Cheryl A. Leichter

Genome of the house fly, Musca domestica L., a global vector of diseases with adaptations to a septic environment

BackgroundAdult house flies, Musca domestica L., are mechanical vectors of more than 100 devastating diseases that have severe consequences for human and animal health. House fly larvae play a vital role as decomposers of animal wastes, and thus live in intimate association with many animal pathogens.ResultsWe have sequenced and analyzed the genome of the house fly using DNA from female flies. The sequenced genome is 691 Mb. Compared with Drosophila melanogaster, the genome contains a rich resource of shared and novel protein coding genes, a significantly higher amount of repetitive elements, and substantial increases in copy number and diversity of both the recognition and effector components of the immune system, consistent with life in a pathogen-rich environment. There are 146 P450 genes, plus 11 pseudogenes, in M. domestica, representing a significant increase relative to D. melanogaster and suggesting the presence of enhanced detoxification in house flies. Relative to D. melanogaster, M. domestica has also evolved an expanded repertoire of chemoreceptors and odorant binding proteins, many associated with gustation.ConclusionsThis represents the first genome sequence of an insect that lives in intimate association with abundant animal pathogens. The house fly genome provides a rich resource for enabling work on innovative methods of insect control, for understanding the mechanisms of insecticide resistance, genetic adaptation to high pathogen loads, and for exploring the basic biology of this important pest. The genome of this species will also serve as a close out-group to Drosophila in comparative genomic studies.

Multiplicative interaction between the two major mechanisms of permethrin resistance, kdr and cytochrome P450-monooxygenase detoxification, in mosquitoes

Epistasis is the nonadditive interaction between different loci which contribute to a phenotype. Epistasis between independent loci conferring insecticide resistance is important to investigate as this phenomenon can shape the rate that resistance evolves and can dictate the level of resistance in the field. The evolution of insecticide resistance in mosquitoes is a growing and world‐wide problem. The two major mechanisms that confer resistance to permethrin in Culex mosquitoes are target site insensitivity (i.e. kdr) and enhanced detoxification by cytochrome P450 monooxygenases. Using three strains of mosquitoes, and crosses between these strains, we assessed the relative contribution of the two independent loci conferring permethrin resistance, individually and when present together. We found that for all genotype combinations tested, Culex pipiens quinquefasciatus exhibited multiplicative interactions between kdr and P450 detoxification, whether the resistance alleles were homozygous or heterozygous. These results provide a basis for further analysis of the evolution and maintenance of insecticide resistance in mosquitoes.

Insecticide resistance in house flies from the United States: Resistance levels and frequency of pyrethroid resistance alleles

Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein, we report the first widespread survey of insecticide resistance in the USA ever undertaken for the house fly, Musca domestica, a major pest in animal production facilities. The levels of resistance to six different insecticides were determined (using discriminating concentration bioassays) in 10 collections of house flies from dairies in nine different states. In addition, the frequencies of Vssc and CYP6D1 alleles that confer resistance to pyrethroid insecticides were determined for each fly population. Levels of resistance to the six insecticides varied among states and insecticides. Resistance to permethrin was highest overall and most consistent across the states. Resistance to methomyl was relatively consistent, with 65-91% survival in nine of the ten collections. In contrast, resistance to cyfluthrin and pyrethrins + piperonyl butoxide varied considerably (2.9-76% survival). Resistance to imidacloprid was overall modest and showed no signs of increasing relative to collections made in 2004, despite increasing use of this insecticide. The frequency of Vssc alleles that confer pyrethroid resistance was variable between locations. The highest frequencies of kdr, kdr-his and super-kdr were found in Minnesota, North Carolina and Kansas, respectively. In contrast, the New Mexico population had the highest frequency (0.67) of the susceptible allele. The implications of these results to resistance management and to the understanding of the evolution of insecticide resistance are discussed.

Multiple origins of kdr-type resistance in the house fly, Musca domestica.

Insecticide resistance is a model phenotype that can be used to investigate evolutionary processes underlying the spread of alleles across a global landscape, while offering valuable insights into solving the problems that resistant pests present to human health and agriculture. Pyrethroids are one of the most widely used classes of insecticides world-wide and they exert their toxic effects through interactions with the voltage-sensitive sodium channel (Vssc). Specific mutations in Vssc (kdr, kdr-his and super-kdr) are known to cause resistance to pyrethroid insecticides in house flies. In order to determine the number of evolutionary origins of kdr, kdr-his and super-kdr, we sequenced a region of Vssc from house flies collected in the USA, Turkey and China. Our phylogenetic analysis of Vssc unequivocally supports the hypothesis of multiple independent origins of kdr, super-kdr and kdr-his on an unprecedented geographic scale. The implications of these evolutionary processes on pest management are discussed.