192 



INSECTS INJURIOUS TO STAPLE CROPS. 



end to end, at the end of the third brood there would be 

 enough to encircle the earth at the equator over four times. 

 Eyiemies. — It is thus very fortunate that the cotton- 

 worms have many deadly enemies which commence their 

 warfare upon them as soon as the first aj^pearance of 

 spring, and continue it with increasing ardor throughout 



Fig. 108. — Cotton-worm ^gg-Y>dir2i^\te {Trichogramma pretiosa). a, 

 adult female, greatly enlarged; b, ovipositor; c, female antenna; 

 d, male antenna. (From Fourth Kept. U. S. Entomological 

 Commission.) 



the season. A little insect which lives inside of the eggs 

 and is known to science as Trichogramma pretiosa is one of 

 the most efficient of these. Mr. Hubbard once observed 

 in Florida that from 75 to 90 jDer cent of the fourth brood 

 of eggs and 90 per cent of the fifth were destroyed by this 

 parasite, while only three or four eggs in a hundred 

 escaped in the sixth brood. 



One of the most useful parasites of the caterpillar was 

 noticed to destroy nearly all of the chrysalids of the last 



