(Curtis, 1843)
Taxonomic note
Diaspidiotus ostraeformis belongs to a group of species that are difficult to assign to distinct genera - see Genus Diaspidiotus, Background.
Diagnosis
Scale cover of adult female circular, convex, grey, 1.4-1.9 mm in diameter, with subcentral (rarely, central), orange-yellow exuviae DIASOST4.jpg . Male scale cover similar to that of female, but smaller and elongate oval, with yellow subterminal exuviae (Davidson and Miller, 1990) DIASOSTL.jpg . Exposed body of adult female pyriform, lemon yellow in life DIASOST3.jpg . Adult male winged (Ghauri, 1962).
Body of slide-mounted adult female membranous, approximately pyriform, 1.2-1.5 mm long, sometimes with slight constriction between meso- and metathorax DIASOSTS.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 and second lobes well developed, slightly convergent, second lobes each slightly notched on outer margin, usually as shorter than associated marginal seta; third lobes usually represented by points, occasionally absent; fourth lobes absent. Paraphyses present between positions of third lobes only, shorter than the lobes, usually thickened towards their inner ends. Plates between lobes fimbriate; each median lobe with paraphysis on inner basal angle smaller than that on its outer basal angle DIASOSTZ.jpg .
The adult male of D. ostreaeformis was described by Bustshik, 1958, and Ghauri, 1962.
Host range
Diaspidiotus ostreaeformis has been recorded from hosts, mostly trees, belonging to 41 genera and 18 plant families (Davidson and Miller, 1990). Preferred hosts are deciduous fruit and nut trees in the family Rosaceae, and roses (Gill, 1997), but it is also common on forest trees (Zahradník, 1990a). Hosts include species of: Abies, Acer, Aesculus, Alnus, Betula, Calluna, Caragana, Carpinus, Catalpa, Chaenomeles, Cornus, Corylus, Cotoneaster, Crataegus, Cydonia, Cytisus, Fagus, Ficus, Fraxinus, Gleditsia, Juglans, Malus pumila, Malus spp., Morus, Myrica, Olea, Ostrya, Phoenix, Platanus, Populus, Prunus spp., Pyrus spp., Quercus, Rhamnus, Rhododendron, Ribes, Rosa, Salix, Sorbaria, Sorbus, Spiraea, Syringa, Tilia, Ulmus and Vaccinium.
Affected plant stages: vegetative, fruiting and post-harvest stages
Affected plant parts: on bark of twigs and branches DIASOST1.jpg ; sometimes also fruits and leaves
Biology and ecology
Diaspis ostreaeformis is a bisexual species that has one generation per year and overwinters as second instar larvae, in obligate winter diapause (Kozár, 1990b; Davidson and Miller, 1990). In central Europe, the adults appear at the end of April, and in northern Europe one or two months later. Egg-laying continues for two months; each female lays 60-200 eggs (usually about 110 - Zahradník, 1990a). The first instar lasts 45-80 days (Kosztarab and Kozár, 1988).
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.
The pheromone of D. ostreaeformis is not known. The component compounds of the D. perniciosus pheromone do not attract males of D. ostreaeformis.
Symptoms
Diaspidiotus ostreaeformis infests mostly bark on the stems and branches of trees, causing drying of the tissues (Zahradník, 1990a). Sometimes it can be found on the fruits, where it causes red spots. In cases of heavy infestation, branches or entire plants, may die.
Economic impact
This species often reaches high population densities, and was listed as a pest of deciduous fruit trees of world importance by Kozár, 1990b; D. ostreaeformis is polyphagous pest on deciduous trees, especially rosaceous species such as plums (Kosztarab and Kozár, 1988; Kosztarab, 1996). It was regarded as one of the most important pests of apple in the northern USSR (Konstantinova, 1976). It is also an important pest of apple, plum, cherry and ornamentals in different parts of the world (Konstantinova, 1976; APPPC, 1987; Davidson and Miller, 1990; Kozár, 1990b), for example in Hungary (Kozár and Drozdjak, 1988), New Zealand (McLaren, 1989), Italy (Viggiani, 1985), Switzerland (Mani et al., 1993; Kozár et al., 1994), European Russia (Kozár and Konstantinova, 1981), Australia (Baker, 1977) and Canada (Ker and Sears, 1986). Charles and Henderson, submitted, recorded D. ostreaeformis as a pest on economically important plants in New Zealand. Danzig and Pellizzari, 1998, mentioned that this species is often a pest in the Palaearctic region, and Foldi, 2001, listed it as an occasional pest in France. Argyriou, 1990, recorded it damaging olives in Italy and Turkey. Diaspidiotus ostreaeformis is of occasional importance in forests (Zahradník, 1990a).
