Si Hyeock Lee

As an obligatory parasite of humans, the body louse (Pediculus humanus humanus) is an important vector for human diseases, including epidemic typhus, relapsing fever, and trench fever. Here, we present genome sequences of the body louse and its primary bacterial endosymbiont Candidatus Riesia pediculicola. The body louse has the smallest known insect genome, spanning 108 Mb. Despite its status as an obligate parasite, it retains a remarkably complete basal insect repertoire of 10,773 protein-coding genes and 57 microRNAs. Representing hemimetabolous insects, the genome of the body louse thus provides a reference for studies of holometabolous insects. Compared with other insect genomes, the body louse genome contains significantly fewer genes associated with environmental sensing and response, including odorant and gustatory receptors and detoxifying enzymes. The unique architecture of the 18 minicircular mitochondrial chromosomes of the body louse may be linked to the loss of the gene encoding the mitochondrial single-stranded DNA binding protein. The genome of the obligatory louse endosymbiont Candidatus Riesia pediculicola encodes less than 600 genes on a short, linear chromosome and a circular plasmid. The plasmid harbors a unique arrangement of genes required for the synthesis of pantothenate, an essential vitamin deficient in the louse diet. The human body louse, its primary endosymbiont, and the bacterial pathogens that it vectors all possess genomes reduced in size compared with their free-living close relatives. Thus, the body louse genome project offers unique information and tools to use in advancing understanding of coevolution among vectors, symbionts, and pathogens.

This study establishes deltamethrin resistance in a common bed bug, Cimex lectularius L., population collected from New York City (NY-BB). The NY-BB population was 264-fold more resistant to 1% deltamethrin in contact bioassay compared with an insecticide-susceptible population collected in Florida (FL-BB). General esterase, glutathione S-transferase, and 7-ethoxycoumarin O-deethylase activities of NY-BB were not statistically different from those of FL-BB. cDNA fragments that encoded the open reading frame of voltage-sensitive sodium channel alpha-subunit genes from the FL-BB and NY-BB populations, respectively, were obtained by homology probing polymerase chain reaction (PCR) and sequenced. Sequence alignment of the internal and 5' and 3' rapid amplification of cDNA ends (RACE) fragments generated a 6500-bp cDNA sequence contig, which was composed of a 6084-bp open reading frame (ORF) encoding 2027 amino acid residues and 186-bp 5' and 230-bp 3' untranslated regions (5' and 3' UTRs, respectively). Sequence comparisons of the open reading frames of the alpha-subunit genes identified two point mutations (V419L and L925I) that were presented only in the NY-BB population. L925I, located the intracellular loop between IIS4 and IIS5, has been previously found in a highly pyrethroid-resistant populations of whitefly (Bemisia tabaci). V419L, located in the IS6 transmembrane segment, is a novel mutation. A Val to Met mutation at the corresponding position of the bed bug V419, however, has been identified in the tobacco budworm as a kdr-type mutation. This evidence suggests that the two mutations are likely the major resistance-causing mutations in the deltamethrin-resistant NY-BB through a knockdown-type nerve insensitivity mechanism.

A serine to glycine point mutation of acetylcholinesterase (AChE, EC 1.1.1.7) was identified in an azinphosmethyl-resistant strain of Colorado potato beetle [Leptinotarsa decemlineata (Say)]. The position of the mutation corresponds to Val 238 of the Torpedo AChE and represents the first amino acid residue to form the alpha-helix, alpha-E'1. The predicted secondary structure of the mutation-containing region of AChE suggested that the transition from the turn to the alpha-helix occurs sooner in the sequence when serine is replaced by glycine. Thus, conformational changes in the AChE due to the alpha-helix deformation were expected to impinge upon both the catalytic and the peripheral binding sites, resulting in the modification of the bindings of organophosphorus insecticides and other ligands to these sites. The mutation appeared to be associated with the fitness of the beetle. The intrinsic rate of increase of the azinphosmethyl-resistant (AZ-R) strain was relatively low when the beetles were reared on the Russet Burbank potato cultivar, but was relatively high when they were reared on the NDA 1725-1 potato cultivar. Because these two potato cultivars contain different amounts of steroidal glycoalkaloids (e.g., alpha-solanine and alpha-chaconine), the different fitness of the AZ-R strain on different potato cultivars may be partially attributed to the increased sensitivity of the azinphosmethyl-resistant form of AChE to the inhibition by alpha-solanine and reduced sensitivity to alpha-chaconine as previously reported.