312 INSECTS AND MAN 



parasites living within the body of a single caterpillar may 

 be anything from a single individual to two hundred. That 

 this beneficial parasite has not come up to expectations in 

 America appears to be due to the fact that some unknown, 

 yet apparently necessary, alternate host is absent from 

 that country. With this perfunctory account of but a 

 fraction of the work that has been done in the United 

 States to control the gipsy and brown-tail moths, we must 

 bid adieu to the subject, though well aware that it deserves 

 more extended treatment, if only because it represents the 

 most stupendous effort that has ever been made by man, 

 aided by insect allies, to gain the upper hand in a war to 

 the death with an insect enemy. 



Let us consider a few of the other cases. The Florida 

 citrus growers, like their Californian brethren, have been 

 and are seriously handicapped by a minute insect known 

 as the citrus white fly, Aleyrodes citri, a near relative of 

 the scale insect that has proved so destructive in California ; 

 in fact, the citrus white fly and the cottony cushion scale 

 were once included in the same family, the Coccidce, though 

 nowadays scientists place the former in a separate family, 

 the Aleyrodidce or mealy wings. 



The citrus white fly attacks the leaves of citrus-trees in 

 battalions, and, by destroying their assimilative powers, 

 weakens and eventually destroys the trees. The eggs are 

 laid on the undersides of the leaves, to the number of 

 many thousands, so that each leaf appears as if sprinkled 

 with dust; each female laying on an average about one 

 hundred and twenty-five eggs. When first hatched the 

 young six-legged insect resembles a small louse in general 

 appearance, and is so small and transparent that its pre- 

 sence is easily overlooked. For a time the immature 

 insect crawls about the leaves, but eventually it inserts 

 its long thread-like beak into the leaf tissues and then 

 remains stationary till it becomes adult. Nourishment is 

 derived from the plant juices, which are sucked up through 



