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Card mounting specimens

Card mounting specimens

Several methods have been used in the past for mounting specimens dry. These include mounting

  1. on a micro-pin and staging,
  2. flat on clear acetate rectangles,
  3. directly onto the side of a pin, and
  4. on card triangles or rectangles.

Only the last two are dealt with here because the other methods are considered to be totally unsatisfactory.

The following equipment is necessary before proceeding.

A good quality sable paint brush, 000 grade. Push a size 0, nylon-headed continental pin into the handle end of the brush until about 15 mm is showing and pull or squeeze off the nylon head with a pair of forceps. Do not cut off the end with a pair of wire cutters because this will result in the end being pointed rather than flat.

Card triangles or rectangles manufactured from good archival-quality card, preferably 4-ply (Schoellershammer "450 glatt" or 495 g/m2). Thinner, 2-ply card should be avoided because the card will ultimately become loose on the pin and begin to swivel. Card triangles about 10 mm long with a base about 3-3.5mm wide or card rectangles about 14 x 5 mm are ideal.

  • A pinning stage.
  • Pins: preferably No. 5 continental size.
  • A pair of fine, watchmaker's forceps.
  • A fine pin mounted in a good needle holder or matchstick.
  • Adhesive: either water-soluble glue or shellac (soluble in 95% alcohol).

It is important that if water-soluble glue is used then it must be water soluble after it has been dry for several months. Many apparently water-soluble glues become insoluble in water after drying or leave a white residue on the specimen. The latter is particularly the case with plant gums. The best glues are made from animal products. It is usually necessary to have available an array of water-soluble glues of different consistency. Glue can be kept in 50 x 12 mm glass tubes with polythene stoppers to prevent the consistency of the glue changing too rapidly when it is being used. Higher humidity and larger specimens require relatively thicker glue; in the same way lower humidity and smaller specimens require relatively thinner glue. It is important to judge correctly the consistency required. If the glue is too thin then it will spread over the specimen, not hold it down and later crack badly so that there is a risk of the specimen becoming detached. If it is too thick then it will be dry before the specimen can be properly mounted. In general, the glue should never be thin enough that it flows rapidly from the bottom of an inverted tube. Correct assessment of the glue consistency will come with experience and practice. Shellac has an advantage over glue in that it does not dry as quickly. Although this may make mounting easier, the fact that the specimen is not fixed in place for some time after mounting makes arrangement of antennae, wings and legs more difficult.

Freshly killed specimens can be mounted straight away but other dry specimens must be relaxed prior to mounting to minimise breaking of antennae, legs, etc. (see "Relaxing material"). Those in alcohol can be dried using one of the methods described below (see "Drying specimens from alcohol). Mounting must always be done with the aid of a stereomicroscope and never by naked eye.

Specimens usually remain slightly flexible after critical-point drying, or drying with HMDS, but may be very difficult to mount if the wings are not positioned over the back or the antennae are tucked underneath the body. With care and a lot of practice it is possible to manipulate the antennae, legs or wings provided that this is done with a fine pin placed as close as possible to the base of the appendage. If the wings are folded or if it is necessary to soften a specimen slightly then it can be softened in a single drop of 95% alcohol on a card and dried whilst flattening the wings as described above. The risk of collapse is minimal if this is done fairly quickly .

It is often the case that chalcids die with the wings in such a position that mounting them without covering the wings in glue becomes very difficult indeed. This is particularly true of specimens that die with the wings held in front of the body. To overcome this, place the specimen on its back and gently hold in position with a pair of forceps. Push the forewing back at its base with a fine pin, at the same time twisting the wing slightly so that its ventral surface faces forwards. With luck and a little practice the wing should stay in this position until the specimen in mounted; it can be then manoeuvred into the desired position.

Mounting on card points. This is easiest if the end of the card point to be used is bent slightly upwards near its apex. The point can then be laid flat on the stage of a stereomicroscope with its apex clear of the stage.

Method:
Touch a small amount of adhesive onto the apex of the point with the end of the pin in the handle of the paint brush.

Quickly turn the brush around and slightly moisten the very tip of the brush with a minute amount of saliva.

Pick up the specimen by touching the point of the brush against the left mesopleuron and attach it by means of the right mesopleuron to the glue on the card point. Position the specimen horizontally with the lower and upper parts of the body freely exposed.
If the glue is of the correct consistency and the whole operation is done rapidly, then the specimen should now be attached firmly to the card point via the mesopleuron.

Gently press the specimen onto the adhesive with the brush.

