Perlesta napacola, a new species in the Perlesta frisoni species group (Plecoptera: Perlidae)

Perlesta napacola, a new species of nearctic stonefly (Plecoptera: Perlidae), is described from a single location in eastern Illinois. This species is most closely related to those in the Perlesta frisoni species group, the male members of which exhibit patches of sensilla basiconica on the tenth tergite and an aedeagus without a caecum. This group at present includes P. etnier, P. frisoni, P. nelsoni, and P. teaysia. It differs from its group members by the combination of a spineless paraproct, subgenital plate with rounded lobes and U-shaped notch, and in having a sessile egg collar and shallow follicular cell impressions. The new species was found in a springbrook draining a relict beech and maple forest in a ravine in eastern Illinois. A key to the group is provided.