Lace bugs use their sucking mouthparts to feed on plant sap. Damage ranges from many small white spots on the leaves to distortion or complete destruction of plant tissue, depending on the host plant. Some feed on many different types of plants while others feed only on a narrow range or single species.
Lace bugs are common pests of a variety of ornamental trees and shrubs. The adults have highly ornamented wings and a hood-like structure covering the head. The entire surface is covered with veins that look like lace. The most common lace bug pests in Ohio include the sycamore lace bug (Corythucha ciliata), hawthorn lace bug (C. cydoniae), hackberry lace bug (C. celtidis), oak lace bug (C. arcuata), basswood lace bug (Gargaphia tiliae), azalea lace bug (Stephanitis pyriodes), rhododendron lace bug (S. rhododendri), and andromeda lace bug (S. takeyai). The hawthorn lace bug often attacks cotoneaster, pyracantha, flowering quince, crabapple, mountain ash and shadbush (Amelanchier) as well as hawthorn while the basswood lace bug commonly attacks lindens. The rhododendron lace bug also can be found on mountain laurels. The rest of the species are fairly well restricted to their namesake hosts.
Lace bugs are usually detected when their damage to the leaves of host plants becomes evident. The nymphs and adults live on the lower surface of leaves and suck juices through slender, piercing mouthparts. This produces yellow or whitish spots on the upper surface of the leaf. As the insects feed, they deposit a hard, varnish-like excrement onto the leaf surface. These are called tar spots or resin spots.
Once the damage is noticed, the adults and nymphs can be looked for by turning over affected leaves. Adult lace bugs are about 1/8" x 1/16" wide. They are somewhat rectangular in outline. The nymphs are oval in outline and often covered with long spines. Most of the lace bugs move rather slowly when disturbed but the hackberry lace bugs tend to drop from the leaves that are touched.
Most lacebugs spend the winter as eggs that hatch in early spring. There may be several generations during a season. With multi-generation species, numbers early in the season are so small that feeding symptoms may not be noticed. Populations peak in late summer and results of their feeding can make plants unsightly.
Lace bugs can be divided into 2 groups: those that attack deciduous trees and shrubs, and those that attack evergreen shrubs. Lace bugs that attack deciduous plants spend the winter in the adult stage by hibernating on the plant under bark or near the plant in leaf litter. Lace bugs that attack evergreens over winter in the egg stage attached to the leaves.
The hawthorn lace bug is one type that attacks deciduous plants. The adults hibernate under loose bark of their host plants as well as among leaf litter. They become active in early to mid-May and return to the new leaves. The females soon begin to lay eggs along the larger veins on the lower leaf surface. The females may lay eggs for a considerable time, often extending into June. The eggs hatch in a couple of weeks and the nymphs cluster together and feed. Each nymph sheds its skin (molts) five times before the adult stage is reached. Growth to the adult stage usually takes three to four weeks. Peak numbers of this pest are usually present in July. Only one generation occurs per year. Related species of lace bugs such as the oak, sycamore and hackberry lace bugs have 2 and sometimes 3 generations in a summer.
The azalea lace bug (an example of a lace bug that attacks evergreens) over winters in the egg stage. The eggs are partially inserted into the leaf tissues along the midvein and are covered with the resin-like excrement of the female. The nymphs hatch in the spring, usually mid-May, after the danger of frost is over. They feed in small groups on the under surface of leaves and molt five times before becoming adults. The adults mate and lay eggs for a second generation by mid to late-July. Often there is a third generation in the late summer and early fall. The andromeda and rhododendron lace bugs have similar life cycles.
Plants that attract lace bugs should be monitored early in order to determine if an infestation is building. Elimination of the first generation of lace bugs is necessary if visual damage is to be avoided. Existing spotting and yellowing of leaves will not disappear once the lace bugs have been controlled.
Insecticides such as Insecticidal Soap, Summer Horticultural Oils, Dursban, Malathion, Orthene, Sevin may be used depending on the species or cultivar. Always read product labels carefully before buying. Look for information on phytotoxicity that can occur on sensitive plants or under some environmental conditions. Repeated treatments may be needed to control these pests effectively.