UC San Diego

Cacti (family Cactaceae) are an important part of desert ecosystems. These plants are known for their many defensive adaptations, but occasionally, when a cactus becomes damaged or stressed, it becomes prone to invasion by microorganisms, which induce rot within the cactus. Rotting cacti host a diverse assemblage of desert arthropods, particularly beetles (Coleoptera) and flies (Diptera). Detailed research on cactus arthropods has been mostly limited to flies, while cactus beetles remain relatively understudied. This thesis serves as an investigation of the taxonomy, phylogenetics, and host- cactus preferences of the cactophilic species of the beetle genus Carcinops. For this study, five hundred and fifty Carcinops specimens were collected from rotting cacti in the Sonoran Desert. Key morphological differences between species were evaluated and summarized. Detailed photographs were taken of all known cactophilic Carcinops species and were used to construct an interactive identification key. COI sequenced were used to create a gene tree. Based on species distributions among different species of cacti, some species of Carcinops appear to exhibit host-plant specificity, although not to the degree seen in some species of cactus Drosophila. Populations of C. rugula and C. stenocereus showed evidence of genetic isolation from mainland Mexican populations, possibly due the Gulf of California acting as a geographic barrier. One new species of Carcinops was discovered during the course of this research, and is described herein