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Genitals in science

Exciting geometrid moths…

B. Sc. Dominic Wanke is a master student in the Department of Entomology at the State Museum of Natural History in Stuttgart. For his master thesis he is working on moths of the genus Triphosa.

“I prepare the genitals of geometrids”.In such a manner I respond with a wink to the question of what I am actually workingon during my master’s thesis…

Thereby concealing that the preparation of genitals is only one part of a diverse taxonomic investigation. In fact, I am working with moths (Lepidoptera), more specifically with one of the most species-rich families within this order: the geometrid moths (Geometridae). Within this family more than 21,000 species are known worldwide and many of them are important pests in forestry and agriculture. The name “geometrids” refers to the locomotion of their caterpillars, which move by stretching and contracting their bodies. This is due to their reduced or lacking abdominal legs.

My master thesis focuses on a revision of the genus Triphosa in the Middle East and Central Asia. This is necessary because information on species and their distribution in this region is either absent or confused. One reason for thisis the inconspicuous appearance of these moths.

Fig. 1: Habitus of two European Triphosa species: Triphosa sabaudiata (A) und Triphosa tauteli (B). Specimens of this genus are difficult to determine through color and wing pattern alone. (D. Wanke)

About working with moth genitalia…

So how can such inconspicuous and similar species be distinguished? The answer can be found in the genitalia structures. Males and females of the same species should be able to copulate and produce fertile offspring. In many insects the sexual organs of both sexes engage in a lock-and-key mechanism. The male genitals in particular are often complexly-built and show species-specific characters, which must be examined and described so that they can be used for the identification of species. In butterflies and moths, this process resemblesa small ritual consisting of several steps:

• maceration

• dissection

• staining

• slide-mounting

In the first step, the whole abdomen is carefully removed by upward pressure and boiled in potassium hydroxide. During this process, called maceration, fat and muscle tissues are separated from the sclerotized (hardened) parts of the abdomen and genitalia structures. The abdomen is opened laterally with micro scissors to remove the genitalia. Afterwards, it is cleaned with a fine brush so that all characters can be reliably identified. Subsequent staining provides better contrast for observation and documentation. Finally, for mounting, a drop of inclusion resin is placed on a slide in which the preparation is carefully positioned before it is covered with a coverslip.

Putting genitals into perspective…

During this work I noticed that the male genitalia of the moths I am revising have a certain structure that is a species-specific character. However, in mounted slide preparations this character was hardly visible since this two-dimensional view does not reflect the natural shape of the genitals, which usually lie folded within the abdomen. It seemed therefore to be useful to photograph these structures in their natural, folded state and in alcohol before embedding them. Photographing genitals in alcohol is a common process, but is complicated by drift and movement caused by the low viscosity of the alcohol. To avoid this, they have often been placed in hand sanitizer gel, which has a higher viscosity than alcohol. Unfortunately, the viscosity of this gel was still not high enough to photograph these mobile structures. I therefore had to find a solution to produce comparable and describable pictures of these structures by somehow keeping them still. After some trials, the solution was quite simple: the halved tip of a pipette glued to a petri dish helped me take comparable photos in alcohol.

Fig. 2: Comparisons of the male genitalia capsules of Triphosa sabaudiata (A, C) and Triphosa tauteli (B, D). A and B: Photos of slide-mounted genitalia. C and D: Photos of genitalia temporarily fixed in a halved pipette tip. Black arrows point to important diagnostic features. Comparison in embedded slide-mounts (A, B) is difficult, whereas in the temporary mount (C, D) all differences are clearly visible. (D. Wanke)

A positive side effect…

During summer 2018 the 10th Forum Herbulot, an international congress for specialists working with Geometridae, took place at the Natural History Museum of Stuttgart. There I was given the opportunity to present ongoing results and problems within the genus Triphosa. During the conference I met scientists who showed interest in the way I took the photos of the folded genitalia. They were enthusiastic about this simple method and encouraged me to publish it, which resulted in my first small publication


References

Wanke D, Rajaei H (2018) An effective method for the close up photography of insect genitalia during dissection: a case study on the Lepidoptera. Nota Lepidopterologica 41(2): 219-223. https://doi.org/10.3897/nl.41.27831

Hausmann, A. (2011) The Geometrid Moths of Europe, Vol. 1. Apollo Books, Vester Skerninge, Denmark, 282 pp.

Robinson GS (1976) The preparation of slides of Lepidoptera genitalia with special reference to the Microlepidoptera. Entomologist’s Gazette 27: 127–132.

Scoble, M.J. (1999) Geometrid Moths of the World: a catalogue (Lepidoptera, Geometridae). Vol. 1 and 2, Stenstrup: CSIRO Publishing and Apollo Books, p. 1016

Su YN (2016) A simple and quick method of displaying liquid-preserved morphological structures for microphotography. Zootaxa 4208 (6): 592–593.
http://dx.doi.org/10.11646/zootaxa.4208.6.6

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