Biology Reference
In-Depth Information
and 1955, it appeared near Melbourne,Victoria, an area of cooler climate.
The population here has only one generation annually and produces eggs
that hatch in less than half the time as eggs in New South Wales and
Queensland. Allozyme studies also revealed that Victoria moths show sig-
nificant differences in allele frequencies at several loci.Thus, in about 100
generations or fewer, the moth has made substantial adjustment to cli-
matic conditions (Murray 1982).
Few cases of evolutionary adaptation of introduced biocontrol insects
to new hosts have been documented, aside from the example cited at the
beginning of this chapter. Arnett and Louda (2002) tested the host plant
preferences of
Rhinocyllus conicus
for musk thistle (
Carduus nutans
) and var-
ious native thistles after about 28 generations had elapsed since introduc-
tion of the beetle for musk thistle biocontrol.They found no evidence of
a preference shift. In the Old World, however, this beetle is known to have
biotypes adapted to several thistle species of different genera (Zwölfer and
Preiss 1983). The beetles introduced to North America included two of
these forms (Goeden et al. 1985).
An interesting case of evolutionary adaptation by an introduced bio-
control insect to a target host was documented by Messenger and van den
Bosch (1971). A parasitic wasp,
Bathyplectes curculionis
, introduced for con-
trol of alfalfa weevils of the genus
Hypera
,was initially only weakly effec-
tive against the Egyptian alfalfa weevil,
H. brunneipennis
, because larval
weevils killed 35-40% of the wasps eggs by an immune response. Fifteen
years after the wasp's introduction, however, it had largely overcome the
weevil's immune response, and egg mortality had dropped to only 5%.
Microorganisms introduced for biological control have shown evolu-
tionary adaptation to their target hosts. Channer and Gowen (1992), for
example, examined patterns of infection of nematodes of the genus
Meloidogyne
by the obligate bacterial parasite
Pasturella penetrans
. They
found that populations of both organisms tended to be genetically het-
erogeneous. For the bacterial parasite, which produces spores that attach
to the nematode host, experiments showed that culturing the bacterium
on one nematode biotyps increased the effectiveness of spore attachment
to that biotype and reduced its effectiveness for other biotypes.
Perhaps the best-studied case of evolutionary change involving
microorganisms is that of the myxoma virus (
Leporipoxvirus
spp.). Rapid
evolutionary adaptation by the virus was expressed as a reduction in vir-
ulence following its introduction to Australia for biological control of the
European rabbit (
Oryctolagus cuniculus
). The myxoma virus, an endemic
disease of cottontail rabbits (genus
Sylvilagus
) in South America, had been
