Biology Reference
In-Depth Information
illustrate the complexity of evolutionary responses that alien invaders such
as these corn rootworms can show in agricultural ecosystems.
The European corn borer (
Ostrinia nubilalis
), a moth, is another exam-
ple of an insect pest that has shifted from one crop plant to another. It was
apparently introduced to North America near Boston, Massachusetts, in
about 1914 in broom corn or sorghum (
Sorghum vulgare
) material
imported for the manufacture of brooms. This insect quickly became a
major pest of maize (
Zea mays
), as well as many other crop plants. It also
infests a wide range of wild native and alien plants. Since its establishment,
biotypes differing in host specificity and number of annual generations
have appeared (Hudon and LeRoux 1986).Three forms have been distin-
guished, characterized by one (univoltine), two (bivoltine), or several
(multivoltine) generations during the year.
Pornkulwat et al. (1998) used random amplified polymorphic DNA
analysis to distinguish these biotypes.The multivoltine biotype, character-
istic of the southern United States, farthest from the presumed point of
introduction in Massachusetts, was most distinct. It is likely that the form
introduced was univoltine or bivoltine and that the multivoltine biotype
has evolved in North America. It is also possible that separate introduc-
tions of corn borers differing in life history patterns occurred. Additional
studies of these biotypes of the corn borer in New York State and Italy
showed that they differ in the isomer composition of attractant
pheromones produced by females (Cardé 1983). These differences may
reflect a founder effect associated with the introduction of the corn borer
to North America. In New York, however, three races of univoltine and
bivoltine forms differing in pheromones have been noted in corn borer
populations (Glover et al. 1991). One pheromone type shows a bivoltine
annual cycle, the other both univoltine and bivoltine patterns. Some
hybridization occurs, but the two pheromone races show partial repro-
ductive isolation. Thus, some of these forms may represent incipient
species (Cardé et al. 1978).
The Hessian fly (
Mayetiola destructor
) provides a good example of
another evolutionary pattern: the ongoing evolutionary interaction
between an insect herbivore and a set of host species.This species is per-
haps the most serious insect pest of wheat throughout the world. Hessian
fly also attacks barley, rye, and occasionally oats. Both wheat and the Hes-
sian fly are alien species in North America and many other world regions.
In North America, the Hessian fly appeared on Long Island, New York,
in 1779, perhaps having been introduced in wheat straw used as bedding
for horses of European soldiers during the Revolutionary War.The Hes-
