Contents - Faperta

58 Biotechnological Approaches for Pest Management and Ecological Sustainability
1966) or increase (van Emden and Bashford, 1976), depending on the nature of insect
plant interactions in different crops. These techniques can also be used to study consumption
and utilization of food by insects. The following procedure may be followed
to screen the test material using detached leaf assay.
• Detach a leaf with a petiole (fi rst fully expanded leaf of cotton, pigeonpea, groundnut,
sunfl ower, or tomato) or a 7- to 10-cm growing terminal branch of chickpea,
pigeonpea, saffl ower, or an infl orescence (15 cm long) of pigeonpea, chickpea,
cotton, or tomato, and place it immediately in agar-agar (3%), or insert the petiole
or the infl orescence in sugar or Arnon solution in a plastic or conical fl ask of appropriate
capacity (250 to 1000 mL) or insert the leaf petiole or the branch into 3%
agar-agar (10 to 15 mL) solution poured on to one side of the plastic cup.
• Release an adequate number of neonate or third-instar larvae that result in maximum
differences between the resistant and susceptible genotypes.
• Record data on leaf/pod feeding, larval survival, and larval weights at four to six
days after infestation, when the differences between the resistant and susceptible
checks are maximum, and more than 80% of the leaf area/pods are damaged in
the susceptible check. Evaluate leaf/pod damage on a 1 to 9 scale (where 1 10%
leaf area/pods damaged, and 9 80% leaf area/pods damaged).
Leaf Disc or Pod/Boll Assay
Leaf discs of appropriate size or pods and bolls at the susceptible stage can also be used to
assess the genotypic resistance to insects. The leaf discs and pods/bolls can be offered to the larva
in no-choice, dual-choice, or multi-choice assays. The bioassays can be carried out as follows.
• Place a fi lter paper at the bottom of the Petri dish (7.5 cm diameter), and another
fi lter paper inside the lid, and moisten the fi lter paper inside the lid with 2 to 3 mL
of water. This keeps the excised plant parts in a turgid condition.
• Take a leaf disc of appropriate size (2.5 to 5 sq. cm) from the mid-portion of the fi rst
fully expanded leaf, a pod, or a boll (7 to 10 days old), and place in a Petri-dish
arena in no-choice, dual-choice, or multi-choice conditions.
• Release neonate or third-instar larvae in the Petri dish arena, as appropriate.
• Record data on extent of leaf/pod feeding, larval survival, and larval weights at
48 or 72 hours after infestation, when the differences between the resistant and
susceptible genotypes are maximum.
Oviposition Nonpreference
Antixenosis for oviposition is a major component of resistance to insects and, therefore, it
can be used as one of the criteria to evaluate relative resistance of test genotypes to insect
pests. For this purpose, the plants can be grown in pots in the greenhouse or 20-cm long
branches or infl orescences can be brought from the fi eld and placed in a conical fl ask containing
water, sugar (1%), Hoagland, or Arnon solution. The oviposition preference can be
studied under no-choice, dual-choice, or multi-choice conditions.
• Raise plants in pots in the greenhouse or take infl orescences from the fi eld and
place them in a conical fl ask (250 mL capacity) containing water or 1% sucrose or