Pantomorus ruizi was redescribed by Morrone & Lanteri (1991) and is probably close to Pantomorus auripes (Scataglini et al. 2005). It has been classified either as Pantomorus or as Naupactus and differentiates from Pantomorus auripes because is usually larger; the vestiture is grey with longer erect setae on the elytra; 1ª and 2ª funicular articles are subequal in length; the pronotum is rugose, with curved flanks; and the elytra are more convex.

Pantomorus ruizi is probably is probably parthenogenetic (Lanteri 1995b, Lanteri & Normark 1995). The first instar larvae was described by Marvaldi & Loiácono (1994). A niche modeling analysis suggests that western coast of USA, South Africa and southeastern Australia are suitable environments for its establishment (Lanteri et al. 2013b).

Eupatorium buniifolium Hook. & Arn. (= chilca negra) and Baccharis sp (Asteraceae), Larrea nitida Cav. (= jarilla) (Zygophyllaceae), Stipa sp (Poaceae) and Schinus areira L. (= aguaribay) (Anarcadiaceae), all of them typical of the arid regions of South America (Morrone & Lanteri 1991, Lanteri et al. 2002a).

Among the cultivated plants there are Solanum tuberosum L. and Medicago sativa L. (Solanaceae) in Argentina and Chile; Pyrus communis L., Prunus avium L. (Rosaceae) and Ribes rubrum L. (Grossulariaceae) in Argentina; and Vitis vinifera L. (=vid) (Vitaceae) in Chile (Elgueta 1993, Lanteri et al. 2002a). It also feeds on Lolium sp, Euro-Asiatic grass broadly extended in the Pampean biogeographic province. In recent years it was found eating needles of Pinus ponderosa Dougl. ex Laws (Pinaceae) in Patagonia, Chubut (Gómez & Lanteri 2006).

It is mainly associated with native vegetation of the Pampean, Espinal and Monte biogeographic provinces and also occurs in Patagonia, being the only Naupactini broadly distributed in that area.