No-choice Cage Technique to Screen for Resistance to Sorghum Midge (Diptera: Cecidomyiidae)

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Abstract
A cage technique to screen sorghum cultivars for resistance to sorghum midge, Contarinia sorghicola (Coquillett), under no-choice conditions was developed and standardized. Forty adult midges collected during morning hours (0800-1100 hours) from flowering sorghum panicles and introduced into the cage at the top- to half-anthesis stage for 2 consecutive d resulted in maximum midge damage in the susceptible cultivar ‘CSH 1’. Wire-framed cage covered with a blue bag caused the most damage in ‘CSH 1’. This technique is useful for verification of midge resistance observed under field conditions. Resistance of 21 sorghum cultivars to sorghum midge was compared under no-choice cage and natural conditions for four seasons. Of 15 cultivars reported to be resistant to sorghum midge under natural conditions, only three (‘DJ 6514’, ‘TAM 2566’, and ‘IS 12666C’) showed repeatable levels of resistance under no-choice conditions during the four seasons. ‘TAM 2566’ and ‘IS 12666C’ were less attractive to the midges (<4 midges per five panicles) than the midge susceptible hybrid sorghum ‘CSH 1’ (19 midges per five panicles) under field conditions. Fourteen cultivars that were either less attractive to adult midges or had ≤12% florets with midge larvae under natural conditions showed a susceptible reaction under no-choice testing in the cage. Cultivar reactions to midge were stable under the cage over four seasons (except ‘IS 2328’). Using first two principal component cluster analysis, ‘TAM 2566’ and ‘DJ 6514’ were grouped together as the most resistant cultivars. Sources of resistance to midge thus placed in different groups can be used to increase levels of midge resistance by hybridization among cultivars belonging to different groups.

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