. An annotated list of the important North American forest insects. Forest insects. TARMEES' BULLETIN 15 82. Figure 3.—Larva or grub of a pine bark beetle {Ijjs sp.). Enlarged 10 diameters AMBROSIA BEETLES The ambrosia beetles (fig. 4) or pinhole borers, which are the adults of the second class, closely resemble the bark beetles in gen- eral appearance. Their work differs considerably, however, and can easily be distinguished. After the ambrosia beetles enter the bark they bore immediately into the sapwood and sometimes into the heartwood, where they extend their galleries in all directions, e
. An annotated list of the important North American forest insects. Forest insects. TARMEES' BULLETIN 15 82. Figure 3.—Larva or grub of a pine bark beetle {Ijjs sp.). Enlarged 10 diameters AMBROSIA BEETLES The ambrosia beetles (fig. 4) or pinhole borers, which are the adults of the second class, closely resemble the bark beetles in gen- eral appearance. Their work differs considerably, however, and can easily be distinguished. After the ambrosia beetles enter the bark they bore immediately into the sapwood and sometimes into the heartwood, where they extend their galleries in all directions, each making a hole about the size of a pinhead. (Fig. 5.) While boring these tunnels they push out sawdustlike par- ticles, which either fall out loosely in piles (fig. G)', or come out in stringlike masses (fig. 7) as if being squeezed from a tube. These borings are white, whereas those of the bark beetles are usually brownish and fall loosely from the holes in the bark. In cer- tain cases much of it, however, remains in the tunnels. The galleries of the ambrosia beetles are round, always free from borings, and quite often their walls are stained black. Their food is not the wood, but a substance called " ambrosia," which is a coating formed of a minute fungus that is propagated by the beetles themselves. It is this that stains the walls of their gal- leries.* The damage by these borers is caused almost entirely by the adult beetles, as the larvae, until mature, stay either in the original gallery or m separate cells where they are in most cases cared for and fed by the beetles. Beetles of this group do not often cause much damage to wood after it has been put into log cabins or rustic work if the trees are cut in the fall of the year, be- cause then it has seasoned by the time the beetles are flying and is too dry to be in a suitable condi- tion for them to work in it. If the wood is cut green, however, and is used during the period of insect activity, it may be at
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