A new case of hemidystrophy in Trogidae is here described and illustrated. The teratological specimen was identified as a male of Omorgus (Omorgus) alternans (MacLeay, 1827), being the first record of a teratological specimen of a trogid from Australia. While teratological cases provide limited taxonomic insights, they offer significant understanding of the environmental influences on insect development. The study emphasizes the importance of documenting such anomalies, contributing to the broader knowledge of developmental biology in insects, particularly within the under-researched Australian Trogidae

Anomalies, Australia, hemidystrophy, morphology, Omorginae, teratology

According to Balazuc (1948), the modern concept of teratology can be defined as the study of specimens that present one or more exceptional anatomical abnormalities or malformations (also see Ujházy et al. (2012) for a historical overview of the concept). These malformations can be caused by several endogenous or exogenous factors, such as disruptions during embryonic or postembryonic development, physical or chemical components, or even parasitism (Balazuc 1948, 1969; Clark and Belo-Neto 2010; Ujházy et al. 2012).

Teratological cases were reported in different groups of insects (Balazuc 1948, 1951, 1955, 1958; Goretti et al. 2020; Taszakowski and Kaszyca-Taszakowska 2020). For Coleoptera—the most diverse group in Insecta—several cases were published with Tenebrionidae (Ferrer et al. 2014), Cerambycidae (Castro-Tovar et al. 2014), Staphylinidae (Asiain and Marquez 2009), Histeridae (Degallier and Gomy 2007), Oedemeridae (Castro-Tovar et al. 2014), Carabidae (Ghannem et al. 2015), and Cleridae (Burke et al. 2018). For the superfamily Scarabaeoidea, cases have been reported for families such as Scarabaeidae (Clavijo-Bustos et al. 2022; Deschodt et al. 2023), Cetoniidae (Gasca-Álvarez et al. 2017), Melolonthidae (Guzmán-Vásquez et al. 2020), Geotrupi­dae (Bunalski and Lubecki 1990), Lucanidae (Balazuc 1948), and Trogidae (Romero-Samper 1993; Verdugo 2013). For a list of teratologies in Scarabaeoidea, see Gasca-Álvarez et al. 2017).

Trogidae MacLeay, 1819 is a widespread family of Scarabaeoidea with five extant genera and c. 350 valid names (Strümpher et al. 2016; Costa-Silva et al. 2024). To date, just two cases of abnormalities are known for European species of trogids: a symphysocery in Trox (Granulitrox) cotodognanensis Compte, 1985, described by Verdugo (2013), and a bilateral cystelytry in Trox (Granulitrox) hispanicus Harold, 1872, by Romero-Samper (1993). Although teratological specimens do not provide relevant taxonomic information, the description and reporting of these morphological anomalies is of utmost importance, as they can offer crucial information about the influences of environmental conditions during the development stages of insects (Savini and Furth 2004). Thus, the main goal of the present study is to report a teratological case in the Australian species of Trogidae. This is the first teratological case in trogids from the Australian region.

During a visit to the Canadian Museum of Nature (CMNC) to study Trogidae specimens, I had the opportunity to examine a teratological specimen of Trogidae. The taxonomic revision of the Australian Trogidae (Scholtz 1986) was used to identify the specimen as a male of Omorgus (Omorgus) alternans (MacLeay, 1827). The aedeagus was also examined in order to confirm the identification.

Photographs of the specimen’s habitus were taken using a Leica Z16 APOA apochromatic zoom system with a DMC 5400 camera. The plate was generated using Adobe Photoshop CS6. The nomenclature used here follows Balazuc (1948) for anatomical abnormalities and Costa-Silva et al. (2024) for external morphology of Trogidae.

Data from the specimen labels were transcribed verbatim in quotation marks (“”). A forward slash (/) was used to indicate a new line on the same label. Any additional or explanatory information was given in square brackets ([]). All handwritten information is bold and italics.

I am grateful to the Stewart and Jarmila Peck Visiting Scientist Awards in Entomology for the financial support to visit the Canadian Museum of Nature (CMNC—Ottawa, Canada) and to Andrew Smith and François Génier (CMNC) for all support during my visit to the institution. I also thank Gimo Daniel (NASMUS) for his comments and suggestions. A special thanks to the Post-Doctoral Fellowship Programme from the University of Pretoria and Prof. Catherine Sole (University of Pretoria, South Africa) for the provision of all laboratory facilities.