Distribution. Potato leafhopper is found throughout the humid, low-altitude regions of eastern United States, occurring as far west as eastern Colorado (DeLong, 1931). It occurs in eastern Canada, including the Prairie Provinces, but is most damaging in southern Ontario. Potato leafhopper successfully overwinters in Gulf Coast States from Louisiana to Florida and disperses northward annually. Leafhoppers typically arrive with warm fronts in midwestern states during April to mid-May, and in northern states and the Canadian provinces during June (Medler, 1957). In late summer and autumn months they are carried southward again by cold fronts (Taylor and Reling, 1986). Apparently it is a native species.
Host Plants. Potato leafhopper feeds on over 200 wild and cultivated plants, though fewer species are suitable for nymphs than adults, and males have a wider host range than females (Lamp et al., 1994). Vegetable hosts include bean, broad bean, cowpea, cucumber, eggplant, Jerusalem artichoke, lima bean, potato, pumpkin, rhubarb, squash, and sweet potato.
Also attacked are field crops such as alfalfa, clover, soybean, sugarbeet, sunflower and tobacco, as well as woody plants such as apple, cherry, hickory, maple, oak, redbud, rose, and walnut. The most suitable crop hosts are alfalfa, bean, cowpea, and potato. In much of the economic entomology literature this species is referred to as "bean leafhopper," which is indicative of a major host preference and damage potential. Indeed, 61% of the plant species fed upon by potato leafhopper are legumes. Poos and Smith (1931) evaluated the oviposition behavior of potato leafhopper in several crop plants and reported the following preference (from most preferred to least): potato, cowpea, dahlia, non-pubescent soybean, alfalfa, bean, pubescent soybean, and red clover. Lamp et al. (1984) studied leafhopper survival on various weed; nymphs developed successfully on smartweed, Polygonum pennsylvanicum; pigweed, Amaranthus retroflexus; shepherdspurse, Capsella bursa-pastoris; dandelion, Taraxacum officinale; and carpetweed, Mollugo verticil-lata. Castor bean, Ricinus communis; and pokeweed, Phytolacca sp. have also been observed to support nymphal development (Beyer, 1922), and many other weed hosts are known (Lamp et al., 1994).
Many woody hosts are of significance only for firstgeneration leafhoppers; apparently their suitability declines as plant tissue matures (Poos and Wheeler, 1943). However, feeding and overwintering apparently can occur on loblolly pine (Taylor et al., 1993); during early spring, as adult leafhoppers terminate reproductive diapause, they shift their feeding to deciduous trees and legumes (Taylor and Shields, 1995). (See color figure 12.)
Natural Enemies. Biological agents affecting potato leafhopper are either few in number, or not well studied. Egg parasitoids (Hymenoptera: Mymaridae and Dryinidae) sometimes are abundant. Generalist predators such as spiders, lacewings, nabids, lady beetles, and ants destroy these leafhoppers, and the fungus Erynia radicans is effective during warm, moist weather (Beyer, 1922). Natural control of leaf hoppers was reviewed by DeLong (1971).
Life Cycle and Description. Where potato leaf-hopper overwinters, the adult is the overwintering stage. During the winter months the adult leafhopper is in reproductive diapause. After leafhoppers invade an area in the spring, several overlapping generations may occur. Four generations are known from Ohio, but the last is small. Six generations are possible in Virginia (Poos, 1932) and are documented in Florida (Beyer, 1922). Even as far north as Ontario, 2-3 generations may occur. Invading leafhoppers sometimes produce a generation on deciduous hosts before moving to annual crops, because the latter have not yet emerged from the soil (Flanders and Radcliffe, 1989).
from closely related Empoasca species. Adults emit sounds that apparently represent intraspecific communication, but the sounds are barely audible to the human ear (DeLong, 1971). Adult longevity is typically 30-60 days. Adults normally mate within 48 hours after emergence. The post-mating pre-oviposi-tion period is 3-8 days.
Potato leafhopper biology was given by many authors, including Fenton and Hartzell (1923), DeLong (1938), Simonet and Pienkowski (1980), and Hogg (1985). A bibliography was published by Gyrisco et al. (1978).
Potato leafhoppers feed on phloem or mesophyll tissue (Backus and Hunter, 1989) and secrete a toxin into the plant. Plant respiration is increased and photosynthesis is decreased by leafhopper feeding (Ladd and Rawlins, 1965). Feeding results in curling, stunting, and yellowing of potato foliage. The chlorotic tissue eventually becomes necrotic, initially at the leaf margins. The damage is called "hopperburn," because the plant appears to have been singed by fire. The toxin is not systemic, and the level of damage is directly proportional to the number of leafhoppers feeding. Reduction in crop yield is often significant. In potatoes, though the normal number of tubers may be produced, they are very small. Beans similarly stop production of pods once attacked, and existing pods usually develop incompletely. Damage is exacerbated by drought. Potato leafhopper is not known to transmit plant pathogens.
Insecticides. Standard practice for many vegetable growers is to apply insecticides to the foliage on a regular schedule to prevent injury. Systemic insecticides applied at planting also can provide excellent long-term control of leafhoppers and prevent hopper-burn. However, as few as two well-timed foliar applications aimed to control peak nymphal populations can be adequate to prevent injury by leafhoppers (Radcliffe, 1982). Subsequent reinvasion, of course, may warrant additional treatments. Cancelado and Radcliffe (1979) estimated that insecticide treatment would be economic at densities of one leafhopper per potato leaf. Cucurbits are susceptible to hopper-burn, but are usually not severely damaged unless the plants are also water stressed.
Cultural Practices. The wide host range of potato leafhopper and highly dispersive nature of the insects eliminates consideration of crop rotation and many other cultural practices. Consideration should be given to proximity of infested crops, however, especially if they are reaching maturity or are about to be harvested. Harvesting alfalfa, for example, could drive both adults and nymphs from the alfalfa in search of food. Leafhopper nymphs do not survive long without vegetation, so clean cultivation between fields is helpful, but adult movement will not be deterred by this tactic. Row covers protect small plantings from dispersing leafhoppers.
Host-Plant Resistance. Plant resistance offers potential for leafhopper management. Leafhoppers are affected by the hairiness of foliage and petioles. In general, pubescent soybean varieties are less suitable for potato leafhopper, but the presence of hooked leaf hairs (trichomes) that impale nymphs is more important than trichome density (Poos and Smith, 1931). Leaf hairiness is also a major, but not exclusive, component of resistance in eggplant (Poos and Haenseler, 1931). Glycoalkaloids also have been implicated in resistance, and glandular trichomes associated with wild Solanum impede leafhopper mobility and feeding, resulting in death (Radcliffe, 1982). Nymphs are especially subject to death from glandular exudates (Tingey and Laubengayer, 1981). Some potato, bean, and alfalfa varieties display considerable resistance but none are immune to damage (DeLong, 1971).
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