Disruption of the odorant coreceptor Orco impairs foraging and host finding behaviors in the New World screwworm fly.

The evolution of obligate ectoparasitism in blowflies (Diptera: Calliphoridae) has intrigued scientists for over a century, and surprisingly, the genetics underlying this lifestyle remain largely unknown. Blowflies use odors to locate food and oviposition sites; therefore, olfaction might have played a central role in niche specialization within the group. In insects, the coreceptor Orco is a required partner for all odorant receptors (ORs), a major gene family involved in olfactory-evoked behaviors. Hence, we characterized the Orco gene in the New World screwworm, Cochliomyia hominivorax, a blowfly that is an obligate ectoparasite of warm-blooded animals. In contrast, most of the closely related blowflies are scavengers that lay their eggs on dead animals. We show that the screwworm Orco orthologue (ChomOrco) is highly conserved within Diptera, showing signals of strong purifying selection. Expression of ChomOrco is broadly detectable in chemosensory appendages, and is related to morphological, developmental, and behavioral aspects of the screwworm biology. We used CRISPR/Cas9 to disrupt ChomOrco and evaluate the consequences of losing the OR function on screwworm behavior. In two-choice assays, Orco mutants displayed an impaired response to floral-like and animal host-associated odors, suggesting that OR-mediated olfaction is involved in foraging and host-seeking behaviors in C. hominivorax. These results broaden our understanding of the chemoreception basis of niche occupancy by blowflies.

Phenotypic polymorphism of Chrysomya albiceps (Wiedemann) (Diptera: Calliphoridae) may lead to species misidentification.

Species identification is an essential step in the progress and completion of work in several areas of biological knowledge, but it is not a simple process. Due to the close phylogenetic relationship of certain species, morphological characters are not always sufficiently distinguishable. As a result, it is necessary to combine several methods of analysis that contribute to a distinct categorization of taxa. This study aimed to raise diagnostic characters, both morphological and molecular, for the correct identification of species of the genus Chrysomya (Diptera: Calliphoridae) recorded in the New World, which has continuously generated discussion about its taxonomic position over the last century. A clear example of this situation was the first record of Chrysomya rufifacies in Brazilian territory in 2012. However, the morphological polymorphism and genetic variability of Chrysomya albiceps studied here show that both species (C. rufifacies and C. albiceps) share very similar character states, leading to misidentification and subsequent registration error of species present in our territory. This conclusion is demonstrated by the authors, based on a review of the material deposited in major scientific collections in Brazil and subsequent molecular and phylogenetic analysis of these samples. Additionally, we have proposed a new taxonomic key to separate the species of Chrysomya found on the American continent, taking into account a larger number of characters beyond those available in current literature.

The mitochondrial DNA control region of Muscidae flies: evolution and structural conservation in a dipteran context.

The structure and evolution of the mtDNA control region (CR) and its flanking genes in economically important dipterans from the family Muscidae (Brachycera: Calyptratae), Haematobia irritans, Musca domestica, Atherigona orientalis, and Stomoxys calcitrans are presented in this paper, along with the description of short noncoding intergenic regions possibly related to CR flanking sequences in Stomoxys calcitrans and Ophyra aenescens mtDNAs (ScIR and OaIR, respectively). S. calcitrans showed a large CR with an approximately 550-bp element tandemly repeated and a duplicated tRNA(Ile) gene. The characterization of H. irritans, M. domestica, A. orientalis, and S. calcitrans CR sequences led to the identification of seven conserved sequence blocks homologous to the elements previously described for Calliphoridae and Oestridae species (Brachycera: Calyptratae). Comparative analysis with Drosophila species (Brachycera: Acalyptratae) revealed four conserved regions. The putative functional roles of the conserved elements in the regulation of replication and transcription processes are addressed. The characterization of the structural organization of the mitochondrial genome CR demonstrates the plasticity of the mtDNA molecule in family Muscidae.