Crop loss caused by D. ostreaeformis on different hosts is difficult to assess. The trees lose vigour, their life expectancy is shortened, and some parts of the plants may die. In addition, this species is morphologically very similar to D. perniciosus, a quarantine pest in different parts of the world (Kozár, 1990b). D. ostreaeformis also causes red spots on the fruits, and quarantine specialists often refuse import or export of infested fruits or plants because D. ostreaeformis is difficult to distinguish from D. perniciosus (Kozár, 1990b).
Detection and inspection methods
In heavy infestations of D. ostreaeformis, greyish scales can be found on the bark. Lower levels of infestation can be found by laboratory examination, using stereomicroscope analyses of branches, following the survey system described by Kozár, 1990, and Kozár, 1990c. Red spots on the fruits can indicate infestation. This sign deserves attention, because the more dangerous, and in many countries quarantine-restricted, D. perniciosus produces the same symptoms.
Phytosanitary risk
Diaspidiotus ostreaeformis is mentioned on quarantine lists (Burger and Ulenberg, 1990).
Natural enemies
Diaspidiotus ostreaeformis has a large number of parasitoids that have been studied in detail, especially in the Palearctic Region (Hornok and Kozár, 1984; Kosztarab and Kozár, 1988). Usually these natural enemies are efficient regulators of D. ostreaeformis, and they keep down the population in natural habitats. In cases of inefficient chemical control of D. ostreaeformis in orchards, the natural enemies may be killed and local outbreaks can result. The pest can cause bigger problems in continents where it was introduced accidentally (for example, New Zealand, Argentina and Australia) and where no good natural regulation occurs. The efficiency of natural enemies is also reduced in urban areas by pollution, as a consequence of which D. ostreaeformis can cause damage on ornamental plants.
Parasitoids:
- Ablerus atomon
- Aphytis mytilaspidis, attacking: nymphs, in North America, Europe, northern Asia, India, New Zealand
- Coccophagoides moeris, attacking: nymphs, in Europe, former USSR
- Encarsia aurantii
- Encarsia citrina, attacking: nymphs, in Europe, northern Asia, New Zealand
- Epitetracnemus zetterstedtii, attacking: nymphs, in Europe, North America, northern Asia
- Pteroptrix dimidiata
- Pteroptrix maritimus, attacking: nymphs, in Europe, northern Asia
- Thysanus ater
- Zaomma lambinus
Predators:
- Chilocorus renipustulatus, attacking: nymphs, adults, in Europe, former USSR
- Cybocephalus politus
- Hemisarcoptes malus
Pathogens:
- Fusarium larvarum, attacking: nymphs, adults, in Hungary
Distribution
See Diaspidiotus ostreaeformis distribution.
Microscopic examination of slide-mounted adult females is required for authoritative identification to species. To distinguish D. ostreaeformis from other Diaspidiotus species, the most important character is the plates between the lobes, which are needle-like in D. ostreaeformis, not heavily fimbriate.
In life, D. ancylus (Putnam) (convex scale, Putnam scale, cochenille de Putnam, falsa escama de San José, conchuela blanca de la ramilla) DIASANS.jpg could be confused with D. ostreaeformis (Claps et al., 2001a) but in slide-mounted adult females, D. ancylus differs in possessing three marginal plates between the second and third lobes DIASANP.jpg . In contrast, D. ostreaeformis has only two marginal plates between the second and third lobes DIASOSTZ.jpg .Diaspidiotus ancylus is [l][m]Glossary[/m][r]dimorphic[/r]dimorphic. The leaf form of this scale has 3 pairs of well-developed pygidial lobes and has been called Abgrallaspis [Hemiberlesia] howardi (Cockerell) in the past (Gill, 1997); it would key out as Hemiberlesia lataniae in the Picture Key. Diaspidiotus ancylus is a polyphagous species known from Canada (Ontario), USA (continental including Arizona, California, Indiana, Iowa, New Mexico, New York, Tennessee), Mexico, Central America, Brazil (Sao Paulo), Chile (first to eighth regions), Spain (Huelva), Portugal, Germany, South Africa and Australia; it is often found on the bark of branches and trunk, and sometimes on leaves, of basswood, elm and maple. Hosts include species of Acer, Aesculus, Betula, Carya, Catalpa, Celtis, Cephalanthus, Crataegus, Cydonia, Fagus, Fraxinus, Hydrangea, Juglans, Liriodendron, Maclura, Malus sylvestris, Muehlenbeckia, Olea europaea, Oxalis, Persea americana, Populus spp., Prunus spp., Pyrus, Quercus, Ribes, Robinia spp., Salix, Sorbus, Tilia, Ulmus, Viburnum and Vitis vinifera (Munting, 1971a; Konstantinova, 1976; Nakahara, 1982; Zahradník, 1990a; Amparo Blay Golcoechea, 1993; Kosztarab, 1996; Miller, 1996; Gill, 1997; Danzig and Pellizzari, 1998; Claps et al., 2001a; CSIRO, 2001; The Natural History Museum collection, London, UK). Immature stages of D. ancylus can be mistaken for D. perniciosus (Claps et al., 2001a). This species has been a pest on walnuts, cranberries, blueberries and on elms and other ornamentals in the USA in the past; it is probably native to North America (Gill, 1997). Diaspidiotus ancylus was listed as a pest of deciduous fruit trees of regional importance by Kozár, 1990b; heavy infestations can kill twigs and branches (Kosztarab, 1996). One or two generations per year have been recorded in the USA, and overwintering is as adult females (second instar females in Chile) (Kosztarab, 1996). This species does not occur in the former USSR, but featured on the list of quarantine pests for this region (Konstantinova, 1976).
