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Volume 28, Number 2
171
months thereafter. Some wrinkling of the skin had occurred in the freezer, but the colors were excellent, including tubercles. The fact that the kitchen freezer used was self-defrosting apparently answers the question of where the moisture went. It seems that had a well-ventilated box been used, the same results could have been achieved in several months instead of two years.
Richard S. Peigler, 303 Shannon Drive, Greenville, South Carolina 29607.
FREEZE-DRYING AND VACUUM DEHYDRATION: INSTRUMENTATION
Some time ago I reported on the process of freeze-drying and vacuum dehydration for the preservation of immatures (Dominick 1972, J. Lepid. Soc. 26: 69-79). Since then, experience has led to some modification of procedure and equipment. These recommendations form the substance of this article. It is assumed that the reader has before him the previous report (of which a few reprints are still available), for this article will proceed point by point on that basis.
The pump oil should be changed regularly, otherwise the efficiency of the pump may be seriously impaired. An oil change is recommended after every 20 hrs. of operation, so a disconnect coupling (an "O" type ring) is desirable. Such disconnect couplings will also be found useful for anyone desiring to construct a mobile field unit.
The inside diameter of the tubing is of no great consequence in the system described. However, % in. tubing is recommended over ^4 in., for two minor reasons: first, a slightly more efficient pull-down time will result, and second, the larger diameter is a bit easier for the amateur to flare or solder.
Next, it is advantageous to lower the temperature of the freezer below the -7° C (20° F) previously recommended, since opening the freezer door can quite easily raise the temperature to above freezing. By removing the taped end of the thermostat from the ice-making compartment and gently bending it out of the way into the rear of the larger compartment, the temperature of the whole unit may be lowered to between -12 to -15° C (10 to 5° F), while the ice-making compartment goes down to about -24° C (-15° F). The resulting increase in drying time is not sufficient to be of practical concern. This lower temperature, in fact, is theoretically more suitable for the preservation of integrity of the cells.
Previously the suggestion was made that Duco or similar cement would help preserve the integrity of the permanent joints. The suggestion is erroneous, for proper flaring alone guarantees the adequacy of sealing. If the flare (or soldering) is not properly made, no amount of posthumous treatment will help.
As for killing the animal, I have largely abandoned the method of very quick deep freezing, which often agitates the larva so much that presentation of a lifelike attitude becomes difficult. It also influences the cellular integrity by destructive crystal formation. Slow freezing in the main compartment in general seems best. In case an undesirable attitude prevails, correction should be made as soon as possible, before the larva is frozen through. Try to avoid thawing a frozen specimen, for this has undesirable effects on some of the color pigments. Try to manipulate the larva when it is just cold enough to be dormant, but before cellular freezing. Frank R. Hedges, Houston, Texas, suggests that contact with the ambient air after any degree of freezing might change some of the chemically activated color pigments, and my own experience tends to bear this out. In such a case the larva may be put straight away into a cold desiccator and left to freeze to death, applying vacuum only when thoroughly frozen. One may have to sacrifice a lifelike posture in favor of coloration. More experimentation is needed. Other methods of killing are
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Journal of the Lepidopterists' Society
satisfactory, for example, cyanide or boiling water. With regard to ethyl acetate and other organic solvents, one must consider the possibility of solubilizing effects on certain plastics used in the apparatus. Properly processed larvae tend in general to retain their color well, with the exception, in my limited experience, of some greens and a few reds.
Concerning the equipment, first there are the desiccators. I now use exclusively the Nalgene vacuum chamber with neoprene gasket. It is made of transparent polycarbonate and may be ordered with gasket and plastic top. It stands about 25 cm high, and the recommended freezer holds two with ease. A further blessing is that they need not (in fact must not) be greased. If one is careful to keep the contact surfaces free of dust, dirt and ice crystals, these desiccators will hold the vacuum very well. A further advantage is that the plastic will not break and splinter to the dangerous proportion of a glass vessel in case of an implosion.
As for pumps, valves and manometers as well as all the fittings, I have recently been in touch with a company whose catalogue offers such equipment of commendable quality at good prices. For example, I have been told by two refrigeration experts that the pump I now use is rated at a vacuum of 0.1 micron, but will not pull down in practice to better than 25 microns/Hg, which is still adequate for the purpose. To understand the need for a high vacuum efficiency in the process, one must realize that 1 micron equals approximately 1/25,400 in. Hg, and remember that any pressure above 1-200 microns in the system renders the vacuum operation meaningless.
Some companies also supply high vacuum line valves, copper tubing, "O" type disconnect fittings, and for the permanent joints, a method of soldering requiring only the heat from a small propane torch. Such a method of fixing the permanent joints, of course, eliminates the task of flaring, a job extremely difficult to accomplish successfully where there are numerous joints in close proximity to one another.
Practical suggestions as to specific companies have been published recently in the News.
My warm thanks to Dr. Hermann A. Flaschka, who has taken time to edit and correct the original manuscript with humor as well as detail, and to Dr. Theodore D. Sargent, who has performed further needed surgery.
Richard B. Dominick, The Charleston Museum, Charleston, South Carolina 29401.
THE DISTRIBUTION AND LARVAL FOODPLANT RELATIONSHIPS OF SATURNIA WALTERORUM (SATURNIIDAE)
Saturnia walterorum Hogue & Johnson is perhaps the rarest saturniid in the United States, occurring locally in southern California. There are relatively few field data available for this moth. Fewer than 30 specimens have been collected and most specimens in collections have been reared from eggs secured from captured females. Sala & Hogue (1958, Lepid. News 12: 17-25) described the life history of S. walterorum reared under laboratory conditions. It is the purpose of this paper to present new information on flight period, distribution, and larval host records. A future publication will examine the taxonomic relationship between S. walterorum and S. mendocino Behrens.
Saturnia walterorum is known only from 4 coastal counties in southern California: San Luis Obispo, Los Angeles, Orange, and San Diego. One specimen in the Los Angeles County Museum of Natural History is labeled "Cajon Valley." This label may refer either to El Cajon Valley in San Diego County or Cajon Pass in San Bernardino County. Suitable habitats seem to exist in at least 4 additional