It is possible that the grazing on the stems is from a new batch of eggs. I didn't read all the article so don't know how long it would take for eggs to hatch but I doubt it would take long, the lily won't have been in growth over winter so it has to be a quick process.
If the larvae make their way into the stem when they are very small, which they would do, then you might not easily find their entry holes which could be further up the stem. It's a large stem so with plentiful food they might not go to the bulb, they do that when the stem is small and doesn't provide sufficient nutrients.
Once you start to look seriously, you will find a myriad of bugs you never knew existed. It's a real eye opener, your recognition skills when looking at plants develop into spotting tiny insects where once you wouldn't have seen them.
Sue, we have to thank all those people who put billions of old documents on the internet, there's teams of people who do this for free. 20 years ago there was very little on the internet, it was still quite new.
