Argynnis idalia occidentalis

Zhang et al. (2020), following Simonsen et al. (2006), place Speyeria as a subgenus within Argynnis.

Prairie populations of regal fritllaries are described as a subspecies separate from the typical now nearly extinct eastern version of this species based on a morphometric analysis of wing spot characters and examination of mitochondrial DNA. Since the wing characters are almost certainly genetically based, even by those alone this taxon would be better founded than some butterfly subspecies. Unfortunately material from only one of the two or three known extant S. I. IDALIA populations was used for the mtDNA study. However the five individuals from that Pennsylvania population differed from all of the western populations with five synapomorphies. Still strictly speaking all this demonstrates is that Pennsylvania individuals are more similar to each other than to those from hundreds of kilometers farther west. Notably Wisconsin, Nebraska, Missouri and Iowa individuals did not cluster together (Williams' Figure 4). Also note that specimens from a large area of potential contact between these taxa (Ohio, Indiana, Michigan) were not included in the wing character or DNA analyses. S. idalia occidentalis coincides with the "prairie ecotype" previously recognized by Schweitzer in this database which was reported to differ from eastern populations in habitat acceptability. Specifically eastern populations use of a variety of mostly wet anthropogenic habitats, while more western ones are virtually restricted to prairie remnants, including native pastures etc. The biology of S. idalia occidentalis has been well studied (for example all of the Swengel studies). Note however, that Williams' statements regarding habitat and foodplant preferences for S. i. idalia are largely inaccurate. See documentation for that subspecies and the EMG for the species for details. This is provisionally accepted as a valid subspecies but from the analyses presented in its description the possibility of a large scale cline cannot be ruled out, especially since wing spot variation within (as opposed to between) the two subspecies is not explored. This account by Dale Schweitzer with input from Jason Weintraub.

The ranks for this subspecies is the same as that for the full species because all but three remaining populations (as of 2007) are this subspecies. However obviously this subspecies has declined less (about 98- 99%) than the eastern one (>99.9%). This is the Regal Fritillary of the prairies.

The exact boundary (presumably including parts of Illinois or Indiana) between this and the nearly extinct eastern subspecies idalia is unknown, as is the extent of the presumed blend zone. However, populations west of Illinois and the prairie parts of Wisconsin are/were mostly or entirely this subspecies. At minimum the range was southern Manitoba and eastern Montana south to Oklahoma and Colorado east into Wisconsin. Populations in and east of Ohio, and probably Michigan, were subspecies idalia.

See full species account, all but three known extant EOs are this subspecies.

See species account, all but two or three known extant EOs are this subspecies. Threats include small population sizes, natural and unnatural fluctuations, conversion of prairie remnants to agriculture, pesticides and herbicides, isolation and ill-conceived prescribed burning. See EMG for details but generally the species is likely to survive on preserves of about 100 acres or larger if burn rotations include three or more units and at least three non-burn years for recovery. However five year minimum intervals are strongly recommended. It is very unlikely to survive complete burns and these have permanently eradicated populations e.g the one at Resthaven WMA in Ohio. It appears to thrive best where fire is not part of the management process. Its fire sensitivity is not greatly different from other specilist prairie Lepidoptera.