Non-destructive detection across landscapes of mass marked insects

Background/Question/Methods

For over 65 years, mark-release-recapture (MRR) field experiments have utilized colored powers and dyes to examine insect movement and behavior.  A small amount of ultraviolet (UV) reflective powder on an insect is easily detected with UV lights.  Insect MRR studies typically release marked insects or mass mark them in the field, recapture them in traps, and count them under UV lamps in the lab to determine when or how far they moved.  It is difficult to monitor insect behavior and movement over multiple time points with this technique because of the destructive sampling of captured insects.  Newer technologies such as harmonic radar have overcome destructive sampling, but these techniques are expensive, labor intensive, and consequently limit sample size.  Protein marking allows mass marking, but requires destructive sampling and follow-up lab work. Thus, there is a need for a field-based mass marking technique that is cheap, fast, and does not require destructive sampling.  Recent advances in lighting technology allowed us to develop a completely field-based, non-destructive mark and detection technique that improves classic fluorescent marking.  We compared at night the distance of detection of fluorescently marked insects illuminated by handheld ultraviolet lasers, light-emitting diodes (LEDs) and xenon light sources.

Results/Conclusions

Using small, handheld, high-power UV LED flashlights and clear protective goggles, we detected from 16 m stink bugs marked with yellow fluorescent powder.  The xenon light and clear goggles enabled us to detect red-marked bugs at 20 m.  With red-lens goggles and a high-power, near-UV laser (405 nm) equipped with a thin line lens, we detected red-marked individuals at 12 m.  Standing 9 m from a tree line, the laser illuminated a 25-m band of even intensity light, which allowed scanning of several trees at once from base to canopy.  Marking with powders allows mass marking of insects and powerful mobile UV light sources permits non-destructive detection of insects in situ.  Importantly, detected individuals could be left in the system for future, possibly long-term, monitoring.  The relatively high detection distance associated with these techniques will allow discovery and non-destructive sampling of dispersing insects, or possibly other animals, across and within different landscapes (e.g. fields, forests etc.) with only modest investments in equipment.