Molecular identification of two closely related species of mealybugs of the genus Planococcus (Pseudococcidae)

Authors: RUNG, A. - USDA,SEL; Scheffer, Sonja; EVANS, G. - USDA APHIS; MILLER, DOUGLASS - RETIRED, USDA, SEL

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2008
Publication Date: 5/1/2008
Citation: Rung, A., Scheffer, S.J., Evans, G., Miller, D. 2008. Molecular identification of two closely related species of mealybugs of the genus Planococcus (Pseudococcidae). Annuals of the Entomological Society of America. 101(3):525-532.

Interpretive Summary: Scale insects are serious agricultural pests and are common invasive species in the U.S. This research provides a molecular identification tool that allows identifiers to distinguish between two mealybug species (citrus mealybug and minor mealybug); these species are difficult or impossible to determine using morphological characters. The molecular tool is especially important to U.S. quarantine because the minor mealybug does not occur in the U.S. but is frequently intercepted at U.S. ports-of-entry. Results of the research will allow quarantine personnel to accurately distinguish these species and prevent the minor mealybug from becoming a pest in the U.S.

Technical Abstract: Morphological identification of the mealybug species Planococcus citri (Risso) and P. minor (Maskell), two serious agricultural pests, is often complicated by the existence of intermediate forms and a lack of knowledge of the intraspecific variation that occurs in each species. In this paper, we have explored the utility of two molecular markers, the mitochondrial gene cytochrome oxidase I (COI) and the nuclear gene, elongation factor 1 α (EF-1α) to ascertain the identity of these species and to provide reliable characters for their identification. Results from Maximum Parsimony analysis of DNA sequence data from both genes indicate the existence of a third clade from the Hawaiian Islands, whose members are distinct from both P. citri and P. minor. The individuals that group in this additional clade, though morphologically identical to P. citri, cluster with P. minor in ca 50% of the cladograms obtained with the COI, and 80% of the cladograms obtained with EF-1α. Our studies show that COI, in combination with morphological and geographical data, can be used to accurately identify the P. minor clade, the P. citri clade and the clade from the Hawaiian Islands in most cases. Given a few instances in which identification resulting from COI and EF-1α were in conflict, however, our results must be interpreted with caution and until additional studies are performed, no changes are proposed in the taxonomy of this species complex.