February, '17] REEVES: alfalfa weevil 125 



the pest may prove less harmful in higher altitudes and latitudes, but 

 that is scant comfort for alfalfa growers in regions threatened by its 

 steady approach. 



These are the reasons for the existence of the alfalfa weevil investi- 

 gation. It was taken up by the Bureau of Entomology in 1910, and 

 now employs five entomologists and a clerk. The equipment includes 

 a one-room office, a four-room laboratory, and the usual instruments 

 and supplies. The annual pay-roll is $8,390, the rent, $450, and other 

 expenses, $1,500. 



The practical results of the investigation have been to develop five 

 methods of controlling the weevil, to discover and publish its occurrence 

 in new territory and to study the factors which determine its spread. 

 The practical control measures are flooding with sediment, spraying 

 with arsenical poisons, pasturing, harrowing the stubble, and colonizing 

 parasites. None of these methods is entirely perfected, and not all 

 are equally valuable, but all are useful, and all are in actual use. 



Flooding with Sediment 



Covering the field with muddy water in early spring causes a deposit 

 of silt over the surface of the ground, which imprisons the adults and 

 the eggs contained in dry stems. It is an effective way of protecting 

 the crop, but it is only possible in the undesirable condition where the 

 irrigation system is without a settling reservoir. This condition 

 obtains in many small systems, and it is then possible to carry the 

 muddy spring floodwater over the fields and cover them several inches 

 deep. This practice was first seen in a field situated in a ravine at 

 Fort Herriman, Utah, where the creek ran along one side of the field 

 and had overflowed and covered a portion of the field with silt and 

 gravel. The buried portion was free from weevil injury, while the 

 rest of the field was considerably damaged. We had no authentic 

 history of the field and were unable to show that the mud had killed 

 the weevils, but later an experiment which had been under unusually 

 close observation for several months was ruined by being flooded with 

 sediment. The Utah-Idaho Sugar Company had allowed us, with the 

 Agricultural Experiment Station, to use a field of alfalfa at Saratoga 

 Springs which was watered by the flow from a hot spring. A series of 

 experiments with irrigation and cultivation at different seasons of the 

 year had been begun in the fall and carried on throughout the winter, 

 and careful examinations of the plats made at short intervals to deter- 

 mine the number and condition of the weevils present under various 

 treatments. Some of the examinations were made at times when the 

 ground was frozen hard and had to be dug up with pick and shovel, 

 thawed out, dried, and sifted to find the weevils. Consequently, our 



