196 INSECTS AFFECTING FIELD CROPS 



Joint Worms. The different species of this group, Isosoma, 

 are four-winged flies. They live through the winter as larvae or 

 pupae in cells in the stem of wheat and some other grains. The 

 adults emerge in spring after the young grain hag thrown up 

 stems so that several joints have become exposed. The female 

 places her eggs in these stems and the larvae feed within, becoming 

 full grown by the time the straw is hardened. They pass the winter 

 in the cells thus made. 



Injury. This is a serious pest in the wheat regions west of the 

 Mississippi River. The damage varies from being slight to a 

 total loss of the entire crop. ' Swellings and other malformations 

 arising from the presence of this insect often occur in infested 

 straw. Such straw is brittle and woody. By cutting off the sap 

 supply from the head, worms prevent the filling out of the kernels. 

 The wind also breaks down these brittle straws. At threshing 

 time its presence is shown by hard bits of straw containing larvae 

 appearing in the threshed grain. 



Control. The following suggestions are not always applicable; 

 a farmer must select such as are practicable for the circumstances 

 existing on his farm : Fields should be worked into the best possible 

 condition before seeding. Sow as early as possible, and use early- 

 maturing varieties. Fields should be well fertilized, thus inducing 

 rapid and vigorous growth. Practice rotation of crops. Plow 

 under or burn stubble in late fall. Burn all infested straw which 

 has not been fed or used by the last of April. 



INSECTS ATTACKING CLOVER AND ALFALFA 



The Clover-seed Chalcid. This tiny, four-winged fly (Bruco- 

 phagus funebris How.) is sometimes erroneously referred to as a 

 "weevil" by farmers. It deposits its eggs in the young seeds. 

 This gives rise to a tiny grub, which devours the entire contents of 

 the seed. It may also enter larger seeds. It transforms from the 

 larval form to the pupal form within the seed (Fig. 215). 



Injury. This insect has been so destructive in places that the 

 raising of clover for seed has been abandoned. In clover-raising 

 sections of Minnesota the depredations of this insect cause an 

 annual loss of many thousands of dollars. The clover itself is not 

 injured by its work. Affected seeds are more or less misshapen 

 or undersized and can, for the most part, be detected in the mass 

 of seed offered for sale. 



Control. Cut the hay crop while heads are still green to pre- 

 vent the maturing of the pest and the consequent attack on ths 



