Beetle infestation is more serious if the beetle is

a vector of a tree pathogen, and such tree diseases

can have serious consequences that can also affect

trees grown away from monocultures. The most

famous example is the Dutch elm disease fungus

Ophiostoma novo-ulmi, which is spread by elm bark

beetles of the genus Scolytus (Curculionidae). The

female bark beetle carries fungal spores in special

organs called mycangia, and inoculates them into

the tree in which she lays her eggs, so that the

larvae developing in their tunnels can feed on

the fungal fruiting bodies. In the case of Dutch

elm disease, the fungus being transmitted by the

beetles became extremely pathogenic to the trees,

and killed millions of elms in Europe, Asia, and

North America.

Insect pests can be much more damaging

outside their native range, where the local trees

of the genus that they attack have not evolved

alongside them, and where specific parasites and

predators that usually keep the pest

numbers under control are absent.

Examples include forestry pests and

pests of amenity planting such as street

and garden trees, like Agrilus planipennis,

the Emerald Ash Borer (Buprestidae),

and Anoplophora glabripennis, the Asian

Longhorn (Cerambycidae), both much

more problematic in North America than

they are in their native China.

Under adverse climatic conditions, even a

native species can become a very serious forestry

pest. The Mountain Pine Beetle Dendroctonus

ponderosae (Curculionidae), for example, has been

responsible for the death of millions of acres of

pine forest in North America, peaking in 2009,

after a series of dry summers placed trees under

environmental stress. This, coupled with mild

winters, failed to reduce the beetle populations to

manageable levels.

left | Agrilus planipennis

(Buprestidae) Emerald

Ash Borer, an introduced

pest from China, emerges

from an infested ash tree

in the USA.

below | Ambosiodmus

lecontei (Curculionidae)

From North America, this

female has laid eggs and

is cultivating white fungus

for the larvae to eat.