Tries picking up volunteers with invites (8)
I believe the answer is:
attempts
'tries' is the definition.
('attempt' can be a synonym of 'try')
'picking up volunteers with invites' is the wordplay.
'picking up' is a reversal indicator.
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'with' says to put letters next to each other.
'invites' becomes 'tempts' (tempting is a kind of inviting).
'ta' reversed gives 'at'.
'at'+'tempts'='ATTEMPTS'
(Other definitions for attempts that I've seen before include "Efforts, endeavours" , "Makes a stab at" , "Endeavours, tries" , "Tries, makes an effort" , "Endeaavours, tries" .)