Lygus Bug Damage to Table Beet Seed Plants

Abstract

The possible effect of lygus bug infestations on quantity and quality of developing table beet seeds was investigated by artificially infesting caged portions of plants in the field, each portion being approximately one-third of one plant. The caged parts of bolting plants were exposed to constant numbers of male lygus bugs, Lygus hesperus Knight, with levels of infestation continuously maintained lit 1, 2, 4, 8, and 16 bugs per cage for periods of 40 and 42 days. Yield data from two experiments show that average amounts of seed per unit of plant exposed to lygus bugs ranged from 15% to 25% below the yields recovered from control plants. The differences in yields between the portions of infested plants and the controls or between the several levels of infestation were not significant. However, when the yield data from the second of two experiments were corrected for inequalities between caged portions of plants, and computed on a per plant basis, differences between the checks and the several groups of exposed plants appear to be significant. The converted data show that equivalents of 7.5 to 50.7 bugs per plant (or 2 to 16 bugs per cage) reduced seed yield 33% to 44%. The highest level of infestation, 16 bugs per cage, also perceptibly increased the yield of seeds classified as small seeds. Exposure to lygus bugs caused a decrease in the weight of individual seeds of two size categories, those graded as large seeds and as small seeds. The reduction in weight of seeds appeared to be economically important at levels of 8 to 16 bugs per cage (22.8 to 50.7 bugs per plant). The numbers of germinating beet seeds and viable germs per seed were substantially reduced by exposure to lygus bugs in two experiments, decreasing as the number of bugs were increased, and were significantly lower for both the large and small seeds. The decrease in percentage of beet seed viability approached 60% at 8 or 16 bugs per cage. A minimum germination of 85% is needed to produce an adequate number of plants in the field.