White worm eating steam / wood

[mycycads]

Hi all,

I have large (1.5m) cycads ( E. lehmannii) over the past four months I have had to chop (to the closest health living tissue) at least 30cm off the head of both cycads. Each time its the same culprate a white worm that eats the woody part of the cycad. It basically turns the wood into wood filings and carries on laying more and more with a result of tons of these white worms. I know this sounds gross but it looks like a white worm full of puss.

I have three questions:
1. Anyone know what they come from - ants, moths ?
2. Anyone know how to prevent this? I use poisons on the effected area but they keep coming back.
3. Now that i have had to cut away to the healthy part of the plant to stop the rot, how can I seal it as its currently exposed? Any suggestions on what to use to seal the top of the stem?