A Potential Insect Pest of Azaleas
A. G. Wheeler, Jr., Bureau of Plant Industry
Pennsylvania Department of Agriculture, Harrisburg, PA
Jon L. Herring, Systematic Entomology Laboratory
Fed. Res., Sci. Educ. Admin., USDA
The mirid bug, Rhinocapsus vanduzeei Uhler, which feeds on the stamens of azaleas, is briefly described and figured to allow field recognition of the immature and adult forms. A summary of the seasonal history and damage to azaleas is given. Its potential as a serious pest affecting seed production is discussed.
Azalea growers must contend with a variety of insect problems, including the well-known black vine weevil, azalea leafminer, azalea lace bug, and numerous other pests. Recently, a small black and reddish-orange plant bug, Rhinocapsus vanduzeei Uhler, has attracted the attention of home gardeners and nurserymen. Although this insect has been known to science since 1890 and is generally distributed from Ontario south to North Carolina and west to Missouri, its habits have remained obscure. This insect has no official common name but it might well be called the azalea plant bug. R. vanduzeei is of interest to azalea growers because it feeds on stamens, thus destroying pollen and possibly affecting seed production. In addition, this bug often bites gardeners while they are working with their azaleas.
Studies conducted at the Pennsylvania Department of Agriculture have helped to clarify the habits of R. vanduzeei on azaleas as well as the biology of four other species of plant bugs associated with ericaceous plants. The results will be reported in a technical article by Thomas J. Henry and the first-named author of this paper. In this paper we are providing azalea growers with a brief description that should allow recognition of the immature and adult bugs in the field and a summary of the seasonal history and damage on azaleas. The human reaction to the painful bite of R. vanduzeei, a chigger like welt, will be described and figured by David G. Hall in a forthcoming volume he and collaborators will publish on biting and stinging arthropods.
Field Recognition of Rhinocapsus vanduzeei
Rhinocapsus vanduzeei adult feeding on stamen
Photo by James F. Stimmel
Rhinocapsus vanduzeei third instar nymph
Photo by James F. Stimmel
Rhinocapsus vanduzeei is a plant bug belonging to the family Miridae, the largest family of the true bugs (order Hemiptera). Other members of this family that might be familiar to gardeners and nurserymen are the tarnished plant bug and Honeylocust plant bug.
R. vanduzeei has sucking mouthparts in the form of a long proboscis or beak used to extract juices from its host plant. The possession of a beak readily distinguishes this plant bug from similarly colored beetles, which have chewing mouthparts. The bug feeds mainly on or within azalea flowers but can be found resting on the foliage. When disturbed on a leaf, the bugs quickly retreat to the underside, then reappear suddenly at the top of the leaf on the opposite side.
The newly hatched bugs, or first-stage nymphs, are bright red and less than 1 mm long. Later stage nymphs range from 1.5 to 3.0 mm long and are nearly vermilion, with the wing pads somewhat darker. On certain red-flowered varieties of azaleas the nymphs are well camouflaged.
Adult bugs are about 3.5 to 4.0 mm long and oblong-oval with a shiny, polished appearance. They are not as brightly colored as the nymphs. In the field the wings appear orangeish, although in older specimens the wings become dark brown to black. Most of the remaining parts of the bug are orange, including the underside and the head, except for its face which is black. The first segment of the antenna is yellowish, the second segment black at its apex, and segments 3-4 somewhat dusky.
Eggs over winter in the stems of azaleas. In the vicinity of Harrisburg, Pa., they begin to hatch in early to mid-May. Egg hatch appears to take place sooner on early-blooming varieties. The newly hatched nymphs feed mainly on the petals and stamens where they have been observed to pierce both the filaments and anthers. Although laboratory observations were made only on stamens that had shed their pollen, the bugs were seen to feed on pollen grains that had fallen onto the petals. (Pictured above)
R. vanduzeei has five nymphal or immature stages. The first adults mature during the first week of June. There is a single generation annually with the adults soon mating, laying eggs that will over winter, and then dying. In the Harrisburg area adults usually have disappeared by early to mid-July.
In northern Pennsylvania development is about two weeks behind that in the Harrisburg area. At Ithaca, N.Y. adults do not appear until late June - early July. In the vicinity of Washington, D.C. adults may develop as early as mid-May.
In the literature the only host plants recorded for R. vanduzeei are two species of wild red raspberry, Rubus spp. We also have found this bug breeding on raspberry (at Ithaca, N.Y. during June and July), but native and cultivated azaleas are the preferred food plants.
In Pennsylvania and in the Pine Barrens of New Jersey, R. vanduzeei has been found on wild swamp azalea, Rhododendron viscosum. In nurseries and ornamental plantings in Pennsylvania this bug breeds on numerous species of evergreen and deciduous azaleas, with populations more common on deciduous varieties such as flame azalea, R. calendulaceum, plus its Ghent hybrids, and Korean azalea, R. yedoense poukhanense. In the Cornell Plantations at Ithaca, N.Y. a population of the bug was observed on Cumberland azalea, R. bakeri.
Observations made by two leading azalea growers at Silver Spring, Md., Dr. August Kehr and Mr. Judson Hardy, have supplemented our data. During 1972-75, Dr. Kehr found R. vanduzeei on R. bakeri, R. calendulaceum, and R. viscosum. Mr. Hardy observed the bug on these same three species in 1975.
Although breeding is apparently restricted to azaleas and, to a lesser extent, raspberries, the adults will disperse widely when their host plants have finished blooming. Adults can then be found on a variety of ornamental trees and shrubs, often within the flowers.
Although a large population of R. vanduzeei may slightly deform azalea flowers, this plant bug probably is important only on plants grown for seed. Feeding on stamens by nymphs and adults may cause the filaments to atrophy. Mr. Hardy has observed that flowers infested with the bug lacked pollen but had normal pistils. Even though this species prefers to feed on floral parts, it is unlikely that this plant bug is an obligatory flower feeder. Later stage nymphs have been observed to complete their feeding on an early blooming evergreen azalea after all flowers had dropped from the plant. Control measures, however, may become necessary if large numbers of the bug are discovered on azaleas being grown for seed. In addition, homeowners occasionally have requested chemicals that might help control R. vanduzeei and thus keep them from being bitten when they work among their azaleas.
We are especially grateful to James F. Stimmel, Bureau of Plant Industry, Pennsylvania Department of Agriculture, for his excellent photographs of R. vanduzeei. We thank August Kehr and Judson Hardy, Silver Spring, Md., for sharing with us their observations of this bug on azaleas, and David G. Hall, Arlington, Va., for his interest in the biting habits of this species. Thomas J. Henry and K. Valley, Bur. 'PI. Ind., Pa. Dept. Agric., kindly reviewed the manuscript.