ALFALFA 



359 



varies from year to year, depending on the local abundance 

 of the insects. The species that cause most damage are 

 Melanoplus differentialis and Melanoplus bivittatus. They 

 are more likely to be destructive in seasons when drought 

 causes a shortage in natural food supply and in areas 

 where the proportion of uncultivated land is large, as 

 under these circumstances they congregate in the culti- 

 vated fields. 



Two effective means 

 of destroying these in- 

 sects are by the use of 

 the hopper-dozer and 

 poisoned baits. The 

 hopper-dozer is essen- 

 tially a shallow pan with 

 a vertical back one or 

 two feet high. The pan 

 contains water covered 

 with a layer of kerosene. 

 When this is dragged 

 over the field, many of 

 the insects jump directly 

 into the pan or fall into 

 it after striking the 

 back. 



The most effective poisoned bait is the Griddle mixture 

 made by mixing one pound of paris green and one pound 

 of salt in one-half barrel of fresh horse manure. Grass- 

 hoppers eat the bait very readily and are killed by the 

 poison. Where grasshopper eggs are known to be abun- 

 dant in an alfalfa field, many may be destroyed by disking 

 in the fall or winter. 



The alfalfa leaf weevil (Phytonomus posticus), a native 



FIG. 38. Adult form of the alfalfa 

 weevil (Phytonomus posticus) : Adults 

 clustering on and attacking a spray of 

 alfalfa. (Slightly enlarged.) 



