Contents - Faperta

Evaluation of Transgenic Plants and Mapping Populations for Resistance to Insect Pests 51
• Infest the crop with eggs or neonate larvae at the susceptible stage of the crop as
appropriate.
• After one week, check the plants for insect infestation. Record data on plant damage
and insect numbers as appropriate.
• At maturity, record data on number of fruiting bodies, insect damage (e.g., number
of pods or bolls infested), and yield of the infested and uninfested plants or plots.
• Select the genotypes based on insect numbers/damage, and grain yield, in comparison
to the resistant and susceptible checks of similar maturity.
Artifi cial infestation in the fi eld provides useful information on plant resistance based
on antibiosis and tolerance components of resistance. However, it does not account for
antixenosis for oviposition, which is an important component of resistance to insects in
several crops. This technique has been used extensively in cereal crops, but has not been
tried on a large scale in grain legumes, fi ber, and vegetable crops. One of the reasons for
this may be the absence of a pocket where the larvae can be released through the Bazooka
applicator. Use of sticky materials is limited to eggs, which upon drying may pose problems
for egg hatching. Therefore, there is a need to refi ne this technique for large-scale application
in legumes, vegetables, and fruit crops.
Planning the Rearing Schedule and Egg and Pupal Storage
Studies on plant resistance should ideally be carried out by infesting the plants or plant
parts of the same age and growth stage as subjected to insect attack under natural conditions.
Therefore, efforts should be made to have the laboratory-reared insects available for
infestation at the most susceptible stage of the crop. For this purpose, planning for multiplication
of insects and planting of the test material should be undertaken two to three months
in advance. In case there is a mismatch between the availability of insects and the crop
growth, one can hasten or slow-down insect development in the laboratory. If the insect
rearing is delayed, the temperature in the rearing room can be increased by 2 to 3°C to speed
up insect development. If the insect culture is ready earlier than the test material, one can
delay the insect development by: (1) reducing the temperature in the rearing room, (2) storing
the eggs or pupae at low temperatures (e.g., spotted stem borer, C. partellus and pod
borer, H. armigera eggs can be stored at 10 to 12°C at the black head stage (two days after
eggs-laying) for nearly 10 days in the refrigerator (Dhillon and Sharma, 2007). The eggs can
be taken out four to six hours before use in laboratory or fi eld infestations. The pupae of
Heliothis/Helicoverpa can also be stored for two to three months in deep-freeze, and taken out
as and when the insects are required for bioassay. This information has been used effectively
for large-scale screening of the test material for resistance to insects.
Caging the Plants with Insects
Caging the test plants with insects in the greenhouse or in the fi eld is another dependable
method of screening for insect resistance. In this method, considerable control is exercised
over maintaining a uniform insect pressure on the test entries, and plants are infested at
the same phenological stage. This protects the insects from natural enemies and also
prevents the insects from migrating away from the test plants. Cages can be designed to
cover the whole plants, such as those of chickpea, saffl ower, sunfl ower, and tomato, or to
cover only the plant parts that are damaged by the insects, such as panicles of sorghum