What is the ethical way to fix these gaps in timber floors without damaging the house (rental)

The house is built on timber instead of concrete and we are having bad pest problems (small cockroaches). We have had our house sprayed and do the bombs every so often.

I know they make a sealant for timber floors but I’m wondering if that is ethical to do since it is not my house? Or if not ethical, more so, will he be able to notice? There are heapssssss of gaps. Like maybe 50-100 I need to fill. He is also not the type of landlord I can talk to about this pest issue, he gaslighted me every time I tried to talk about how bad the issue was in general, and gave the response of “there shouldn’t be” (any cockroaches). We live in a hot area and it’s common for cockroaches here. Of course there would be 🤦‍♀️ but by closing gaps and regular pest treatment it does seem to keep it down to nearly 0.

Sorry off topic back to the gaps. It’s not letting me add photos but I will add photos in the comment of how bad the gaps are.