Forage Grasses Elicit Emigration of Adult Potato Leafhopper (Homoptera: Cicadellidae) from Alfalfa-Grass Mixtures

Abstract

Mixtures of alfalfa and forage grasses were tested to determine their affect on Empoasca fabae (Harris) density and emigration behavior. In 1990 and 1991, field plots seeded to alfalfa alone or mixtures of alfalfa with smooth bromegrass, orchardgrass, or timothy were sampled using a suction sampler. Numbers of adult potato leafhoppers were reduced by 22-48% in alfalfa-forage grass mixtures containing either smooth bromegrass seeded at 5.6 kg/ha or orchardgrass seeded at 1.1 kg/ha compared with alfalfa monoculture seeded at 14.6 kg/ha. Alfalfa intercropped with timothy showed both decreases and increases in leafhopper populations compared with the alfalfa monoculture. In 1995, field-cage studies examined the emigration behavior of adult potato leafhoppers from stands containing plots of 100% orchardgrass, 100% alfalfa, and combinations of the 2 species. Increasing orchardgrass stem density did not significantly increase the number of leafhoppers emigrating. However, increases of orchardgrass leaf surface area and biomass were significantly correlated with increases in emigration. Significantly more leafhoppers emigrated when orchardgrass plants were interspersed among the alfalfa (67%) compared with equal densities of orchardgrass planted in a discrete patch (51%). Incorporating a forage grass species at a density that increases the frequency of leafhopper-grass contacts should increase movement within the stand, possibly leading to emigration out of the field. This understanding of pest insect behavior in alfalfa-grass intercrops may lead to varietal selection of grasses that will offer long-term preventative management of potato leafhoppers.