A morphological study was made of a population of Anopheles
(Nyssorhynchus) rondoni (Neiva and Pinto) from northern Mato
Grosso, Brazil. This population usually lacked the primary
key character of a dark basal band on hindtarsomere 3, i.e.,
hindtarsomere 3 was all white as in most other members of the
subgenus. It was determined that this species can be
recognized instead by the presence of a dark spot on the
thorax made up of a large dark prescutellar space that is
contiguous with a concolorous central area on the scutellum.
A secondary character of a dark area on the costa created by
the fusion of the humeral dark, presector dark and sector dark
proximal spots is also usually reliable. Regression analyses
comparing the lengths and ratios of the dark bands on
hindtarsomeres 2 to those on 3 describe a straight line
relationship. This suggests that the 'atypical' population is
at one end of a character gradient. We propose that in the
subgenus Nyssorhynchus individuals that have a long basal band
on hindtarsomere 2 are more likely to also have a basal band
on hindtarsomere 3. The pupal stage of this species has not
been previously described. Reared-associated specimens from
this study show that the pupa can be easily differentiated
from all other Nyssorhynchus by the relatively stout, usually
2 or 3 branched (1-5), setae 1 and 5 on segments IV-VII.
