NATURAL CONTROL. 13 



cabbage, and cauliflower. It may be distinguished from the tobacco 

 (hrips by its color, which is yellowish. 



Anthotlirips niger Osborii is another species which was very abun- 

 dant at Quincy the summer of 1905. In oats and wheat bordering 

 Ihe tobacco fields it was found breeding in vast numbers with the 

 wheat and tobacco thrips. It was also occasionally taken on tobacco 

 and tomato. It is a strong flyer, and may be further distinguished 

 from the tobacco thrips by its much larger size and black color. 



A few sjDecimens of .Eolothrvps hieolor Hinds were taken on oats 

 and wheat in the vicinity of tobacco fields. This species may be 

 distinguished by the white or yellowish pigmentation of the first 

 three segments of the abdomen. 



Chirotknps crassus Hinds was taken in October and Noveml>er in 

 large numbers in the sheaths of grass growing in tobacco fields. It 

 Avas at first mistaken for the tobacco pest, because of the similarity 

 in color, but may be easily distinguished, as it does not have the 

 jumping habit of the tobacco thrips. 



NATURAL CONTROL. 



Rains. — Of the natural checks, rain is the most important. It is 

 known that nearly all thrips thrive during warm and dry weather, 

 and that they are washed from their food plants and destroyed in 

 numbers b}^ rain. This is true of the tobacco thrips in that it is 

 washed oil' by heavy rains, yet unless the rain continues for several 

 days few seem to be destroyed, for at the end of the first or b}' the 

 second clear day following the writer has found it on the leaves in as 

 large numbers as ever. 



The influence of rain upon the pest, however, was very noticeable in 

 its effect during the summer of 1905. Up to the latter part of June 

 very little rain had fallen, and the drought was showing its effect on 

 the unirrigated fields. At this time the dry spell was broken and 

 rains were heavy and frequent. The June, 1905, rainfall, which was 

 nearly three times that of the preceding June, yet still below the nor- 

 mal, jiearly all fell during the latter part of the month and Avas fol- 

 lowed by the heavy July rainfall, which was the greatest since 1900. 

 and more than tAvice that of 1901. As a result the thrips were kept off 

 the lea\'es, the plants grcAv rapidly, and ])riming Avas forced into 

 tAventy cUia's Avhere it usually takes thirty. The sand lea\^es were lost 

 in large part because of this rapid ripening and the leaves affected to 

 (lie greatest extent by Avhite A'ein Avere thus eliminated from the crop. 

 As the result of these Aveather conditions, Avhite vejns in the late to- 

 bacco were reduced to a A'ery small percentage. 



The great amount of injury in 1904 Avas undoubtedly due to the 

 exceptionally droughty season. This Avill be shown by the accom- 

 panying chart (fig. 2) of total monthly precipitation for the last 

 seA^en years. That during 1905 and 190('. the injury was so much 



