The policies for price drops vary dramatically depending on the airline and when you purchased your ticket.
For most US airlines, if the price drop occurs within 24 hours of you booking, you can generally just cancel your original booking and rebook at the lower price - but that's not he situation here so that doesn't help you.
Beyond 24 hours, some airlines have specific policies around price drops. In JetBlue's case, within 5 days of booking they will issue a credit if a price drops and you contact them. Beyond that 5 days, they will still issue a credit, however it is treated as a change and thus the change fee will be taken from the value of the credit. The change fee will depend on the specific ticket, but will likely be more than the difference in this case, so probably not worth it.
Other airlines have different policies. For example, United Airlines will give a credit minus a $50 fee if you contact them within 30 days of booking. Southwest will give you a credit for the full amount due to their lack of change fees for any booking.
Keep in mind that the cheaper fare may also have different conditions, such as not including carry-on bags, having a higher cancellation fee if you do need to make a change, etc. Again this will depend on the airline and whether they offer different fare types.