Patterns among host plants of potato leafhopper, Empoasca fabae (Homoptera: Cicadellidae).

Abstract

Ecological characteristics of potato leafhopper, Empoasca fabae (Harris), including polyphagy, suggest that non-economic plant species in the landscape may be important to its population ecology. The objectives of this study were to compile a host list, to ascertain taxonomic and ecological patterns within the list, and to determine host utilization in non-crop habitats. The host plant list included 220 species in 100 genera and 26 families. Fabaceae represented 47% of the genera and 62% of the species. Yet, the list includes a diversity of taxonomic groups within the class Magnoliopsida, representing highly divergent chemistry and morphological types. Ecological classifications, based on such characteristics as habitat, growth form, and origin, were similarly diverse. Thus, the di versity of plant species suitable for reproduction suggests that non-crop habitats may be a significant source of potato leafhopper populations after spring migration into northern states. Also, the ability of leafhopper adults to utilize additional species (e.g., grasses, pines) as refugia provides a secondary role to non-crop habitats. Yet, our limited data suggest that utilization of non-crop habitats for reproduction is restricted to a relatively few nat uralized hosts (e.g., deciduous trees). Host finding behavior, operating at a landscape or habitat level, as well as abiotic and biotic factors within habitats, may limit host utilization in non-crop habitats. The potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), has long been recognized as an economic pest of many crops including alfalfa, potato, bean, and soybean in the midwestern and eastern United States and Canada (DeLong, 1938). Research has concentrated on dynamics of this pest in crop systems, yet three ecological characteristics of the species suggest that non economic plant species outside of crop systems may be important in its population ecology. First, it is highly polyphagous, reproducing on a wide range of plant species and families (Poos and Wheeler, 1943, 1949). Second, adults are highly mobile, traversing both long (interregional) and short (interhabitat) distances (Medler, 1957; Poston and Pedigo, 1975; Flanders and Radcliffe, 1989). Third, it is multivoltine, with three to five overlapping generations per year, and indi viduals have a life span of up to six months (DeLong, 1938). Adults have been collected in several habitats outside of crop systems, including deciduous forest, forest understory, old field, and newly-disturbed habitats (Lamp et al., 1989 and unpubl. data; Taylor, 1993). As a result, non-crop habitats are believed to con tribute significantly to potato leafhopper population dynamics (Poos, 1935; Hogg and Hoffman, 1989). As a group, leafhoppers have restrictive host ranges (Putnam, 1941; DeLong, 1965). Part of the reason for the wide host range of potato leafhopper may lie in its ability to vary feeding behaviors in response to its host plant. For example, 1 Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755. 2 Department of Entomology, University of Nebraska, Lincoln, Nebraska 68583. Accepted for publication 16 April 1994. This content downloaded from 157.55.39.208 on Wed, 28 Sep 2016 06:30:20 UTC All use subject to http://about.jstor.org/terms VOLUME 67, NUMBER 4 355 Backus and Hunter (1989) found that adults on alfalfa fed on vascular tissues, whereas on beans they fed on mesophyll tissues. Furthermore, adults settle on different portions of the two hosts (Backus et al., 1990). Artificial plant breeding and plant introductions into North America may have enhanced the host range of the leafhopper. For example, plant resistance workers have long noted an association of susceptibility to this leafhopper species with lack of pubescence and other physical characteristics in original germplasm lines of soybean, potato, and alfalfa (Broersma et al., 1972; Robbins et al., 1979; Tingey, 1985; Brewer et al., 1986a, b). In part, this physical resistance is because trichomes impede the normal attachment of individuals to the plant surface (Lee et al., 1986). A chemical basis for resistance to feeding is less frequently cited compared to a physical basis. For example, comparisons of closely-related Solanum species suggest that tri chome presence and not glycoalkaloid content is associated with resistance (Tingey and Sinden, 1982). Alternatively, Raman et al. (1979) found interrupted feeding behavior in response to feeding on glycoalkaloid within artificial diet in the absence of physical resistance factors, and that increased glycoalkaloid content was as sociated with greater resistance among potato cultivars. A larger study of 100 species of Solanum found potato leafhopper resistance associated with both the glycoalkaloid tomatine and glandular trichomes, and that artificial selection led to increased susceptibility by potato leafhopper (Flanders et al., 1992). These studies suggest that potato leafhopper is able to feed as an adult on a wide range of plant species, although certain morphological and chemical factors limit their host utilization for reproduction. Fewer plants serve as hosts for female oviposition as well as survival of small nymphs in comparison to those that serve as hosts for adult feeding (Lamp et al., 1984b). As a consequence, nymphs develop on fewer species compared to species suitable for adult survivorship. Furthermore, potato leafhopper response to genetically diverse and phenotypically variable plant populations within species shows considerable variation. The list of plants suitable for reproduction (hosts), other plant taxa not suitable for reproduction (non-hosts), and actual utilization of hosts in nature may suggest patterns in host plant selection by potato leafhopper. Although the host plant lists published by Poos and Wheeler (1943, 1949) are extensive, they are not conducive to the analysis of patterns because the species were not grouped by taxonomic classification or ecological characteristics. Also, additional host plants have been discovered since their publications. A more complete listing and its analysis was desired toward the goal of greater under standing of the role of non-economic plant species in the population ecology of potato leafhopper and the relationship between plant characteristics and accept ability by potato leafhopper. The objectives of this study were to compile a complete host list for this leafhopper, to determine taxonomic and ecological patterns within the host list, and to determine major groups of non-host plants. Furthermore, we compared the compiled host list to actual utilization of hosts at two disparate sites.