10 A carology 



used in the past and can be found in the hterature. Recently a new 

 method has been evolved that is satisfactory for many mites. The 

 directions for preparing and using polyvinyl alcohol (PVA) mounting 

 medium follow: 



1. Dissolve "Elvanol" 71-24 (Du Pont polyvinyl alcohol) in four vol- 



umes of water by stirring at about 90 C. 



2. Filter the solution until it is no longer murky. 



3. Concentrate the clear filtrate on a water bath until it has the viscosity 

 of Karo syrup. (A scum will form on the surface during the process 

 of evaporation but will redissolve when stirred into the solution.) 



4. Add 22 parts of lactic acid to 56 parts of the PVA concentrate to 

 make the finished mounting medium. 



5. Use like any mountant. Materials may be mounted directly from life, 

 any aqueous solution, or alcohol. 



The large amount of shrinkage of PVA causes it to shrivel the soft- 

 bodied mites (Tetranychidae) and to crush some of the larger, brittle 

 ones (Oribatei). The solution should be used with discretion. 



In most cases, however, other methods are more useful. Temporary 

 mounts may be made in any clearing agent such as glycerin, mineral 

 oil, phenol, lactic acid, etc. Satisfactory permanent mounts can be 

 made with aqueous solutions of gum arable, chloral hydrate, and 

 glycerin. One of the best of the modified Berlese solutions is Hoyer's. 

 At the United States National Museum specimens have been preserved 

 in this for twenty years without deteriorating. It is an excellent medium 

 for the Tetranychidae which are one of the more difficult groups to 

 mount. The formula is: 



50 grams distilled water 



30 grams gum arable (clear crystals) 



200 grams chloral hydrate 



20 grams glycerin 



The ingredients should be mixed at room temperature in the above 

 sequence. In the more humid areas, such as the Gulf States, the cover 

 glass should be ringed to prevent absorption of moisture. Other ex- 

 cellent Berlese mixtures are published but as yet the perfect mounting 

 medium has not been found. 



Workers at the University of California have developed a metho- 

 cellulose formula which has proved to be excellent for many mites. 

 Their formula is: 



