Biology Reference
In-Depth Information
9.
Evolutionary Adaptation
by Alien Herbivores
“These data [on variability and selection] indicate that change and the
potential for change are so great that the current patterns of host use
should probably be seen as ecologically dynamic and not an end result
of coevolutionary processes over millennia.”
—B
ERNAYS AND
G
RAHAM
(1988)
The codling moth (
Laspeyresia pomonella
), native to the Middle East, is a
pest of apples, pears, plums, and apricots throughout temperate regions of
the world. This moth reached North America in about 1750 and spread
rapidly through fruit-growing areas, reaching the Pacific Coast in less than
25 yr. In California, where it had appeared by 1873, it first was a pest of
apples (
Malus pumila
) and pears (
Pyrus communis
). In the early 1900s, how-
ever, it began to attack English walnuts (
Juglans regia
), and by 1930, it had
become a major walnut pest (Phillips and Barnes 1975) and had begun to
attack plums in the Los Angeles area. Still later, in the 1960s, it became a
serious pest of plums (
Prunus domestica
) in the San Joaquin Valley.
Host shifts by the codling moth have involved the evolution of distinct
races specializing on apple, walnut, and plum. Oviposition preference
tests, for example, showed that the apple race only rarely would oviposit
on walnut or plum, whereas the walnut and plum races strongly preferred
walnut (Phillips and Barnes 1975). Attempts to condition the walnut and
plum races by forcing them to oviposit on apple for up to13 generations
showed that the preference for oviposition on walnut and plum was still
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