Diagnostic markers for Planococcus ficus (Signoret) and Planococcus citri (Risso) by random amplification of polymorphic DNA-polymerase chain reaction and species-specific mitochondrial DNA primers

Planococcus ficus (Signoret) and Planococcus citri (Risso) (Hom., Pseudococcidae) are important phytophagous
components in different agroecosystems. The two species may coexist in the same environment and are most
difficult to distinguish by morphological features. The aim of this study was to find genetic markers suitable for
distinguishing P. ficus from P. citri, to assist in the rapid identification of field specimens. By using synthetic sex
pheromone-baited traps, pure male populations of both species were collected from a vineyard and from a citrus
orchard in northern Sardinia, Italy. Individual males of citrus and vine mealybugs were preliminarily examined by the
random amplification of polymorphic DNA (RAPD) technique. Among twelve 10-mer random primers, the
oligonucleotide OPL-12 generated several markers suitable for distinguishing between the two species. This primer was
then used to characterize individual males and females of both mealybug species collected near pheromone-baited traps
in vineyards and orange orchards from different geographic areas. Reference samples from other regions of southern
Italy were also included. A clear differentiation of the two species was accomplished according to their pattern of
amplification, thus confirming a high level of intra-specific genetic homogeneity. Consequently, two fragments of the
cytochrome c oxidase I gene from P. citri and P. ficus were compared and two pairs of species-specific polymerase chain
reaction (PCR) primers were developed based on diverging sequences. These primers allowed sensitive and reliable
PCR identification of both males and females of P. citri and of P. ficus of different geographic origin.