Troutnut Forum > Fly Hatch Talk > Are Isonychia mayflies technically multibrooded?
This topic is about the Mayfly Genus Isonychia
Sporadic hatches are rarely as outstanding as those of Isonychia. On streams with good populations, they are reliably hatching in light numbers, here and there, for most of the evening through most of the mid- to late season.
The spinners, and occasionally the duns, produce more concentrated action, but the real value of the Isonychia hatch is its duration and the size of the flies; large trout become ever watchful for them, even when they aren't emerging.
All the species of Isonychia are similar in appearance and behavior. Read more...
There are 17 more specimens...
The Discussion
| Troutnut | July 23rd, 2006, 12:44 am | |
| Fairbanks, AK Posts: 1113 | Here's what I've written in my article on Isonychia about their hatching:Some Isonychia species are multibrooded, but not in the same way as most other multibrooded mayflies like the Baetidae. In those species, the flies emerging in midsummer or Fall are the offspring of the earlier hatch from the same year. In Isonychia, the Fall emergers are offspring from the previous Fall. They are present as half-grown nymphs when the first of their generation emerge. Although Isonychia broods have distinct peaks, some may be found on the water at any time in between. I'm curious if they can really be called multibrooded or not, since they don't produce more than one generation per year (as far as I know). They simply have distinct populations within the same generation which emerge at different times during the year. Does that count? All my books are packed up in boxes right now so I don't have a technical definition of the term handy. | |
| Jason Neuswanger The Troutnut | ||
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| Taxon | July 23rd, 2006, 2:59 am | |
| Mercer Island, WA Posts: 478 | Jason- My understanding is that, in order for a species to be considered bivoltine, both an individual and its offspring would need to complete their lifecycles within a twelve month period. And of course, in order for a species to be considered trivoltine, the individual, their offspring, and the offspring's offspring would need to complete their lifecycles within a twelve month period. I realize Merritt & Cummings has a table listing Isonychia bicolor as "bivoltine" and Isonychia spp. as "bi- or trivoltine (?)". However, my belief is that Isonychia spp. are really univoltine, as the life cycle for an individual is ~12 months. In any event, I haven't been successful in finding a reference to Isonychia being multibrooded. Is that something you read while compiling notes? | |
| Roger Rohrbeck www.FlyfishingEntomology.com | ||
| Troutnut | July 23rd, 2006, 12:13 pm | |
| Fairbanks, AK Posts: 1113 | I'm not sure where I heard that they're multibrooded, actually, and now that you mention it I don't see the term used in my notes. I've changed the paragraph accordingly:Some people say the Isonychia species are multibrooded, but this is not technically correct, even though their pattern of emergence is similar. In true multibrooded mayflies like the Baetidae, the flies emerging in midsummer or Fall are the offspring of the earlier hatch from the same year. In Isonychia, the Fall emergers are offspring from the previous Fall. They are present as half-grown nymphs when the first of their generation emerge. Thanks. | |
| Jason Neuswanger The Troutnut | ||
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