Insects that feed on a single source of food can have an imbalance in dietary nutrients. Bed Bugs feed only on blood which is deficient for the B vitamin complex. The evolutionary line leading to insects lost the genes needed to produce B vitamins long ago. However, insects retain genes necessary for uptake and conversion of B vitamins from their diet or from symbionts.
Like many insects, bed bugs harbor a bacterial symbiont, Wolbachia. Wolbachia receives protection, access to nutrients and distribution in the environment from Bed Bugs. Wolbachia uses some of the nutrients to synthesize excess vitamins including Vitamin B which allows the Bed Bugs to thrive. What is good for the Bed Bugs is good for Wolbachia.