1957 ] Ghouri and McFarlane — Reproductive Isolation 31 
periments between the two strains which show that they 
are reproductively isolated. 
Methods 
Eggs of the “Pakistani” strain were obtained from 
females collected near Usta Mohammad, West Pakistan, 
and sent to us by the Department of Plant Protection, 
Government of Pakistan, Karachi. 3 The “Canadian” strain 
was collected from the basements of Macdonald College. 
Dr. A. B. Gurney of the U.S. National Museum, Washing- 
ton, D.C., very kindly confirmed the writers’ identifications. 
Virgin females were obtained by segregating the sexes 
as soon as the ovipositors could be detected in the hoppers. 
Single pairs were kept in two-pound ointment jars and 
groups of two or more pairs in one-gallon candy jars. 
Crossing experiments were laid according to the plans 
shown in Tables I and n. Oviposition dishes containing 
moist sand were provided after 4 to 5 days and thereafter 
on alternate days until the female died. All eggs laid by 
each female were counted and incubated. The spermathecae 
of a number of females were examined for sperms at 
various intervals ranging up to two months after the ex- 
periments were begun. 
Observations 
The results of the crossing experiments are shown in 
Table I. The number of eggs laid in crosses within a 
strain, as shown in the table, does not represent the total 
egg production of the females, but only the number of 
eggs examined in order to establish that development was 
taking place. 
The eggs laid in crosses between individuals of the same 
strain and in the stock cultures usually hatched, whereas 
eggs laid in crosses between the strains invariably failed 
to develop and died 4 to 6 days after incubation. The 
spermathecae of 9 females in the latter crosses, examined 
at different intervals during the active oviposition period 
of stock females of similar age, were devoid of sperms, 
3 We are grateful to the Department of Plant Protection for supplying 
eggs of the Pakistani strain. 
