Cantharidin analogues and their attractancy for ceretopogonid flies (Diptera: Ceratopogonidae)

Avoiding cantharidin through ionotropic receptors

The discernment and aversion of noxious gustatory stimuli profoundly influence homeostasis maintenance and survival of fauna. Cantharidin, a purported aphrodisiac, is a monoterpenoid compound secreted by many species of blister beetle, particularly by the Spanish fly, Lytta vesicatoria. Although the various advantageous functions of cantharidin have been described, its taste analysis and toxic properties in animalshave been rarely explored. Our study using Drosophila melanogaster examines the taste properties of cantharidin along with its potential hazardous effect in the internal organs of animals. Here, we find that cantharidin activates bitter taste receptors. Our findings show that specific ionotropic receptors (IR7g, IR51b, and IR94f) in labellar bitter-sensing neurons, along with co-receptors IR25a and IR76b, are responsible for detecting cantharidin. By introducing the IR7g and IR51b in sweet and bitter neurons, naturally expressing IR76b and IR25a, we show that these genes are sufficient for cantharidin perception. Moreover, we witness the deleterious ramifications of cantharidin on survival and visceral integrities, shedding light on its hazardous effect.

New Evidence of Canthariphily: Tilloidea transversalis (Coleoptera: Cleridae) Sequestering Cantharidin From Lydus trimaculatus (Coleoptera: Meloidae)

Cantharidin (CTD) is a defensive compound autogenously and exclusively produced by two phylogenetically related beetle families: Meloidae and Oedemeridae. Although this molecule usually acts as a strong deterrent against potential predators and parasites, some arthropod species, collectively named 'canthariphilous species', are attracted to CTD. Some species can sequester CTD from the CTD-producing species, using it as a chemical defense against enemies. The present paper focuses on the first-ever description of canthariphilous interactions between a checkered beetle species (Coleoptera: Cleridae) and a CTD -producing species. Field observations revealed individuals of the phytophagous beetle Tilloidea transversalis (Charpentier, 1825) (Coleoptera: Cleridae) biting individuals of the blister beetle Lydus trimaculatus (Fabricius, 1775) (Coleoptera: Meloidae). Laboratory behavioral experiments followed to verify if this peculiar behavior of T. transversalis also occurs on other co-occurring species. Moreover, chemical analyses were performed to assess whether T. transversalis can sequester CTD. Our results show that T. transversalis only attacks CTD-producing species. However, while chemical analyses prove that T. transversalis can sequester CTD from the hemolymph of L. trimaculatus, some clues (based on a CTD-baited traps sampling) suggest that this beetle, contrarily to other canthariphilous species, does not appear to show a high attraction to pure synthetic CTD. Thus, other unknown signals, alone or in combination with CTD, could be implicated in triggering the canthariphilous behaviors of T. transversalis.

Millipede Defensive Compounds Are a Double-Edged Sword: Natural History of the Millipede-Parasitic Genus Myriophora Brown (Diptera: Phoridae)

Toxic defensive secretions produced by millipedes in the orders Julida, Spirobolida, Spirostreptida, and Polydesmida are highly repellent to most vertebrate and invertebrate natural enemies, but a few insects have evolved mechanisms to overcome these defenses. We demonstrate that highly specialized parasitic phorid flies in the species-rich genus Myriophora use volatile millipede defensive compounds as kairomones for host location. Of the two predominant quinone components in the defensive blend of juliform millipedes, 2-methoxy-3-methyl-1,4-benzoquinone alone was sufficient to attract adult flies of both sexes; however, a combination of 2-methoxy-3-methyl-1,4-benzoquinone and 2-methyl-1,4-benzoquinone increased attractiveness nearly threefold. We further discuss oviposition behavior, adult and larval feeding habits, life history parameters, and the potential competitive interactions between phorid flies in the genus Myriophora and other millipede-associated insects.

3-hydroxy-3-methyl glutaryl coenzyme A reductase: an essential actor in the biosynthesis of cantharidin in the blister beetle Epicauta chinensis Laporte

Cantharidin (C(10)H(12)O(4)) is a monoterpene defensive toxin in insects involved in chemical defence as well as in courtship and mating behaviours. It is relatively well known in the medical literature because of its high anticancer activity and as an effective therapy for molluscum contagiosum. However, little is known about its biosynthesis pathway in vivo, and no enzyme involved in cantharidin biosynthesis has been identified. The purpose of this study was to identify the crucial enzyme that is involved in the biosynthesis of cantharidin. Using the homology cloning method, a 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMGR) gene, the rate-limiting enzyme in the mevalonate pathway, was cloned from the blister beetle Epicauta chinensis. Quantitative reverse transcription PCR and gas chromatography methods revealed that the HMGR transcripts had a positive correlation with cantharidin production in the beetles (R = 0.891). RNA interference (RNAi) knockdown of HMGR mRNA expression was achieved by microinjection of a specific double-stranded RNA with more than 90% RNAi efficiency, and an apparent decrease of cantharidin production was observed. Furthermore, the HMGR mRNA was greatly upregulated by exogenous juvenile hormone III (JH III), and cantharidin production was also raised in males; however, when injecting the JH III with RNAi of HMGR mRNA at the same time, cantharidin production did not rise. These results demonstrate that HMGR is an essential enzyme in cantharidin biosynthesis in the blister beetle E. chinensis, which further verifies previous research results demonstrating that cantharidin is synthesized de novo by the mevalonate pathway in blister beetles.

Mosquito repellent attracts Culicoides imicola (Diptera: Ceratopogonidae)

A plant-derived mosquito repellent, based on the oil of Eucalyptus maculata var. citriodora Hook, was evaluated against the biting midge Culicoides imicola Kieffer. Suction black light-traps covered with repellent-impregnated polyester mesh and deployed near horses attracted large numbers of C. imicola, which were seen near the treated net within a few minutes of the start of the experiment. Initial collections in the traps were approximately 3 times as large as those in control traps with untreated mesh. Numbers collected in treated traps were similar to untreated control traps after 4 h. Traps with mesh treated with DEET or another plant-derived (Meliaceae) proprietary product, AG1000, acted as repellents relative to the control. The differential activity of repellents against blood-feeding Diptera is discussed.