62 
Psyche 
[March 
the x chromosome, by the Australian females than by Floridian fe- 
males. Two of these Australian males had 33 chromosomes, as com- 
pared with 34 for the parthenogenetic female (Table 1). No males 
have ever been observed in the Floridian culture in the more than 
15 years that this colony has been maintained. Seiler (1967) stated 
that in the moth Solenohia triquetrella F.R., the older and more 
stabilized the parthenogenesis becomes, the rarer are the males which 
are produced. Whether the occasional production of parthenogenetic 
males in the Australian colony indicates a more recent development 
(in nature) of parthenogenesis than the Floridian clone is unknown. 
Dr. Narbel-Hofstetter (personal communication) has suggested that 
if non-disjunction and therefore loss of an x chromosome occurred 
in the triploid form, the result would be xx /aaa and not an x /aa 
like that formed in the diploid clone. We have never seen intersexes 
in the triploid clones. 
One male nymph from Thailand (Sakaerat District) had 33 
chromosomes (Fig. 7). This was collected in the field and is pre- 
sumed to be the parthenogenetic species whose female chromosome 
number is 34 (Table 1, Fig. 8) or 35 (Table 1, Fig. 10) in 
Thailand. 
The parthenogenetic male from Australia (33 chromosomes; 
Fig. 6) and the Hawaiian males of P. indicus (2n = 35 or 37; Figs. 
1, 2) are non-functional when crossed with Floridian (53 chromo- 
somes; Fig. 13) or Australian females (34 chromosomes; Fig. 5) 
(Roth, 1967). Thus, males of P. indicus or the occasionally pro- 
duced males of P. Surinam ensis cannot introduce genes into the 
parthenogenetic population even though they mate with females; 
every parthenogenetic female is genetically isolated. This incom- 
patability can be accounted for in P. surinamensis by the fact that 
its parthenogenesis is apomictic; although the parthenogenetic male 
undergoes meiosis, the diploid number is maintained in the female 
as a result of the absence of chromosome reduction (Matthey, 1948), 
and amphimixis cannot occur (Seiler, 1967). The lack of success 
in crossing the parthenogenetic male with P. indicus may be explained 
by the difference in chromosome numbers between these two species. 
The thelytokous parthenogenesis exhibited by P. surinamensis is 
not unique; White (1954) and Narbel-Hofstetter (1964) have 
listed several cytologically similar (polyploids and aneuploids) par- 
thenogenetic species. Parthenogenesis in P. surinamensis conforms 
well with White’s (1954, p. 341) statement that since no pairing of 
chromosomes takes place during maturation of the eggs in an apomic- 
