Biology Reference
In-Depth Information
Evolutionary Adaptation of Native Herbivorous
Insects to Introduced Crop Plants
The Colorado potato beetle (
Leptinotarsa decemlineata
) is a native North
American insect whose original host appears to have been buffalo bur
(
Solanum rostratum
), a spiny broad-leafed herb of the potato family
(Solanaceae) occurring from Mexico north into the southwestern United
States (Harrison 1987). Buffalo bur itself may have been native to south-
ern Mexico, and, when it was introduced to more northern areas by
early Spanish settlers, the beetle may have followed this host plant (Hsiao
1978). In the southwestern United States, the Colorado potato beetle uses
other native species of solanaceous plants, such as silver-leaf nightshade
(
Solanum eleagnifolium
) and hoe nightshade (
S. sarrachoides
). When the
closely related cultivated potato (
Solanum tuberosum
) was introduced to the
United States in the early 1800s, it was quickly adopted as a host by the
beetle, which acquired its name from the new association. It has also
become a serious pest of tomato (
Lycopersicon esculentum
), a member of the
same plant family.
The new hosts of the Colorado potato beetle have enabled an enor-
mous expansion of its geographic range. In many areas, the beetle now
occurs where its ancestral host plants are absent. Genetically distinct host
races have developed on a number of native and cultivated solanaceous
plants (Hsiao 1978, 1982).To determine the extent of adaptation to new
hosts, Harrison (1987) conducted a series of feeding preference tests with
beetles obtained from native hosts in Arizona, potato plants in Alberta,
Canada, and tomato plants in Maryland. Beetles from all populations were
given the choice of buffalo bur, silver-leaf nightshade, potato, and tomato.
Beetles that had developed on native plants in Arizona showed high pref-
erence for the two native host plants but low preference for potato and
tomato. Beetles from Alberta and Maryland showed high preferences for
all plants, both the native host and crop plants. Since the tests were done
on newly emerged beetles from laboratory cultures, these results indicated
strongly that genetic adjustments had been made by the Alberta and
Maryland populations.The change was an expansion of host range, rather
than a shift, however, since all beetles retained a high preference for the
ancestral hosts.
In another study on the Colorado potato beetle, Horton et al. (1988)
examined growth and survival of beetles on buffalo bur, hoe nightshade,
and potato in Colorado. Success of the beetle appeared to reflect the local
