Track3D setup for blowflies

A challenging Track3D setup: Tracking insect flight in 3D in a large wind tunnel

A Track3D system for the study of flight behavior of blowflies Calliphora vicina and other pest species in three dimensions is now operating at the Department of Plant Health and Plant Protection of Bioforsk, at Ås, Norway.

Bioforsk is a Norwegian institution that conducts applied and specifically targeted research linked to multifunctional agriculture and rural development, plant sciences, environmental protection, and natural resource management. Several research divisions are located in all regions of Norway. At the Plant Health and Plant Protection centre of Ås, near Oslo, scientists Geir K. Knudsen, Anders Aak and Gunda Thöming aim at finding a way to control species which cause damage in fish industry and agriculture.

In northern Norway, particularly in Lofoten, high quality stockfish is hung on wooden racks, exposed to cold air and wind to dry. Blowflies lay their eggs in these fish, which obviously causes dramatic economic losses in the fish industry. To prevent insects to find and lay eggs in dried fish, the first thing to do would be to understand how insects locate their targets; which visual or olfactory stimuli they use and how they estimate distances. Then methods can be developed to disrupt this orienting process.

Uncovering the secrets of insect flight and orientation in space is a challenge of modern biology that requires the best technology currently available. At Bioforsk, Track3D has been installed for an existing wind tunnel. This wind tunnel is quite large (200 x 60 x 90 cm) relative to the size of the insect (about 1 cm). Using normal wide-angle lenses would introduce a source of inaccuracy due to fish-eye effects. For this purpose rectilinear wide-angle lenses are used, which greatly improve accuracy as shown by the 3D positioning accuracy data.

A large wind tunnel also requires a larger calibration system. For small wind tunnels, one calibration frame suffices. For the large ones, a calibration frame that can be attached to other frames of the same type and size is designed. This way, most of the space within the tunnel can be measured accurately.

Lighting is a third issue. Because blowflies need a light source from above to perform the orienting behavior when approaching the target, backlighting - to illuminate the bottom of the wind tunnel and improve the contrast with the animal – could not be used. However, some experimenting with the light position eventually led to obtaining three-dimensional flight tracks with a detection rate of up to 100%.

After some additional adjustments to the wind tunnel to improve image contrast, the researchers at Bioforsk are ready to acquire the first set of experimental tracks.

This Track3D setup makes use of the most advanced Noldus software applications, Media Recorder 1.0 for obtaining synchronized high resolution videos from two cameras and EthoVision XT 8 for video tracking.