494 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 14 



from day to day as shown by the accompanying diagram (Figure 11). 

 By the end of three weeks practically three-fourths of the field had been 

 damaged. 



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Fig. 11 Diagram illustrating infestation of onion field by thrips tabaci which 

 had hibernated in field of alfalfa. 



It is interesting to note in this connection that an adjacent cornfield 

 did not serve as an obstruction to the spread of thrips as has often been 

 supposed. By July 15, not only was the north end of the field covered 

 by the pest, but also an area of "white blast" was to be found on the 

 west side of a smaller field beyond the com. The thrips had moved 

 over the com from the large field already mentioned. Control measures 

 were attempted by the use of two knapsack sprayers, applying the nico- 

 tine sulphate spray advised by the U. S. Dept. of Agriculture, but 

 negative results were obtained. Three hundred bushels of onions were 

 harvested by this man from the five acres. This represented a loss of 

 75% over his 1918 crop. This loss was directly due to the infestation, 

 since surrounding fields which were free from thrips yielded as much as 

 four himdred bushels per acre under the same conditions of temperature 

 and precipitation. Adults of Thrips tabaci were found in the alfalfa 

 blossoms July 30 after the 1919 onion crop was harvested. It will 

 be interesting to determine whether or not thrips will continue to 

 winter over in the alfalfa field in the future and thus continue to menace 

 the onion crop in that vicinity. 



