The Barcelona Municipal Institute of Parks and Gardens classes plant pests and diseases into three groups, according to the harm they cause:
Pests that represent a risk to the safety/health of city residents and urban biodiversity
“Group A” pests include the pine processionary (Thaumetopoea pityocampa) and the red palm weevil (Rynchophorus ferrugineus). The pine processionary causes defoliation of pine trees and other conifers, and their caterpillars can cause hives in people and domestic animals. The red palm weevil, for its part, causes the death of palm trees if they are not treated.
Pests that affect the comfort of city residents and which can sometimes exceed tolerance thresholds*
The most common pests are the sycamore lace bug (Corythuca ciliata), the sycamore seed bug (Belonochilus numenius) and the Tulip-tree aphid (Illinoia liriodendri).
Pests that affect the comfort of local residents but which do not exceed tolerance thresholds* or are rare
*A tolerance threshold is the barometer for determining whether or not an insect is classed as a pest. It is linked to economic values in agriculture but there are no established standards in gardening.