(Comstock, 1881)
Taxonomic note
Diaspidiotus juglansregiae belongs to a group of species that are difficult to assign to distinct genera - see Genus Diaspidiotus, Background.
Diagnosis
In life, female scale cover circular, fairly flat, up to 3 mm diameter, light tan or light grey to red-brown, with yellow to orange subcentral exuviae DIASJL4.jpg . Male scale cover elongate oval, smaller than that of female, grey-brown, with yellow to orange subterminal exuviae (Davidson and Miller, 1990) DIASJUL.jpg . Male crawlers often settle side by side, just inside the edge of their mother's scale cover, giving an impression of petals of a flower DIASJL2.jpg . Body of living female bright yellow to reddish orange, deeply notched twice on either side of the thorax (Stoetzel, 1975; Gill, 1997) DIASJL3.jpg . Adult male alate, with orange body (Stoetzel, 1975).
Body of slide-mounted adult female membranous, approximately pyriform but with two constrictions; one between pro- and mesothroax, and one between meso- and metathorax DIASJUS.jpg . Anus smaller than a median lobe, situated at least 2.4 times its own length from base of median lobes; perivulvar pores present in five groups. Pygidium with median lobes well developed, somewhat convergent, each slightly notched on outer margin; second lobes small, rounded, shorter than associated marginal seta; third lobes small and rounded, fourth lobes absent. Paraphyses present between positions of third lobes only, shorter than the lobes, thickened towards their inner ends. Plates between lobes simple; median and first interlobular spaces each containing only one plate DIASJUP.jpg .
Host range
Diaspidiotus juglansregiae has been recorded from hosts, mostly trees, belonging to 40 genera in 10 plant families (Davidson and Miller, 1990). Preferred hosts are deciduous trees, especially Juglans and Fraxinus species (Zahradník, 1990a); it is occasionally found on conifers (Gill, 1997). Hosts include species of: Adelia, Betula, Cornus, Fraxinus, Gleditsia, Juglans, Photinia, Pinus, Populus, Prunus, Rosa, Salix, Sorbus, Ulmus, Vitis and Zanthoxylum.
Affected plant stages: vegetative growing, flowering and fruiting stages
Affected plant parts: on the bark of stems and trunks DIASJL1.jpg , often hidden under bark flakes or under the host's epidermis
Biology and ecology
On the East coast of the USA there is one generation per year and overwintering is as second instars; in other parts of the USA there may be two or more generations each year, and overwintering is usually as adult females (Davidson and Miller, 1990; Zahradník, 1990a; Gill, 1997). Scale covers are often formed under the epidermis of the host's bark and stems (Davidson and Miller, 1990). In Tennessee, each female lays 3-52 (average 34) eggs, which hatch in 2-5 days (Lambdin et al., 1993).
Crawlers are the primary dispersal stage and move to new areas of the plant or are dispersed by wind or animal contact. 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
Infestations of D. juglansregiae may cause unsightly or dead lower branches, and heavy infestations may kill trees (Kosztarab, 1996).
Economic impact
This scale was listed as a pest of deciduous fruit trees of regional importance by Kozár, 1990b. In California, D. juglansregiae can be a serious pest of some ornamental trees, killing Betula species and killing or severely weakening Fraxinus species; elsewhere in the USA it is regarded as a minor pest of walnut orchards (Gill, 1997). Infestations of D. juglansregiae may cause unsightly or dead lower branches, and heavy infestaions may kill trees (Kosztarab, 1996).
Detection and inspection methods
In good light, examine the bark closely for circular, light tan or light grey scale covers, especially under bark flakes (Kosztarab, 1996).
Natural enemies
Parasitoids:
- Coccidencyrtus sp., in USA (Ohio)
- Coccidencyrtus ensifer, in USA (Kentucky, Ohio)
- Metaphycus californicus, in California
- Plagiomerus sp., probably diaspidis, in USA (Ohio)
- Zaomma lambinus, in USA (Ohio)
Predators:
- Adalia bipunctata, in USA (Kentucky, Ohio)
- Cheyletomimus sp., in USA (Ohio)
- Chrysopa ? nigricornis, in USA
- Chilocorus stigma, in USA (Kentucky, Ohio)
- Thyreophagus entomophagus, in USA (Ohio)
- Lucoppia sp., in USA (Ohio)
Distribution
See Diaspidiotus juglansregiae distribution.
Microscopic examination of slide-mounted adult females is required for authoritative identification to species.
Diaspidiotus forbesi (Johnson) DIASFOS.jpg could be misidentified as D. juglansregiae but differs in lacking plates between the median lobes and between the median and second lobe on each side DIASFOP.jpg. In contrast, D. juglansregiae has very slender, simple plates in these positions DIASJUP.jpg. Diaspidiotus forbesi is a polyphagous species known from Canada, continental USA (including New Mexico; rare in California), Mexico and South Africa; it is often found on the bark of hosts belonging to 22 genera in 11 plant families, including species of Carya, Cornus, Crataegus, Fraxinus, Malus, Prunus and Pyrus (Nakahara, 1982; Davidson and Miller, 1990; Kosztarab, 1996; Miller, 1996; Gill, 1997; The Natural History Museum collection, London, UK). Diaspidiotus forbesi is a well-known pest of fruits, mainly apples, also on cherries and peaches, in North America (Kozár, 1990b; Kosztarab, 1996); there are two generations per year (Davidson and Miller, 1990); overwintering is as mated females in Ohio (Kosztarab, 1963). In life, scale cover of adult female 1.5-2.5 mm long, circular to oval, dirty grey, more or less convex, with orange or dark marginal to subcentral exuviae; male scale cover elongate oval, dark grey with paler margin, smaller than that of female; exuviae orange, subterminal (Davidson and Miller, 1990; Gill, 1997). Adult males are wingless (Kosztarab, 1963). DIASFOL.jpg
In the field, Diaspidiotus juglansregiae could be confused with Howardia biclavis; but in D. juglansregiae the living female's body is yellow and is usually found on deciduous hosts, whereas that of H. biclavis is not (Gill, 1997).
Comments
Diaspidiotus juglansregiae is a temperate species native to North America. It has not been recorded outside the Americas.
Western Hemisphere
Canada: present, no further details (Davidson and Miller, 1990)
Mexico: present, no further details (Davidson and Miller, 1990; Miller, 1996)
Peru: present, no further details (Zahradník, 1990a)
USA: general distribution in continental USA (Davidson and Miller, 1990; Gill, 1997)
California: widespread (Gill, 1997)
Kansas: The Natural History Museum collection, London, UK
Kentucky: present no further details (Mussey and Potter, 1997)
Massachusetts: The Natural History Museum collection, London, UK
Mississippi: The Natural History Museum collection, London, UK
Ohio: The Natural History Museum collection, London, UK
Tennessee: The Natural History Museum collection, London, UK