Hello and welcome to FF! Mealworms and other chitinous beetle larvae are very hard to digest and provide little nutrient. Also; they can cause impaction in frogs. You are far better up feeding insects smaller than distance between frogs eyes. Gut load the crickets with lettuce, carrots, and cherios cereal 24 to 48 hours before feeding the frog. Can place crickets on a shallow glass dish and most of them will remain on dish until eaten.

You need to add CA and vitamin supplements to their diet, more info on that in here: http://www.frogforum.net/food-feeder...schedules.html. For more care information on FBTs you can visit this link: Frog Forum - Fire-Bellied Toad Care and Breeding - Bombina orientalis and relatives. Good luck !