Figure 5
The relationship between measured humus content, soil depth and P. horticola density. x-axis: humus content in soil samples (%; 0 – 10 cm soil depth), y-axis: P. horticola mean grub number per m2, size of circles: maximum depth of A-horizon (small = 15 – 20 cm, large = 25 – 30 cm); R2 corr. = 0.38, p = 0.006 according to a multiple linear regression; dashed line = linear regression of P. horticola grub density on humus content in the soil; color of circles: white = grub damage had never been observed by the farmers (undamaged sites), dark = sites had recently been affected by grub damage (damaged sites).