For captive frogs, mealy worms are a favourite (you can normally get these from pet shops and feed them on flour, oatbran and/or unprocessed bran) - but make sure they're not too big for your frog!). You might also add some carrots to moisten the feed a little (potatoes, apples etc. will tend to make the feed too moist and encourage mites). However, you should note that there are a few problems with using mealworms as a food item:

they have no calcium

they are mostly fat

they may cause constipation in smaller frogs

It is best to only use mealworms for frogs larger than 5cm and to coat them with vitamins (get this in powder form from your pet store) before feeding them to frogs.