Directions for Collecting and Preserving Insects

by Charles V. Riley

Fig. 111.—Slide case, showing method of labeling case and of numbering and labeling slides (original).

In the mounting of Aphides the same difficulty is avoided in a measure by Mr. G. B. Buckton, author of “A Monograph of the British Aphides,” by first placing a few dots of balsam on the glass slide, to which the insect is transferred by means of a moistened camel's-hair brush. The efforts of the insect to escape will cause it to spread out its legs in a natural position and a cover glass may then be placed in position and a drop of the balsam placed at the side, when, by capillarity, it will fill the space between the slide and cover glass and the limbs will be found to have remained extended. If three or four drops of the balsam are put on the glass the wings may also be brought down and caught to them so that they will remain expanded in shape for examination.

[Preparing and Mounting the Wings of Lepidoptera.]—The student of Lepidoptera will frequently find it necessary in the study of the venation of wings to bleach them or denude them of their scales in some way. Various methods of bleaching and mounting the wings of these insects have been given, and a few of them may be briefly outlined.

The simplest and quickest, but perhaps the least satisfactory, method is to remove the scales with a camel's-hair brush. This will answer for the larger forms and where a very careful examination is not required. For more careful examination and study the wings are first bleached by the action of some caustic solution and then mounted in balsam for permanent preservation. Chambers's method for Tineina, Tortricina, Pyralidina, and the smaller moths generally, is as follows: The wing is placed on a microscopic slide in from 3 to 4 drops of a strong solution of potash, the amount varying according to the size of the wing. A cover of glass is then placed in position on the wing as in ordinary mounting.

The quantity of liquid should be sufficient to fill the space beneath, but not sufficient to float the cover glass. The mount is then placed over an alcohol flame, removing it at the first sign of ebullition, when the wing will be found denuded, if it be a fresh specimen. An old specimen, or a larger wing, will require somewhat more prolonged boiling. The fluid is drawn off by tilting the glass or with bibulous paper, and the potash removed by washing with a few drops of water. The cover glass is then removed and the wing mounted either on the same slide in balsam or floated to another slide, or at once accurately sketched with the camera lucida. Permanent mounting, however, is always to be recommended.

The Dimmock method of bleaching the wings of Lepidoptera, given in Psyche, Vol. i, pp. 97–99, is as follows: He uses for bleaching a modification of the chlorine bleaching process commonly employed in cotton bleacheries, the material for which is sold by druggists as chlorate of lime. The wings are first soaked in pure alcohol to dissolve out the oily matter, which will act as a repellant to the aqueous chlorine solution. The chlorate of lime is dissolved in 10 parts of water and filtered. The wings are transferred to a small quantity of this solution and in an hour or two are thoroughly bleached, the veins, however, retaining a light brown color. If the bleaching does not commence readily in the chlorine solution the action may be hastened by previously dipping them in dilute hydrochloric acid. When sufficiently decolorized the wings should be washed in dilute hydrochloric acid to remove the deposit of calcic carbonate, which forms by the union of the calcic hydrate solution with the carbonic dioxide of the air. The wings are then thoroughly washed in pure water and may be gummed to cards or mounted on glass slides in Canada balsam, first washing them in alcohol and chloroform to remove the moisture. If either of the solutions known as eau de labaraque and eau de javelle are used in place of the bleaching powder, no deposit is left on the wings and the washing with acid is obviated. This process does not dissolve or remove the scales, but merely renders them transparent, so that they do not interfere with the study of the venation.

Prof. C. H. Fernald (American Monthly Microscopical Journal, i, p. 172, 1880), mounts the wings of Lepidoptera in glycerin, after having first cleared them by the Dimmock process. After bleaching and washing, the wings are dried by holding the slides over an alcohol flame, and a drop of glycerin is then applied and a cover glass put on at once. By holding the slide again over the flame until ebullition takes place the glycerin will replace the air under the wings and no injury to the structure of the wings will result, even if, in refractory cases, the wing is boiled for some little time. The mount in this method must be sealed with some microscopic cement, as asphalt or Brunswick black.

A method of mounting wings of small Lepidoptera for studying venation, which I have found very convenient, is thus described by Mr. Howard in Insect Life, Vol. i, p. 151:

“Some years ago we used the following method for studying the venation of the wings of small Lepidoptera. We have told it since to many friends, but believe it has not been published. It is in some respects preferable to the so-called ‘Dimmock process,’ and particularly as a time-saver. It is also in this respect preferable to denudation with a brush. The wing is removed and mounted upon a slide in Canada balsam, which should be preferably rather thick. The slide is then held over the flame of an alcohol lamp until the balsam spreads well over the wing. Just as it is about to enter the veins, however, the slide is placed upon ice, or, if in the winter time, outside the window for a few moments. This thickens the balsam immediately and prevents it from entering the veins, which remain permanently filled with air and appear black with transmitted light. With a little practice one soon becomes expert enough to remove the slide and cool it at just the right time, when the scales will have been rendered nearly transparent by the balsam, while the veins remain filled with air. We have done this satisfactorily not only with Tortricidæ and Tineidæ, but with Noctuids of the size of Aletia and Leucania. The mounts are permanent, and we have some which have remained unchanged since 1880. Prof. Riley had for some years before this been in the habit of mounting wings in balsam, in which of course the scales cleared after a time.”

Prof. John B. Smith recommends a modification of the Dimmock process of bleaching the wings of Lepidoptera, publishing it in Insect Life, Vol. i, pp. 291, 292, as follows: