Keeping stored products at or below what moisture content can help retard the development of many mite species?

To effectively retard the development of many mite species in stored products, it is essential to maintain the moisture content at or below 30 percent. This threshold is critical because higher moisture levels can create an environment conducive to mite proliferation, as mites thrive in humid conditions. When the moisture content is kept at 30 percent or below, it limits the availability of water needed for mite reproduction and survival, helping to manage infestations.

While the other options suggest higher moisture content levels, they do not provide the necessary conditions to effectively control mite populations. Keeping moisture content above 30 percent can lead to increased growth and activity of various mite species, heightening the risk of damage to stored products. Thus, maintaining moisture content at or below 30 percent is a key practice for ensuring effective pest management in storage facilities.