New Analysis Refines Taxonomy of Dermestid Beetles
By John P. Roche, Ph.D.
Beetles in the family Dermestidae are scavengers that are important as grain pests, ecosystem recyclers, and forensic tools. Accurate information on identifying the genera and species in this group is valuable to pest control, trade restrictions on grain pests, estimates of biological diversity, and forensics. A new study by researchers at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Canberra, Australia, published in November in Insect Systematics and Diversity, shares a molecular and morphological analysis of dermestid beetles to improve our understanding of the group’s evolutionary relationships.
The family Dermestidae contains about 1,700 species, known by various names including the hide beetles, skin beetles, larder beetles, and carpet beetles. Example species include the khapra beetle (Trogoderma granarium), a serious pest of grain; the hide beetle (Dermestes maculatus), which can be used in forensics; and the black carpet beetle (Attagenus unicolor), which can damage carpets and clothes.
Dermestids are important economically because they can cause serious losses to stored grain. The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service estimates that khapra beetle infestations often destroy 30 percent of the infested grain product. Dermestid pests of grain are difficult to control because they can live for long durations without food, and they hide in cracks and other locations that allow them to avoid control measures such as fumigation. On the positive side, dermestids provide vital ecosystem services as scavengers. They are also important to taxidermy because they are used to clean flesh off of bones and to forensics because beetles feeding on corpses can help law enforcement estimate when an individual died.
Yu-Lingzi Zhou, Ph.D., senior curator in Coleoptera at CSIRO’s Australian National Insect Collection, and colleagues examined mitochondrial genome sequences of 477 species of dermestid beetles using a technique called genome skimming. Genome skimming samples a smaller proportion of the genetic code than full-genome sampling, allowing it to effectively answer questions in evolutionary biology at a lower cost.
It is important to have an accurate picture of the taxonomy of groups, but the taxonomy of Dermestidae has been changing considerably in past decades, and analyses have been incomplete, with some genera of the group being inferred from only one individual female beetle. A new phylogeny of the group was published in 2021, but it was based on only 16 new and 15 publicly available samples. The present study by Zhou and colleagues is much more extensive, looking at 477 specimens representing all subfamilies, about 90 percent of recognized tribes and subtribes, and 80 percent of genera. (Tribes and subtribes are groups above the level of the genus but below the level of the family.) It is the first comprehensive analysis of the phylogeny of Dermestidae.
To construct their phylogenetic trees, Zhou and her colleagues used a leading technique in phylogenetic analysis called maximum likelihood analysis. This is a statistical method that calculates the probability that the observed DNA sequences are consistent with a particular phylogenetic tree representing evolutionary relationships among species.
In their study, they found support for the Dermestidae family containing six subfamilies:
Subfamily Megatominae is the largest group and contains the most species.
The mitochondrial DNA data collected in this study are able to resolve questions that were unanswerable using morphological characters alone. For example, Zhou and colleagues report, “We found that morphological characters traditionally used for delimiting Megatominae genera show pervasive homoplasy [i.e., they arose through convergent evolution] and thus are of limited value.” But their genomic data were able to delineate members of this group into three tribes: Ctesiini, Anthrenini, and Megatomini.
The investigators found that what had previously been called the genus Trogoderma and had been believed to be a single evolutionary group was actually made up of members of different evolutionary branches—or, what evolutionary biologists call “polyphyletic.” The species are now split into the genus Trogoderma in the Northern Hemisphere and the genus Eurhopalus in the Southern Hemisphere. Trogoderma in the Northern Hemisphere includes pest species such as khapra beetle; the warehouse beetle (Trogoderma variabile), and Trogoderma glabrum, sometimes known as the the glabrous cabinet beetle. Thus, native species of the genus Trogoderma, including the khapra beetle, are not present in Australia. “As khapra beetles are also transported in packaging material of non-food goods,” the authors report, “countries that are free of the khapra beetle enjoy significant trade advantages when exporting to other countries that haven’t been infested yet.”
In addition to their phylogenetic analysis, the investigators conducted an extensive morphological study of Dermestidae, including the morphology of different developmental stages of the species. “The combination of molecular analyses and thorough research on the morphology of adults, larvae, and pupae have allowed reconstruction of the most comprehensive phylogeny of the family, with most major clades and relationships among them recovered with high levels of support,” they write.
The genomic data Zhou and colleagues collected in their study have been submitted to the National Center for Biotechnology Information’s GenBank and so will be available to other scientists for additional analysis of the group. With improved methods and wider availability of genomic data, further improvements in our understanding of Dermestidae will allow for improved control and refined utilization of members of this important group.
Insect Systematics and Diversity
John P. Roche, Ph.D., is an author, biologist, and science writer with a Ph.D. in the biological sciences and a dedication to making rigorous science clear and accessible. He writes articles and books, and does writing and editing for universities, scientific societies, and publishers. Professional experience includes serving as a scientist and scientific writer at Indiana University, Boston College, and the University of Massachusetts Medical School, and as an editor-in-chief of science periodicals at Indiana University and Boston College.