species identification
I would like to express my gratitude to Prof. Dr. Horst Aspoeck and Zdravko Kolev for their kindness to dedicate me into their vast experience on this topic.
In order to view a specimen's genitalia to detail the entomologist needs a binocular stereomicroscope with a maximum magnification of at least 40 x. (for larger species)
The morphology of the genitalia of some very hard to determine insects species is used as a relatively constant and reliable character for species identification (especially in male specimens). However, observing the dried specimen through a stereomicroscope does not reveal enough of the mostly concealed morphology of the genital apparatus.
As to make the genitalia visible, the abdomen of the insect, where these organs are situated, needs to be made transparent. This is achieved by cutting off the abdomen from the specimen and treating it with low concentrated KOH (potassium hydroxide). There are two possibilities: to dip the test tube with the abdomen and KOH into boiling water for 5-7 minutes, or to leave the test tube over night and proceed on the next day. KOH decomposes the soft tissues from the abdomen and leaves out only the highly resistant chitin. The advantage of this method is that the genitalia contain structures which are very strongly chitinized compared to other structures in the abdomen. That makes the genital apparatus perfectly visible under the stereomicroscope. After KOH treatment the abdomen is placed in (not necessarily) distilled water.
Further, a preparation of the genitalia (through removal of all other remaining structures) in 70% alcohol under the microscope can be performed, especially if drawing is intended. After that the genitalia can be glued to a mounting card after draining on filter paper and dried (this method is suitable for butterflies).
Otherwise the observation of the genitalia is carried out in glycerine. Glycerine has a very high viscosity and allows the specimen to be manipulated and viewed easily under the microscope from all aspects.
Glycerine is also a perfect storage medium, for the unlimited repetitive investigation of the specimen is possible. Small containers are available, which can be pinned through the plug and attached to the investigated mounted insect. Otherwise the test tubes with the genitalia should be strictly labelled (locality an date) and assigned to the dried insect specimen.
The identification of typical species characters is carried out by means of specialized literature.
