Tarnished Plant Bug (Hemiptera: Miridae): Effect on Seed Weight of Grain Amaranth

Abstract

Grain amaranth, Amaranthus cruentus L., is a potential, alternative crop for midwestern farmers. The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a potentially serious pest of amaranth, feeding on grain amaranth and causing developing seed to shrivel and discolor. Field tests were conducted during 1987 and 1988, at Ames, Iowa, to determine the effect of L. lineolaris on amaranth seed weight. The treatments included artificially (by hand) infesting heads with selected numbers of tarnished plant bugs and determining the effect of tarnished plant bug density, the effect of a naturally occurring tarnished plant bug population, and the effect of tarnished plant bug feeding duration. In 1987, when 50 tarnished plant bugs were caged on developing heads for 8 wk, seed weight decreased by 82%. When 10 bugs were caged on developing heads, there was no significant decrease in seed weight. In 1988, when 12 bugs were caged on developing heads for 8 wk, seed weight decreased by 80%. In 1987, when tarnished plant bugs were caged on developing heads for 2, 4, 6, or 8 wk, seed weight significantly decreased by 39.5% between the second and fourth week of feeding. In 1988, tarnished plant bugs feeding on the developing heads for 5 wk reduced seed weight by 57.6%. During 1987, naturally occurring tarnished plant bugs feeding continuously on the terminal heads significantly reduced seed weight by 28.2% between the third and fifth week of feeding.