1 1 



sure on the cover glass will flatten them out to their natural form. 



Pupae may be mounted in xylol balsam by dehydrating them in 

 xylol for a few hours or a day. 



With adults the best results are obtained by a somewhat longer 

 process of dehydration. They may be killed in hot water or in a 

 cyanide bottle. They are then placed in thirty-five per cent alcohol, 

 a few drops of ether on the surface of which will dissolve the wax 

 from the wings and bodies of the insects and allow them to sink. 

 After an hour the specimens are run successively through the follow- 

 ing : Fifty, seventy, eighty, ninety, ninety-five and absolute alcohol ; 

 then an equal mixture of absolute alcohol and xylol ; and finally, 

 pure xylol, leaving them at least an hour in each. 



The alcohol and xylol should be kept in small vials, tightly 

 stoppered and correctly labelled. The specimens may be removed 

 from one vial to another by means of a pipette or dropper and a 

 toothpick, the latter acting as intermediary ; the specimens being de- 

 posited on the end of the toothpick and then placed in the next vial 

 in the series. This allows the transference of the specimens with a 

 minimum amount of the lower percentage alcohol being transferred 

 at the same time to the higher. An equally satisfactory, and per- 

 haps less troublesome, method is to keep the specimens in the same 

 vial and to replace the dehydrating media, successively returning 

 each in due time to its stock vial. 



For the study of the tracheal system, specimens of the imma- 

 ture stages may be mounted in xylol by the ordinary method, except 

 that they should not be left more than five minutes dehydrating in 

 xylol. If a large number of specimens are mounted, some of them 

 will almost invariably show the main branches of the tracheal system 

 as conspicuous dark lines, owing to the presence of air in them. 



For the study of the life history, leaves of plants with eggs or 

 young attached, may be kept for two or three weeks in tightly stop- 

 pered bottles containing a little wet cotton. If moisture collects on 

 the sides of the bottle, the cork should be removed for a short time 

 each day, otherwise the leaves will soon turn dark and decay. 



In determining the results of treatment with insecticides, posi- 

 tive conclusions within a few days after the treatment is applied, as 

 to whether or not the young insects are alive, are difficult to obtain. 

 When placed upon their backs, the live larvae and pupae usually 



