Biology Reference
In-Depth Information
quencies. The short-winged morphs essentially lacked flight muscles
and were capable of egg production earlier than long-winged morphs.
On the flamegold tree, however, about half of the long-winged morphs
also lacked flight muscles and thus were flightless. These individuals
were also able to produce eggs earlier than long-winged bugs that were
able to fly.Thus, selection apparently favored the maintenance of more
individuals capable of flight in balloon vine areas, where flight was
advantageous to enable bugs to locate new seed-producing plants
throughout the year. In areas of flamegold trees, selection favored early
egg production during the short period of the year when seeds were
available.
A third example of a shift of native herbivores to noncrop plants
involves the western anise swallowtail butterfly (
Papilio zelicaon
), which
uses 40 or more native species of plants of the carrot family (Apiaceae)
and the rue family (Rutaceae) (Thompson 1993). In California, this but-
terfly has begun to use fennel (
Foeniculum vulgare
), an invasive alien plant
of the carrot family that is abundant in many locations. Populations on
native plant hosts produce only a single brood each year, since these plants
are available for only a short period. Populations feeding on fennel, how-
ever, produce two or more broods annually, since this coarse weed remains
green throughout the summer.
Thompson (1993) conducted oviposition preference tests, using labo-
ratory-reared butterflies obtained from a population near Sacramento,
California, that was using fennel as its host plant.These tests compared egg
laying on fennel with egg laying on two locally available native host plants
and a third plant used as a host by related swallowtail species. All groups
of butterflies tested deposited eggs on fennel and the two native host
plants. Overall, however, a significant preference for fennel was shown at
the expense of one of the native food plants. In this case, therefore, only
a slight evolutionary adjustment had been made to the new alien host, in
spite of its availability in California for perhaps 50-100 yr.
Besides use of several fruit crop trees discussed above, flies of the genus
Rhagoletis
have adapted to alien honeysuckle (
Lonicera
) species in the
northeastern United States (Schwarz et al., submitted). In this case, the
population appears to be a hybrid of the native blueberry (
R. mendax
) and
snowberry maggot (
R. zephyria
) flies.This new form of
Rhagoletis
appears
to be widely distributed in regions where alien hosts occur and has appar-
ently arisen within the last 250 yr.
Native herbivorous insects have also shifted to introduced aquatic
