Biosystematics of the Turpentine Beetles Dendroctonus terebrans and D. valens (Coleoptera: Scolytidae)

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Controlled experiments and diagnostic differences in previously unreported morphological characters confirm that Dendroctonus valens LeConte and D. terebrans (Olivier) are valid species rather than color morphs of a single biological species. D. terebrans from distant localities (Florida and Massachusetts) produced fertile hybrids. D. valens females from the western part of its range (Arizona, California) paired with eastern (New York) males laid eggs which developed into advanced embryos but did not hatch. In the laboratory, males did not discriminate in entering galleries of conspecific and heterospecific females, but 2 d after males of either species were given access to females, conspecific pairs were significantly more frequent than heterospecific pairs. Observations of beetle interactions in bark-glass sandwiches indicated that males readily attempt to copulate with females, regardless of species, but females consistently reject or ignore heterospecific males. Both species had male meiotic cells with 13 autosomal bivalents and sex chromosomes in a parachute configuration to give the formula 13AA + Xyp. However, a D. terebrans from east Texas displayed an autosomal fusion and the formula 12AA + Xyp. Two of five D. terebrans specimens from Florida were heterozygous for a fusion chromosome. Individuals of the two species differed diagnostically by the configuration of spurs on the metatibia, the density of striations on the pars stridens of the terminal abdominal sternum, the shape of the seminal rod of the male genitalia, and by the relative lengths of abdominal sterna 5 plus 6 versus sternum 7. We postulate that D. valens and D. terebrans have strong negative interactions in the Appalachian Mountains and Atlantic coastal areas where ranges of the two species meet. Females compete for the same host material, and males will readily join a female of either species. Rejection of the heterospecific male and failure of eggs to hatch (should interspecific insemination occur) will prevent gene flow between species.