Comparing electrophoretic mobility patterns of 14 enzymes of nine strains of cultured avian trypanosomes and two strains of cultured mammalian trypanosomatids revealed marked differences between the strains isolated from Falco sparverius and those isolated from other host raptors as well as among the avian trypanosomatids and the mammalian ones. These results supported the differentiation of two species of raptor trypanosomes based on other criteria: size, form, in vitro growth behavior, surface carbohydrate expression, lectin-mediated agglutination, and qualitative activity profiles of 19 enzymes. The results indicate that biochemical characteristics, particularly isoenzyme electrophoretic data, are useful and objective additions to the traditional criteria used to type and classify Trypanosoma spp. of birds. Trypanosoma bennetti n. sp. from F. sparverius is described as a new species, and the other avian trypanosome strains are identified as T. avium Danilewsky, 1885. A phylogenetic tree, constructed by methods of numerical taxonomy, revealed that T. bennetti n. sp. is distantly related to T. avium as well as to T. rhodesiense and Leishmania chagasi.

Nine trypanosome strains from five species of raptors were cultivated in vitro in a monophasic medium. Two morphologically distinct trypanosomes were observed in culture: those from American kestrels (Falco sparverius) were smaller than the other strains. The two kestrel (KT) trypanosome strains showed in vitro growth kinetics that differed from the larger trypanosomes, and the KT strains, unlike the others, required hemin in the medium for growth. The effectiveness of eight plant lectins to induce the agglutination of cultured trypanosomes was studied as a means of differentiating the various strains. It was found that lectins from Lens culinaris and Ricinus communis (type I) were particularly effective in distinguishing the KT strains from the other raptor trypanosome strains. Based on the results of experiments in which lectin-mediated trypanosome agglutination was inhibited by the addition of various monosaccharides, it is concluded that all of the avian trypanosomes studied express surface methyl α-D-mannoside, D(+)-galactose, and (or) α-lactose. Only the relatively large raptor trypanosome isolates expressed N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and α-L(−)-fucose on their surfaces. The differences in lectin-binding characteristics between the two morphologic types of raptor trypanosome were as great as those among each of the avian trypanosomes and the mammalian trypanosomatids Leishmania chagasi and Trypanosoma rhodesiense.