Contents - Faperta

Molecular Markers for Diagnosis of Insect Pests and Their Natural Enemies 481
They have also been found to be useful for detection of alien strains or species, which may
be unadapted to hosts or genotypes present, and lead to failure of control operations
(Hufbauer, Bogdanowicz, and Harrison, 2004). Allozymes, RFLP, RAPD, microsatellite,
and mtDNA-based markers have been used for differentiating biotypes and sympatric
species (Laroche et al., 1996; Hoy et al., 2000; Hufbauer, Bogdanowicz, and Harrison, 2004).
The tephritid fruit fl ies, Bactrocera philippinensis (Drew and Hancock) and B. occipitalis
(Bezzi) are of signifi cant importance as quarantine pests (Yu et al., 2005). Real-time qualitative
PCR using SYBR green assay with melting curve analysis has been developed to
identify these two symptomatic species, and can be used as a rapid detection technique in
quarantine inspection.
Phylogenetics and Population Structure
The advent of molecular techniques to allow discrimination of species and identifi cation
of genetic polymorphism within and between populations has added a new dimension for
understanding taxonomic relationships, evolution, and epidemiology of insect pests and
their natural enemies. Molecular techniques are being used in ecological research to elucidate
the structure of populations and to estimate gene fl ow between populations occupying
discrete habitats or utilizing different host species. Such population studies are valuable
for assessing the effects of habitat fragmentation, and may be useful to develop ecological
modifi cation strategies for maintaining biodiversity on farmland and promoting sustainable
pest management. Assessing gene fl ow among populations in agricultural ecosystems
will also aid risk assessment of the release of genetically modifi ed organisms into the
environment. Ribosomal DNA and mtDNA have been used widely in phylogenetic studies.
Several studies have used molecular phylogenetic approaches to ascertain the phylogenetic
position of Aphidinae and the relationship of the taxa within the family (Belshaw
and Quicke, 1997; Downton and Austin, 1998; Smith et al., 1999). Simultaneous application
of morphological and molecular data has also been used to resolve the relationship among
the apocritan wasps (Dowton and Austin, 2001).
Studies on basal relationships in Coleoptera have been based on the mitochondrial cox1
(Howland and Hewitt, 1995) and the nuclear small subunit rRNA genes (Caterino et al.,
2002), but the use of a single locus in these cases has been found to be insuffi cient to resolve
the main phylogenetic questions. Using EST-based approaches that do not rely on degenerate
PCR would be of great advantage, and the utility of this approach has been tested by
producing phylogenetic trees for the basal groups of Coleoptera from 66 genes coding for
ribosomal proteins (RP). The use of nuclear genes as a source of phylogenetic data requires
an appreciation of the complex nature of genome evolution, involving gene loss, duplications,
expansion of gene families, and functional diversifi cation. Assignment of gene orthology
is diffi cult even between fairly closely related groups such as the dipteran, Anopheles
gambiae (Giles) and D. melanogaster, where genes diversifi ed independently in each lineage
(Zdobnov et al., 2002). Increased taxon sampling can improve the confi dence of orthology
assignments by identifying the origin of gene copies, facilitating inferences on gene duplications,
clarifying the relationship between gene content, and the diversity of lineages
(Parkinson et al., 2004).
The ISS-PCR markers have been used to study geographic variation in population structure
of the egg parasitoid, Gonatocerus ashmeadi Girault of the grassy winged sharp-shooter,
Homalodisca coagulata (Say) (de Leon and Jones, 2005). The molecular data indicated restricted
gene fl ow using six populations from the United States and Argentina. Ji et al. (2003) characterized
fi ve polymorphic loci in cotton bollworm, Helicoverpa armigera (Hubner), from two