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Beetle feeding habits

them—in fact, humans extract some of these

chemicals to make insecticides such as pyrethroids.

The relatively few groups of insects that have

successfully circumvented plant defenses, either by

metabolizing them or by storing them to use for

their own protection, have become extremely

species-rich and abundant as a result. These

include butterflies and moths (Lepidoptera) and

several superfamilies of beetles, particularly the

families Chrysomelidae (Chrysomeloidea), the

leaf beetles, and Curculionidae (Curculionoidea),

the weevils, which are two of the largest groups in

the whole animal kingdom, both exceeding 30,000

known species.

Plant-feeding, or phytophagous, insects are

usually specialized to feed on a single genus or

species of plant, which allows them to adapt to

overcome the specific chemical protection of their

target host plant. Over long periods of time, some

plants evolve increasingly powerful toxins, and

herbivores adapt by developing ever more effective

means of detoxifying the compounds. This is

called an “evolutionary arms race,” and it

increases the association between the insect and

the host plant, since the specialized insects become

the only herbivores able to feed on the toxic plant,

and may even be attracted by the smell of the very

chemicals evolved to combat them. The closeness

of the association between phytophagous beetles

and specific plants may have driven the

diversification of beetles, since their ancestors

were feeding on the ancestors of flowering

plants, which diversified rapidly.

Phytophagous insects are also usually adapted

to feed only on a particular structure of the

host plant. So, for example, an oak tree may have

LIVE PLANT TISSUE

Living plants, in forests, vegetated swamps, and

grasslands, cover much of the world’s land surface

and shape terrestrial habitats; most of the

nutrients in land ecosystems are locked up in living

plants. Any animals that can adapt to feed on this

vast resource can reap great ecological benefits.

Unlike animals, plants cannot hide or run away;

nor can they defend themselves with horns or

jaws—but they are, nevertheless, difficult to eat for

most animals. For a start, the cellulose of which

they are built requires a complex intestine, usually

including symbiotic bacteria, to extract any

nutrition from it. Additionally, many plants

produce toxic defensive compounds specifically to

prevent insects and other herbivores from eating

left | Scolytus multistriatus (Curculionidae) Adults and

larvae of Elm Bark Beetle feed on living trees, and can

transmit the tree-killing Dutch elm disease fungus.