228 NATURE-STUDY 



bug has been introduced into this country to help fight the 

 scale and other insects which injure the fruit trees in Cali- 

 fornia. 



The injurious cotton-boll weevil has an enemy in the form 

 of a certain species of ant. 



Ichneumon-flies are interesting and beneficial insects. 

 One form, the Thalessa, is a wasp-like insect, with a long 

 slender body terminating in a very long thread-like ovipositor. 

 By means of this instrument the female penetrates the bark 

 of trees to the burrows of larvae of the borers, and inserts her 

 eggs in the bodies of these insects. The eggs hatch out and 

 the grubs then feed upon the vitals of the host. In time the 

 host succumbs. By this time the ichneumon grubs are ready 

 to leave or to pupate. They burrow their way out of the 

 host and pupate in the borers' burrow or tunnel, from which 

 they emerge as winged insects. There are other kinds of 

 ichneumons and other parasitic insects, particularly the 

 Microgasters and Chalcis-flies and the Tachinid and Syrphus 

 Flies, which attack caterpillars and other insects by laying 

 their eggs in them to hatch out there and destroy them. The 

 large Grape, Cecropia, Cynthia, etc., Caterpillars are often 

 thus affected. Generally before the caterpillar reaches the 

 pupal stage its parasites have run their larval course and, 

 boring their way out through the walls of the sick caterpillar, 

 spin their cocoons on its surface. The caterpillar quickly 

 dies from the effects. It is interesting to note that the 

 mother insect seems to use judgment in laying her eggs in 

 other insects. If the host is small only one or a few eggs 

 are laid in it. If large then a greater number, according 

 to the abundance of the food supply. The affected cater- 

 pillars sometimes manage to live until they form the chrys- 



