It is odd they don't mention that paper, but there is a caveat buried near the bottom in about prior studies showing it in higher insects and how fly brains are

It is odd they don't mention that paper, but there is a caveat buried near the bottom in about prior studies showing it in higher insects and how fly brains are more primitive than butterflies. IIRC only about 2/3 to 3/4 of butterflies of the type tested retained the aversion response, and only if they were of a certain age - they needed to have certain cells developed in caterpillar form to be able to remember. It is possible that the species they studied simply does not retain memories or that they missed the development window or that the method they used would not detect memories - the butterfly study showed aversion behavior to smell, this one does not measure behavior at all - it's possible that some behavior was retained but they did not measure it, though I think the particular cells they studied in flies is the same one the butterfly studies relied upon existing to work. Off the top of my head, monarch butterflies taking multiple generations to travel up and down the west coast to and from Mexico each year implies if not conscious memory as we think of it, some sort of genetic imprint of how and where to travel that is mind blowing to me.