Species composition and injury to sorghum by panicle feeding bugs in Niger

Abstract

Eurystylus marginatus Odhiambo (Hemiptera: Miridae) was the most important and abundant insect pest of sorghum panicles in Niger in 1985 and 1986. First generation adults initially infested sorghum panicles in late August, and two succeeding generations developed on sorghum. Economic losses were manifested in yield and grain quality reduction. A commonly grown indigenous variety Mota Galmi, suffered 14% yield loss and 19% grain vitrosity reduction in field trials in which E. marginatus density averaged 80/panicle. Among 14 other sorghum varieties grown under natural conditions, vitrosity was decreased 20% on average (range 0–-47%). Headcage experiments using 20 female/male pairs of E. marginatus on each of three varieties resulted in losses ranging from 19–62% of grain weight/panicle, 1000-kernel weight, per cent low density grain, and vitrosity. Damage resulted from both oviposition and feeding. Among seven panicle and glume characteristics, percentage coverage of grain surface by glumes, and the time from anthesis to opening of the glumes were significantly correlated with reduced head bug numbers. Among varieties, grain damage was not highly correlated with head bug numbers; but within varieties, increasing head bug numbersclearly caused increased damage. Measureable damage occurred with as few as five female/male head bug pairs per panicle. Most E. marginatus eggs were oviposited into exposed, apical portions of sorghum grains during the milky stage of kernel development. Grain of variety CE90 were vulnerable to oviposition for less than 1 week after glumes opened.