The circular open field was
constructed as previously described by Itoh et al. (1994)
with some modification (Figure 1). The apparatus was an
aluminum tub-shaped enclosed with a circular base 75
cm in diameter. The top opening had a diameter of 85 cm
and the wall had a height of 85 cm. On the bottom, two
concentric circles with diameters of 25 and 50 cm were
drawn resulting in 3 circular fields, inner, middle and
outer zones. In the middle of the inner part, a stainless
rod with the diameter of 1 cm was installed for the
application of repellent-paper roll. The middle zone and
the outer zone were further divided into eight and
sixteen equal parts by lines, respectively.