April, '14] HEWITT: THRIPS INJURING OATS 217 



varies from two weeks in the early spring to about four days in mid- 

 summer. The winged adults appear in May or June. The whole 

 life cycle occupies from twelve to thirty days. Korolikoff found that 

 the species injurious to cereals which he investigated passed the winter 

 in the green, soft tissues of the leaf sheaths of young plants, and that 

 in the spring they migrated to the early cereals and later to the sum- 

 mer crops. He found that they migrated from one sp'ecies of plant to 

 another; for example, from rye to wheat and oats. He states that 

 their injuries were caused chiefly by the fact that they feed upon the 

 juices of the different parts of the flowers, and especially on the ovary, 

 that is, in cereals, the young grain. 



Other Species of Thrifs Attacking Oats 



Hinds. (1. c.) records the following species as attacking oats: jEoIo- 

 thrips fasciatus Linn., and Limothrips avencB Hinds. 



Control Measures. 



As Anaphothrips striatus feeds on grasses and is able to migrate with 

 the greatest ease, the difficulties of control would appear to be very 

 great. The destruction of weeds, especially Graminse, is essential, and 

 this would also apply to volunteer crops. As the insects hibernate 

 in places where they have been feeding, such as the stems of cereals 

 which have been cut and have died down, under rubbish and in crev- 

 ices, the hibernation period would appear to afford one of the best 

 opportunities for employing control measures. Such measures would 

 be of a cultural nature, such as deep ploughing of the soil. As an al- 

 ternative and additional measure the burning of the stubble of an 

 infested crop would undoubtedly destroy large numbers of the hiber- 

 nating individuals. Grain which has been infested might be cut as 

 early as possible to prevent the further reproduction of the thrips. 

 After threshing, the screenings and chaff, which contain large num- 

 bers of the insects, should be burnt. Where early varieties of oats can 

 he grown advantage may be taken of the fact that these are less 

 likely to be injured than the later ripening varieties. Korolikoff rec- 

 ommends the sowing of "bait" or "trap" crops. He suggests that 

 rye or oats sown round the fields under cultivation about a fortnight 

 before the sowing of the winter cereals might attract the thrips and 

 afford them shelter while the crops are growing. When the trap crops 

 are removed later a large number of the thrips are removed also. 



References 



Gary, L. R. The Grass Thrips. Maine Agric. Exp. Sta. Bull. 83. 1902. 

 Fernald, H. T. and Hinds, W. E. The Grass Thrips. Mass. Agric. Coll. Bull. No. 



67, 1900. 

 Fletcher, J. Ann. Repts. Bet. and Ent., Exp. Farms, Canada, 1888, p. 89, and 



1892, p. 3. 



