136 NEBRASKA STATE HORTICULTURAL SOCIETY 



The so called "Thick-headed Flies" or Conopidae do not resemble any 

 of the two-winged insects already mentioned. As their name signifies, 

 they have exceptionally wide heads, considerably wider than the body; 

 the body without bristles and usually without hair; the abdomen club- 

 shaped, i. e., narrowed at the hase, sometimes quite wasp-like. These 

 insects are parasitic upon adult bees and wasps. The egg is laid directly 

 upon the host while in flight, and the young larva, when it hatches, 

 burrows within the body of the insect taking up a position with its head 

 towards the rear end of the host. The larva pupates within the host, 

 when the adult emerges it escapes by eating its way out. The attack 

 of these insects is not confined to the bees and wasps, but some are also 

 parasitic on grasshoppers upon which they work in a very similar 

 manner. 



Of the four-winged insects only the Braconids are to any extent 

 parasitic on adult insects. Often one of our little "lady-birds" or lady- 

 bug" may be seen clinging to leaf, dead. On looking beneath the beetle 

 there is seen a little silken cocoon of a Braconid which has issued from 

 the body of the host in order to go into the resting stage. It will be 

 remembered that when other members of this group attacked the larvae 

 there were many parasites to each host, and thej' all spun cocoons on 

 the back of host or within the body. Here, however, there is only one 

 parasite to each host. Another example of these parasites attacking 

 adult insects is the parasitism of plant-lice. Comstock says that it is very 

 interesting to watch these little Braconids ovipositing in the bodies of 

 plant-lice. When one has selected a plant-louse in which to oviposit she 

 stands with her head towards it, and bending her abdomen under her 

 thorax between her legs she darts her ovipositor forward into the body 

 of the plant-louse. These parasites do not construct cocoons, but undergo 

 their stages within the dry skins of the plant-lice. When the adult 

 parasite emerges it cuts a circular lid in the back of the host. One side 

 of the lid is left attached, and one may often find the skins cf whole 

 colonies of plant-lice with these little round holes in their backs. 



There is still a small group of parasitic insects which has not been 

 mentioned but which are very interesting from the fact that they are so 

 entirely different from the forms which we have been considering. The 

 males have four wings but the front pair are only slender, leathery, club- 

 shaped apprendeges, while the hind pair are very large and fan-shaped. 

 The females have no wings at all and greatly resemble a larva in form. 

 They are parasitic upon bees and wasps and it is in the bodies of these 

 insects that they pass their pupal stage. The name Strepsiptera is 

 applied to this strange group of insects. 



While the relation between parasite and host as it has been discussed 

 is a simple one, it is by no means the whole story of parasitism. These 

 primary parasites, feeding upon the tissues of their host, may in turn be 

 parasitized by what are called secondary parasites. These secondary 

 parasites may also be victimized by tertiary parasites and, in very rare 



