Biology Reference
In-Depth Information
tral America,Venezuela-Brazil, and the region from Colombia to Peru. In
Argentina, a still different haplotype, unique to this world region, is com-
mon.These patterns indicate that multiple introductions have occurred to
the New World from the Mediterranean region or Africa. Single haplo-
types occur in fruit fly populations in Hawaii and Australia. Australian
populations might have been founded by flies from the Mediterranean
region or the Andean region of South America. Hawaiian populations
probably came from the Venezuela-Brazil area of eastern South America.
Mediterranean fruit flies have appeared occasionally in Florida, Texas,
and California (Gasparich et al. 1997). These small outbreaks have been
attacked vigorously with baited traps, release of sterile males, and insectici-
dal sprays, the result usually being that eradication was claimed. Each out-
break has usually been considered as a new invasion, rather than an upsurge
of a population reduced to an undetectable level. In California, for exam-
ple, six outbreaks were recorded between 1975 and 1994 (Carey 1996).The
locations of several of the outbreaks are similar and suggest that an estab-
lished population exists. Haplotypes of most of the fruit flies in the six out-
breaks match that common in Central America (Gasparich et al. 1997), so
one or more introductions from this region may account for most out-
breaks. In 1992, however, a different haplotype appeared in both northern
and southern California, indicating that an independent introduction from
a region other than Central America had occurred.Thus, at least two intro-
ductions, and possible more, have led to the California outbreaks.
In Florida, five outbreaks of Mediterranean fruit fly occurred between
1962 and 1994 (Gasparich et al. 1997). None of the haplotypes appearing
in Florida can be traced to Central America. Furthermore, the haplotypes
appearing in 1962-63, 1984 and 1994, and 1990 were different, indicat-
ing that four independent introductions probably occurred. Thus, multi-
ple introductions have played a major role in the invasion of various world
regions by this insect pest, with resurgence of populations from very low
levels very likely playing a role in sudden outbreaks of the species in Cal-
ifornia. In any case, a very complex evolutionary potential is now present
because of the existence of Mediterranean fruit fly populations of differ-
ing genetic makeup in different world regions.
Invasion Routes of Alien Species
Genetic analyses can help to identify major invasion routes, particularly
those followed by aquatic invaders. The spiny cladoceran (
Cercopagis pen-
goi
), a native of the Black and Caspian Seas of western Asia, colonized the
