Contents - Faperta

44 Biotechnological Approaches for Pest Management and Ecological Sustainability
locations. As far as possible, efforts should be made to select locations where appropriate
attention can be given to managing the trials and evaluation of the test material for resistance
at the appropriate stage.
Adjusting Planting Date
The test material should be planted such that the most susceptible stage of the crop is
exposed to maximum or optimum levels of insect infestation. Fortnightly or monthly
plantings of a susceptible cultivar during the cropping season can also be used to determine
the optimum time for planting the test material. Most of the crops planted 20 to
25 days later than the normal planting times are exposed to heavy insect damage. The
periods of maximum insect abundance can also be determined through monitoring of
insect populations through light or pheromone traps. Sorghum crop planted during the
second week of July in southern India is exposed to heavy damage by shoot fl y, A. soccata,
sorghum midge, S. sorghicola, and head bug, Calocoris angustatus (Lethiery) (Sharma et al.,
1992). Most of the crops (cotton, maize, pigeonpea, tomato, sunfl ower, and sorghum)
planted during July in South Asia are exposed to heavy H. armigera infestations during the
rainy season, while October is the optimum time to plant the test material (chickpea,
tomato, and saffl ower) during the post-rainy season for resistance screening (Sharma et al.,
2005a). Similar planting times should be determined for different insect pests and their
crop hosts in each region to maximize the chances for obtaining adequate levels of insect
infestation for resistance screening.
Manipulation of Cultural Practices
Cultural practices can be manipulated to increase the activity of certain insects in the fi eld
(Hollingsworth and Berry, 1982). Closer spacing leads to greater incidence of rice gall
midge, Orseolia oryzae Wood-Mason (Prakasa Rao, 1975). Lower planting densities lead to
greater infestation of sorghum shoot fl y, A. soccata, and sorghum midge, S. sorghicola
(Sharma et al., 1992). A drought-stressed sorghum crop suffers greater severity of spotted
stem borer, Chilo partellus (Swinhoe) damage, while sprinkler irrigation during the fl owering
stage increases the severity of sorghum midge and head bug, C. angustatus (Sharma
et al., 1992). Fertilizer application increases the damage by planthopper, A. biguttula biguttula
and bollworms, E. vittella and H. armigera in cotton.
Planting Infester Rows
Planting susceptible cultivars as infester rows along the fi eld borders or at regular intervals
in the fi eld can be used to increase insect infestation in the test material. The infester
rows may be planted 20 to 25 days earlier, or an early fl owering crop or cultivar can be
used as infester rows so that the fl owering in the infester rows occurs earlier than the test
material in the case of insects feeding on the reproductive parts (Figure 3.1). There should
be suffi cient time for the insect to multiply on the infester rows, and then move to the test
material (Sharma, Vidyasagar, and Leuschner, 1988a; Smith, Khan, and Pathak, 1994).
Insects collected from nearby fi elds can also be released in the infester rows. Insects can
also be attracted to the infester rows by kairomones (e.g., fi shmeal for sorghum shoot fl y)
(Figure 3.2). Plant material with diapausing insects (e.g., chaffy sorghum panicles with
midge larvae or stalks of cereal crops with diapausing larvae of stem borers) can also be
spread in the infester rows to increase the severity of insect damage. The infester rows