Juniper and Minute Cypress Scales

Classification

Common name: Juniper scale, Minute cypress scale

Scientific name: Carulaspis juniperi (Bouché, 1851), Carulaspis minima (Signoret, 1869)

Family: Diaspididae (hard scales)

Order: Hemiptera (true bugs)

Summary

Juniper and minute cypress scales (C. juniperi and C. minima, respectively) are pests of junipers, cypresses, arborvitaes, and other trees and shrubs in the family Cupressaceae (Figure 1). Infestations are generally light and do not affect healthy plants. However, heavy infestations can cause needle drop, branch die back, or even kill entire plants.

Figure 1. Carulaspis scales on eastern white cedar (Thuja occidentalis). Photograph by Oliver K. Reichl via iNaturalist, used under a CC BY-NC-ND 4.0 license.

Description and identification

Female scales are covered by a waxy test, or coating, which is approximately 1/16 inches (1.5 mm) across, circular, and white with a yellow center, so somewhat resemble tiny fried eggs (Figure 2). Immature males are slightly smaller than females, elongate with longitudinal ridges, and white with yellow at one end. The yellow on female and male tests are exuvia, or shed exoskeletons, of former nymphal stages. If the tests are pulled up, the scale insect itself can be observed beneath the test. Crawlers are tiny and yellow. Mature males emerge as winged insects that resemble tiny wasps walking on an infested twig; males do not feed, so only live and are apparent for a short time.

Figure 2. Female Carulaspis on common juniper (Juniperus communis). Note the round shape and white coloration with yellow center. Photograph by Lorin Timaeus via iNaturalist, used under a CC BY 4.0 license.

Juniper and minute cypress scales are similar in appearance in hand and under low magnification, so require examination of slide-mounted specimens under a compound microscope to differentiate. However, both species have similar life histories in Pennsylvania, so species ID is not as crucial as it is for other scale species. (For readers outside of Pennsylvania, this is not always the case, so depending on your location the species may need to be distinguished to get adequate control).

Distribution

Juniper and minute cypress scales have been spread around the world through the plant trade as many species of Cupressaceae are popular ornamentals. In North America, both species are found throughout the eastern United States and parts of adjacent Canada, as well as the West Coast from California to British Columbia. Minute cypress scales prefer warmer climates compared to juniper scales, so while both species are found throughout the eastern United States, juniper scale tends to be more common in northern areas, such as Pennsylvania, while minute cypress scales tend to be more common in the Southeast.

Host plants

Juniper and minute cypress scales feed primarily on trees and shrubs in the family Cupressaceae, which includes junipers (Juniperus), cypresses (Cupressus), arborvitae (Thuja), oriental arborvitae (Platycladus) false cypress (Chamaecyparis), incense cedar (Calocedrus decurrens, which includes a number of native and ornamental species. They have also been recorded on Atlas and Lebanese cedar (Cedrus atlantica and C. libani), spruces (Picea), pines (Pinus), and yews (Taxus).

Life history

Juniper and minute cypress scales overwinter as mated females. In cooler areas, there is a single generation per year, while in warmer areas there may be two generations per year. In Pennsylvania, the life cycles of both species are in synchrony: eggs are laid beginning in late-April through mid-May and peak crawler emergence is in late May, scales mature through the summer, and adult males emerge and mate with adult females in early July. There have apparently been no investigations of these species in the southern United States, so it's unclear if there is one or two generations per year or if their life cycles are in synch as they are further north.

Damage

The first indication of plant injury caused by this scale insect is the loss of normal lustrous color. As an infestation becomes more severe, foliage on individual branches will look chlorotic or yellow and may eventually die. Entire plants are known to die as the result of severe infestations (Figure 3).

Figure 3. Carulaspis scale damage to an ornamental plant. Note the discolored needles and branch die back. Photograph by Joe LaForest via Forestry Images, used under a CC BY-NC 3.0 US license.

Management

Despite the fact that neither species is native to Pennsylvania, there are a variety of natural enemies that feed upon juniper and minute cypress scales. Dustywing larvae and adults feed on eggs and other life stages of this scale insect, lady beetle larvae and adults are often associated with infestation, and at least four species of wasp parasitoids are known to attack them. When scale infestations are small, keeping infested plants healthy can be enough to allow natural enemies to keep the scales in check. If trees are stressed (e.g., due to being recently transplanted or drought), reducing stress through adequate watering or other mitigation efforts can help keep scale populations from growing.

If infestations grow larger and trees begin to decline, registered insecticides can be applied from late May through June to reduce crawler populations, which are the life stage most susceptible to chemical controls as they lack the waxy test of older life stages. Because natural enemies often help keep the scales in check, horticultural oil should be applied first and, if the desired control is not reached, then broader spectrum insecticides tried in subsequent years. Additionally, dormant oil can be applied in early April when temperatures are above 40°F to control overwintering females.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

References

García Morales, M., D. B. Denno, D. R. Miller, G. L. Miller, Y. Ben-Dov, and N. B. Hardy. 2016. ScaleNet: A literature-based model of scale insect biology and systematics. Database. doi: 10.1093/database/bav118.