant pathologist with responsibility for soybean diseases. He is the one who first discovered Asian soybean rust in North America in 2004. In 2005 he was involved in a nationwide monitoring effort to track the dissemination of urediniospores of Phakopsora pachyrhizi from overwintering sites in the Gulf South to the Midwest. This effort involved the use of passive spore traps that relied upon particulate matter being captured on a glass slide coated with petroleum jelly. These slides were then examined with a light microscope. These traps were placed strategically in southern states with the assumption that spores would be monitored as they were carried by prevailing winds to Mid Western states. In July of 2005, several spores that resembled the soybean rust pathogen were observed in a trap located in central Louisiana (Fig. 1). This finding presented a conundrum to research and extension professionals because the poor image quality of the spores on the slide could not be used to make a positive identification, and yet, if this was the soybean rust pathogen, it was vitally important to publicize this finding so that appropriate control measures could be initiated in the immediate vicinity of the spore trap and production areas further north could be alerted. It was this gap in our aerobiological sampling technology that prompted Schneider to embark on a research program to develop a better means of sampling and identifying airborne spores.

The primary shortcoming of existing technology was the poor image quality inherent in light microscope views of spores captured on adhesive surfaces in impact traps. This limitation also applied to commercially available impact traps with a clock-driven adhesive tape. The solution to this problem was to use a scanning electron microscope (SEM). However, this required that the capture medium be electrically conductive, and this precluded the use of adhesive tape or slides coated with petroleum jelly. An early version of the spore trap developed by Schneider used a solar powered exhaust fan that drew air at low velocity across carbon coated adhesive stub that could then be examined with a SEM (Fig. 2). The shortcoming of this early model was that high air flows could not be used and capture efficiency was very low. As luck would have it, it was at this time that Erik Durr, a designer, inventor and engineer, became involved with the project. He devised several spore traps that used the principle of electrostatic precipitation to attract particulate matter from the airstream onto a carbon-coated SEM stub. This allowed the use of a high velocity exhaust fan because spores no longer depended upon passive capture on the medium; they were now forcefully attracted to the stub at very high capture efficiencies. Several spore trap models were developed and tested based upon this principle (Fig. 3). The primary engineering drawback to these early models was the need to deliver electrical current through a rotary connector to the trapping mechanism, which was located in a wind vane apparatus. After numerous fluid dynamics calculations and simulations, we concluded that there was no need for a wind vane design. Rather, it was far more efficient to process large volumes of air through an omnidirectional device. Furthermore, wind vane apparatuses do not turn into very low velocity air currents, and in this situation their capture efficiency is reduced to even lower levels.

Fig. 1. Three rust-like spores observed on a petroleum jelly coated slide from a passive spore trap in 2005.

Figure 2. An early prototype of a spore trap that captured particulate matter on a SEM stub coated with a carbon adhesive.

After designing, fabricating, testing and refining numerous prototypes that employed electrostatic precipitation, a model was finally constructed that is rugged, consumes very low electrical current, processes large volumes of air at very high capture efficiency, and is completely programmable and quantitative (Fig. 4). This device, known as the Ionic Spore Trap, is now protected by U.S. and international patents, and D&S Electrostatic Samplers, LLC was granted a license to manufacture and market it.

Figure 3. Prototype of wind vane Ionic spore trap.

Figure 4. The Ionic Spore Trap