The in-between period of time when an aquatic or terrestrial hatch has waned/finished and we wait for the next "major" fishable hatch. When the the anticipated "hatch" occurs it is fly fished pre-during-post the appearance of the food item. "Fishing the hatch" is not mutually exclusive relative to fly fishing method/imitations employed, whether one probes the bottom water column, the "transition zone", or on/in/near the surface film (meniscus).
An example; the first-brood, BWO emergence on both the Truckee (BT) and Little Truckee (LT) rivers has ceased.
On the BT we are awaiting the infamous "Big Bugs of June"; the Winged, Black Carpenter Ants, Golden Stoneflies and the western Green Drakes. Personally I do not consider the March Browns a major hatch, it is too sparse; although one can argue it's nymphal form is an effective ploy right now. And, one can suggest that the Goldens are just as sparse...true. I would suggest that although the Goldens are as sparse a hatch as the March Brown; the former has a two-three year life cycle. Hence in its nymphal form it is always available...in various sizes. Also, as an adult, it is of high-caloric value to a big trout which will venture to the surface to ingest the big bug*. Always remember that a trout's survival in the wild is dependent on its efficient use of energy; the food item's caloric value has to out-weigh the energy-expended...maximizing input while minimizing output.
* two years ago Yo Joe duped a 25" Brown to the surface. The area is now called "Walter's Bend".
On the LT, we now anticipate the appearance of the Pale Morning Duns. As mentioned above the BWO's are gone and the winter stones, although some are still flitting around during the warmth of the day, seems to lack the trout's attention.While guiding on Friday; we tried a bit of everything at all levels of the water column. The only pattern that got attention and eaten, at the surface, was a black, foam beetle (hint: a reliable "tweener" fly).