THE PEAR THRIPS. 7 



ing eggs on such plants. The insect has proved itself a strictly fruit- 

 tree pest, and it is carried to weeds and lives on them or on other 

 plants only by accident. 



LIFE HISTORY AND HABITS. 



THE EGG, THE OVIPOSITOR, AXD OVIPOSITION. 



The thrips egg is bean-shaped (fig. 2), light-colored, almost trans- 

 parent, and is very large in proportion to the size of the abdomen 

 when seen within the body of the adult female. It is about 0.33 mm. 

 long by actual measurement. 



The ovipositor (fig. 3) is made up of four distinct plates. Each 

 plate is pointed, has a serrate outer edge, and is operated by powerfid 

 muscles and plates within the abdomen. The pairs on each side fit 

 together along the inner edges with a tongue-and-groove-like structure, 

 which in action renders possible a sliding back and forth, or sawing 

 motion. The ovipositor is protected 

 within a sheath in the ventral tip of 

 the abdomen when not used, but before 

 and during ovipositing it is lowered 

 until almost at right angles to the 

 body. 



Oviposition accompanies feeding. It 

 seems necessary, indeed, that before the 

 ovipositor can be inserted through the 

 plant epidermis the thrips must first 

 weaken or break an opening through 

 this tissue with the mouth-parts. The 

 successive operations of lacerating the 

 plant tissue, lowering the ovipositor, placing an egg, and withdrawing 

 the ovipositor require from four to ten minutes, and may be briefl}' 

 described as follows: After making an incision with the mouth parts 

 the insect moves forward, lowers and inserts the ovipositor, and by 

 operating the tiny saws she makes a deep incision in the plant tissue. 

 While the ovipositor is still deeply set in the plant, an egg is con- 

 ducted through the cavity between the plates and deposited under- 

 neath the epidermis. The ovipositor is withdrawn and the egg is 

 thus left deeply embedded within the plant. During the oviposition 

 period one often finds a branch or a tree, or even many trees, on 

 which almost all thrips are ovipositing at the same time. 



The small, fragile, just-exposed blossoms, stems, and leaf petioles, 

 and later the midribs and veins on the back side of the leaves, and 

 still later even the leaf tissue itself, are the places preferred for ovi- 

 positing. A thrips always places her eggs in the tenderest of the 

 plant's tissue. There is danger of the ovipositor getting caught if the 

 tissue is hard. Also, it is necessary during eg^g^ development that the 



Fig. 3. — The pear thrips (Euthrips pyri): 

 ovipositor and end of abdomen from 

 side. Much enlarged (original). 



