Flying insects perhaps so equally affected by heat (6)
I believe the answer is:
aswarm
'flying insects perhaps so' is the definition.
(insects may be aswarm or swarming)
'equally affected by heat' is the wordplay.
'equally' becomes 'as' (synonyms).
'affected by heat' becomes 'warm' (heat makes things warm).
'as'+'warm'='ASWARM'
(Other definitions for aswarm that I've seen before include "Teeming" , "Crowded" , "Like bees often are" , "Crawling" , "crowds everywhere" .)