I. Introduction: White apple leafhopper (WALH) is the most important leafhopper on apple. This species is a native insect in the eastern states, but is now distributed throughout fruit-growing regions of North America. Its importance has increased in recent years as a result of resistance to organophosphate insecticides. Rose leafhopper (RLH) has recently acquired pest status in some mid-Atlantic orchards.

II. Hosts: Apple is the main host of WALH, but this species may also be collected from peach, cherry, plum, and hawthorn in the second generation. The apple cultivars `Empire' and `Liberty' are relatively susceptible to WALH. Primary hosts of RLH include multiflora rose, and wild and cultivated brambles. Apple serves as a summer host for this leafhopper.

III. Description: Adults are white, forming an elongate wedge about 1/8 inch (3 mm) long (photo 1). Adults of WALH may be distinquished from those of RLH by observing genitalia differences under a microscope. Nymphs are white to pale yellow (photo 2), and are less than 1/16 inch (1 mm) long when they hatch from eggs. First instar nymphs of the two leafhopper species are virtually indistinguishable. Later instars of RLH may be distinguished by a series of small black spots on the thorax and wingpads (photo 3), which are lacking in WALH.

IV. Biology: WALH overwinters on apple in the egg stage. Eggs may be seen as longitudinal swellings on one to five-year-old wood (about pencil-diameter). Eggs begin to hatch at the late pink or early bloom stage; hatching is usually complete by petal fall, or shortly thereafter. There are five nymphal instars; shed skins from earlier instars may be found clinging to the underside of the leaf since nymphs generally wander little. Nymphal development takes about 30 days in the first generation. Adults from the first generation begin to appear during late May and usually peak in mid-June. These adults oviposit in leaves, inserting eggs into leaf petioles and midribs, and fly when disturbed. Second generation leafhoppers are present from early August through the fall. Nymphal development of this generation takes about 20 days.

RLH overwinters in the egg stage on multiflora rose and brambles. There are three generations per year, the first of which occurs on the winter hosts. Adults disperse to apple and begin laying eggs in early June. The second generation of nymphs begin to appear on apple during late June to early July, and become adults in late July (incorrect timing for WALH). Third generation nymphs are present during mid-August, becoming adults in mid-September (overlapping development of WALH).

An egg parasite, Anagrus epos Girault (Hymenoptera), overwinters inside the eggs of WALH and also attacks eggs during the summer. Predatory mirids (Hemiptera) may attack nymphs, especially in the second generation.

V. Injury: Nymphs feed on the underside of mature apple leaves. Feeding by adults is not considered as important because they feed for shorter intervals of time and the stylets do not penetrate into the leaves as far as nymphal stylets. Stylets are inserted through mesophyll tissue up into palisade cells. Feeding occurs in one to two of the two to three cell layers of this tissue. Feeding sites are associated with white stippling visible on the top of the leaf (photo 4). Visible injury can range from light stippling along the midrib to complete chlorosis. The stylets radiate in several directions from the point of insertion, therefore substantial stippling may be associated with a relatively low number of feeding sites. Stippling may give an overly severe impression of the impact of feeding, because white areas result partly from reflectance of light by air that has entered injured areas, not simply from removal of leaf cell contents. High leafhopper populations can result in sufficient honeydew deposits to cause black speckling on the surface of the fruit (photo 5). An abundance of adults at harvest can also be a nuisance to pickers. Injury by RLH is thought to be similar to that of WALH.

VI. Monitoring: Examine the undersides of ten randomly selected leaves per tree and determine the average number of leafhopper nymphs per leaf. This should be done during the period from petal fall through first cover for first generation WALH, from late June through mid-July for second generation (first generation on apple) RLH, and beginning in early August for second generation WALH and third generation (second generation on apple) RLH. Trees also may be examined in early June for the appearance of RLH adults migrating to apple from multiflora rose or brambles.