a somewhat larger group occasionally causes losses in forest products, while most 
species have never been economically important. 
Two subfamilies are recognized (/354): the Hylesininae and the Scolytinae. The 
Hylesininae are generally rounded behind, have a series of teeth or granules on the 
anterior margin of each elytron, and have the head visible from the dorsal aspect. 
The Scolytinae usually have a declivity at the posterior end, have no armament on 
the anterior margin of the elytra, and have the head either partly or completely 
concealed from above by the pronotum. Another mode of dividing the family 
Scolytidae is by feeding habit. The scolytid beetles of concern in the forest feed on 
the inner bark (phloeophagy), seeds and cones (spermophagy), wood (xylophagy), 
or on mutualistic fungi that they culture in wood (xylomycetophagy or ambrosia 
habit). The taxonomic divisions of the family do not necessarily correspond with 
the feeding groupings because the various modes of feeding have repeatedly 
evolved independently. This discussion of Scolytidae lists the genera and species by 
feeding habit and by approximate phylogenetic order within the feeding groups. 
Identification of some of the more important genera and species can be made by 
using illustrations and the descriptions of beetles’ morphology, gallery systems. and 
hosts. For the most part, taxonomic treatises on the Scolytidae of North America 
(7356) and Canada (/53) should be consulted when a reliable identification of a 
species of litthe economic importance is necessary. 
Scolytid adults are typically soft and yellowish when first formed but soon 
harden and turn reddish to dark brown or black. They are cylindrical beetles, from 
about 0.9 to 9.5 mm long. The larvae are white, curved, legless grubs with 
enlarged thoracic segments. The heads and mandibles are usually strongly scle- 
rotized and dark red-brown. Larvae of the Scolytidae are very similar to those of the 
Curculionidae (weevils). 
When scolytids attack, the adults construct entrance tunnels into the inner bark 
(phloem), pith, wood, or cone axil, depending on the species. The entrance tunnel 
empties into a nuptial chamber or is simply elongated into an egg gallery. In 
conifers, pitch and sap may exude from these holes and harden at the bark surface 
to form a pitch or resin tube. Ambrosia beetles and most bark beetles push boring 
dust out through the holes. Egg tunnels of bark beetles may be entirely in the 
phloem but more often engrave the wood. Egg tunnels of wood-feeding (xy- 
lophagus) species may be deeply cut into the wood surface or may be completely in 
the wood. Tunnels of ambrosia beetles are always in the sapwood and may be 
simple, branched, or compound. The females of most species deposit their eggs 
individually in niches cut into the sides of the tunnel and cover them with fragments 
of bark or wood. Others deposit groups of eggs in larger niches or grooves and 
cover them with boring dust. Still others, particularly some of the pith beetles and 
ambrosia beetles, place their eggs free in the tunnels. 
When bark beetle larvae hatch they feed away from the egg tunnel, usually at 
right angles to it. Many species can be recognized by their host and gallery pattern. 
Ambrosia beetle larvae remain in the egg tunnel and feed on fungi growing on its 
walls. Most Scolytidae pupate in cells at the ends of larval galleries, in the wood, in 
the outer bark, or between the wood and bark. The adults remain in those cells until 
their exoskeletons harden, sometimes even longer. While there, they usually feed 
on whatever phloem or xylem remains after the larvae finish feeding. When ready 
to emerge, the beetles gnaw holes through the bark to escape. The majority of a 
particular colony will emerge within a few days. The ambrosia beetle adults emerge 
through their parents’ entrance tunnels. 
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