Contents - Faperta

96 Biotechnological Approaches for Pest Management and Ecological Sustainability
FIGURE 4.7 Sorghum cultivar ICSV 745 with high levels of resistance to midge, Stenodiplosis sorghicola, which
can be deployed as a principal component of controlling this pest.
For such insects, even low levels of antixenotic and antibiotic resistance would be useful in
delaying the time required to reach the damaging levels. However, for insects that invade
a crop in large numbers due to immigration, such as Heliothis/Helicoverpa and the armyworms
M. separata, Spodoptera exempta (Walker), and S. frugiperda, grass hoppers, and
locusts, the effects of HPR in suppressing insect populations and damage may not be
apparent in the fi rst few generations. The infl uence of insect-resistant varieties on insect
populations can be demonstrated by making use of the simple insect models of Knipling
(1979) as adopted by Adkisson and Dyck (1980), and Sharma (1993). Kennedy et al. (1987)
demonstrated the usefulness of even low levels of resistance through simulation models.
They suggested that maize with antixenotic resistance might not reduce the damage by
H. zea, while maize with antibiotic type of resistance could cause nearly 50% mortality in
the fi rst- and second-instar larvae. However, it will take the insect nearly 23 generations to
overcome the antixenotic resistance by 50%, while it will require only seven generations
for overcoming the antibiotic type of resistance. A combination of antixenotic and antibiotic
resistance is more durable (Gould, Kennedy, and Johnson, 1991). When the two types of
resistances are combined, the insect would take 32 generations to overcome the antibiotic
Midge damage (%)
90
80
70
60
50
40
30
20
10
0
DJ 6514
AF 28
TAM 2566
IS 15107
FIGURE 4.8 Sorghum midge, Stenodiplosis sorghicola, damage in different genotypes of sorghum.
CSH 1
Swarna