A Study of Key Characteristics for Distinguishing Several Drosophila affinis Subgroup Species, with a Description of a New Related Species

Certain characteristics of Drosophila affinis subgroup species reported as useful for species identification were reinvestigated in D. affinis, algonquin, athabasca, azteca, narragansett, and tolteca, and new criteria for species separation were sought. Both laboratory strains (in some cases kept at different temperatures) and wild specimens were studied. Special attention was paid to sex combs and other male fore- tarsal characteristics. Number of sex comb teeth is very useful, even though not 100% reliable, for distinguishing D. affinis from D. algon- quin. The "sex comb index" (length of first tarsal segment divided by length of longest sex comb tooth) and the "tarsal segment index" (length of first tarsal segment divided by length of second tarsal segment) were found to be very effective for separating D. affinis from athabasca and appear likely to be useful for separating D. azteca from tolteca. Number of primary clasper teeth appears likely to be helpful (but not 100%) for distinguishing D. atha;basca '(8 or more) from azteca (usually 6 or less) ; these two species are often poorly distinguishable on the basis of mesonotum striping. Testis shape would seem to be a good basis for distinguishing D. algonquin (less coiled) from tolteca (more coiled). A new species, D. novitskii, is described from collections in Colorado. A modified key for separating American D. affinis subgroup species is presented.