Techniques to Screen for Resistance to Insect Pests

Sorghum, pearl millet, chickpea, pigeonpea and groundnut are the most important crops in the semi-arid tropics. These crops are damaged by several insect pests, of which the most important pests in the SAT are:

• Sorghum shoot fly (Atherigona soccata), stem borers (Chilo, Busseola and Diatraea), sugarcane aphid (Melanaphis sacchari), sorghum midge (Stenodiplosis sorghicola), and head bugs (Calocoris angustatus and Eurystylus oldi) in sorghum.

• Stem borer (Coniesta ignefusalis) and head miner (Heliocheilus albipunctella) in pearl millet.

• Pod borer (Helicoverpa armigera) in chickpea. • Pod borers (H. armigera and Maruca vitrata) and pod fly

(Melanagromyza obtusa) in pigeonpea.• White grubs (Holotrichia spp.), leaf miner (Aproaerema

modicella), and tobacco leaf caterpillar (Spodoptera litura) in groundnut.

Insect pests cause an estimated loss of over US$10 billion annually in the semi-arid tropics. Since insecticide use is not economical under subsistence farming conditions, it is important to develop cultivars with resistance to insects. To achieve these objectives, we have standardized several techniques to screen and select for resistance to insect pests.

A B

C D

Plate 1. (A) Interlard fishmeal technique for resistance to shoot fly, (B) artificial infestation technique for stem borer, (C) infester row technique for midge and head bugs, and (D) use of hot spot locations and planting time to screen for resistance to Helicoverpa.

Plate 2. Cage technique to screen for resistance to (A) shoot fly, (B) midge, and (C) head bugs in sorghum; (D) no-choice cage and (E) detached leaf assay techniques to screen for resistance to Helicoverpa armigera in chickpea.

A B C

D E

Techniques to screen for resistance to insects under field conditionsWe have standardized the interlard fishmeal and no-choice cage techniques to screen for resistance to shoot fly, artificial rearing and field infestation techniques for stem borers, and infester row and no-choice cage techniques for resistance to sorghum midge and head bugs in sorghum, and under natural infestation for resistance to H. armigera in chickpea and pigeonpea, andH. albipunctella in pearl millet (Plate 1).

Techniques to screen for resistance to insects under greenhouse/lab conditionsWe have also standardized no-choice and multi-choice cage techniques to screen for resistance to shoot fly, sugarcane aphid, sorghum midge and head bugs in sorghum, and no-choice and multi-choice cage and detached leaf assay techniques to screen for resistance to H. armigera in chickpea, pigeonpea, groundnut and cotton; and for tobacco leaf caterpillar in groundnut (Plate 2).

These resistance screening techniques are being used to evaluate germplasm, segregating breeding lines, mapping populations, and transgenic plants for resistance to insect pests. Many of these techniques are also being used by the national programs for developing cultivars with resistance to insect pests.

HC Sharma, SL Taneja, K Leuschner and KF NwanzeInternational Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh India

Nov 2009