Bugs in grand, large pines (8)
I believe the answer is:
glitches
'bugs' is the definition.
('glitch' can be a synonym of 'bug')
'grand large pines' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'large' becomes 'L' (eg in clothes sizes).
'pines' becomes 'itches' (I can't justify this - if you can you should believe this answer much more).
'g'+'l'+'itches'='GLITCHES'
'in' is the link.
Can you help me to learn more?
(Other definitions for glitches that I've seen before include "bugs" , "Irregular faults in machines" .)