I am looking for a publication showing parameres of Nysius thymi and Nysius ericae. In Pericart 1998 (Faune de France), I found only drawings of genital orifice. Do you know about some works showing it?
Well. If you do not find such drawing in literature, it is probably because paramere shape in Nysius are complex and relatively similar between species. As pointed out by Schmitz & Péricart (1993: 176) "...la forme des paramères des mâles varie assez peu et leur apparence est trop affectée par l'angle d'observation pour que ce caractère ait une utilité pratique" (i.e. the shape of the parameres varies rather little and their appearance is affected too much by the angle of observation to be an useful character. (in "Contribution à une mise en ordre de la nomenclature du genre Nysius DALLAS (sensu lato) pour la région paléarctique (Hemiptera, Lygaeidae)". Nouvelle Revue d'Entomologie (N.S.), 10 (2): 173-186. (Cf. also Péricart, Lygaeidae, p. 210, third paragraph).
For a comparison of both species, check the same paper, Schmitz & Péricart (1993), p. 179 (and figs 5-6, p. 178). For Schmitz & Péricart, shape of pygophoral opening is the best character to separate these assumed sibling species.