Arrange the antennae and fore wings so that segmentation and proportions of the segments of antennae and venation and distribution of setae on the fore wings can be seen clearly.
If the correct amount of saliva was put onto the tip of the paint brush for step (3) then it should be dry enough, at this pint, for the tip to be used for arranging the wings and antennae without any risk of covering them with saliva. Specimens which may be slide mounted subsequently must have the wings completely free of adhesive.

The fore wings may present some difficulty in that they are often folded flat over the back of the specimen. It will be necessary then to manipulate the wing by pushing a fine pin beneath it right at its base and levering the wing outwards away from the body. If the specimen has been killed using ethyl acetate and subsequently relaxed an acetic acid atmosphere the wings will probably stay in place, but if it has been mounted from alcohol or has been killed in some other manner it may be necessary to brace the wings against each other at their anal angles.
Push a pin through the base of the card and position the card at the desired height using the pinning stage.

Add to the pin a data label which records at least locality, host, date of collection, date of emergence of parasitoid and collector's name.

The main disadvantages of mounting on card points are two-fold. Firstly the specimens are not afforded much protection and secondly several important diagnostic characters on the antenna and fore wing are more difficult to see. These can be overcome partly by placing a card rectangle immediately beneath the specimen. It is very important that the rectangle is hard up against the point (except, of course, at its apex where the insect is attached). Even if there is a slight separation there is a danger that if the card is knocked from below it will be pushed upwards thus damaging or dislodging the specimen. It must be noted that mounting on card points may make subsequent preparations of specimens for slide mounting more difficult.

Mounting on card rectangles. In the past chalcidoid workers who have mounted specimens on card rectangles have mounted the specimens flat on the card so that important characters of the face or ventral surface of the body are very difficult to see. These problems can be overcome by mounting the specimen on its side with its axis forming an angle of between 45 and 80º with the surface of the card thus exposing the face, mandibles and most of the venter of the thorax and gaster (Fig. 5, below).

Although rather more difficult to master than mounting on points it affords several distinct advantages:

  1. Specimens have a greater surface area in contact with the card and therefore they can be attached better, eg by the gaster and head if required,
  2. the process of mounting is quicker,
  3. specimens are protected by the card, and
  4. characters of the antenna and forewing are easier to see against a white background.

The process is not described here in full because for the most part it is similar to that described for mounting on card points, except that is even more important that the specimen to be mounted is flexible.

Specimen mounted on card rectangle so that face, mandibles and ventral surfaces of thorax and gaster are exposed.
Fig. 5 Specimen mounted on card rectangle so that face, mandibles and ventral surfaces of thorax and gaster are exposed.

Method:
Put a drop of adhesive, about half to two-thirds the volume of the thorax of the specimen to be mounted, at the point where imaginary lines bisecting the top corners of the card intersect.
Place the specimen on the adhesive by means of the lower part of the mesopleuron so that its body is tilted at an angle of between 45 and 80º to the card. It should be positioned on its right side, lengthways along the card with its head towards the far end.

Arrange the antennae and wings as outlined above. If the specimen is destined for a slide preparation then ensure that the antennae, head and wigs are free of adhesive.
Push a pin through the opposite end of the card and mount at the desired height.

Assessing quality card-mounted specimens

The following scoring system can be used to self-assess how well you are mounting chalcidoids on cards. Note that some scores get negative points: mounting specimen on its back, mounting specimen with wings folded under the body, covering the wings or antennae with glue. Although scores of 5 or 6 may be acceptable for identification purposes, specimens mounted to this standard would often fall short of the requirements for research. A score of 8-10 should be the target, and although a perfect score of 10 is desirable it is certainly not possible to achieve this with every specimen.


Scores for self-assessing quality of card-mounted specimens

State
Score
Specimen well attached by glue (at least by mesopleuron)
1
Rectangle mount

Specimen axis 30-45° to card (including head)

1

Specimen axis 0-29° or 46-90° to card

0.5
Point mount

Specimen either with scutum or mesopleuron uppermost

1

Specimen on back

-5

Pair of wings free of glue and saliva, flat with venation and setation clearly visible (score for each side: max. 2 points if both pairs thus and propodeum clearly visible dorsally)

1
Pair of wings under body
-1
Antennae free of glue, intact and well displayed with all segments clearly visible (score per antenna - maximum 2 points if both antennae thus)
1
Both pairs of wings glued or folded
-5
Both pairs of antennae embedded in glue of otherwise obscured
-5
Legs well displayed and not obscuring side of thorax
1
Hypopygium and ovipositor clearly visible
1
Mouth and face free of glue
1
Dorsum of head and thorax and setae free of glue and undamaged
1
Maximum score
10

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Last updated 07-Jun-2004 Dr B R Pitkin