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BARK BEETLES

CURCULIONIDAE: SCOLYTINAE

S

colytinae, bark beetles, is a weevil subfamily

that lost the characteristic weevil rostrum and

became wood borers. Bark beetles live between

the wood and the bark of coniferous or deciduous

trees. Most are host-specific, attacking only one

genus or species of tree. A few are polyphagous,

which means they feed on a broad range of hosts,

and even fewer feed on herbaceous plants,

especially legumes (Fabaceae).

Many species excavate intricate tunnels under

the bark, with tunnel patterns identifiable to genus

or species. These often consist of a central tunnel,

excavated by the female, and smaller tunnels

radiating away from it, where her eggs have hatched

and the larvae dig their own tunnels, growing in the

process. In many species, the female has pocketlike

organs called mycangia from which she introduces

spores of fungi, which then grow and provide food

for the larvae.

Some of these fungi are pathogenic to the trees,

so some bark beetles are vectors of tree diseases,

such as the genus Scolytus, which spreads Dutch elm

disease Ophiostoma novo-ulmi, a fungus that killed

millions of mature elms across Europe, Asia,

and North America in the late twentieth

century. Some elms remain, but when they

reach a certain size, they are infested by

the beetles and killed by the fungus, so the

gigantic elms that form the background to

many eighteenth-century paintings have

disappeared from the landscape. Other

bark beetles, of the genus Dendroctonus,

attack climate-stressed conifers in North

America, and the results of outbreaks are

discussed in the section on forestry (see page 58).

subfamily

Scolytinae

known species

6,000

distribution

Worldwide except Antarctica

habitat

Forests, anywhere with trees. Only a few

species feed on herbaceous plants

size

1–9 mm

diet

Wood and wood-feeding fungi

notes

Scolytinae are now recognized as true

weevils, but for many years they were

classified as a separate family of their

own because they lack the beaklike rostrum,

the projection of the front of the head

with the mandibles at its apex, which was

considered a defining weevil feature.

The rostrum is used by weevils as a drill

to prepare a hole for egg laying, but in

CURCULIONIDAE: SCOLYTINAE