Contact-Induced Emigration of Potato Leafhopper (Homoptera: Cicadellidae) from Alfalfa–Forage Grass Mixtures

Abstract

Studies were conducted to evaluate the mechanisms leading to increased potato leafhopper, Empoasca fabae (Harris), emigration from alfalfa-forage grass mixtures. A laboratory behavioral bioassay was used to measure daily emigration rates of adult leafhoppers from alfalfa, Medicago sativa L.; smooth bromegrass, Bromus inennis Leyss.; orchardgrass, Dactylis glom.erata L.; and timothy. Phlewn pratense L., alone and in 1:1 mixtures of each grass with alfalfa. Emigration was "=9-foldgreater from pure bromegrass and orchardgrass treatments versus alfalfa alone, and "=5-foldgreater than from mixtures of alfalfa and each grass species. In a 2nd experiment, alfalfa and forage grasses were separated by a barrier permeable to plant volatiles. Only 31% of the potato leafhoppers placed on alfalfa adjacent to either alfalfa or grass emigrated. However, when introduced to the side containing a forage grass, <85% of the leafhoppers emigrated, regardless of adjacent plant. Thus, stimuli obtained from physical contact with the grass versus grass volatiles alone were required to elicit emigration. Observations of potato leafhoppers on single plants of smooth bromegrass, orchardgrass, and alfalfa revealed that individuals fed on all 3 species; however, the frequency and duration of probing differed as did mean residency time (10.7 h alfalfa, 7.5 h bromegrass, 5.9 h orchardgrass). These experiments suggested that physical contact is necessary to elicit emigration from grasses. By increasing emigration, alfalfa-forage grass mixtures may reduce potato leafhopper damage to alfalfa. Additionally,intercropping with forage grasses may lower the number of feeding bouts on alfalfa and reduce subsequent hopperbum.

Interaction of Insects and Weeds in a Snap Bean Agroecosystem

“…We observed ≈1.5 times as many leafhoppers in weed-free snap bean plots compared to those in plots with crabgrass. Our results show a similar trend to other research that has reported reductions in potato leafhopper populations in grass-legume cropping systems (Hammond and Jeffers, 1990;Oloumi-Sadeghi et al, 1989;Roda et al, 1997aRoda et al, , 1997bRoltsch and Gage, 1990). In contrast, potato leafhopper numbers in plots with pigweed were not significantly different from those in plots with crabgrass and only once were different from numbers in weed-free plots.…”

“…Lamp et al (1994) reported that pigweed and four other broadleaves were suitable hosts for potato leafhopper nymphal development and adult oviposition, but that crabgrass was among the least suitable hosts for this insect. The emigration of potato leafhoppers from grassy plots has been attributed to the physical contact between the grass and leafhoppers (Roda et al, 1997b;Roltsch and Gage, 1990). The potential of reducing potato leafhopper damage to a crop through the use of plant diversification is well documented (Barnes and Shaeffer, 1985;DeGooyer et al, 1999;Hammond and Jeffers, 1990;Hutchins and Pedigo, 1989;Lamp, 1991;Lefko et al, 2000;Roda et al, 1997aRoda et al, , 1997b.…”

“…When alfalfa was intercropped with smooth bromegrass (Bromus inermis Leyss) and orchardgrass (Dactylis glomerata L.), biomass loss was 0 to 35% of the biomass loss in the alfalfa monoculture (DeGooyer et al, 1999) . The reduction in the number of potato leafhoppers in grassy weeds has been attributed to the negative reaction of potato leafhoppers to the stimuli obtained from physical contact with the grass (Roda et al, 1997b).…”

Within-Field Manipulation of Potato Leafhopper (Homoptera: Cicadellidae) and Insect Predator Populations Using an Uncut Alfalfa Strip

“…CULTURAL MANAGEMENT TECHNIQUES, e.g., strip harvesting or intercropping, have been used to manage many insect pests (Lamp 1991;Smith et al 1994;Giles 1996;Roda et al 1997aRoda et al , 1997bGiles andObrycki 1997a, 1997b). Strip harvesting, developed as a component of alfalfa pest management in the 1940s, consists of leaving several uncut strips of alfalfa at harvest (Scholl and Medler 1947, Schlinger and Dietrick 1960, Stern et al 1964.…”

Effect of Intercropping on Oviposition and Emigration Behavior of the Leek Moth (Lepidoptera: Acrolepiidae) and the Diamondback Moth (Lepidoptera: Plutellidae)

“…In many cases it has been shown that insects colonize monocultures and polycultures to the same extent, but there is a higher emigration rate from an intercrop compared with a monoculture. (Bach 1980a(Bach , 1980bRisch 1981;Kareiva 1983;Elmstrom et al 1988;Rämert and Ekbom 1996;Roda et al 1997).…”