Biosystematics of the Dendroctonus frontalis (Coleoptera: Scolytidae) Complex

The validity of Dendroctonus frontalis Zimmerman, D. brevicomis Leconte, D. mexicanus Hopkins, D. vitei Wood, D. approximatus Dietz, and D. adjunctus Blandford as distinct species is supported by breeding experiments, karyology, male genitalia, and external morphology. The most recent synonymies proposed for this group, D. frontalis (= arizonicus Hopkins), D. brevicomis (= barberi Hopkins), and D. adjunctus (= convexifrons Hopkins), are corroborated. D. frontalis from several localities in the southeastern United States, Arizona, and Mexico produced fertile hybrids in all combinations tested. D. brevicomis from Arizona paired with beetles from California produced larvae readily. Pairings of D. mexicanus or D. brevicomis with D. frontalis produced no larvae. No breeding experiments were conducted with D. vitei , D. adjunctus , or D. approximatus . Karyotypes of all species were distinguishable by chromosome number, configuration of sex chromosomes, or size and centric position in autosomes. Male meiotic formulae were: D. frontalis , 7AA + XyP; D. mexicanus , 5AA + XyP; D. brevicomis and D. approximatus , 5AA + neo-XY; D. adjunctus 6AA + neo-XY. D. vitei was not studied cytologically. Seminal rods of male genitalia readily distinguished all species of the D. frontalis complex. Previously described details of the external morphology were insufficient to separate D. frontalis , D. mexicanus , and D. vitei with confidence. Mean pronotal widths differed significantly in all species comparisons except D. brevicomis vs. D. mexicanus . Under strong illumination, the pronotum and elytra of D. vitei were equally pigmented, whereas the elytra of D. frontalis and D. mexicanus were lighter than the pronotum. D. frontalis occurs at elevations of less than 2,000 m on east and west coastal-facing slopes of the Mexican Sierra Madre ranges where its key hosts are Pinus oocarpa and P. teocote. D. mexicanus occurs at 1,800–2,500 m in the central Mexican highlands and in semiarid forests of P. leiophylla and P. montezumae on interior slopes of the Sierra Ranges. The known range of D. vitei is extended to northeastern Mexico; its key host from Central America northward is P. pseudostrobus. D. frontalis apparently occurs frequently in association with D. vitei , but neither species was identified in association with D. mexicanus . The occurrence of D. mexicanus in Central America is not confirmed.