LOCUST PLAGUE—UVAROV 341 
swarms can arise from the scattered locusts of the solitary phase on 
the coasts of the Red Sea, in Baluchistan, and in Mauretania. 
The fact that the great locust invasions are due to very small be- 
ginnings has important implications, for once the original outbreak 
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‘Ficurp 2.—Map of Africa showing the spread of swarms of the migratory locust 
(Locusta migratoria migratorioides R. & F.) during the last outbreak. The 
outbreak commenced in 1928 in the two centers on the Middle Niger shown in 
black and spread in the same year over the area numbered 1. The areas gradu- 
ally invaded during each of the following years are numbered consecutively. 
Generally, two generations were produced each year. The arrows represent 
only the main lines of migration, smaller seasonal movements not being shown. 
areas are known, they can be put under permanent observation and 
any tendency on,the part of the solitary locusts to form incipient 
