374 General Biology 



Three parts fish oil, one part kerosene. Apply with small spray 

 pump. 



Two parts crude cottonseed oil or fish oil, one pint pine tar. Apply 

 with large paint brush. 



PARASITIC INSECTS 



Many kinds of insects live parasitically for part of their lives, and 

 many live as parasites for their whole life. The true sucking lice and 

 the bird lice live as external parasites on the bodies of their host through- 

 out their entire lives, but they are not fixed — that is, they retain their 

 legs and power of locomotion, although they have lost their wings 

 through degeneration. The lice deposit their eggs on the hair of the 

 mammal or bird that serves as host. The young hatch and immediately 

 begin life as parasites, either sucking the blood or feeding on the hair 

 and feathers of the host. There are several families of the order 

 Hymenoptera, all of whose members live as parasites during their larval 

 stage. These hymenopterous parasites are called ichneumon ( ) 



flies. (Fig. 242.) The ichneumon flies are parasites on other insects, 

 especially of the larvae of beetles, moths, and butterflies. According 

 to Ealand, "the ichneumon flies do more to keep in check the increase 

 of injurious and destructive caterpillars than do all our artificial remedies 

 for these pests. The adult ichneumon fly is four-winged and lives an 

 active, independent life. It lays its eggs either in or on or near some 

 caterpillar or beetle grub, and the young ichneumon, when hatched, 

 burrows into the body of its host, feeding on its tissues, but not attack- 

 ing such organs as the heart and nervous ganglia, whose injury might 

 mean immediate death to the host. The caterpillar lives with the ichneu- 

 mon grub within it, usually until nearly time for its pupation. In many 

 instances, indeed, it pupates with the parasite still feeding within its 

 body, but it never comes to maturity. The larval ichneumon fly pupates 

 either within the body of its host or in a tiny silken cocoon outside of 

 its body. From the cocoons the adult winged ichneumon flies emerge, 

 and after mating find another host on whose body to lay their eggs." 



As an example of a parasite living upon another parasite, though 

 one of these uses a tree as its host, the remarkable ichneumon fly 

 Thalessa (Fig. 242) is an excellent example. This animal, which has a 

 very long, slender, flexible ovipositor, finds a spot in a tree where the 

 insect Tremex columba ( ), commonly called the 



pigeon horntail, has deposited its eggs about a half inch below the sur- 

 face of a growing tree. When these eggs are converted into larva, the 

 larva digs still deeper into the tree, filling up the open space behind it 

 with tiny chips. Through a very extraordinary instinct the Thalessa 

 finds the spot opposite where the Tremex larva lies and "elevating her 

 long ovipositor in a loop over her back, with its tip on the bark of the 

 tree, she makes a derrick out of her body and proceeds with great skill 



