Refuses to eat but one thing

[Thetragician]

I wasnt sure if i should put this is behaviour or diet but i had two rats who were a bonded pair and one passed about a month ago the other has been doing okay he ate a lot and gained some weight but about a week ago he started refusing any food except meal worms which ive only given to him twice i still give him his regular food to see if he will eat but but he just leaves it there and doesnt really touch it i have another rat im trying to bond him with but its taking time is there anything i should do to get him to eat or watch to make sure hes okay?

 

[SQ]

what is his regular food?

 

[Thetragician]

Usually its oxbow adult rat food pellets and i give him fruits and veggies here and there which he used to love and now hes turning those down too