Biochemical evidence that Dendroctonus frontalis consists of two sibling species in Belize and Chiapas, Mexico
Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae: Scolytinae) is a major economic pest of pines in the United States, Mexico, and Central America. We report biochemical investigations relevant to the taxonomic status and semiochemistry of two distinct morphotypes of D. frontalis recently detected in the Central American region. Morphotype A beetles (pre-episternal area of prothorax of both sexes smooth, bulging callus on anterolateral margin of prothorax of females) and morphotype B beetles (pre-episternal area of prothorax of both sexes with fine ridges, reduced female callus) collected in infestations in Chiapas, Mexico differed significantly in their production of 10 behaviorally-active compounds occurring in the genus Dendroctonus, including the major pheromone components for D. frontalis. Notably, host attacking morphotype B females produced hundreds of nanograms of both endo-brevicomin and frontalin, whereas morphotype A females produced simlilar amounts of frontalin but subnanogram quantities of endo-brevicomin. Reanalysis of a published D. frontalis trapping study in Chiapas indicated that both morphotypes responded in greatest numbers when frontalin and endo-brevicomin baits were both present. In addition, we quantiÞed 18 different cuticular hydrocarbons (the methyl-branched alkane components) from both morphotypes collected in Belize and Chiapas as well as morphotype A beetles from the southeastern United States, and principal component analysis revealed nonoverlapping clusters associated with either morphotype. This evidence of two distinct, complex phenotypes coexisting in the same sites and host trees supports the hypothesis that the D. frontalis morphotypes represent separate species and consequently indicates that the taxonomy of D. frontalis should be re-evaluated in the Central American region.
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