blastcat's Journal

Invertebrate iridescent virus 31 (IIV-31) is a species of invertebrate iridescent virus in the genus Iridovirus. IIV-31 infects multiple Isopoda species and causes iridescent blue or bluish-purple color due to the reflection of light off a paracrystalline arrangement of virions within the tissues; this virus will always lead to the death of the host.

On May 11, 2022, I found an individual that seemed to display the coloration of an individual infected with IIV-31 (A); however, it seemed like a molt to me. I collected the individual and placed it in a container. The next day there was no blue coloration; therefore, it was indeed a molt. I did not think further about this phenomenon until yesterday; I was observing Onescidae respiration when submerged in water (does not harm the isopod), one of the molting individuals, when unsubmerged, suddenly displayed a blue coloration (D) after submerging another species which also turned blue (C) I had finally figured out what caused the odd coloration in that A. vulgare.

This color change is similar to how IIV-31 creates the color change in its host via paracrystalline arrangement of virions within the tissues. When a molt is exposed to high humidity, the molting cuticle is either saturated or water gets trapped under the molt; this causes a blue or bluish-purple color due to the light reflection off the altered cuticle. Individuals in the first molting stage have a more intense blue coloration, most probably due to the structure of the cuticle at that time. This discovery may provide insights into how IIV-31 alters the coloration of its host. Since this has not been recorded in the scientific literature, it may be possible that before genetic analysis, this phenomenon had been mistaken for IIV-31; the only visual difference between the two is that the coloration IIV-31 causes is darker.

A) Armadillidium vulgare. B) Ligidium elrodii. C) Porcellio dilatatus. D) Cylisticus convexus

All Porcellionides pruinosus and Porcellionides floria should be left at the genus level. Most if not all of the identifications here on iNaturalist are based on the size of the white banding on the antennae or orange-tented uropods to distinguish the two Porcellionides sp. in the United States; however, this has been proven to be very inconsistent within populations.

It's more reliable to look at the length vs. width of the flagellum and the apical peduncle article. P. pruinosus have much shorter and stubbier peduncles and flagella, contrasting with P. floria which has noticeably longer and skinnier peduncles and flagella. Granted, this is still subject to variation and not all populations in the Porcellionides pruinosus "complex" have been examined for this either. Currently, the only way to tell these two apart, aside from molecular sequencing, is with a mixture of the tubercles, scale setae, and antennae; the former is difficult to judge and the second needs a very high magnification microscope. Even then you can't be certain due to how poorly defined P. pruinosus and P. floria are. For this reason; I would recommend keeping all Porcellionides pruinosus and Porcellionides floria at the genus level.