REPRODUCTIVE ISOLATION 
IN THE HOUSE CRICKET 
(ORTHOPTERA: GRYLLIDAE) 1 
By A. S. K Ghouri 2 and J. E. McFarlane 
Entomology Department, 
Macdonald College, P.Q., Canada 
The existence of considerable geographic variation in 
the morphology of the field cricket, Acheta assimilis Fab., 
in North America has caused much confusion in its tax- 
onomy, and although the variants are now commonly 
grouped into one species, the work of Fulton (1952) has 
shown that this solution is no longer acceptable. Fulton 
found that four “physiological races” of this insect which 
are reproductively isolated exist in North Carolina, and 
that although they show some average structural dif- 
ferences, intergradation between the races prevents the 
identification of specimens on morphological grounds. 
The house cricket, Acheta domesticus (Linn.), is an 
insect with a cosmopolitan distribution but, surprisingly, 
has been the subject of very little work, although its 
availability and ease of rearing should have favoured its 
use as a laboratory animal. In the course of a study on 
the physiology of the development of this insect (Ghouri 
and McFarlane, in preparation), we have compared a strain 
obtained from Pakistan, where it lives in the field, with 
one obtained in Canada and have found rather large dif- 
ferences in their rates of development, among other charac- 
teristics, although morphologically they are quite similar. 
This report is concerned with the results of crossing ex- 
1 This paper is based on a thesis submitted to McGill University by 
A. S. K. Ghouri in partial fulfillment of the requirements for the Ph.D. 
degree. 
2 Present address : Department of Plant Protection, Government of 
Pakistan, Karachi. 
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