I´m trying John´s key and I just don´t see it. Algarobius should have the scutellum twice as long as wide. This scutellum looks just like the one identified as Acanthoscelides pallidipennis to me (which goes the other way in the key)
Is this a male or a female? (female should have 2 deep polished sulci on the pygidium)

has stouter antennae than this one so if this one *is* that species, it must be a female. As for the scutellum, the image is pretty small and the angle may be a little off. Although I tend to agree, I suppose the scutellum might be twice longer than wide.

To which species do you refer concerning sulci?

No, I don´t doubt the id by John Kingsolver is ok. I am trying to get familiar with seedbeetles by using the key to genera from american beetles by John Kingsolver on pictures in the guide. I´m failing to get some like this one keyed though. I guess you just have to know them
scutellum (1.5 to 2X)longer than wide goes to Alga*ROB*ius, while scutellum subquadrate goes the other way.....I would go the other way here