Unfortunately until a thorough taxonomic analysis is done, on all the larvae of the 60 odd species in subfamily Perginae. Then subfamily level is the best identification. Any assumption of species level identification must be, at this stage, erroneous as there is too much doubt, too many unknowns. The only process to unravel this, is for all the species to be observed and recorded through all their life stages. Preferably a batch for each to allow and identify any variations. Then once a comparative taxonomic/morphological study is done on the results, will we conclusively understand if any of the species larvae have reliable key diagnostics that may allow valid identification.
If we continue to identify larvae(on an assumption) then we will perpetuate potential falsehoods. This can cause what I call a "online misidentification feedback loop". A situation where someone makes a guess/educated or otherwise; posts it online; another person looking for an id on a similar sees the first and so on and so forth.....Before long there are scores of similar looking organism all identified to species level. All done without any authoritative guide to prove or disprove.