Although lace bugs are commonly present and occasionally destructively abundant on the foliage of various garden plants and many native trees and shrubs, they are seldom noticed.
The leaf damage which results from their feeding is often conspicuous, but the insects themselves are minute, retiring, and, therefore, rarely observed.
Since these small insects usually prefer certain plants, they eventually attract attention and require control.
Host Plants For These Troublesome Species
Among the more troublesome are three closely-related species that select as host plants, such valuable ericaceous shrubs as the following:
- Rhododendrons
- Mountain laurels
- Azaleas
- Japanese andromeda
Because the foliage may be badly discolored and the plants seriously injured by heavy infestations, some knowledge of these lace bugs and their habits will be useful to gardeners.
Noticeable Damages To Lookout For
A yellowish mottling of the upper surface may be conspicuously noticeable on the rich, green leaves of such evergreen shrubs as mountain laurel and rhododendron.
As the insect population increases during the summer, entire leaves may become whitened, and, in extreme cases, the injured leaves may curl, turn brown and even drop prematurely.
Often an entire plant looks dull and unhealthy and lacks the normal, glossy appearance characteristic of such broad-leaved evergreens.
On closer study, individual, damaged leaves will often have a few too many adult and immature lace hugs on the lower surface.
That side of such leaves will be more or less thickly dotted with varnish-like spots of lace bug excrement. Usually, the insects remain on the lower leaf surface, which shelters and protects them.
Both young and adult forms have sucking mouthparts. They insert their stylets into the leaf and suck out the contents of the leaf cells. This kills the cells and discolors the tissues, which is apparent on the upper leaf surface.
Lace Bugs’ Distinctive Form
Lace bugs are easily recognized because of their distinctive form. However, the small size makes it almost imperative to have some magnifying instrument available to really appreciate their appearance in detail.
But for this purpose, a ten-power hand lens is fairly satisfactory. The adults are so small that they are measured in millimeters.
The shortest of the three herein considered is the rhododendron lace bug which may be only 3.3 mm. long, while the largest is the andromeda lace bug which may be as much as 4 mm. long.
Since three millimeters is only about 1/8 of an inch, their minuteness is evident. Their flat, blackish bodies are covered by gauze-like membranous wings, which are finely netted.
At the widest point across, they measure only 2 to 2.4 mm. from the edge of one wing to the other.
The head is covered by a hood resembling the wings in texture and pattern. The margins of the thorax are also membranous, expanded, and flaring erect.
Species Of Lace Bugs
The rhododendron lace bug is a uniform, dingy straw color, whereas the azalea lace bug has sonic smoky brown markings, and the andromeda lace bug has a similar pattern of blackish hue on the hood and front wings.
The three kinds are readily distinguishable.
Rhododendron Lace Bug
Shortest but broadest is the species that feeds by preference on rhododendrons and mountain laurel. It is a native American form and looks very unlike the other two, which are of Oriental origin.
This native insect has a very small hood, and the front wings arc more broadly rounded at their distal ends. The surface of the wings has numerous fine, silky hairs.
Azalea Lace Bug
Of medium length is the azalea lace bug. It has a much larger and more rounded hood than the rhododendron lace bug.
The surface of the wings is smooth, and, except for scattered markings, the membranous areas are transparent.
This insect selects different types of azaleas for food plants, including certain evergreen varieties and deciduous types. However, it bears a marked resemblance to the third species.
Andromeda Lace Bug
The body length of the andromeda lace bug averages a bit longer than the other two. It has by far the largest, most globose hood, and the dark markings are in sharp contrast on the otherwise cellophane-like body surface.
This insect has only recently become well established in Connecticut, where it feeds almost exclusively on the foliage of the Japanese andromeda.
Life Cycles
The life cycles of both the rhododendron and azalea lace bugs are reasonably well known, and the little evidence at hand suggests that the life history of the andromeda lace bug is essentially the same.
Members Of The Same Genus
The three insects discussed here are members of the same genus. However, unlike other temperate zone lace bugs whose habits are recorded, these species live over winter in the egg stage.
As is usual, they lay their eggs in the leaves of their host plants. The basal end of an egg is inserted into the leaf tissue on the tower leaf surface, commonly close to a vein.
The younger leaves are selected on the evergreen plants, which remain on the plant all winter. Eggs laid in late summer will hatch when the weather becomes favorable, late May or June.
The young nymphs feed after hatching and molt five times, at three to six-day intervals, to pass through five nymphal stages before transforming into adults at the time of the fifth and final molt.
Depending on the temperature, availability of food, and other environmental factors, development from hatching to maturity requires a month or more. Then, the adults feed and mate to produce eggs for the next generation.
Two or three broods may occur in New Jersey and Southward in one season. In central New England, probably only one cycle is completed annually. However, since the climate is more severe.
Controlling Lace Bugs
Since lace bugs feed by piercing the epidermis of the leaf and extracting the fluid substances from the tissues within, they are controlled by contact poisons.
To effect good control, careful spraying or dusting of the undersides of the leaves is essential.
The aim is to cover the insects themselves with suitable contact insecticides. Unfortunately, nymphs and most adults will succumb to nicotine sulfate if a goad sticker and spreader are also employed.
The nicotine sulfate is used at the rate of 1 part to 800 parts of water; if a strong soap is used, five pounds to 50 gallons of water will suffice.
D.D.T. preparations have also proved effective and have the advantage of poisoning insects that merely walk over a surface previously sprayed.
Furthermore, the D.D.T. residual spray film on the foliage remains poisonous to insects for several days or even weeks in some instances.
The major problem is to spray the underleaf surfaces thoroughly since the lace bugs are seldom found elsewhere. This can be done by using powerful sprayers equipped with the proper nozzles.
Best Control: Spraying
The best control is obtained if the spraying is done early in the season when the eggs are hatching.
Spray about five days after hatching starts and a second time five days later or as weather conditions and the lace bug population dictate.
Since the azalea lace bug may infest deciduous plants, garden sanitation procedures in Fall and Spring, such as the raking and burning of fallen leaves that possibly bear eggs, should greatly reduce and limit the possibilities of a heavy infestation developing.
Regularly examining the plants during the growing season and prompt spraying, when indicated, will prevent the growth of a large population with injury to the shrubs.
44659 by Norman S. Bailey