Functional characterization and fitness cost of spinosad-resistant alleles in Ceratitis capitata

[EN] The sustainability of control programs for the Mediterranean fruit fly, Ceratitis capitata, for citrus crops in Spain has been threatened by the development of resistance to malathion and lambda-cyhalothrin in recent years. Spinosad is widely used without apparent loss of efficacy. However, a highly resistant strain, JW-100s, has been obtained after laboratory selection. Spinosad resistance in JW-100s has been associated with different mutant alleles of the alpha 6 subunit of the nicotinic acetylcholine receptor (Cc alpha 6) including an isoform-specific truncation allele, Cc alpha 6(3aQ68*). Using the GAL4 > UAS system in Drosophila melanogaster to demonstrate expression of this truncated alpha 6 subunit, in a d alpha 6 loss-of-function genetic background, does not rescue susceptibility to spinosad, while the expression of Cc alpha 6 wild-type isoforms does. We have also generated C. capitata isolines from JW-100s homozygous for: (1) the Cc alpha 6(3aQ68*Delta 3b-4) allele, which contains the mutation 3aQ68*, and (2) the Cc alpha 6(3aQ68*-K352*) allele, which contains the mutations 3aQ68* and K352*. Neither of these produce complete Cc alpha 6 transcripts. The frequency of resistant alleles declined when in competition with individuals carrying the wild-type allele. Through extensive testing of both biological and behavioral fitness traits, we identified a reduced ability of Cc alpha 6(3aQ68*Delta 3b-4) males to detect the parapheromone and to mate with females carrying the Cc alpha 6(3aQ68*-K352*) allele in competition experiments. Thus, not only the potential for spontaneous resistant mutations to arise in Cc alpha 6 but also their fitness costs must be considered when planning resistance management strategies for C. capitata.This work received financial support from CICYT (AGL2016-76516-R). The Spanish MINECO granted A. Guillem-Amat a predoc (BES-C-2014-068937) and a mobility (EEBB-I-16-11336) fellowships. We gratefully acknowledge Maria Torne (Dow Agro-Science Iberica) for providing technical grade spinosad, Charles Robin (University of Melbourne) for assisting with bureaucratic issues with the Australian Government, Tinna Yang (University of Melbourne) for the keeping and shipping of the flies and Sandra Vacas (Universitat Politecnica de Valencia) for the scientific advice on electroantennography.Guillem-Amat, A.; Ureña, E.; López-Errasquín, E.; Navarro-Llopis, V.; Batterham, P.; Sánchez, L.; Perry, T.... (2020). Functional characterization and fitness cost of spinosad-resistant alleles in Ceratitis capitata. Journal of Pest Science. 93(3):1043-1058. https://doi.org/10.1007/s10340-020-01205-xS10431058933Abbas N, Mansoor MM, Shad SA et al (2014) Fitness cost and realized heritability of resistance to spinosad in Chrysoperla carnea (Neuroptera: Chrysopidae). 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Burkholderia mallei expresses a unique lipopolysaccharide mixture that is a potent activator of human Toll-like receptor 4 complexes

Burkholderia mallei, the aetiologic agent of glanders, causes a variety of illnesses in animals and humans ranging from occult infections to acute fulminating septicaemias. To better understand the role of lipopolysaccharide (LPS) in the pathogenesis of these diseases, studies were initiated to characterize the structural and biological properties of lipid A moieties expressed by this organism. Using a combination of chemical analyses and MALDI-TOF mass spectrometry, B. mallei was shown to express a heterogeneous mixture of tetra- and penta-acylated lipid A species that were non-stoichiometrically substituted with 4-amino-4-deoxy-arabinose residues. The major penta-acylated species consisted of bisphosphorylated d-glucosamine disaccharide backbones possessing two amide linked 3-hydroxyhexadecanoic acids, two ester linked 3-hydroxytetradecanoic acids [C14:0(3-OH)] and an acyloxyacyl linked tetradecanoic acid, whereas, the major tetra-acylated species possessed all but the 3′-linked C14:0(3-OH) residues. In addition, although devoid of hexa-acylated species, B. mallei LPS was shown to be a potent activator of human Toll-like receptor 4 complexes and stimulated human macrophage-like cells (THP-1 and U-937), monocyte-derived macrophages and dendritic cells to produce high levels of TNF-α, IL-6 and RANTES. Based upon these results, it appears that B. mallei LPS is likely to play a significant role in the pathogenesis of human disease

