It's not about proof that damage is done. It's about not knowing if damage IS being done.
I listed some of the ingredients in one of the marking pens sold on the market on a previous post in this thread. Look up some of those ingredients, and then tell me how safe it would be just based on the ingredients. I would double-dare you any day to allow these product to come in contact with your skin (or nails...your choice) and be applied for the rest of your life.
I looked at the ingredients, I asked for the MSDS for the products, and discussed this with the manufacturers. Not one will suggest that it should be applied to the backs of queens.
It's not about proof that damage is done. I don't have a million dollar lab to look into this. And to date, these products have not been tested or approved for bee application. So we just do not know what, or if, damage is happening.
But I find it amazing the rationale of some, who think nothing of applying everything from acrylic paint to superglue to the backs of queens. On the surface it seems wrong. Not knowing it to be safe and tested, may suggest caution, or at least a discussion into the possibilities may seem worthy.
We certainly know today, as compared to just a few short years ago, that the beehive is a complete working organism being effected by compounding issues with chemicals. Chemicals build up, possible coming in contact with other chemicals (and some out of our control), making the possibilities endless in what effects bees, with some combinations deadly.
Instead of beekeepers asking "show me proof that damage is being done" we should as beekeepers be demanding from the products we purchase.."Show me proof that NO damage is being done".
We have had studies and clear proof that the use of Coumophos is detrimental to queens. And yet, the product is still being sold to beekeepers. So just because it is on the market, you should not put blind trust in the marketing or previous "manufacturer" testing of products. We are a small sliver of an industry. We lack the resources, funding, and ability to look into some of these issues. So we will continue to be sold known detrimental products, until we either educate ourselves better to what we are placing in our hives, or change the products by simple supply/demand dynamics of the market place.
One of the paint pen manufacturers was very proud of the number of units sold via bee supply houses. Only when I asked about testing and if they openly would go openly on the record about their products being as such, did they get very defensive and the conversation ended abruptly. The last thing I want to do is possibly cause detrimental damage to another beekeepers hives, by being a surrogate salesmen, pushing such products, by the very nature of promoting marking queens. What has happened over the years is the casual promotion of the procedure of marking queens, to boost the sales of products through bee supply companies, which are out to make a buck.
Like I said, show me a product with proof of it's safeness, and I may very well promote marking also. But as it now, beekeepers are left buying a host of various products, and none tested or shown to be safe.