10 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 
Permanent slide mounts of the larvae (or of male genitalia) are 
conveniently made with Berlese’s chloral-gum solution or one of its 
modifications. A formula used by the writers is as follows: 
Gum arabic (clear lumps or powdered)__________--__ grams__ 8 
DISEER Hwatenesi ee Bre re ee ee om rd see milliliters__ 8 
Gy COr ty es cs 5c Re pe Ng pee milliliters__ 5 
Ghioral> hy Grace: 25226 ie eee ee eee eee grams__ 70 
Glacial acetic 1ciG ==. eee Cea ee Op eae milliliters__ 3 
The gum arabic is dissolved in the water, and the other ingredients 
are added in the order given. The thick solution is strained thr ough 
clean muslin and is then usually sufficiently cleared. Powdered gum 
arabic (or gum acacia) appears to give as good results as the lump 
gum and is more easily dissolved. Gater’s (58) modification of 
Berlese’s formula, which has been used extensively, contains 5 ml. of 
glucose sirup instead of glycerin, 10 ml. of distilled water, and 74 gm. 
of chloral hydrate. The glucose sirup is prepared with equal parts 
of glucose and water. In cold weather, however, white crystals may 
form in fresh preparations that contain glucose; therefore, honey 
appears to be preferable for use in this formula. Larvae may be 
mounted in chloral-gum medium direct from water or from a preserva- 
tive after rinsing in water. Several weeks are required for the mounts 
to harden, but the process may be hastened by placing them in a warm 
incubator. The cover glasses may be sealed by ringing with cellulose 
cement. 
Suitable balsam mounts of entire larvae require somewhat pro- 
longed dehydration and hardening in alcohol. Good mounts can 
be obtained in Euparal after dehydration in Cellosolve. 
For taxonomic study or for identification of species difficult to 
determine, it is frequently desirable to have both the larval skin 
and the adult of the same individual. For such rearings a nearly 
mature larva is isolated in a separate dish, and when pupation occurs 
the larval skin is removed with a pipette, spread out carefully on a 
slide, and a mount prepared in the chloral-gum medium. The dish 
or vial containing the pupa should be covered with cloth or a larger 
dish or plugged with cotton, and after the adult emerges sufficient 
time (about 24 hours) should be allowed for the sclerotin to become 
thoroughly hardened, before it is killed. The specimen is then 
placed in the collection with a number corresponding to that given 
the larval skin. If a balsam mount of the larval skin is desired, the 
specimen may be cleared on the slide with carbol-xylol or other 
medium. 
Adult mosquitoes are usually collected while they are biting or 
resting in secluded corners inside or underneath buildings, in tree 
holes, ete. A chloroform killing tube (fig. 5) is convenient for this 
purpose. It may be prepared by placing a half-inch layer of cut 
rubber bands in the bottom of a large shell vial or test tube, saturat- 
ing the rubber with chloroform, and ¢ covering with a plug of crumpled 
paper and a circle of stiff paper. The writers prefer a shell vial seven- 
eighths of an inch in diameter and about 5 inches long. When the 
tubes are kept tightly corked, the rubber retains the chloroform for 
some time. As moisture is lable to condense on the inside of the 
tubes, the dead mosquitoes should not be left in them long. Cyanide 
may also be used in the killing tubes, but it has a slower killing action 
and should be handled with extreme caution since it is a deadly poison 
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