Ill feeling of mum when confronting insects (6)
I believe the answer is:
malice
'ill feeling' is the definition.
(ill feeling can mean malice or animosity)
'mum when confronting insects' is the wordplay.
'mum' becomes 'ma' (ma can mean mother).
'when confronting' is a charade indicator (letters next to each other).
'insects' becomes 'lice' (louse is a kind of insect).
'ma'+'lice'='MALICE'
'of' acts as a link.
(Other definitions for malice that I've seen before include "Spite - desire to hurt" , "evil intent" , "Spite or spleen, perhaps aforethought" , "Spite, venom" , "Malevolence, spite" .)