(Comstock, 1881)
Diagnosis
In life, scale cover of adult female 2.0-3.0 mm diameter, circular, flat to slightly convex, dark grey with black subcentral exuviae MELOBL1.jpg . Ventral scale quite well developed. Male scale cover smaller and more elongate than that of female, grey, with black subterminal exuviae (Davidson and Miller, 1990; Gill, 1997). Body of adult female pale, often with a pinkish tinge (Gill, 1997). Adult male winged MELOBL4.jpg .
Body of slide-mounted adult female broadly pyriform, membranous, front of head not protruberant MELOBS.jpg . Pygidium broad (subtended by an angle greater than 90°), with very long macroducts; dorsal submedian macroducts absent; fringed plates present, perivulvar pores present; three pairs of rounded lobes present, fourth lobes small and bluntly pointed. Paraphyses present, obviously thickened towards their inner ends; a few short, irregularly spaced paraphyses present lateral to fourth lobes. Paraphyses in first and second interlobular spaces up to twice as long as the other paraphyses MELOBP.jpg .
Host range
Melanaspis obscura has been recorded from hosts belonging to 7 plant families (Borchsenius, 1966). However, Davidson and Miller, 1990, recorded hosts in only five genera and three plant families (with the main hosts being Carya and Quercus), saying that the other records may be erroneous. Hosts may include species of: Acer, Carya spp., Castanea, Cornus, Fagus, Fraxinus spp., Juglans, Planera, Prosopis, Prunus, Quercus spp., Sapindus, Ulmus, Viburnum and Vitis.
Affected plant stages: vegetative growth, flowering and fruiting stages
Affected plant parts: on the bark MELOBL3.jpg , often under the loose outer bark flakes, making the scales difficult to find
Biology and ecology
Melanaspis obscura has one generation per year in Maryland, Ohio and Louisiana; in Maryland it overwinters as second instars on red oak but on white oak, overwintering occurs as first instars, suggesting the presence of sibling species (Stoetzel and Davidson, 1971; Stoetzel and Davidson, 1973). Males are common (Kosztarab, 1996).
Crawlers are the primary dispersal stage and move to new areas of the plant or are dispersed by wind or animal contact; in heavy infestations, the crawlers tend to settle under the covers of previous generations (Davidson and Miller, 1990). Mortality due to abiotic factors is high in this stage. Dispersal of sessile adults and eggs occurs through human transport of infested plant material.
Symptoms
In the USA, only hosts grown in ornamental or urban situations are damaged MELOBDAM.jpg . Pin oak and willow oak seem particularly susceptible to damage; prolonged infestation causes the bark to become knurled, and often results in dieback (Deitz and Davidson, 1986). Stems may become distorted and small trees are sometimes killed (Davidson and Miller, 1990). On pecan in the southern USA, M. obscura frequently kills branches less than 3 inches (8 cm) in diameter, and generally weakens the trees so that they become susceptible to woodborer attack (Gill, 1997).
Economic impact
Melanaspis obscura is native to the eastern United States, where it never damages native oak forest; but even within this area it is a serious urban pest of ornamental oaks, causing dieback even on large trees. It is regarded as one of the most important shade tree pests in the eastern USA (Davidson and Miller, 1990). Danzig and Pellizzari, 1998, describe this species as a dangerous pest in the Palaearctic region. In the USA, the scale is often abundant on oaks in parks and gardens, despite high levels of parasitism; it is among the most serious pests of shade trees in Maryland (Stoetzel and Davidson, 1971) and causes serious damage to oaks in Ohio (Kosztarab, 1963) and Florida (Dekle, 1976). Gill, 1997, said it is a serious pest of oaks in the eastern USA, and a pest of pecan throughout the south, causing gradual dieback of branches of 3 inches diameter or less (Ebeling, 1959; Woodroof, 1967).
Detection and inspection methods
In good light, examine rough, knobbly areas of bark closely for cryptic, convex grey scale covers MELOBL3.jpg .
Phytosanitary risk
Melanaspis obscura is known only from Canada, the USA and Japan, and could pose a serious risk to oaks in other Palaearctic countries if accidentally introduced there (Davidson and Miller, 1990).
Natural enemies
A number of fungi, thrips, parasitic Hymenoptera and predaceous mites, mirids and coccinellid beetles occur in association with M. obscura (Stoetzel and Davidson, 1973). Ehler, 1995, and Ehler, 1997, record successful biological control of M. obsura in California using Encarsia aurantii.
Parasitoids:
- Ablerus clisiocampae, in USA (California)
- Coccobius varicornis, in USA (California)
- Coccophagoides fuscipennis, in USA (California)
- Encarsia aurantii, in USA (California)
Predators:
- Corticoris signatus, attacking females, in USA (Pennsylvania)
- Leptothrips sp., in USA
- Myiomma cixiiformis, attacking females, in USA (Pennsylvania)
Distribution
See Melanaspis obscura distribution.
Microscopic examination of slide-mounted adult females is required for authoritative identification to species.
Comments
Melanaspis obscura is native to the eastern USA south of the Great Lakes and east of Texas (Gill, 1997); it is known only from North America and Japan.
Asia
Japan: present, no further details (Kawai, 1980; Danzig and Pellizzari, 1998)
Western Hemisphere
Canada
Ontario: present, no further details (Nakahara, 1982)
USA
Alabama: present (Deitz and Davidson, 1986)
Arkansas: present (Deitz and Davidson, 1986)
California: restricted to part of Sacramento only - eradicated elsewhere (Gill, 1997)
Connecticut: present, no further details (Deitz and Davidson, 1986)
Delaware: present, no further details (Nakahara, 1982)
District of Colombia: present (Deitz and Davidson, 1986)
Florida: present, no further details (Nakahara, 1982)
Georgia: present (Deitz and Davidson, 1986)
Illinois: present, no further details (Deitz and Davidson, 1986)
Indiana: present (Deitz and Davidson, 1986)
Iowa: present (Deitz and Davidson, 1986)
Kansas: present (Deitz and Davidson, 1986)
Kentucky: present no further details (Mussey and Potter, 1997)
Louisiana: present (Deitz and Davidson, 1986)
Maryland: present (Deitz and Davidson, 1986)
Mississippi: present (Deitz and Davidson, 1986)
Missouri: present (Deitz and Davidson, 1986)
New Jersey: present (Deitz and Davidson, 1986)
New York: present, no further details (Nakahara, 1982)
North Carolina: present (Deitz and Davidson, 1986)
Ohio: present (Deitz and Davidson, 1986)
Oklahoma: present (Deitz and Davidson, 1986)
Pennsylvania: present (Deitz and Davidson, 1986)
South Carolina: present (Deitz and Davidson, 1986)
Tennessee: present (Deitz and Davidson, 1986)
Texas: present (Deitz and Davidson, 1986)
Virginia: present (Deitz and Davidson, 1986)
West Virginia: present (Deitz and Davidson, 1986)