ENTOMOLOGY 45 



The lime and sulphur sprays prove to be superior from the 

 standpoint of effectiveness and cost. They are to be recommended 

 to the use of fruit growers as the most valuable spring spray for trees 

 still dormant. Besides being a contact insecticide of high value 

 against other fruit tree insects, it is also valuable as a fungicide. 

 (Bui. 80, Part VIII, B. of E. U. S. Dept. Agr.; Bui. 30 Col. Agr. 

 Exp. Sta.) 



The Pear Thrips.* Injury to the various fruit trees by this spe- 

 cies is caused by the feeding of the adults on the developing buds 

 and early blossoms, by deposition of eggs into the fruit stems, leaf 

 stems, and newly formed fruit, and by the feeding of the larvae in 

 the blossoms and on the young fruits and foliage. On pears the 

 greater injury is produced by the adults, which often prevent the 

 trees from blooming, while on prunes and cherries the larvae fre- 

 quently prevent a crop of fruit from setting after the trees have come 

 into full bloom. Also, the deposition of eggs into the fruit stems of 

 prunes and cherries so weakens the stems that much of the young 

 fruit falls. The feeding injury is not produced by a biting or chew- 

 ing process. By rasping the tender surfaces in the developing fruit 

 buds and the young fruits with their hardened or chitinous mouth- 

 parts, the thrips rupture the skin, causing an exudation of sap which 

 is often followed by more or less fermentaion, especially before 

 blooming. The feeding by larvae on prunes after blooming causes 

 the well-known thrips "scab," while most of the scarred and mis- 

 shapen pears are caused by the work of the adults. 



The adults or winged form of the thrips first appear on the 

 trees about the middle of February and emergence from the ground 

 continues till early April, maximum emergence, however, occurring 

 in late February and early March. The pear thrips is in some re- 

 spects an unusual insect in that it remains in a dormant or semidor- 

 mant 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 completely destroy all prospects 

 of a crop of fruit, in many cases within a very few days. The trees 

 are attacked at the period of bud swelling and blossoming, when they 

 are most susceptible to injury. These minute insects come literally 

 in swarms, and may, if left alone, completely 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 appeared 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. (Cir. 131, B. of E. U. S. Dept. of Agr.; Bui. 68, Part 

 I, Revised B. of E. U. S. Dept. Agr.) 



Spraying is by far the most common and the most satisfac- 

 tory means for controlling the pear thrips on all classes of deciduous 

 fruit trees in California. Only the most efficient spray materials 

 should be used, namely, the combination of distillate-oil emulsion 

 and tobacco extract or distillate-oil emulsion and nicotine solutions. 



* See illustration on page 839. 



