g6 
Psyche 
[September 
pound 5 sex determining mechanism. The diploid number was 12 and 
the MCA number was 24. No heteromorphic chromosomes were 
present. However, the collection was made at the beginning of the 
study when methods were not yet perfected for making temporary 
squashes permanent, and before photographic equipment was avail- 
able. For this reason, only a few drawings were made. This dif- 
ference in karyotype morphology may have resulted from inadequate 
technique, but more likely it represents a different species. 
Discussion 
To date at least 19 species representing 10 genera in the family 
Tephritidae have been investigated cytologically by several authors. 
It is apparent even from the few species thus far studied that a great 
deal of chromosomal variation exists within the family. Such varia- 
tion not only includes characteristic positions of the kinetochore, 
secondary constrictions, and chromosome length, but also involves 
differences in chromosome number and sex determining mechanisms 
as well. These differences can be put to good use in the identification 
of immature forms and may possibly aid in establishing phylogenetic 
relationships. It must be stressed that cytotaxonomy is seldom if ever 
a “solve all” method of identification, and it is not surprising that 
three species of Anastrepha show no distinct chromosome differences. 
It is probable that as more species in this genus are investigated 
chromosome patterns will be found similar to the ones reported here 
as morphologically distinct. A combination of several criteria, in- 
cluding chromosomal variations, gross morphology of the larvae, and 
various ecological aspects of the species in question, may therefore 
be necessary before accurate identification can be made. 
With such limitations in mind, the following key is presented as 
a tentative means of separating the larvae of six of the nine Mexican 
Tephritidae investigated cytologically so far. Due to the similarities 
of some female karyotypes, the key is based on the chromosome morph- 
ology of the male karyotype whenever it is known. This makes it 
advisable to study at least eight larvae (assuming a 1 :i sex ratio) 
in a given collection to be fairly certain that all are not of the same 
sex. No suitable means has yet been found to determine the sex of 
immature forms in this family without resorting to karyotype analysis. 
5 Schrader’s (1928) terminology is followed here. A compound sex deter- 
mining mechanism is one in which the X or the Y is represented by more 
than one element in contrast to a multiple sex determining mechanism in 
which there is an adherence of chromosomes belonging to different pairs. 
