Contents - Faperta

70 Biotechnological Approaches for Pest Management and Ecological Sustainability
The responses of insects to volatile stimuli have been studied for several insects. Several
designs of olfactometers have been used to observe insect behavior (Traynier, 1967; Sharma
and Franzmann, 2001). Olfactory responses are also studied physiologically by electroantenograms
(Visser, Van Straten, and Maarse, 1979; Guerin and Visser, 1980; Guerin,
Stadler, and Buser, 1983; Saxena and Okech, 1985; Khan, Ciepiela, and Norris, 1987), electroretinograms,
and by electronic feeding monitors (McLean and Weigt, 1968).
Selection Indices
In addition to low insect damage and/or low insect numbers on the resistant genotypes,
several crops possess the ability to recover from insect damage and produce the same or
more yield under insect infestation, for example, in the case of H. armigera damage in
chickpea, pigeonpea, and cotton, certain genotypes have the ability to produce a second
fl ush when the fi rst fl ush is heavily damaged. In the case of damage by shoot fl y, A. soccata
and spotted stem borer, C. partellus in sorghum, the plants have the ability to produce axial
tillers when the main plant is damaged, depending on the availability of nutrients and
water in the soil. In some cases, the resistant genotypes have the ability to withstand higher
insect numbers or damage. Several indices can be used to measure plant resistance or
tolerance to insects based on insect numbers or damage and yield under infested and
uninfested conditions. Some of the indices that can be used to select genotypes based on
one or more damage parameters, and yield under infested and uninfested conditions are
discussed below.
Tolerance Index
Tolerance to insect damage can be measured in terms of plant damage per unit number
of insects.
No. of insects per plant
Tolerance rating _____________________
Damage rating .
This system identifi es the cultivars that suffer relatively low insect damage despite having
a high insect population. N. Panda and Heinrichs (1983) calculated tolerance and
antibiosis indices based on insect dry weight.
Insect dry weight on the test cultivar
Tolerance ________________________________________
Insect dry weight on the susceptible cultivar .
Loss in Grain Yield
Tolerance to insect damage can also be measured in terms of loss in grain yield. Loss in
grain yield of a test genotype under insect infestation relative to that under uninfested
conditions is measured as:
Loss in grain yield (%) [GYI _______________
UN – GYIIN] 100
GYIUN