Fungus still covering wings of aphids (5)
I believe the answer is:
yeast
'fungus' is the definition.
(yeast is a kind of fungus)
'still covering wings of aphids' is the wordplay.
'still' becomes 'yet' ('yet' can be a synonym of 'still').
'covering' indicates putting letters inside.
'wings of' says to hollow out the word (remove centre letters) (letters on the two wings removed).
'aphids' with its middle taken out is 'as'.
'yet' going around 'as' is 'YEAST'.
(Other definitions for yeast that I've seen before include "Fungus used in fermenting" , "Alcohol-producing fungus" , "Fungus used in brewing and baking" , "Bread-making component" , "Brewer's agent" .)