Gene content evolution in the arthropods

Arthropods comprise the largest and most diverse phylum on Earth and play vital roles in nearly every ecosystem. Their diversity stems in part from variations on a conserved body plan, resulting from and recorded in adaptive changes in the genome. Dissection of the genomic record of sequence change enables broad questions regarding genome evolution to be addressed, even across hyper-diverse taxa within arthropods. Using 76 whole genome sequences representing 21 orders spanning more than 500 million years of arthropod evolution, we document changes in gene and protein domain content and provide temporal and phylogenetic context for interpreting these innovations. We identify many novel gene families that arose early in the evolution of arthropods and during the diversification of insects into modern orders. We reveal unexpected variation in patterns of DNA methylation across arthropods and examples of gene family and protein domain evolution coincident with the appearance of notable phenotypic and physiological adaptations such as flight, metamorphosis, sociality, and chemoperception. These analyses demonstrate how large-scale comparative genomics can provide broad new insights into the genotype to phenotype map and generate testable hypotheses about the evolution of animal diversity

Deletion of the nicotinic acetylcholine receptor subunit gene Dα1 confers insecticide resistance, but at what cost?

Nicotinic acetylcholine receptors (nAChRs) have vital functions in processes of neurotransmission that underpin key behaviors. These pentameric ligand-gated ion channels have been used as targets for insecticides that constitutively activate them, causing the death of insect pests. In examining a knockout of the Dα1 nAChR subunit gene, our study linked this one subunit with multiple traits. We were able to confirm previous work that had identified Dα1 as a target of the neonicotinoid class of insecticides. Further, we uncovered roles for the gene in influencing mating behavior and patterns of sleep. The knockout mutant was also observed to have a significant reduction in longevity. This study highlighted the severe fitness costs that appear to be associated with the loss of function of this gene in natural populations in the absence of insecticides targeting the Dα1 subunit. Such a fitness cost could explain why target site resistances to neonicotinoids in pest insect populations have been associated specific amino acid replacement mutations in nAChR subunits, rather than loss of function. That mutant phenotypes were observed for the two behaviors examined indicates that the functions of Dα1, and other nAChR subunits, need to be explored more broadly. It also remains to be established whether these phenotypes were due to loss of the Dα1 receptor and/or to compensatory changes in the expression levels of other nAChR subunits

The wiggle index: an open source bioassay to assess sub-lethal insecticide response in <i>Drosophila melanogaster</i>

Toxicological assays measuring mortality are routinely used to describe insecticide response, but sub-lethal exposures to insecticides can select for resistance and yield additional biological information describing the ways in which an insecticide impacts the insect. Here we present the Wiggle Index (WI), a high-throughput method to quantify insecticide response by measuring the reduction in motility during sub-lethal exposures in larvae of the vinegar fly Drosophila melanogaster. A susceptible wild type strain was exposed to the insecticides chlorantraniliprole, imidacloprid, spinosad, and ivermectin. Each insecticide reduced larval motility, but response times and profiles differed among insecticides. Two sets of target site mutants previously identified in mortality studies on the basis of imidacloprid or spinosad resistance phenotypes were tested. In each case the resistant mutant responded significantly less than the control. The WI was also able to detect a spinosad response in the absence of the primary spinosad target site. This response was not detected in mortality assays suggesting that spinosad, like many other insecticides, may have secondary targets affecting behaviour. The ability of the WI to detect changes in insecticide metabolism was confirmed by overexpressing the imidacloprid metabolizing Cyp6g1 gene in digestive tissues or the central nervous system. The data presented here validate the WI as an inexpensive, generic, sub-lethal assay that can complement information gained from mortality assays, extending our understanding of the genetic basis of insecticide response in D. melanogaster