Nautes Pascoe, 1866

Nautes Pascoe, 1866 and Tarpela Bates, 1870

As discussed above, Nautes and Tarpela are together separated from “ Helops ” primarily on the basis of flight. This is not a binary system, however. Some species, like Helops arizonensis Horn, 1874 have fully macropterous and flighted males while females have wings shorter than the elytra and have not been observed to fly to lights where males are readily collected. Indeed, even for species of “ Helops ” which have historically been classified as flightless, largely due to the distance between the middle and hind coxae and the general body form, possess reduced metathoracic wings ( Fig. 4 View FIGURE 4 ). Nautes , Tarpela as well New World “ Helops ” have been found to be without any dependable genus-level defining morphological character(s) and thus not satisfactorily distinguished in any keys. This has discouraged taxonomic works on North American helopines due to the inability of new species to be reliably placed to genus.

Nabozhenko & Ando (2018: 283) agreed and suggested that “The main and indistinct differences between Nautes-Tarpela and New World Helops are in the structure of the prosternal process and mesoventrite. Tarpela and Nautes have projected prosternal process and very deeply depressed mesoventrite with strongly elevated and flat or weakly convex lateral margins of mesocoxal process.” This is true of the type species of both Tarpela and Nautes but does not fit into the huge amount of variation we found in both the prosternal process and the mesosternal excavation in the 147 species we examined. We outline these variations below:

Prosternal process:

1. completely declivious rounded behind procoxae. ( Fig. 8 View FIGURES 7–11 )

2. straight but declivious (various angles) ( Fig. 7 View FIGURES 7–11 )

3. declivious rounded then straight

4. declivious straight then upcurved ( Fig. 9 View FIGURES 7–11 )

5. completely straight ( Fig. 11 View FIGURES 7–11 )

Mesosternal lateral elevations and mid cavity:

1. completely flat ( Fig. 7 View FIGURES 7–11 )

2. slightly inflated, cavity shallow ( Fig. 8 View FIGURES 7–11 )

3. slightly inflated, cavity deep

4. moderately inflated, cavity shallow

5. moderately inflated, cavity deep ( Fig. 9 View FIGURES 7–11 )

6. strongly inflated, rounded, cavity shallow

7. strongly inflated, rounded, cavity deep ( Fig.10 View FIGURES 7–11 )

8. strongly inflated, angulate, cavity deep ( Fig. 11 View FIGURES 7–11 )

Various combinations of these characters exist and some variation within species was also found. Prosternal processes vary from completely declivious to declivious but then straight to then upcurved to partially declivious. Mesosterna vary from completely flat to slightly inflated to moderately inflated to strongly inflated but rounded (as in both Nautes fervidus Pascoe and Tarpela browni Bates ) to strongly inflated with anterior apex angulate as in T. catenata Champion , T. costata Champion , T. thoracica Champion ( Fig. 12 View FIGURE 12 ) and T. recticulata Champion. However , T. occidentalis (Allard) from Jamaica ( Fig. 13 View FIGURE 13 ) which would seem to fall in this group morphologically, the prosternal process is decumbent to decumbent and sometimes upcurved and the mesosternum is shallow with sides only slightly inflated. The inconsistency and wide variation of both the prosternal process and the mesosternum, even within a single species discounts using these characters as generic differential characters.