There are two major panicle pests of sorghum in AustraUa, the sorghum midge, Stenodiplosis sorghicola (Coquillett), and hehothis, Helicoverpa armigera (Hübner). During the past 10 years the management of these pests has undergone a revolution, due principally to the development of sorghum hybrids with resistance to sorghum midge. Also contributing has been the development of the use of a nuclear polyhedrosis vims (NPV) for the management of heliothis. Investigations were carried out into the mechanisms of midge resistance, the development of economic thresholds for sorghum midge and the annual determination of official thresholds for new hybrids, midge management using cultural methods, the effect of midge-resistant sorghum on hehothis, the effect of heliothis on midge-resistant sorghum and the use of NPV for heUothis management. The practical apphcation of the results of this research has led to a massive reduction in the use of synthetic insecticides for the management of panicle pests of sorghum in Austraha. The current management of sorghum panicle pests and future trends are discussed.
The components of resistance to sorghum midge, in 20 genotypes of grain sorghum were assessed in six glasshouse trials by caging females on panicles. Fewer eggs were laid in sessile spikelets and a lower percentage of such spikelets was infested in all resistant lines compared with susceptible lines, indicating that ovipositional antixenosis was the major component of resistance involved. Pedicellate spikelets were not infested in lieu of sessile spikelets. In one line, antixenosis to ovary-feeding by larvae was indicated.
Another glasshouse trial using two midge-susceptible and five midge-resistant hybrids also showed that the only mechanism of resistance in these hybrids was ovipositional antixenosis.
The conclusion was that resistance to sorghum midge in all the sorghum material in Australia was due to ovipositional antixenosis.