Biology Reference
In-Depth Information
C. rosa
individuals from Kenya from those from South Africa (
Douglas and
Haymer 2001
), if additional populations from each geographic region can be
tested and the utility of the length variation is confirmed.
Armstrong et al. (1997)
reported efforts to identify tephritids for quarantine
purposes in New Zealand using 18S and 18S
+
ITS regions of ribosomal DNA.
These were amplified from larval DNA by the PCR and 19 species in four genera
were evaluated. Restriction analysis of the 18S product provided poor resolu-
tion, even at the generic level. Digestion of the 18S
+
ITS PCR product gener-
ated 13 diagnostic haplotypes using four restriction endonucleases. Six of 10
Bactrocera
species could not be diagnosed separately with this method despite
analyzing the effects of 22 restriction enzymes. However, all six species are con-
sidered high risk with respect to their likely establishment in New Zealand, so a
diagnosis of suspicious larvae as
Bactrocera
would result in the same response by
regulatory authorities.
The above-described studies provide an overview of some of the approaches
that could be taken to use molecular methods to identify
C. capitata
immature
stages and to discriminate
C. capitata
from other tephritids. However, additional
research is required before these approaches could be used in specific quaran-
tine procedures and none are useful for all objectives. For example, if a DNA
probe is intended to identify
C. capitata
immatures when tephritid larvae are
found in infested fruit in border inspections, then the probe should be validated
against all potential fruit fly species that might be introduced (recall that
≈
250
species are considered pests). However, it may not be relevant to identify the
larvae to the species level; rather, it may be relevant only to confirm that the
larvae are from one of the pest tephritid genera, because all would be quar-
antined pests. In addition, the question should be answered as to how often
false positives and false negatives occur under real-world conditions with the
test method? In some ecological studies, it might be relevant to discriminate
between immatures of two, or a few, tephritid species, which would be much
easier, because the test could be validated only against these species.
13.7.4.3 Geographic Origin of Medfly Populations
Efforts to determine the geographic origin of Medfly populations in new envi-
ronments were difficult. Studies were conducted using RAPD-PCR, enzyme anal-
ysis, nuclear introns, mitochondrial DNA, RFLP-PCR, and microsatellites. Some
projects are described briefly to illustrate that each method has strengths and
weaknesses in answering a specific question.
Regulatory agencies often want to know where a pest population came from
because it might allow them to prevent future invasions if they know where to
