16 BULLETIN 173, U. S. DEPARTMENT OF AGRICULTURE. 



pears and 40 to 50 per cent for prunes. If remedial measures are not 

 successfully used against the adult but only against the larvae, it is 

 not to be expected that 50 per cent of a crop will be saved; but the 

 additional treatment against the larvse after the adult treatments 

 have been applied will cause from 10 per cent to 50 per cent more 

 of the crop to remain on the trees. Without taking into account 

 the after effects of migration, good results can be had in pear 

 orchards by spraying against adults alone, if thorough work is done 

 at the proper time. 



INJURY TO PRUNES. 



Next to the pear, thrips injure prunes most severely; and, as the 

 larger fruit area in the Santa Clara Valley is devoted to this kind of 

 fruit, and since the pear thrips has caused the failure over large areas 

 of the prune crop for several years, growers in the Santa Clara Valley 

 have commonly called this particular species the prune thrips. The 

 large acreage of prunes and the general distribution of the pear thrips 

 over the valley, together with the fact that the majority of the thrips 

 are out before many of the buds of the French prunes have started 

 to spread, make it very evident that these little insects, which are ' 

 waiting on the outside of the twigs hi enormous numbers, will at the 

 first sign of life of the prune buds bury themselves into the very heart 

 of the tenderest parts, and rapidly carry on their work of destruction. 

 The numbers that will get inside of a prune cluster is really aston- 

 ishing. Many times the writers have, from a single cluster, taken 

 more than a hundred of these little insects feeding upon the tender 

 blossom stems, the tips of the petals, and the stigma and style of the 

 blossoms when they have opened. These parts mentioned seem to 

 be the choice bits for the adults when feeding upon the prunes. The 

 rapidity with which the thrips can destroy the whole year's crop is 

 astonishing. Many a time orchardists have gone into their prune 

 orchards at the time the buds were about ready to spread, and, with 

 only casual observation, have failed to see these minute, dark-colored 

 insects crawling around or at rest upon the twigs and buds. Upon 

 inspecting the orchard four or five days later, expecting it to be in 

 full bloom, they have been astounded to find practically all the buds 

 destroyed, leaving no hope for a crop that year, the entire orchard 

 presenting a brown, burnt appearance, with only a stray blossom 

 now and then, a sight which is well known now to the majority of 

 the prune growers of the Santa Clara Valley. Anyone who has ever 

 seen one of these prune orchards with the burned, browned, and 

 blasted appearance beside another of snowy whiteness will never 

 forget the contrast. (See PL IV, comparing fig. 1 with fig. 2.) Again 

 there may be a very severe larval injury on prunes, such as was the 

 case in 1911. Very few adult thrips occurred in comparison with 



