Flour beetles are pest of grains and can spend their entire life cycle in a bag of meal. The beetles feed on dry meal and produce metabolic water. They excrete waste into the meal which over time creates a suitable environment for fungi, including those that are pathogens of insects.
The Red Flour Beetle limits fungal growth by also secreting toxic quinones into the meal. The quinones are produced by the epidermal cells of all insects to cross-link skeletal proteins during sclerotization. The red flour beetle produces excess quinones, some of which do not react with proteins but remain in the cuticle and some are release into the meal. The quinones will react with fungal pathogens and other organisms that invade the cuticle. The toxic quinones prevent successful colonization of these beetles. They also protect their food from micro-organism competitors.