Beneficial Insects 



1. ICHNEUMON-FLIES 



(Fig. 5, Plate I, Page 1 1 ; Fig. 7, Plate V, Page 19; Figs. 9 and 10. Plate VI, Page 21) 



Many times when our fields are overrun by a pest we wish that by 

 some magical power we could destroy it and save our crops. Sometimes 

 these pests do disappear as if by magic. Many times we little suspect 

 that the small to medium sized, wasp-like insects, which we observe hov- 

 ering over the field, are the friends that stood by us in our hour of need 

 and wiped out our enemies in an incredibly short time. 



The Ichneumon-flies belong to the same order of insects as the digger- 

 wasps, already discussed. 



These flies have long slender bodies. That of the female is often 

 armed with a long hair-like ovipositor (Fig 7, Plate V, Page 19). This 

 is composed of three parts. The central one is a tube through which the 

 eggs pass, while the two outer ones are the sheath which protects the 

 ovipositor proper. When the insect is alive the three parts are held close 

 together and appear as a single hair-like organ. 



The name "Ichneumon" was suggested by a fancied resemblance to 

 the Ichneumon of Africa, which is a mammal belonging to the same 

 family as the mink and weasel. 



Mention has already been made of two Ichneumon-flies. Figure 5, 

 Plate I, Page 11 is parasitic upon caterpillars and was reared from the 

 western army cutworm. Figures 9 and 10, Plate VI, Page 21 represent 

 a species which destroys the alfalfa looper. 



2. BRACONIDS 



(Figs. 6 and 7, Plate ] Page 11 ; Fig. 14, Plate V, Page 19) 

 Closely related to the Ichneumon-flies is a group known as the Bra- 

 conids. The members of this family are small or minute insects. 



Frequently dead cater- 

 pillars are observed cov- 

 ered with small silken 

 cocoons, or with a mass of 

 these cocoons fastened to 

 some object near them 

 (Fig. 30, Page 136). These 

 caterpillars have been 

 killed by the larvae of 

 some Braconid which 

 have gnawed their way 

 out of the worm and spun 

 cocoons in which to com- 

 plete their own develop- 

 ment. 



One of the most inter- 

 esting forms of this family 

 belongs to the genus Aph- 

 idus. These minute para- 

 sites live within the bod- 

 ies of aphids. When ma- 

 ture the parasite escapes 

 through a hole which it 



Fig-. 30. A Cabbage-worm killed by the Larvae 

 of a Braconid, the Cocoons of which are fastened 

 to the Window-screen near it (Enlarged) 



136 



