How do backswimmers store air for diving underwater?

Backswimmers (family Notonectidae) are aquatic insects that must periodically return to the water's surface to replenish their air supply. They store this air in a bubble held against their bodies, specifically in chambers formed by their folded wings or entrapped by rows of dense, water-repellent hairs.12

While submerged, these air stores function similarly to a gill, allowing the insect to absorb dissolved oxygen from the surrounding water. However, as the oxygen is consumed, nitrogen within the bubble gradually diffuses outward into the water, causing the bubble to shrink. To prevent drowning, the backswimmer must return to the surface to renew its air supply before the bubble disappears. Some specialized genera, such as Buenoa, possess an additional internal oxygen store in the form of hemoglobin-filled cells, which allows them to remain submerged for longer periods while awaiting prey.2341