The mystery pest turned out to be a passionvine hopper nymph. Sorry, I didn't mention they hop when you touch them. And I actually have lots of passionvine hopper adults as well - moth-like creatures which you could see in the bottom-right corner of the image I posted yesterday. I noticed them before but didn't think they were related. One of the articles I found on the bug recommends spraying with Neem oil. Does anybody here have any experience with the substance?