Population structure and gene flow in diamondback moth in Australia and around the world：Current state of knowledge and directions for the future

摘要

The study of population structure investigates patterns of gene flow within a species.Determining boundaries of differentiated populations of Plutella xylostella around the world is important to improve management of insecticide resistance and biological control of this species.Past studies of population structure in P.xylostella have been made using either allozymes or mitochondrial DNA markers.Most have found little evidence of population structure apart from some differentiation between and within continents detected using allozymes.New markers being developed for studies of P.xylostella include ISSR and mierosatellites.Microsatellite markers(simple DNA sequence repeats that vary in length between individuals in a population)have potential to provide information about population movement at different spatial scales and are largely selectively neutral.Unfortunately microsatellites have proven difficult to isolate in Lepidoptera.Once developed.however. Their use is worthwhile provided checks are made for occurrence of null alleles across the geographic range of the species. Plutella xylostella has long been a pest of Brassica vegetables throughout Australia，but in recent years has also caused economic losses in canola(Brassica napus L.，oilseed rape).Microsatellite data demonstrate that P.xylostella in southern Australia forms a panmictic population with no evidence of temporal，spatial or host plant related differentiation.Sufficient gene flow in this species to homogenise allele frequencies across this region is indicated. This finding precludes identification of source populations，movement patterns and rate of dispersal of P.xylostella among cultivated and wild host plants.Microsatellite studies show that moths from Kenya，Asia，Pakistan，North America and Mexico are differentiated from Australian samples.Furthermore.P.xylostella from Australia shows low haplotype diversity at the mitochondfial cytochrome oxidase I(COI)locus compared with populations from other regions.Some inconsistencies are observed between studies using different types of marker and may be caused by sampling at different scales.Further development of genetic markers and validated sampling protocols should be made to aid the definition of global and local population structure in P.xylostella.