Two Species within Dendroctonus frontalis (Coleoptera: Curculionidae): Evidence from Morphological, Karyological, Molecular, and Crossing Studies

Dendroctonus frontalisZimmermann is considered one of themost important economic and ecological forest pests in the United States, Mexico, and Central America. Recently, two apparent morphological variants of this species were discovered occurring syntopically in Central America and southern Mexico. Morphotype A beetles lack a series of Þne parallel ridges on the episternal area of the prothorax that are present on morphotype B. The goal of the present work was to clarify the taxonomic status of the morphotypes of the D. frontalis species complex. Geometric morphometric analyses of seminal rod and spermatheca shape together with the characterization of 16 attributes of externalmorphology revealed differences in quantitative and qualitative characters that distinguished adults of the twomorphotypes fromeachother aswell as from theclosely related speciesDendroctonus vitei Wood and Dendroctonus mexicanus Hopkins. Karyotype analysis of morphotype B revealed a chromosomal formula (5AA Xyp) distinct from that found in morphotype A previously reported forD. frontalis (7AA Xyp). In the laboratory, forced intermorphotype crosses producedF1 progeny but at lower frequency than intramorphotype pairings, and dissections of spermatheca revealed a lower frequency of insemination at least one type of heterotypic cross. Phylogenetic analysis of the D. frontalis species complex based on 786 bp of the cytochrome oxidase I gene indicated that morphotypes B and A are two independent groups with 98% nodal support withinD. frontalis. These data provide compelling evidence that the two syntopic morphotypes represent two distinct sibling species.