Here's one deontological perspective you could take:

It is always wrong to cause unecessary suffering to others.

Now, the subjective traits to be considered here are "unecessary" and "suffering."

It used to be a common belief that animals lacked the capacity to suffer as humans do. They could feel pain, nocioception sure, but whether it caused complex psychological suffering (torment) used to be contenious.

Today, this is certainly not contentious for our closest relatives. All primates possess a theory of mind, long memory, emotional states, complex social behavior like lasting bonds and altruism, and other traits necessary to suffer in significant ways.

So the focus (as long as we are considering primates, obviously nobody cares about model species like drosophilia as they have a greatly dimished capacity to suffer (edit: although I should mention that ranking things based on capacity to suffer leads to pretty awful territories too. Eg, if a human is severely mentally disabled, is more permissible to experiment on them? I think most of us would say no, which raises the question why it's okay to do so for other species)) shifts to whether causing them immense physical pain and torture is necessary.

And this is where I think things get pretty murky, and I will leave the rest up to you! I wish more people were curious about moral philosophy and creating their own consistent ethical framework for the world... I think it's especially important in science and engineering.

Of course, you could use a different model like utilitarianism, but utilitarianism still requires some level of deontological principles or you end up with a pretty extremist moral philosophy (same goes for just having Kantian deontology with no room for utilitarianism, IMO).

edit 2: come to think of it, Jainists would certainly have an issue with experimentation even on drosophilia, so I take that back that "nobody" cares. IIRC they even have a mouth covering to prevent swallowing and killing any insects that might accidentally fly into their mouths, as well as a specialized stick to gently move things like spiders and other insects out of the way. I know most people would scoff at that, but I think their deep respect for all forms of life is beautiful.