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Beetles and humans

During the Neolithic Revolution, some

12,000 years ago, when people started to live in

settled societies, they domesticated the first few

plants as food crops, and many of these were

annual cereals or legumes with large seeds. Arable

farming can be an invitation to pests, because

farmers grow large numbers of plants of a single

species close together in monocultures, in the

same place every year. It seems likely that crop

pests have been with us as long as agriculture has,

and this is supported by evidence of peas bored by

Chrysomelidae: Bruchinae (probably the species

Bruchus pisorum) from archeological sites in Jordan

and Turkey some 8,000 to 9,000 years old.

As the selection of crops we grow has

increased, so has the selection of potential pests,

especially when crops are transported to new

areas. A famous example is the Colorado Potato

Beetle Leptinotarsa decemlineata (Chrysomelidae),

a leaf beetle native to the Rocky Mountains

of North America, where its original host plant

was a native weed, buffalo bur. During the

nineteenth century, with widespread

planting of potatoes imported from

the Andes, the beetle switched

host to this new, abundant

resource, and within 20 years

it was found on potatoes from

coast to coast of continental

USA. In the 1920s it reached

Europe and spread east, until

it occupied a belt around the

whole northern hemisphere,

PESTS OF CROPS

One of the reasons for the great success of beetles

is the close association of many families with

plants, so that almost every plant genus has several

species of beetles feeding on it, many of which are

host-specific. Furthermore, different beetles will

utilize different parts of the plant, which means

that a given host plant may support a range of

beetles. This intense herbivory is, of course,

damaging. Many plants have attempted to avoid

it by becoming annual, growing from a seed to

a mature plant that produces its own seeds in

a single season, then dying off, with its offspring

growing some distance away next season. Beetles

have responded to this by becoming more mobile

and developing senses that allow them to “smell”

their target host plants and home in on them over

long distances.

left | Leptinotarsa decemlineata

(Chrysomelidae) The strikingly

marked Colorado Potato Beetle

is a scourge of potato agriculture

across the northern hemisphere.