Contents - Faperta

Host Plant Resistance to Insects: Potential and Limitations 99
chickpea in combination with natural enemies (e.g., Campoletis chlorideae Uchida) can exercise
considerable effect on population dynamics of the pod borer, H. armigera. If we assume
that there are 10 female moths per hectare in the beginning of the season, each H. armigera
female lays an average of 500 eggs, and there are three generations in a cropping season,
the larval parasite, C. chlorideae results in 20% H. armigera mortality in each generation
(Romeis and Shanower, 1996), and the H. armigera larval mortality is 15% in ICCC 37, 35%
in ICCV 2, and 40% in ICC 506; then there would be 98,260,000 moths in an area planted
with ICCC 37, 43,940,000 moths in the area planted to ICCV 2, and 34,560,000 moths in
the area planted to the resistant cultivar, ICC 506. As compared to the resistant check,
ICC 506, there would be 2.84 and 1.27 times more moths in the areas planted with ICCC 37
and ICCV 2, respectively. There would be 5.55 times more insects in an area planted with a
susceptible cultivar alone as compared to the areas having a resistant cultivar in combination
with the parasitoid, C. chlorideae. The ratio between H. armigera moth populations
(across cultivars) in areas with different cultivars plus control with the natural enemies as
compared to those with the cultivars alone would be 0.51. Thus, natural enemies in combination
with plant resistance can have a dramatic effect on the population dynamics of
insect pests.
Tritrophic Interactions
Biological control processes involve the tritrophic interactions between the plants, the
target pests, and the natural enemies. These interactions are not limited to the impact of
plant chemicals on the target insect and the effect of insect fi tness on natural enemies, but
also include the direct effects of plants on the natural enemies. The physical or chemical
characteristics of the host plant that infl uence the activity and abundance of natural enemies
involve:
Physical interactions
• Physical protection to herbivores from natural enemies.
• Effect of morphological characteristics of the plants on the activity of natural
enemies.
• Effect of plant phenology on the searching ability of natural enemies.
Chemical interactions
• Effects on fi tness of the insect host.
• Effects on the fi tness of the natural enemies.
• Effects on the acceptability of the insect host to the natural enemies.
• Effects on the ratio between insects and the natural enemies.
• Plant chemicals acting as kairomones or allomones to the natural enemies.
It is very likely that plants have evolved mechanisms to attract the natural enemies to
reduce the extent of insect damage, for example, the female parasitoid wasp, Campoletis
sonorensis (Cam.) responds to the volatiles of cotton plant over a short distance, while
searching for its prey, H. virescens. It is easier for the wasp to fi nd the host habitat fi rst
and then the prey within the vicinity of the host plant. Tobacco, cotton, and maize plants