1654 



ENCYCLOPEDIA OP PRACTICAL HORTICULTURE 



on prunes after blooming causes the well- 

 known thrips "scab," while most of the 

 scarred and misshapen pears are caused 

 by the work of the adults. 



Life History 

 Adults 



The adults or winged form of the 

 thrips first appear on the trees about 

 the middle of February, appearing in 

 greatest numbers in late February and 

 early March. 



By the time the fruit buds have swol- 

 len sufficiently to separate the bud scales 

 slightly at the tip the adults force their 

 way within, feeding upon the tenderest 

 portions inside the buds. 



Eggs 



As soon as the first leaf surfaces or 

 fruit stems are exposed egg-laying usu- 

 ally begins, depending somewhat on the 

 variety of fruit attacked Egg-laying be- 

 gins the first days of March and con- 

 tinues till near the middle of April. Most 

 of the eggs are deposited just under the 

 epidermis in the fruit stems, young fruit 

 and leaf stems. The eggs require about 

 eight days to hatch. 



Larvae 



By the time the trees are breaking into 

 full bloom the adults have done most of 

 the damage caused by their feeding, and 

 oviposition is at its height. Many of the 

 earlier appearing adults are dying off and 

 larvae are beginning to appear in num- 

 bers. The very first larvae can usually 

 be found about March 20, and are in 

 maximum numbers on the trees, feeding 

 on the small fruit and young foliage, 

 from the first to middle of April. Reach- 

 ing their full development, the larvae 

 drop from the trees of their own accord 

 or with falling calyces, or are blown by 

 wind or knocked off by rain. After the 

 middle of April the number on the trees 

 diminishes rapidly and by the last of 

 April all the larvae are off the trees and 

 in the ground. Here they work down 

 into the first three or four inches of hard 

 soil below the loose surface mulch and 

 construct a tiny cell, where they remain 

 until the following spring. 



Pupae 



The larvae mostly remain as such in 

 these cells till September, when pupa- 

 tion begins, pupae being most abundant 

 during October and November. Many 

 adults can be found in the ground in De- 

 cember, and by the first of January prac- 

 tically all the thrips are in the adult 

 stage and apparently ready to emerge 

 and go into the trees whenever condi- 

 tions are right. Broadly speaking, the 

 thrips spend two months of the year m 

 the adult, egg and larval condition on 

 the trees and the other ten months of 

 the year as larvae, pupae and adults in 

 the ground. 



Control Measures 



The pear thrips is in some respects an 

 unusual insect in that it remains in a 

 dormant or semi-dormant condition for 

 about ten months of the year. Although 

 on the trees for only two months out of 

 the twelve, it is able in this short time, 

 in the absence of treatment, to com- 

 pletely destroy all prospects of a crop of 

 fruit, in many cases within a very few 

 days. The trees are attacked at the pe- 

 riod of bud swelling and blossoming, 

 when they are most susceptible to injury. 

 These minute insects come literally in 

 swarms, and may, if left alone, com- 

 pletely destroy all of the fruit buds of 

 an orchard in four or five days. Many 

 cases have been known where a delay of 

 four or five days in spraying resulted in 

 loss of the entire crop of fruit, and in 

 some cases half of all the buds were 

 killed in three days after the thrips ap- 

 peared on the trees in great numbers. In 

 view of this condition it is very evident 

 that any means of control must be very 

 thorough and done in the most exacting 

 manner at the proper time. 



Cultivation 



On gravelly and sandy soils plowing 

 to a depth of from seven to nine inches 

 results in killing from 60 to 80 per cent 

 of the thrips present in the soil, but is 

 not a sufficient control, as enough thrips 

 escape to cause great injury to the buds 

 the following spring. 



