April, '14] HEWETT: THRIPS INJURING OATS 211 



Mr. Henry Skinner: Are these temporary storage houses? 



Mr. W. E. Hinds: No, they are permanent houses. We have 

 advised many people to construct temporary fumigation bins. 



Mr. Henry Skinner: It seems to me it would be feasible to have 

 permanent storage houses suitable for fumigation. 



Mr. W. E. Hinds : It is a question of expense. When a man has 

 thousands of bushels of corn in storage it would be impracticable to 

 construct fumigation cribs to retain the entire crop. 



Mr. C. Gordon Hewitt: Is a single fumigation sufficient? 



Mr. W. E. Hinds: All stages may be killed by one treatment but 

 if man}^ of the eggs were not killed a second fumigation would be 

 necessary. We often make one in the early fall and another early in 

 the spring. 



President P. J. Parrott: Dr. C. Gordon Hewitt will present the 

 next paper, entitled "Sterility of Oats cauvsed l)y Thrips. " 



STERILITY IN OATS CAUSED BY THRIPS 



By C. Gordon Hewitt, D.Sc, F. R. S. C. Dominion Entomologist, Ottawa 

 About five years ago specimens of oats with "blighted" ears or 

 spikelets were received from Saskatchewan. The upper spikelets of 

 the affected inflorescences were, as a rule, healthy, green and sound. 

 The lower spikelets, however, were smaller, whitish and shrivelled and 

 varied in size from slightly less than normal length to minute unde- 

 veloped ears. Specimens of oats similarly injured were received from 

 correspondents in Alberta. A farmer who forwarded heads of oats 

 bearing affected spikelets from Vancouver Island, B. C., stated that 

 over 50 per cent, of a fourteen acre field of oats were attacked. In 

 1909, Mr. Angus Mackay, at that time Superintendent of the Dominion 

 Experimental Farm at Indian Head, Sask., informed me that he had 

 noticed the "Silver top" in oats for several years, but more partic- 

 ularly during the preceding year or two. 



The discovery of dried up specimens of thrips in certain of the spike- 

 lets and in the leaf sheaths suggested that these insects might be re- 

 sponsible for the injury. Accordingly, in 1911 I investigated the 

 matter more thoroughly in the experimental cereal plots, at the Cen- 

 tral Experimental Farm, Ottawa, where injured or "blighted" spike- 

 lets of the same character were found in the oat plots, and it was clearly 

 established that this form of sterility in the spikelets was produced 

 by thrips. On these plots the common species and the one which was 

 responsible for the injury was the Grass Thrips, Anaphothrips striatus 

 Osborn.^ Dr. W. E. Hinds kindly confirmed this determination. 



iBagnall (in "A Further Contribution towards a knowledge of the British Thy- 

 sanoptera," Journ. Econ. Biol., 1912, p. 189) states "The Genus Anaphothrips Uzel 

 should be known as Euthrips Targ.-Tozz." 



