Genetic relationships of populations and the origins of new infestations of the Mediterranean fruit fly

A polymerase chain reaction-restriction fragment length polymorphism (PCR-R FLP) approach based on the variation in intron sequences of the glucose-6-p hosphate dehydrogenase (Zw) gene was used to assess genetic variability in 26 populations and infestations of the Mediterranean fruit ny (medfly), Cer atitis capitata. Beginning with the exon-primed intron-crossing PCR (EPIC-P CR) method to amplify introns of this gene, five alleles were identified on the basis of DNA sequence variants. Several of these variants affect recog nition sites for the restriction enzymes RsaI and TaqI. Using these enzymes in successive digestions of the EPIC-PCR products, each of these alleles c an be identified directly from individuals. From this, surveys were conduct ed to document genotypes and allele frequencies in these samples. The relat ionships of existing populations and the invasion process represented by ne w infestations of the medfly were analysed using a principal coordinate ana lysis and the AMOVA method to quantify the distribution of genetic diversit y at different levels in a hierarchical manner. From these results, a frame work of genetic relationships among the populations and infestations is pre sented. In addition, for at least some of the infestations, populations tha t are probably acting as sources of origin have been identified.