Population genetics of the Mediterranean fruit fly Ceratitis capitata in the Western Cape Province, South Africa : invasion potential and dispersal ability

[摘要] ENGLISH ABSTRACT: The Mediterranean fruit fly (medfly), Ceratitis capitata, is a highly invasive species throughout the world and considered as one of the most successful agricultural and economical pests. The increaseof global trade in fruit and human travel combined with the biology of the medfly has allowed thespecies to spread from its proposed Afrotropical origin, to a number of locations throughout theworld. In the Western Cape various control strategies have been implemented to control medflypopulations, including insecticides and more environmentally-friendly techniques such as theSterile Insect Technique (SIT). In order to be effective, however, an SIT program requires someknowledge of the population structure and the movement of individuals between pest-occupiedsites. The identification of sites from which re-invasion is most likely to occur and knowledgeregarding the primary routes through which pests are likely to re-establish are critical to ensuresuccessful SIT programmes. To provide this important information to SIT and area-wide pestcontrol programs in South Africa, sampling at two different spatial scales (regional- and fine-scale)in South Africa was undertaken. Regional scale sampling was done at 13 locations in the WesternCape and fine scale sampling was done at 13 locations within the Ceres-valley. All individuals weregenotyped at 11 polymorphic microsatellite markers and selected individuals from the regionalscale were sequenced for the mitochondrial gene COI. Our results show that populations atregional- and fine-scale in the Western Cape are characterized by high levels of genetic diversity(HEregional = 0.805; HEfine = 0.803). Little or weak population differentiation was detected at theregional- and fine-scales, suggesting overall high levels of gene flow among sampling locations.These findings were supported by coalescent based methods indicating sufficient levels of geneflow to prevent population differentiation between neighbouring (200m) and distant (350km)populations. However, natural dispersal in C. capitata has been shown to rarely exceed 10 km. Assuch, high levels of gene flow between distant populations are more likely the result of humanmediateddispersal, linked to the movement of fresh produce within South Africa. This high level ofgene flow has important implications for pest management practices, as my results suggests that area-wide pest management should be undertaken at a regional scale, rather than on a farm or valleyscale. My results are placed within a management framework, and I argue for more stringent controlwhen fruit are transported within South Africa. Of particular interest for future studies is theinvestigation of gene flow at broader spatial scales (i.e. the whole of South Africa) and acomparison of the genetic diversity, population differentiation and gene flow patterns of C. capitatawith that of Ceratitis rosa will be important to establish a successful pest management strategy inSouth Africa.

[发布机构] Stellenbosch University