Hibiscus: Bud Turns Yellow and Drops , 1 by Snug_As_Bug_Rug

Snug_As_Bug_Rug wrote:
I purchased this hibiscus during the summer and so far it has grown beautifully; however, every time it develops a bud, the bud turns yellow and drops--the yellowed bud stays small despite the hugh dinner-plate sized flowers expected for the hibiscus named Fantasy Charm. I have recently sprayed the plant with bug spray (I did notice some spider mites on the top leaves). Could an insect still be the problem? I know that there is a significant difference in the morning temperature vs the afternoon temp.--it is in a west facing window and gets full p.m. sun. It's in a 7" plastic pot with the roots beginning to emerge through the bottom holes.

Any ideas as to the problem? Many thanks, Snug