Assessing the effect of complex ground types on ground-dwelling
arthropod movements with video monitoring: dealing with concealed
movements under a layer of plant residues
Abstract
1 Understanding the effect of ground types on foraging movements of
ground-dwelling arthropods is a key step to managing their spatial
distribution as required for successful conservation biological control.
Indeed, fine movements at the centimetre scale can strongly influence
the foraging ability of pest predators. However, because RFID or
harmonic tracking techniques are not yet suitable for small species and
video tracking focuses on uniform and light backgrounds, foraging
movements have rarely been studied in relation to ground types. 2 We
present a method to track a ground-dwelling arthropod (the earwig
Euborellia caraibea) at night, walking on two contrasted ground types :
bare soil and soil partly covered with a stratum of banana plant
residues allowing individuals to hide periodically. 3 The tracking of
individuals within these ground types was achieved by infrared light,
tagging individuals, video treatments and semi-automatic cleaning of
trajectories. We tested different procedures to obtain segments with
identical durations to quantify speeds and sinuosities. These procedures
were characterised by the junction time gap between trajectory
fragments, the rediscretisation time of trajectories, and whether or not
to use interpolation to fill in missing points in the trajectories. 4
Earwigs exhibited significantly slower and more sinuous movements on
soil with banana plant residues than on bare soil. Long time gaps for
trajectory junction, extended rediscretisation times and interpolation
were complementary means to integrate concealed movements in the
trajectories. The highest slowdown in plant residues was detected when
the procedure could account for longer periods under the residues. 5
These results suggest that earwigs spent a significant amount of time
concealed by the residues. Additionally, the residues strongly decreased
the earwigs’ movement. Since the technical solutions presented in this
study are inexpensive, easy to set up and replicate, they represent
valuable contributions to the emerging field of video monitoring.