Last night I noticed that one of my irises has been eaten by bugs . When I purchased this iris, the vendors advised me that they had a problem with African lawn beetles so they treated the rhizome like they do when sending to quarantine states. I decided to dig up the rhizome and discard it. I saw a small black bug running away and stepped on it. I suspect it is one of the culprits.

27th March (the top of the mother rhizome)
8th March

Has anyone experienced anything similar? Can beetles chew hard healthy rhizomes? Do you think my neighbouring irises are at risk? Any advice anyone can offer would be a great help to me.

I was intrigued by your question and did a little research. It sounds to me as if this pest may be vulnerable to the same type of controls that are used against Japanese Beetles, here in the U.S.
That is just a guess, and i'm not staking a definitive solution on it, but here is a link i found that may be of some use to you, if indeed, the African Lawn Beetle is the culprit
https://www.paulmunnsinstantla...

Thankyou so much Timothy. If I notice any symptoms in my lawn, the product recommended in that article is worth a try. I wouldn't try it on my irises until I have done more research. I am impressed that you found an Australian article .

I forgot to mention that I have emailed the vendor to see if my chewed rhizome is similar to the problems they were experiencing and to ask for advice. I don't know how they will react.