64 



THE EEPOET OF THE 



^0. 36 



was caused by the fact that the insect injuries produced sterility in the ears and 

 the young and adult insects were found feeding on the flowers, especially on the 

 ovaries which, of course, produce the grain. It was further found that these in- 

 juries take place while the inflorescence is enclosed in the leaf sheath, and on 

 this account the lower ears of the inflorescence are usually the ones to be injured 

 and rendered sterile, as they remain longer in the leaf sheath. In further support 

 of this it was found that where the top of an inflorescence has been held by the leaf 

 sheath, as is sometimes the case, the apical ears may be sterile. Specimens of both 

 these types of injury will be seen in the cases which I am passing around. With a view 

 to ascertaining the extent of these injuries, stalks of different varieties of oats were 

 collected and the number of sterile and perfect ears on each stalk were carefully 

 counted. It may be remarked that in order to eliminate a cause of error result- 

 ing from the unintentional selection of stalks unusually affected, an equal number 

 of stalks were collected by one who was ignorant of the purpose for which the oats 

 were required. It is not intended to give here the complete results of this statis- 

 tical study, but the following facts may be of interest. 



The most severely injured variety of oats on the average was " Banner M,'" 

 19 heads of which variety had an average of 36.3 per cent, of sterile ears. The 

 least attacked was " Abundance, Garton's Begenerated," 11 heads of which gave 



Fig. 29. — Thrips. 



an average of 17.3 per cent, sterile ears. The maximum percentage of sterile ears 

 in all the heads examined was 56.8 per cent, in a head of "Banner M." The 

 minimum percentage of sterile heads was found in a head of " Banner H," of 

 which 3.5 per cent, were sterile. 



Prom these figures it will be realized what a serious effect the injuries caused 

 by these insects may have on the yield and to what extent their injuries may 

 reduce the number of bushels produced, as no other cause of the sterility of the 

 ears could be discovered. 



The Grass Thrips Anaphothrips striatus, is a very small insect measuring about 

 1-1 6th of an inch in length and of a yellowish, or brownish-yellow colour. The 

 adults are provided with four narrow wings which are fringed with hairs, hence 

 the name of the group Thysanoptera. They are also called Physopoda, on ac- 

 count of their possession of bladder-like feet, from which they derive their German 

 name "Blasenfiisse." Their nourishment consists of the juices of the flowers and 

 plants and their mouth parts are very peculiar in that they are adapted for botli 

 sucking and biting. The life history of this species has been previously worked out 

 by Hinds. The females will continue to deposit eggs and young larvae may emerge 

 up to the time the snow falls, when the adults hibernate. Their resistance to a 

 low temperature appears to be very great, as they can withstand an exposure of 

 minus 21 degrees F. In the spring, soon after the snow disappears, the females, 

 which have passed the winter in the leaf sheaths of young plants, become active 



