Sure, mealworms are an okay addition to his diet now and then. not something you want to make up a big part of the diet though. I suggest 10%. Make sure you gutload and calcium dust
Mealworms will eat most any vegetable or fruit, but good/easy ones include papaya, dandelion, butternut squash, carrot, and apple. A quality substrate like this is important also IMHO.
I am asking this, because it has been 4 days now and he doesn't want to eat. So I thought I would try something else in his diet, because at the moment he only get crickets. I don 't know if winter could have something to do with him not eating. What else can I feed him?