Components of resistance to the sorghum head bug, Calocoris angustatus

Abstract

Sorghum head bug, Calocoris angustatus Lethiery (Hemiptera: Miridae) is an important pest of grain sorghum. Population increase, grain damage, and nonpreference of C. angustatus were studied on 10 sorghum genotypes under multi- and no-choice conditions during the 1989–1990 rainy and post-rainy seasons. Under multi-choice field conditions, IS 14334, IS 19955, IS 20740, IS 21444, IS 23748, and IS 17610 (except in rainy season) were not preferred by the adults at the half-anthesis stage, and IS 14334, IS 19955, IS 21444, and IS 17610 also had lower head bug numbers at the milk stage. Head bug population increase was lower on IS 19955, IS 21444, IS 20740, and IS 17610 when infested with 10 pairs of adults under no-choice conditions in the headcage at the half-anthesis and milk stages as compared with the commercial cultivars CSH 1, CSH 9 and ICSV 112. IS 17610 showed high levels of resistance to grain damage, while IS 20740 and IS 21444 suffered moderate levels of grain damage under no-choice conditions in the headcage. IS 14334 and IS 17610 also showed tolerance to head bug feeding, i.e., they suffered lower grain damage per unit population of the head bugs. Multi-, double- and no-choice tests under laboratory conditions confirmed that nonpreference is an important component of resistance to head bugs in IS 14334, IS 19955, IS 23748 and IS 17610. Sorghum genotypes showing nonpreference to adults, low rates of population increase (antibiosis), and tolerance to head bug feeding can be used in a breeding program to increase the levels and diversify the bases of resistance to C. angustatus.