Bottom spot, with blistering pace: ultimately just last on the buzzer (9)
I believe the answer is:
'buzzer' is the definition.
(something which buzzes)
'bottom spot with blistering pace ultimately just last on the' is the wordplay.
'bottom' becomes 'bum' (synonyms).
'spot with blistering' becomes 'bleb' (blister on the body).
'ultimately' says to take the final letters.
'just last on' suggests the final letters (just the last letter).
The final letter of 'pace' is 'e'.
The last letter of 'the' is 'e'.
(Other definitions for bumblebee that I've seen before include "Large furry flying insect" , "Striped buzzer" , "social worker" .)