354 ECONOMIC ENTOMOLOGY 



and bodies. They are recognized by the branched single vein of the 

 fore wings. Their larvae attack many species of caterpillars. Among 

 the more common forms are Pleromalus puparum on the pupae of the 

 White Cabbage Butterfly; Aphelinus on scale insects; Monodontomerus 

 (Breus on the Brown-tail and Gypsy Moths; Tricho gramma on many 

 caterpillars, and Coslopistha nematicida on the Larch Saw-fly. Tetra- 

 stichus, DiBrachys, Coccophagus, Scutellisla, Prospaltella, Eupelmus and 

 Aphycus are other valuable economic forms. 



The four following species are injurious: 



Wheat Joint Worm (Isosoma tritici F tch.). — (Consult Farmers' 

 Bull. 132 and 1006, U. S. Dept. of Agric.) Adut. A minute black 

 4- winged ant-like fly; 3^^ inch long. May. Injurious in the East 

 on account of the larva living in the stems of wheat, sucking the 

 juices and causing a swelling in the stem. Infested plants contain 

 one or more hard woody cells in the stem just above the second or third 

 joint from the ground, in which live the larvae or grubs. On nearing 

 maturity the stems fall or break at the places of injury. 



Eggs. — Small, white, round-oval. Inserted in daytime, singly at a 

 place, in the stem by the sharp ovipositor, but of en as many as 15 

 into one stem. Each female may lay as many as 70 or moe eggs. 

 Hatch in about 14 days. 



Larva. — A yellowish- white maggot, )^ inch long, tips of jaws brown, 

 3 to 4 moults; full grown in 3 weeks; hibernates in wheat straw; 

 forms cell in stem. Most of the larvae change to pupae late in Autumn. 



Pupa. — Yellow to black; 3^^ inch long. 



Parasites.— Ditriponotus aureoviridis , Homoporus chalcidephagus, 

 Eurytoma hoUeri parva, Eupelmus epicasta Walk., all chalcids. 



Control. — Rotation of crops; burning and deep plowing under of 

 stubble when practicable, or harvesting of stubble in spring, collecting 

 with horse-rake and burning; preparation of good seed-bed. 



Wheat Straw Worm {Isosoma grande Riley). — A pest west of the 

 Mississippi; adults emerge in April-May from stubble and lay eggs, 

 and the larvae eat the forming heads of wheat. Adults appear again 

 in June and lay eggs above the upper joints. Larvae pupate by 

 October and winter is passed in the stubble. 



Species of Isosoma (Females) (after Howard) 



A. Mesonotum smooth, polished, shining. — grande. 

 A A. Mesonotum rugulose; abdomen longer than thorax. 



