Alternative techniques to study characters of the genitalia in Lepidoptera

SCIENTIFIC NOTE

Alternative techniques to study characters of the genitalia in Lepidoptera

Fernando M S Dias; Mirna M Casagrande; Olaf H H Mielke

Depto de Zoologia, Univ Federal do Paraná, CP 19020, 81531-980 Curitiba, PR, Brasil; [e-mail]; [e-mail]; [e-mail]

ABSTRACT

The present note aims to describe two alternative methods for observing genitalia in Lepidoptera. The first one provides means to examine both male and female genitalia without spoiling the scales of the abdomen, preserving it attached to the thorax and aesthetically similar to an unexamined specimen. The second one provides ways of observing certain characters on the male genitalia in a non-destructive way, and does not depend on time-consuming removing and dissection of the abdomen. It is expected that the presented techniques will help on morphological studies and on identifying similar species which consistently differ in genitalic armatures.

Key words: Morphology, identification, valva, uncus

As noted by Niculescu (1976), many authors recognize the importance of the genitalia as the most informative specific character in the Lepidoptera, especially the valvae of the male genitalia due to their variation (Fox 1953). It is well known that closely related species or species under similar selective pressures tend to show similar patterns, and those patterns are often obscured by intraspecific variations and/ or seasonal forms, thus adding an element of confusion in identification. Several of these species are only distinguished by genitalic preparations. The present scientific note aims to make known two alternative techniques to access these structures.

The first technique provides means to remove both male and female genitalia without spoiling the scales of the abdomen, preserving it attached to the thorax and aesthetically similar to an unexamined specimen, while allows morphologic study. The researcher should carry out the following steps: 1) detach the abdomen from the thorax and sink it in distilled water for some 18h to 24h; 2) transfer the abdomen to a petri dish with paraffin wax on the bottom filled with water; 3) fix the abdomen sideways with thin insect pins (size 0 or 1) and cut it antero-posteriorly through the pleura using ophthalmologic scissors (Fig 1a), and cut throughout the inter-segmental membrane between the seventh and eight segments in females or between the eighth and ninth segments in males (Fig 1b); 4) open the abdominal cavity, fixing the tergites and sternites with thin insect pins on the paraffin wax; 5) using a thin forceps, remove the genitalia and with it the abdominal content. After removed, the genitalia may be further prepared as usual. Be careful while removing membranous parts of the genitalia, especially the female's bursa copulatrix which is very easily damaged. To preserve definitively after dissection, put the genitalia in a glycerin-filled small test tube, which should be pinned with the insect afterwards; 6) put the emptied abdomen resting on absorbing paper for a while, and then mount it with insect pins on polystyrene foam. Take it to a low temperature stove (circa 30ºC) for a couple of days until it dries completely, then reattach it to the thorax using white glue.

This method has proven to be useful for several taxa of Papilionoidea and Hesperioidea, especially in taxonomic groups where color and pattern of the abdominal scales are an important diagnostic character, as in the Pyrrhopyginae. Even though other methods had been proposed for studying the genitalia without spoiling the abdomen (Chacín 1992), the above-cited method is simpler and suits a wider range of taxa, including small and delicate specimens.

The second technique consists in direct observation of valvae and uncus of the male genitalia without the usual destructive sampling preparations. These structures can be observed by removing the scales of the tip of the abdomen and valvae. The mounted specimen should be fixed sideways in polystyrene foam or other support with the pleural side of the abdomen directed upward. Afterwards, under the stereoscopic microscope and using a thin forceps, the scales should be carefully removed (Fig 2a) and the area cleaned with a soft brush (Fig 2b). In case of asymmetrical genitalia, the procedure should be repeated in both sides.

Although that method is relatively well known among lepidopterists, it's surprisingly unknown among students and many entomologists, including those who curate entomological collections. An example is four closely related species of leafwing butterfly belonging to the genus Memphis (Hübner) that have marked resemblance in its facies, but very different genitalic armatures, especially in the posterior tip of the valvae. Their facies show overwhelming variation and overlapping phenotypes, but their genitalia have unique and stable characters. Those characters are readily observed with that technique, eliminating time-consuming and destructive genitalic preparations.

Acknowledgments

The first author would like to thank Gil Felipe Miranda Gonçalves, Luis Roberto Ribeiro Faria Jr. and an anonymous reviewer, for valuable suggestions and manuscript review, and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the financial support granted.

Received 09/II/09.

Accepted 04/V/09.

Edited by Roberto A Zucchi - ESALQ/USP

• Chacín M E (1992) Técnica para la extracción de la genitalia de Manduca Hübner, 1807 (Lepidoptera: Sphingidae). Bol Entomol Venez 7: 161-165.
• Fox R M (1953) The taxonomic value of male genitalia in the Ithomiidae (Lepidoptera). Entomol News 64: 141-143.
• Niculescu E V (1976) La valeur taxonomique des caractères morphologiques chez les Lepidoptères. Bull Soc Entomol Mulhouse 1976: 1-14.

Publication Dates

• Publication in this collection
  17 Jan 2011
• Date of issue
  Dec 2010

History

• Received
  09 Feb 2009
• Accepted
  04 May 2009