Contents - Faperta

Molecular Markers for Diagnosis of Insect Pests and Their Natural Enemies 479
Restriction Fragment Length Polymorphisms
The restriction fragment length polymorphisms (RFLP) probes allow very fi ne mapping
of loci, and have several advantages over morphological markers. These include the ability
to behave in a codominant manner and detect heterozygotes, whereas the morphological
markers do not detect heterozygotes. The RFLP markers detect greater allelic variation in
natural populations than morphological markers and are unaffected by environmental
effects. The disadvantages of RFLP linkage analysis include the additional time required
to complete an analysis (7 to 10 days) and the use of radioactive isotopes.
Inter-Simple Sequence Repeats
The inter-simple sequence repeats (ISSRs) have shown good promise for studying the
population biology of plants. The ISSRs can be advantageous when time and material costs
preclude development of more robust markers such as locus-specifi c SSRs. ISSRs can
reveal polymorphisms and elaborate detection protocols. These are a valuable addition to
PCR-based markers in studies where genomic fi ngerprinting is appropriate for large-scale
screening of genetic variation in animal populations (Abbot, Withgott, and Moran, 2001).
ISSRs have been used to study variation in aphids, Acyrthosiphon pisum Harris and Pemphigus
obesinymphae Moran, and yellow fever mosquito, Aedes aegypti (L.) (Abbot, 2001).
Application of Molecular Markers for Insect Diagnosis
Diagnosis of Insect Pests and Their Natural Enemies
The addition of molecular techniques to the taxonomist’s arsenal has been one of the major
advances for insect identifi cation. It has shown a great potential to expedite the identifi cation
of cryptic species, unidentifi able life stages, and critical taxa such as disease vectors.
This has led to development of diagnostic kits, enabling nonspecialists to discriminate
rapidly between closely related species of insect pests, which are diffi cult to separate using
conventional taxonomic approaches. It has also made it possible to discriminate between
different isolates of microbial pathogens such as entomopathogenic fungi, which vary in
virulence against the target insect pests, allowing monitoring of the spread and survival
of released strains in the crop environment. Similarly, the spread of exotic or introduced
strains of crop pests and diseases can also be monitored using these techniques.
Correct taxonomic identifi cation is essential for effective pest management, particularly
for identifi cation of natural enemies. RAPDs, SSRs, and allozymes have been widely used
for such studies. RAPDs have been used for distinguishing populations of coccinnellid
beetles from different geographical areas (Roehrdanz and Flanders, 1993), while RFLP and
mtDNA markers have been used as diagnostic markers for distinguishing insect populations
or migration (Hall, 1998; Nielsen et al., 2000) (Table 17.1). RAPDs have also been used
to differentiate between colonies of Ageniaspis citricola Logvin., which showed differences
in life cycle and behavior (Hoy et al., 2000). Allozymes have been used for differentiating
Aphidius ervi Haliday attacking pea aphid, A. pisum, and nettle aphids, Microlophium carnosum
(Buckton) (Atanassova et al., 1998). Enzyme electrophoresis has been used to monitor
parasitism of the aphid, Sitobion avenae (F.) (Walton, Loxdale, and Allen-Williams, 1990),
while Black et al. (1992) used RAPDs to identify two endoparasitic wasps, Diaeretiella rapae