Contents - Faperta

Molecular Markers for Diagnosis of Insect Pests and Their Natural Enemies 485
Detection of Natural Enemy–Insect Host Interactions
Identifi cation of gut contents of predatory insects provides useful information on predator-prey
interactions (Symondson, 2002). Direct observations in the fi eld are quite diffi cult
and cumbersome as both prey and predator can be quite small, and at times hide away
from visual detection. Analysis of gut contents is useful for chewing types of insects, but
not suitable for piercing-sucking types of insects. Immunological assays based on preyspecifi
c protein antibodies have been used widely (Hagler and Naranjo, 1997; Symondson
et al., 1999), but their effi cacy is infl uenced by several factors. To overcome these problems,
several molecular marker-based techniques can be used to study the interrelationships
between the natural enemies and their insect hosts (Symondson, 2002; Greenstone, 2006).
Specifi c probes and markers have been used to detect the prey in gut contents of the
predators (Symondson, 2002). PCR-based probes have been found to be more effective than
protein electrophoresis (Murray, Solomon, and Fitzgerald, 1989; Solomon, Fitzgerald, and
Murray, 1996). SCAR markers derived from RAPD bands have been used to detect
H. armigera (Agusti, De Vicente, and Gabarra, 1999a) and whitefl y, Trialeurodes vaporariorum
(West.) (Agusti, De Vicente, and Gabarra, 1999b) in predator grubs. Multiple copy esterase
genes from Culex quinquefasciatus Say have been detected in carabid, Pterostichus cuprea (L.)
(Zaidi et al., 1999), while Cuthbertson, Fleming, and Murchie (2003) used species-specifi c
mitochondrial primers to detect Rhopalosiphum insertum (Walker) in the gut of the predatory
mite, Anystis baccarum (L.).
A number of studies have used PCRs for analyzing predator gut contents (Agusti, De
Vicente, and Gabarra, 1999a, 1999b; Chen et al., 2000; Hoogendoorn and Heimpel, 2001).
Primer sets that amplify fragments of different lengths, which have a characteristic detection
time, have also been used to estimate the time since feeding from the number of bands
that were detectable (Hoogendoorn and Heimpel, 2001). Shorter fragments can be detected
for a longer time span after ingestion of the prey than the longer fragments in Coleomegilla
maculata DeGeer and Harmonia axyridis (Pallas). Detection time has been found to be
independent of meal size, sex, or predator weight. Primers amplifying fragments of mitochondrial
COI have been used for identifi cation and distribution of the corn borer, Ostrinia
nubilalis (Hubner), larval parasitoids, Lydella thompsoni (Herting) and Pseudoperichaeta
nigrolineata (Walker). Molecular markers indicated three times higher levels of parasitism
than with the conventional methods (Agusti et al., 2005). There were no differences in
parasitism by the two tachinids across geographical regions.
Conclusions
Molecular markers can be used for insect identifi cation, understanding population structure,
and ecological processes at the micro level. They are also useful for understanding the
characteristics of natural enemies, host preference, biotypes, movement, invasion, sex ratio,
population genetics, and interaction with other insects and insecticides. Such information
can be used as a critical input for the success of pest management programs. Information
generated through molecular markers can be used to build a detailed picture of insect
population structure, behavior, and the interactions that will lead to a more effective pest