PRELIMINARY CLASSIFICATION OF SCOLYTOIDEA. 209 



Alnus, Salix, and Populus. In Ipinse the true Pityogenes and Ips 

 are largely confined to Pinus and Picea. In Corthylinse the genus 

 Gnathotrichus is confined to the Pinus group, while Monarthrum is 

 partial to the dicotyledonous trees. In Cr3^pturgin8e the species of 

 Crypturgus, Dolurgus, and Dendrodonus are confined to Pinus and 

 allied genera. In HylesininaB Tomicus (Myelophilus), Hylurgus, and 

 Hylastes are confined to Pinus, while the true Hylesinus and Pteleo- 

 hius are particularly associated with Fraxinus. 



Examples of wide range of Jiost plants. — In Cryphalinse Hypothenemus 

 has a range of host plants from fungi up through many genera of the 

 Monocotyledoneee and Dicotyledonese but is rarely found as an inhabi- 

 tant of the Gymnospermse. Xylehorus has the widest range of all — 

 through the Coniferse and Angiospermse. Dryocoetes is divided be- 

 tween the conifers and allies of Quercus. In Corthylinse the genus 

 Xyloterus is divided between the Gymnospermse and a wide range 

 of the trees of the Angiospermse. Corthylus is confined to a wide 

 range of trees in the Angiospermse, as is also Monarthrum, except 

 in the case of a few records from the Pinus and Juniperus groups. 

 In Scolytin^ the genus Scohjtus as at present recognized is divided 

 between the genera of tiie Finales (except Pinus) and the Amentales 

 and Resales. In Platypodinse there is a wide range of food plants 

 in the trees of the Gymnospermss and Angiospermse. 



Associations of Species of Beetles and Species of Plants. 



In some of the genera which are restricted in the range of host plants 

 as well as in those with the widest range there are many species which 

 are restricted to a single species or group of closely allied species of 

 plants. In Phloeotribinse there are species peculiar to Morus, Celtis, 

 etc., and in Plilceosinus , with but very few exceptions, each species is 

 peculiar to, or prefers, a different species of cypress, cedar, or juniper, 

 or group of allied species. In Scohjtus we find Hicoria, Ulmus, Fagus, 

 Betula, Celtis, Quercus, Ahies, Picea, Pseudotsuga taxifolia, etc., with 

 species of beetles peculiar to each plant genus. 



Summary of Taxonomic Evidence Furnished by Host Rela- 

 tions. 



In a study of the relations between the insects and their hosts some 

 rather striking facts have been determined which have furnished evi- 

 dence to clear much of the confusion in classification based on mor- 

 phological characters alone and in which parallel or analogous char- 

 acters have been mistaken for those of affinity. By the old method 

 of morphological distinction closely allied species and genera have 

 been widely separated in the classification and distantly related ones 

 placed together. A number of such cases have been detected where 

 the host plant and the character of the galleries have been studied. 



