Fasciation in Feverfew

While looking at bugs I noticed that one of the Feverfew flowers (lower centre in the photo) is fasciated. This mutation, which in this case elongates the flower, can be genetic or caused by an insect-borne infection. While I have found a few other cases of similar mutations in Feverfew (Tanacetum parthenium) flowers on the internet, there’s no additional information on what causes this particular mutation.