What environmental condition is necessary for psocids and grain mites to thrive?

Psocids and grain mites are both pests that thrive in environments with high humidity. These organisms require moisture for their survival and reproduction, which is why they are commonly found in areas that provide a damp atmosphere, such as stored grain facilities, basements, and other humid environments. High humidity creates ideal conditions for these pests, as it supports their physical needs and contributes to rapid population growth.

In contrast, dry conditions would limit their ability to survive and reproduce, leading to a decline in their populations. High temperatures can also be detrimental as they might lead to dehydration. Freezing temperatures are generally inhospitable for both psocids and grain mites, as these organisms are not equipped to survive extreme cold. Thus, high humidity is fundamental for the optimal growth and development of psocids and grain mites, making it the correct choice.