THYSANOPTERA AND ORTHOPTERA. 181 



in vain over thirty times in as many different localities, until a single 

 specimen of Euthrips tritici was taken on it. 



METHODS OF COLLECTING AND PRESERVING SPECIMENS. 



There are two ways of collecting thrips. (1) One can go into the 

 field armed with paper bags and other light receptacles, gather flowers, 

 leaves, etc., promiscuously, and examine them at leisure at home or 

 in the laboratory. (2) Mais of the killing fluid may be carried on field 

 trips and the insects placed directly in them. In the latter case it is 

 necessary to take specimens of only such plants as rec^uire identifica- 

 tion. The former method has the advantage of rapidity and of re- 

 quiring the minimum of time in the field. Its disadvantages are that 

 rare material is likely to be lost or overlooked in the bags, and that one 

 can never be sure just what part of the plant bore the thrips in the 

 field. It is more imjiortant in many cases, I believe, for reasons which 

 are explained under the heading of Ecology, to know the nature of the 

 part of the plant inhabited by thrips than to know the species of 

 plant. I have therefore rejected the method of collecting in bags, ex- 

 cept when material was abundant, and then only after carefully noting 

 the exact location of the thrips on the plant. 



Specimens intended for immediate mounting were put directly into 

 xylol, as Hinds (1902, p. 85) recommends. They adhered very readliy 

 to a camel's-hair brush moistened with xylol, and came off as soon as 

 they were dipped into the vial. After remaining in this for from one 

 to several hours, they were mounted in balsam on slides. If left in 

 xylol for a longer time, they tended to become brittle, and antennae 

 were frequently broken between the second and third segments. The 

 A\-ings were usually spread by shifting the cover glass slightly after it 

 had settled on the insect. A twisting motion accomphshed this more 

 readily than a direct lateral shift, and thick Isalsam was found bet- 

 ter than thin. If the covers were moved gently, no serious injury- 

 was done; such injur}' as was done was usually due to brittleness 

 caused by remaining too long in xylol, and would not have been 

 avoided by adjusting the wings with fine bristles before applying the 

 cover. In point of time required, at least, the method of shifting the 

 cover glass has much in its favor, and this is no small item to the 

 field worker. Known species can usually be identified without expos- 

 ing the entire ^ying. If it was found that specimens thus mounted 

 could not be determined with certainty, or that they were undescribed 

 species not fully exposed to view, they were dissolved from the slide 

 with xylol and remounted more carefully. 



In some cases, species were taken in series too extensive to be mounted 

 on slides. These were plunged into a killing fluid in the hope of pre- 



