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

Abstract

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 combs and other male fore- characteristics. Number of 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 segment divided by length of longest comb tooth) and the tarsal segment index (length of first segment divided by length of second 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.