Screening Techniques in Insect Resistance Breeding
Screening for insect resistance is done under the field and glasshouse conditions. In field larger number of plants can be screened than in glasshouse. Moreover, the material is also exposed to other prevalent insect pest of the area. However, in field screening it is not possible to ensure uniform initial infestation of all the plants in a population. The following techniques are used to promote uniform infestation by an insect pest in the field:
1. Inter planting one row of susceptible variety between two rows of the test material.
2. Screening of the plant material in the insect prone areas.
3. Screening of material in the season when there is heavy infestation of an insect pest. For example, there is more infestation of stem borer in rice in off season than in main season. Hence, screening of rice to stem borer should be done in the off seasons.
4. In case of soil pests, such as eelworm in oat and cloves, the test material should be grown in the soil having large populations of such insects.
5. Transferring equal number of eggs to each plant by hand. This is used in rice for stem borer.
In glasshouse smaller number of plants can be screened than in the field. However, results of glasshouse tests are more reliable than field tests. Glasshouse tests have been conducted in rice to stem borer and in alfalfa to spotted alfalfa aphid. Both glasshouse tests. The material found resistant in glasshouse should also be tested under the field conditions.