Anoxia elicits the strongest stimulatory protective response in insect low-oxygen hormesis

The manipulation of oxygen to trigger the stimulatory response known as hormesis is an area of interest in insects that was born almost fifty years ago. Varying low-oxygen treatments have been investigated many times since with differing responses found; some hormetic/some harmful. In this review, we summarize the recent advancements in low-oxygen hormesis with a focus on severe hypoxia and anoxia. These two low-oxygen treatments fall below the critical partial oxygen pressure (PO2, often referred to as Pcrit), the oxygen level where metabolism is impaired, for insects and represent the most robust forms of this type of hormesis, yielding the largest protective responses recorded in insects. We introduce six factors that influence the effectiveness of low-oxygen hormesis: oxygen content, length of and age at treatment, treatment method, sex, and genetic background. Additionally, we present a glimpse at the known mechanism of this type of hormesis.