INSECTS INJURIOUS TO SMALL GRAINS 



127 



under the internal wall-covering or inner epidermis. These larvae 

 in the walls of the straw do not, as a rule, kill the stem, but 

 their effect is to curtail the yield by reducing the weight. The 

 larvae develop rapidly and reach their full growth before the 

 straw has hardened. By October, in the Middle West, though 

 earlier in the South, they pass into the pupal stage, in which, as a 

 rule, they remain until early spring, whereupon they develop to 

 adults and gnaw their way out." In the Northwest, where both 

 winter and spring wheat are grown, the injury is particularly 

 severe to spring wheat, as the adults 

 of the second generation from winter 

 wheat oviposit upon it while it is 

 still young and ruin it in much the 

 same way as the first generation does 

 on the winter wheat in spring. Vol- 

 unteer plants which carry the pest 

 over winter have the same effect in 

 increasing the injury to spring wheat. 

 Control. A rotation of crops 

 which will eliminate the growing of 

 wheat two years in succession on the 

 same land is by all means the most 

 successful and practicable means of 

 control. The adults of the first gene-^ 

 ration are very small and largely 

 wingless; they are unable to migrate Fra. 108. The wheat saw-fly borer 

 far, so that rotation is exceedingly 

 efficacious, though it should be 

 planned so that wheat is not planted 

 next to stubble land, for the edge 

 will become infested by the first gene- 

 ration, and the second generation 

 will then become distributed throughout the field. The burn- 

 ing of stubble and outstanding straw will be advantageous 

 wherever practicable. Clean fallowing in early summer and the 

 abandonment of spring- wheat culture will reduce injury in the 

 Northwest. 



larva, enlarged ; c, larva in wheat- 

 stalk, natural size; d, frass; e, 

 adult female; /, Pachyonerus cal- 

 citrator, female, a parasite en- 

 larged. (After Curits, from 

 "Insect Life.") 



