THE PEAR THRIPS IN CALIFORNIA. 37 



ous at the west end of Hamilton Avenue and along the San Tomas and 

 Santa Clara and Los Gatos Roads. 



On March 30, 1910, still more definite information was gained, and 

 this is probably the most unique record of thrips migration which has 

 yet been taken. The day was bright and rather warm and ended 

 with the evening warm and a gentle breeze blowing from the south. 

 Mr. E. L. Fellows, who was in Santa Clara on this day, started home 

 about 5 o'clock in the afternoon. About 5.15 p. m., out on the 

 Saratoga Road, he noticed a number of small, black insects which 

 covered his face and hands, his hat and clothes, and got into his eyes. 

 When he was one-fourth of a mile north of Meridian Corners he met 

 the thickest part of the swarm, which appeared literally like a black, 

 glistening, seething mass moving up and down like heat waves. 

 From this place the insects became less numerous as he went toward 

 home, which he reached about 6 p. m. He thought the swarm to be 

 about 8 miles long and 4 miles wide, from 4 to 15 feet high, moving 

 at the rate of about 10 miles per hour northward toward San Fran- 

 cisco Bay. As he was not sure concerning the identity of this insect, 

 he gathered several hundred specimens in a paper bag and submitted 

 them to the junior author for identification. They were found to 

 be the pear thrips, Tsenioihrips pyri. This same swarm was noticed 

 by the junior author and by several fruit growers, but they did not 

 have the opportunity to view the whole swarm as did Mr. Fellows. 



Continued observations during the season of 1910 showed that the 

 usual time for migration was from 3 to 6 p. m. on bright, warm days 

 during the latter part of the period of maximum oviposition, which 

 was also about the time many orchards have been so badly injured 

 that the trees will not bloom. 



This migratory habit is undoubtedly influenced chiefly by a desire 

 for a new supply of food, better places for deposition of eggs, and 

 suitable weather conditions, especially the temperature. The 

 direction in which thrps will migrate depends upon the direction the 

 wind is blowing, and the distance at which suitable feeding places 

 are found. 



No distinct migration of the whole brood has ever been observed, 

 such as is the case with some species of Orthoptera. The migra- 

 tion from certain badly infested orchard localities has been in- 

 fluenced, without doubt, by the early destruction of the fruit buds 

 in these orchards. Many instances are known where thrips are 

 numerous and their injury severe in an orchard one year and not 

 very numerous the succeeding year, but they are usually highly 

 injurious again the third year. This phenomenon is more noticeable 

 in pear than in prune orchards, due probably to the fact that a pear 



