STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 



43 



and sawfly larvae, either by inserting eggs within the bodies of their 

 victims or by allowing the victims to swallow the eggs that are deposited 

 on leaves. 



Syrphids or flower flies (Syrphidce) lay their eggs in colonies of plant- 

 lice which are devoured by the larvae. They are large, often bee-like 

 in form. 



The Hemiptera include a few beneficial forms, mostly belonging 

 to the assassin-bug family (Reduviidce). They are predaceous, suck- 

 ing the blood of other insects. Sometimes higher animals, including 

 man, are attacked. The following forms may be noted: 



Melanolestes picipes is a large black form, and Opskcetus pcrsonatus, 

 or masked bed-bug hunter, is black and 

 over 32 inch long. 



The Stink Bug Family {Pentatomidce) 

 also furnishes a few beneficial species, 

 although a very large percentage of the 

 species is injurious to plant life. Two 

 common forms are: Podisus spinosus 

 (spined tree bug) destroys potato beetles 

 and currant worms, and Perillus circuni- 

 cinctus which appeared recently in large 

 numbers in potato fields where it de- 

 stroyed potato beetles (Fig. 42). 



The Damsel Bugs (Nab idee) prey upon 

 leaf-hoppers. 



The Ambush Bugs (Phymatidce) are 

 also predaceous, destroying large numbers of injurious insects. 



Among the Neuroptera are some important beneficial forms, 

 known as aphis-lions and ant-lions. 



The adults of aphis-lions, also called lace-winged flies, are readily 

 recognized by their delicate veined green wings. Their larvae are pre- 

 daceous and destroy large numbers of plant-lice. Their mandibles 

 are very long. The genus Chrysopa is the main one in the family. 



The adults of Ant-lions {Myrmeleonidce) have "long narrow delicate 

 wings and a slender body." The larvae are very predaceous and possess 

 enormous mandibles. They capture their prey by using pitfalls. 



Hyper parasitism. — It happens that many of the primary parasites 

 are often infested with parasites which reduce very appreciably the 



Fig. 42. — Perillus circum- 

 cinclus, an enemy of the Colo- 

 rado potato beetle. 



