36 BULLETIN 173; U. S. DEPARTMENT OF AGRICULTURE. 



March 26 and April 8. The Sugar and Imperial varieties precede the 

 French by about one week. Bartlett pear buds begin to swell the 

 last of February or the first of March, the first clusters usually spread- 

 ing from March 10 to 1 5 and are in full bloom for quite an indefinite 

 period between March 20 and April 10. Pears, prunes, and cherries, 

 which are spreading their bud clusters just after the maximum numbers 

 of thrips are coming from the ground, are the fruits most seriously 

 injured by the pear thrips. 



MIGRATORY HABITS. 



Evidences of the migratory habits of the pear thrips have been 

 noticed at times during the last three or four years. However, no 

 definite observations concerning their migration had been made until 

 the year 1910. Hitherto it had been noted that in some orchards 

 the adults were very numerous early in the season and doing extensive 

 damage. Later observations at an interval of four or five days 

 showed very few adults present, and the entire orchard had the 

 characteristic browned and burnt appearance. It was quite evident 

 that after destroying all the fruit buds the thrips had migrated to 

 other orchards in search of food. 



It was possible to obtain more definite knowledge regarding 

 migration in the year 1910 than had heretofore been known, for the 

 reason that the thrips were unusually numerous throughout all the 

 infested areas that year and weather conditions were such that 

 practically the entire brood emerged from the ground in a few days. 

 Also, following their emergence in great numbers, the weather was 

 sufficiently warm that the destruction of the fruit buds in the various 

 orchards was accomplished in much shorter time than is usually the 

 case. Observations so far indicate that thrips migrate in swarms 

 only on bright , warm days. Numerous instances of supposed migration 

 were mentioned to the writers at various times during the season, the 

 reports stating that the pear thrips were flying in swarms, but most 

 of the cases reported lacked authentic evidence to bear them out, 

 such as the saving of specimens. However, in the afternoon of March 

 28, 1910, the junior author drove out from San Jose toward Saratoga 

 and had great difficulty in keeping both hands on the reins on account 

 of the great numbers of thrips which, flying through the air, filled his 

 eyes and covered his clothes. The prevailing direction of the wind 

 on this day was not observed; no distinct migration or swarm was 

 noted, however, although individuals were numerous flying across the 

 road and could be readily seen when the observer looked toward the 

 sun. They were more numerous on roads running north and south, 

 and extended over a territory of 4 or 5 miles ; they were the most numer- 



