Host-plant preference and oviposition responses of the sorghum midge, Stenodiplosis sorghicola (Coquillett) (Dipt., Cecidomyiidae) towards wild relatives of sorghum

Sorghum midge. Stenodiplosis (Contarinia) sorghicola (Coquillett) is an imp ortant pest of grain sorghum world-wide. Considerable progress has been mad e in screening and breeding for resistance to sorghum midge. However. some of the sources of resistance have become susceptible to sorghum midge in Ke nya, in eastern Africa. Therefore. the wild relatives of Sorghum bicolor we re studied as a possible sourer of new genes conferring resistance to sorgh um midge. Midge females did not lay eggs in the spikelets of Sorghum amplum . Sorghum amplum, and Sorghum angustum compared to 30% spikelets with eggs in Sorghum halepense when infested with five midge females per panicle unde r no-choice conditions. However, one egg was laid in S. amplum when infeste d with 50 midges per panicle. A larger number of midges were attracted to t he odours from the panicles of S. halepense than to the panicles of Sorghum stipoideum, Sorghum brachypodum, S. angustum, Sorghum macrospermum, Sorghu m nitidium, Sorghum laxiflorum, and S. amplum in dual-choice olfactometer t ests. The differences in midge response to the odours from S. halepense and Sorghum intrans were not significant. Under multi-choice conditions, when the females were also allowed a contact with the host, more sorghum midge f emales were attracted to the panicles of S. bicolor compared with S. amplum ,. S. angustum, and S. halepense. In another test, numerically more midges responded to the panicles of IS 10712 compared with S. halepense. whereas t he differences in midge response to the panicles of ICSV 197 (S. bicolor) a nd S. halepense were not apparent, indicating that S. halepense is as attra ctive to sorghum midge females as S. bicolor. The wild relatives of sorghum (except S. halepense) were not preferred for oviposition, and they were al so less attractive to the sorghum midge females. Thus, wild relatives of so rghum can prove to be an alternative source of genes for resistance to sorg hum midge.