The idiom "Put a bug in your ear" means
give somebody a reminder or suggestion relating to a future event
to tell someone something that suggests what they should do (macmillandictionary)
I put a bug in his ear about giving Helen a call.
- Give someone a hint about something (thefreedictionary)
Janet put a bug in her husband's ear about getting the children a dog for Christmas.
In all cases the buzzing of an insect would work as a analogy for having a reminder, hint, advice or appraise to do something in the future.
The direct translation into Spanish (
Voy a poner un bicho/insecto en tu oído) does not work as an equivalent. Is there a Spanish equivalent idiom with the meaning of "hey, don't forget about this".