20 BULLETIN 616, U. S. DEPARTMENT OP AGRICULTURE. 



about an inch square and went through the following antics: Fre- 

 quently it would elevate the abdomen, spreading the wings as in 

 preparation for flight. Then it would crouch flat to the leaf, twisting 

 the abdomen about with a rotary motion, at times leaning far over 

 to one side and often moving backward, slowly turning about in a 

 complete circle. At one time the insect turned completely over and 

 lay on its back for a short space, the abdomen continuously moving 

 as described. At the end of a half hour the ovipositor was slightly 

 exserted from a point very near the tip of the abdomen, which was 

 then arched and its tip brought into contact with the leaf surface. 

 The ovipositor was then inserted in the leaf in a single movement 

 from an almost vertical position to about two-thirds its length. The 

 insect then relaxed slightly and remained quiet in this position for 

 four minutes, when it moved away and rested. Only one egg was 

 deposited. 



PORTION OF PLANT SELECTED FOB OVIPOSITION. 



The citrus thrips oviposits only in those tender tissues which are 

 suitable for food, i. e., the new growth and the young fruit. Eggs 

 are deposited largely in the leaves and fruit in summer and in the 

 stems in fall, more particularly the large tender stems of the orange 

 tree. In summer large numbers of eggs are thrust into the new leaves, 

 leaf stems, fruit and fruit stems, and when the petals have fallen the 

 fruit receptacles become a favorite place of oviposition, which is 

 accomplished under the protection of the sepals. Eggs are never 

 deposited in the blossoms. 



RELATION OF QUALITY AND AMOUNT OF FOOD TO OVIPOSITION. 



Eggs are never deposited in the older leaves and stems and but 

 rarely in the fruit after it is two-thirds grown. The number of eggs 

 deposited in a particular tree will depend exclusively upon the 

 amount of new growth produced by that tree. It is impossible to 

 induce the insects to oviposit in the tough leaves of potted orange 

 trees, though hundreds have been confined upon such plants for many 

 days. Eggs were deposited readily in the same kind of plants when 

 one or more new leaves occurred there, even though only 20 to 25 

 insects were confined through one night only. 



Oviposition does not occur in the minor food plants (including the 

 Valencia orange, pomelo, lemon, pepper tree, Chinese umbrella tree, 

 and grape), regardless of growth, in as great proportion to the 

 number of infesting insects as in the Washington and Thompson's 

 navel oranges. 



KATE OF OVIPOSITION AND NUMBER OF EGGS DEPOSITED. 



The preoviposition period in midsummer, when metabolism is 

 rapid, is three or four days. The highest average daily rate of egg 



