22 American Midland Naturalist Monograph No. 3 



use for the different-sized larvae. Small bubbles usually work out and do 

 not spoil the mount. The finished slide should be kept in a horizontal posi- 

 tion until the medium has hardened; then it may be sealed with ringing 

 cement to prevent further evaporation. 



Euparal is a very good alcohol-soluble mounting medium. Before mount- 

 ing, the larva should be dehydrated by running it up through an alcohol 

 series; 80 per cent, 95 per cent and absolute alcohol are all the graduations 

 necessary. Allow the larva to stand about 5 minutes in each change. Cello- 

 solve (ethylene glycol mono-ethyl ether) may be substituted for the 95 per 

 cent and absolute alcohols. Place some Euparal on a clean slide, orient larva, 

 and apply cover slip as described under the chloral gum mounting method. 

 The drying is fairly rapid and no ringing is necessary. This method has an 

 advantage over balsam in that there is no intermediate clearing step between 

 the alcohol and mounting medium. 



Canada balsam is a common mounting medium which, if properly used, 

 makes excellent, permanent mounts of mosquito larvae. For mounting in 

 balsam, dehydrate the specimen by running it up through an alcohol series 

 as described for the Euparal mounting method. Clear in creosote U. S. P., 

 clove oil, oil of wintergreen, xylene or toluene. Before xylene or toluene is 

 used for clearing, an additional 5-minute step in absolute alcohol is necessary 

 to insure complete dehydration. Specimens cleared in creosote, clove oil, or oil 

 of wintergreen remain more pliable and undergo less shrinkage than those 

 cleared in xylene or toluene. Leave the specimen in the clearing agent until 

 it becomes transluscent; 5 to 10 minutes is generally sufficient. Place some 

 Canada balsam on a clean slide, orient specimen and apply cover slip as 

 described under the chloral gum mounting method. Allow to dry in a hori- 

 zontal position for about 2 weeks. No ringing is necessary. 



A creosote-balsam medium for mounting mosquito larvae is described 

 by Wanamaker (185) and is used extensively by the authors. The pro- 

 cedure is briefly summarized as follows: Prepare the medium by gently 

 heating Canada balsam at about 120-130° F. until most of the solvent is 

 driven off. Dilute this thick balsam to the proper mounting consistency 

 with creosote U. S. P. The larva should be left in 80 per cent and 95 per 

 cent alcohols for 5 minutes each, then in absolute alcohol ior 1 to 2 m-nutes, 

 depending upon the size of the specimen. It is then transferred directly to 

 the creosote-balsam mixture on a clean slide and cover slip applied. Clearing 

 takes place as the medium hardens. No ringing is necessary, but the slides 

 should be left horizontal for 3 or 4 weeks since the creosote-balsam medium 

 dries rather slowly. 



A clearing and mounting medium composed of polyvinyl alcohol (Elva- 

 nol 90A-25), phenol and lactic acid is excellent for mounting mosquito larvae. 

 The PVA-lacto-phenol medium contains 56 per cent PVA (stock solution), 

 22 per cent phenol, and 22 per cent lactic acid by volume. The PVA stock 

 solution is prepared by adding PVA (Elvanol) slowly to cold water, stirring it 

 in thoroughly until the solution becomes as viscous as cold molasses. Any 

 undissolved lumps should be removed by straining. The larval specimen is 



