Adult rhododendron lace bugs are approximately 1/8 inch in length with lace-like, translucent wings. Adults are whitish or off-white in color. The nymphs (immatures) are off-white with darker patches of color and have dark colored spines on their abdomen. Nymphs are wingless. Lace bugs have incomplete metamorphosis, so they pass through three life stages: egg, nymph, and adult (there is no pupal life stage). Nymphs of the rhododendron lace bug may have up to 4 instars (molts). This is uncommon for insects in this family, which typically have 5 instars. The immatures (nymphs) will feed on the lower leaf surface, amongst their cast (shed) skins and black, tar-like, spots of frass or excrement. The rhododendron lace bug overwinters as whitish-yellow eggs (0.4 mm in size) inserted partially in either the leaf veins or most commonly in the mid-rib of the leaf. Younger leaves are preferentially selected by females for egg laying. A single leaf may have few or up to 176 eggs inserted. The number of eggs laid per female is not known. In Virginia, eggs hatch in May. Typically, in geographic locations north of Virginia, egg hatch occurs before the end of May; in warmer climates, egg hatch might occur by late April. In Ithaca, NY, egg laying was reported in late May and early June (Crosby and Hadley, 1915). Egg laying may continue through July. Two generations may occur per year in northern geographic locations, and three per year in southern locations. The entire life cycle of the insect may take approximately 30 days to complete. Adults have been collected from June to September in Connecticut, with some records existing as late as October in Princeton, MA (Bailey, 1951). This is an example of a native North American species that has been previously introduced as a non-native species in Europe (records from Holland; Horvath, 1905 and Dickerson, 1917).
While lace bug feeding occurs on the underside of the leaf, damage from the feeding can be seen on the upper leaf surface. The upper surface of the leaves appears chlorotic, while the undersides have brown or black varnish-like spots (tar spots) of excrement. From a distance, lace bug feeding may resemble spider mite injury to plants. Inspection of the leaf underside (to search for the tar spot-like excrement) can help confirm lace bugs as the cause of the damage. Cast (shed) skins from the nymphs may also remain attached to leaf undersides for some time. Feeding damage from lace bugs can be serious. Early season damage from this insect might mean that foliage remains unsightly and less functional for more than a year. Shrubs planted in sunny locations may suffer entire leaf yellowing/browning and dieback. On occasion, shrubs in sunny locations are killed. Rhododendron lace bugs feed by injecting saliva into the host plant to predigest their food. They then suck out the predigested liquid to feed. This species may be able to feed on over 120 different types of rhododendron.
Begin scouting for lace bug activity in May, particularly the end of May/beginning of June in Massachusetts. Look for signs of chlorotic/stippled leaf surfaces, and flip leaves over to observe the undersides to confirm lace bug presence. Scout plants that have a history of lace bug infestation. Continue scouting throughout the growing season, as lace bugs have multiple generations per year, including into the fall.
Avoid planting host plants in sunny locations, as this abiotic condition may favor lace bug populations. Reduce plant stress and water properly. A strong jet of water from a hose (syringing) may be targeted at the undersides of host plant leaves to dislodge adults and nymphs. Any remaining individuals may continue to feed on the plant.
The impact of natural enemies on lace bug populations is enhanced in shady landscapes with more structural complexity, particularly those with overstory trees and flowering plants (Shrewsbury and Raupp, 2000). Parasitoid wasps are said to parasitize the eggs of the rhododendron lace bug, but the specific species involved are not easily determined at this time.
Abamectin (NL)
Acephate (NL)
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorantraniliprole (NL)
Chlorpyrifos (N)
Clothianidin (NL)
Cyfluthrin (NL)
Deltamethrin (L)
Dinotefuran (NL)
Fenpropathrin (NL)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Malathion (L)
Permethrin (L)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Active ingredients that may be applied systemically include: Abamectin (injected), acephate (injection), azadirachtin (injection, soil drench), chlorantraniliprole (soil drench), clothianidin (soil drench), cyantraniliprole (NL), dinotefuran (soil drench), and imidacloprid (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
