212 ELEMENTARY STUDIES IN INSECT LIFE 



posing mainland of Africa. This is due, it is believed, 

 to the fact that Madagascar has been separated by 

 water from 'the mainland since remote times. This be- 

 lief is strengthened by the notable depth of Mozam- 

 bique channel. From studies of this nature, together 

 with geologic data, islands can be divided into two 

 classes : continental, those once a part of the mainland, 

 and oceanic, those which have never been connected 

 with any one of the continents. 



A study of the modes and possibilities of transpor- 

 tation and introduction of insect life is further profit- 

 able in determining the desirability of the entrance of 

 species injurious to the interests of man. And if such 

 inimical forms are introduced, it may be possible to 

 determine the original habitat of the inimical forms 

 and to seek their natural enemies. The question, then, 

 becomes : Tan these insects be safely introduced to 

 prey upon the injurious insect? As an illustration: 

 The fluted scale some years ago promised fair to greatly 

 curtail and possibly destroy the citrus trees of Cali- 

 fornia. It was found after investigation that this scale 

 was of Australian origin, and that in its native habitat 

 a ladybird beetle, both in larval and adult state, preyed 

 upon this scale. This beetle was successfully intro- 

 duced into California, where it has curtailed the in- 

 crease of the scale and consequently its damage to the 

 citrus industries. 



The Struggle for Life. The progeny of a single fertile 

 female San Jose scale insect for a single season, not 

 reckoning mishaps, is over three billion individuals. 

 The queen of the honey-bee hive during the working- 

 season deposits from two to three thousand eggs daily. 



