Contents - Faperta

Host Plant Resistance to Insects: Potential and Limitations 107
resurgence and helps to conserve the natural enemies, preserve environmental quality,
slow down the rate of selection for insecticide-resistant insect strains, and increase the
profi tability of crop production (Adkisson and Dyck, 1980). Population of M. persicae on
partially resistant varieties has been observed to be about 85% of that on the susceptible
varieties of Brussels sprouts. However, LD 50 of malathion for the aphid on the partially
resistant cultivar was about 55% compared to that of the aphids on the susceptible variety.
Insecticide requirement was much less on the partially resistant variety than that on the
susceptible variety (Muid, 1977). The increased susceptibility to malathion on the partially
resistant variety appeared to be due to the interaction of insecticide with insects of low
vitality. Even with small levels of plant resistance, insecticide concentration can be reduced
to one-third of that required on a susceptible variety (van Emden, 1990). A half dose of
chlorfenvinphos gave equal or better control of the turnip root fl y, Delia fl oralis (Fall.) on
resistant cultivars of Swede (Cruciferae) S 7790 than the full dose on the susceptible cultivar,
Ruta. The reduction in indices of root fl y damage and the increase in percentage
of marketable produce were more pronounced on the resistant than on the susceptible
cultivar (Taksdal, 1993).
Insecticide application did not result in a substantial increase in grain yield of chickpea
variety, ICC 506 with moderate levels of resistance to H. armigera, while four to fi ve sprays
were needed to realize the maximum yield potential of the susceptible varieties such as
Annigeri and ICCC 37 (Wightman et al., 1995). In the case of pigeonpea, insecticide (endosulfan)
and the Helicoverpa-resistant cultivar, ICPL 332 (see Figure 4.10) has a substantial
effect on pod damage and grain yield (Figure 4.11). Pod damage in the Helicoverpasusceptible
cultivar, ICPL 87 was 35.8% in endosulfan-treated plots compared to 70.8% in
untreated control plots. Grain yield was 970.22 kg ha 1 in plots treated with endosulfan
(0.07%) compared to 277.4 kg ha 1 in untreated plots (Sharma and Pampapathy, 2004). In
the Helicoverpa-resistant cultivar, ICPL 332 the pod borer damage ranged from 4.3% in
endosulfan-treated plots compared to 14.3% in the untreated control plots. Grain yield was
1642.8 kg ha 1 in the untreated control plots compared to 1833.6 kg ha 1 in plots treated with
endosulfan. The Helicoverpa-resistant cultivar ICPL 332 resulted in a signifi cant decrease in
H. armigera damage, and thus can be used as a component in integrated pest management
in pigeonpea.
FIGURE 4.10 Pigeonpea cultivar ICPL 332, with moderate levels of resistance to Helicoverpa armigera, which can
be deployed for IPM in combination with other components of pest management.