Biology Reference
In-Depth Information
host plants are members of the genus
Hampea
,a tropical American genus
of the family Malvaceae, to which cultivated and wild species of cotton
(
Gossypium
spp.) also belong (Jones 2001).The boll weevil itself uses two
species of
Hampea
that occur on the Gulf Coast of southern Mexico.
Analysis of the phylogenies of
Hampea
and the
Anthonomus
weevils that
use them indicated that the use of
Gossypium
is a relatively recent ecolog-
ical and evolutionary shift. The range of the two species of
Hampea
used
by the boll weevil coincides with the region of the Mexican Gulf Coast
considered to be the probable site of domestication of upland cotton
(
Gossypium hirsutum
). The boll weevil has followed cotton to many parts
of the world where this crop is grown and exhibits at least two ill-defined
crop races in North America: “southeastern” and “Mexican.” Since the
boll weevil first appeared in the United States in Texas in 1892, the dif-
ferentiation of the southeastern form is probably quite recent. The boll
weevil also shows a race that appears to be confined to the wild species,
Gossypium thurberi
, in southern Arizona and northern Mexico. Based on
analyses of mitochondrial DNA, the Thurber and southeastern races of
the boll weevil differ markedly in haplotypes, although their morphology
is very similar (Roehrdanz 2001). Since the crop race of the boll weevil
was eradicated in Arizona in 1992, no evidence has been found that the
race on wild cotton has moved into cultivated cotton.
Rapid evolutionary shifts or adaptation by a number of alien herbi-
vores have been documented, as illustrated by the codling moth example
introducing this chapter.The western corn rootworm (
Diabrotica virgifera
),
native to Central America, provides a similar example. This crop pest has
invaded regions of maize (
Zea mays
) cultivation in much of North Amer-
ica and became established in maize-growing areas of eastern Europe in
the mid-1990s. In North America, damage by the larvae of this beetle
approaches $1 billion annually. One of the tactics for dealing with this
pest has been crop rotation in which maize is alternated with soybeans
(
Glycine max
). Recently, however, a genetic form of corn rootworm with
preference for oviposition and feeding on soybean has appeared in areas
where this rotation has been practiced (Sammons et al. 1997). Genotypes
of the western corn rootworm that have extended diapause have also
appeared, enabling larvae to survive the rotation period with soybean and
infect the next maize crop (Levine et al. 2002).The northern corn root-
worm (
Diabrotica barberi
) has also evolved a biotype with extended dia-
pause, enabling it to survive for a year during which another crop is alter-
nated with corn (Krysan et al. 1986; Levine et al. 1992). These
developments, together with genetic resistance to various insecticides,
