Most friendly tsetse flies guarding wren, oddly (8)
I believe the answer is:
sweetest
'most friendly' is the definition.
(sweet can mean kind or friendly)
'tsetse flies guarding wren oddly' is the wordplay.
'flies' indicates anagramming the letters.
'guarding' is an insertion indicator.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternating letters of 'wren' are 'we'.
'tsetse' anagrammed gives 'setest'.
'setest' placed around 'we' is 'SWEETEST'.
(Other definitions for sweetest that I've seen before include "Most saccharine or sugary" , "Superlative winning" , "Most sugary or most mellifluous" , "most agreeable" , "Most tender" .)