toxins Article Antiparasitic Effects of Potentially Toxic Beetles (Tenebrionidae and Meloidae) from Steppe Zones Marta Díaz-Navarro 1,2 , Paula Bolívar 1,3 , María Fe Andrés 2 , María Teresa Gómez-Muñoz 3 , Rafael A. Martínez-Díaz 4 ,Félix Valcárcel 5 , Mario García-París 1 , Luis M. Bautista 1 and Azucena González-Coloma 2, *   Citation: Díaz-Navarro, M.; Bolívar, P.; Andrés, M.F.; Gómez-Muñoz, M.T.; Martínez-Díaz, R.A.; Valcárcel, F.; García-París, M.; Bautista, L.M.; González-Coloma, A. Antiparasitic Effects of Potentially Toxic Beetles (Tenebrionidae and Meloidae) from Steppe Zones. Toxins 2021, 13, 489. https://doi.org/10.3390/toxins 13070489 Received: 16 June 2021 Accepted: 11 July 2021 Published: 14 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, 28006 Madrid, Spain; maartadn@gmail.com (M.D.-N.); pbolivar@mncn.csic.es (P.B.); mparis@mncn.csic.es (M.G.-P.); lm.bautista@csic.es (L.M.B.) 2 Instituto de Ciencias Agrarias, CSIC, Serrano 115-dpdo, 28006 Madrid, Spain; mafay@ica.csic 3 Facultad de Veterinaria, Universidad Complutense de Madrid (UCM), 28040 Madrid, Spain; mariateresa.gomez.munoz@pdi.ucm.es 4 Facultad de Medicina, Universidad Autónoma de Madrid (UAM), Arzobispo Morcillo S/N, 28029 Madrid, Spain; rafael.martinez@uam.es 5 Grupo de Parasitología Animal, Departamento de Reproducción Animal, CSIC-INIA, 28040 Madrid, Spain; valcarcel.felix@inia.es * Correspondence: azu@ica.csic.es Abstract: Arthropods and specifically beetles can synthesize and/or sequester metabolites from dietary sources. In beetle families such as Tenebrionidae and Meloidae, a few studies have reported species with toxic defensive substances and antiparasitic properties that are consumed by birds. Here we have studied the antiparasitic activity of extracts from beetle species present in the habitat of the Great Bustard (Otis tarda) against four pathogen models (Aspergillus niger, Meloidogyne javanica, Hyalomma lusitanicum, and Trichomonas gallinae). The insect species extracted were Tentyria peiroleri, Scaurus uncinus, Blaps lethifera (Tenebrionidae), and Mylabris quadripunctata (Meloidae). M. quadripunc- tata exhibited potent activity against M. javanica and T. gallinae, while T. peiroleri exhibited moderate antiprotozoal activity. The chemical composition of the insect extracts was studied by gas chro- matography coupled with mass spectrometry (GC-MS) analysis. The most abundant compounds in the four beetle extracts were hydrocarbons and fatty acids such as palmitic acid, myristic acid and methyl linoleate, which are characteristic of insect cuticles. The presence of cantharidin (CTD) in the M. quadripunctata meloid and ethyl oleate (EO) in T. peiroleri accounted for the bioactivity of their extracts. Keywords: Tenebrionidae; Meloidae; nematicide; antiprotozoal; GCMS; cantharidin; ethyl oleate; otididae Key Contribution: The antiparasitic activity of extracts from beetle species that may be present in the diet of some birds support the hypothesis of their potential dietary antiparasitic effects. 1. Introduction Arthropods contain secondary metabolites (defensins and toxins) characterized by great chemical and biosynthetic diversity [1]. Specifically, coleopterans produce a wide variety of active compounds or metabolites that are medicinal substances or precursors [2,3]. Other Coleoptera acquire toxic substances by sequestering secondary metabolites from dietary sources, which are then transferred from invertebrates to upper trophic levels within the ecosystem [1,4,5]. The consumption of secondary metabolites by animals can affect their parasite and pathogen load, regardless of their toxicity to the animal itself. These effects are of particular interest because there is an urgent need to search for natural products with therapeutic Toxins 2021, 13, 489. https://doi.org/10.3390/toxins13070489 https://www.mdpi.com/journal/toxins