The Relationship Among Pea Aphids, Lygus Bugs, and Alfalfa Seed Yields1
Abstract:Lygus bugs damage alfalfa grown for seed each year but injurious populations of pea aphids (Macrosiphum pisi (Harris)) occur less often. Experiments designed to determine the joint effect of these insects involved application of insecticides of varying degrees of toxicity to each species, resulting in a range of lygus bug and pea aphid populations. Regression analyses of 3 years' data indicate that yields of alfalfa seed can be expressed by the equation, log10 seed yield=log10 40 lygus bugs + pea aphids, when insect populations are determined by sweep-net samples at weekly intervals during the seed-setting period and populations are given as seasonal means. In these experiments applications of endrin proved to be the most satisfactory for control of both insects and resulted in higher yields than any other treatment.