Tachyta (Tachyta) nana (Gyllenhal 1810)

Tachyta nana (Gyllenhal)

This polytypic species is composed of three geographic races here ranked as subspecies. One of these, the nominate, is Palearctic in distribution. I have seen so few specimens of this form that only a few comments can be made at this time. In general, the nominate subspecies members are narrow and subconvex and the pronotum always has a rudimentary carina or tuberculate area laterobasally. This form occurs in Japan, Siberia, and throughout Europe (specimens seen by me). I have seen one specimen from southern China which corresponds perfectly with T. nana kirbyi of northern North America, even in male genitalia. Until more specimens are discovered which prove otherwise, I regard this form as T. n. kirbyi (discussion follows).

A second subspecies, T. nana inornata, is Nearctic and Neotropical in distribution, ranging from 50°N latitude south to Belize and Guatemala. This form has members which are narrow and subconvex as in the nominate form, but which have neither the carina (not even the rudiment) nor a roughened area laterobasally on the pronotum. In two areas, western Montana and western Washington, this form occurs with T. n. kirbyi and apparently the two intergrade. Intergrade specimens are intermediate in broadness and flatness and have a roughened area laterobasally on the pronotum. In no case, however, did I observe even a rudimentary carina on the pronotum as in the nominate subspecies.

The third subspecies, T. nana kirbyi, is northern in distribution, except for more southern scattered localities in the Rocky Mountains or its outliers. As mentioned above, I have seen one specimen from the south of China. Members of this subspecies are very broad and depressed and have a well-developed carina laterobasally on the pronotum.

All of these forms have identical male genitalia. For this reason, I have here ranked the forms as subspecies. However, a careful analysis of many specimens from the area of overlap in North America should be undertaken. Specimens are not presently available for this kind of study. We need to obtain many additional specimens, host tree documentation, and perhaps life-cycle information in order to determine interbreeding capabilities, degree of intergradation of forms, and whether or not we are dealing with species or subspecies.