Genital examination (entomology)

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The genital examination or genital preparation is a technique with which the identification of the species of insects is facilitated and sometimes even made possible.

Basic problem

Image 1: male reproductive organ of Helophorus aquaticus with penis and parameters
Image 2: Prehensor of the female of Cyphon coarctatus left empty pocket, right plate, which is located in the pocket, dissected out

Living beings that can produce reproductive offspring with each other are summarized as a species . As a rule, different types also look different. However, there are also often species that are difficult or impossible to separate based on their external appearance. For example, the geographical location or the biotope in which an insect was found have long been used to determine the species.

Idea of ​​genital examination

Since fertilization takes place via the sexual organs, it follows logically that the sexual organs of the male and female of a species must fit together. Insects have an exoskeleton made of dimensionally stable chitin parts . The sexual organs are also made up of largely dimensionally stable parts made of chitin. According to the lock / key principle, a certain form of a male sex organ must define almost all female individuals whose sex organ the male fits.

It has been shown that the genitals of different species, especially in males, often differ far more from one another than the totality of the external characteristics. The introduction of technology has led to a surge in the number of species described.

Limits of the genital examination

There are several restrictions. On the one hand, practice shows that it is mainly the male genitals that are suitable for an examination. It is true that the laying apparatus of the females is occasionally used to determine the species, but often female animals can still not be reliably assigned to a species.

Another difficulty is that the sex organs are usually hidden inside the body and therefore have to be dissected out first. This is only possible on the dead animal. In addition, the sexual organs are of course relatively small and therefore require better optical equipment for viewing them and a certain degree of manual dexterity for the preparation.

In addition, like all characteristics of a species, the genitals are also subject to a certain variance. Moreover, in some species the structure of the penis is extremely constant, in other species it varies considerably. At least in the introductory phase, if the variance is not yet known, the method intended for more reliable species identification can lead to incorrect determinations.

After all, it has now been established that the lock / key principle does not apply consistently. The structure of the genital organs allows copulation between different species in some cases.

Comments on individual groups of insects

Beetle

In male beetles , the aedeagus (aedoeagus) is examined , the term usually being restricted to the chitinized parts of this organ. These consist of the penis and the paired parameters that are more or less firmly attached to the penis. The female genital organs are usually membranous, but there are exceptions. For example, in the genus Cyphon, the organ that ingests the male's spermatophore (the prehensor) contains chitinized parts. The prehensor of Cyphus coarctatus is shown as an example . It forms a pocket that is reminiscent of the closure of a safety pin (Fig. 2 left). In this there is a plate roughened with teeth (Fig. 2 right).

Performing the genital preparation

For genital preparation, the joint membranes must be flexible. In the case of killed animals, this depends on the means of killing and the time that has passed after killing. If the animal is already dry, appropriate measures must be taken to restore the mobility of the joint membranes.

In the best case, you can cause the genital organ to exit by stroking or pressing in the direction of the tip of the abdomen. Another possibility is to pull out the sex organ by inserting a needle with a hook. There are also swelling agents that cause the sex organ to emerge. Of course, you can also open the abdomen and thus get to the genital organs.

The excised organ should be stored with the insect in such a way that it is also available for later examinations.

swell