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
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
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.
VII. Management: To prevent economic impact from leafhopper feeding, an average of
three nymphs per leaf is recommended as an action threshold for insecticide application.
The action threshold should be lowered to one nymph per leaf where the nuisance to pickers
from adult leafhoppers is a concern during harvest.
Credits: Text prepared by H. W. Hogmire and S. C. Beavers, modified from
the original text in the Mid-Atlantic Orchard Monitoring Guide (original text by D.
G. Pfeiffer, L. A. Hull, D. J. Biddinger and J. C. Killian). Prepared in August, 1998.
Web Site Author: Alan