Are mushroom extracts grown on grain, and is the fruiting body or mycelium used in the production of the extract?

Both the mycelium and the fruiting body are used. The growing medium can vary from batch to batch. (The beta-glucan content is not something we can provide.)
Cordyceps militaris is a species of fungus that can be grown on insects or without insects. The mushroom we use doesn’t use any insects to grow.

Benefits of Cordyceps militaris: It is extremely rich in phytonutrients and contains polysaccharides, which have shown potential in being used as natural antioxidants and immune-boosting nutraceuticals