Diaspidiotus forbesi (Johnson) DIASFOS.jpg could be misidentified as D. ostreaeformis but differs in lacking plates between the median lobes and between the median and second lobe on each side DIASFOP.jpg. In contrast, D. ostreaeformis has very simple plates in these positions DIASOSTZ.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
Diaspidiotus osborni (Newell and Cockerell) (Osborn scale) DIASOSS.jpg is a North American species that could be misidentified as D. ostreaeformis but differs in lacking plates between the median lobes, and in having simple (unfringed) marginal plates and only about 17 macroducts on each side of the pygidium DIASOSP.jpg. In contrast, D. ostreaeformis has simple plates present between the median lobes, fringed marginal plates and about 30 macroducts on each side of the pygidium DIASOSTZ.jpg. Diaspidiotus osborni is a relatively polyphagous species, probably of North American origin. It is known from Canada, continental USA (including Iowa and Virginia; rare in California), Mexico, Central America, Bulgaria, Italy, Sicily, Switzerland and South Africa; it is often found on the bark of twigs, branches and trunks of species of Betula, Carpinus, Carya, Castanea, Cornus, Crataegus, Diospyros, Fagus, Fraxinus, Juglans, Morus, Ostrya, Platanus, Prunus, Quercus, Robinia, Salix, Tilia and Vitis (Munting, 1971a; Nakahara, 1982; Kozár et al., 1994; Longo et al., 1995; Kosztarab, 1996; Miller, 1996; Gill, 1997; Danzig and Pellizzari, 1998; The Natural History Museum collection, London, UK). Scale cover of adult female circular to oval, 1.5 mm long, light grey with orange-yellow suncentral exuviae; exposed body of adult female orange yellow (Kosztarab and Kozár, 1988); males of the first generation are winged but those of the second generation are wingless (Kosztarab, 1996). There are two generations per year in Maryland; overwintering is as mated females (second instars in Virginia - Kosztarab, 1996), and each female produces 4-7 eggs per day the following spring, according to Stoetzel and Davidson, 1974, who studied the immature stages and natural enemies; the characters of the immature stages indicated that D. osborni is probably misplaced in Diaspidiotus. This species is often a pest in parks, especially on oaks and walnuts. DIASOSL.jpg
Diaspidiotus ostreaeformis is often found together with D. perniciosus. In life, the following characteristics may help separate them: D. ostreaeformis overwinters as second-instar larvae, D. perniciosus as first instars; D. ostreaeformis lays eggs, while D. perniciosus is ovoviviparous. In the laboratory, using microscopic characters, D. ostreaeformis DIASOSTZ.jpg possesses groups of perivulvar pores that D. perniciosus DIASPEP1.jpg lacks.
Diaspidiotus uvae (Comstock) (grape scale) could be misidentified as D. ostreaeformis but differs in lacking plates and a macroduct between the median lobes, and in having only about 20 macroducts on each side of the pygidium DIASUVP.jpg. In contrast, D. ostreaeformis has simple plates and a macroduct present between the median lobes, and about 30 macroducts on each side of the pygidium DIASOSTZ.jpg. Diaspidiotus uvae is a relatively polyphagous species known from Canada, USA (Alabama, Arkansas, possibly California, Connecticut, District of Colombia, Delaware, Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Maryland, Missouri, Mississippi, North Carolina, New Jersey, New York, Ohio, Pennsylvania, Tennessee, Texas, Virginia and West Virginia), Mexico, Central America, Argentina (Buenos Aires), Brazil (Bahia, Minas Gerais, Paraná, Rio de Janeiro, Rio Grande do Sul, Sao Paulo), Portugal (southern Azores and Madeira), Spain (Almería, Málaga and Canary Is), and South Africa; it is often found on or under the old, loose bark of Vitis vinifera but is also found on species of Betula, Carya, Catalpa, Crataegus, Eriobotrya, Fraxinus, Gleditsia, Gossypium, Maclura, Manettia, Nerium, Platanus, Populus, Rhus, Robinia and Yucca (Nakahara, 1982; Kosztarab, 1996; Amparo Blay Golcoechea, 1993; Gill, 1997; Danzig and Pellizzari, 1998). Severe infestation by D. uvae can retard the growth of grapevines (Chua and Wood, 1990). There is one generation per year and overwintering is as adult females in Ohio; the females are ovoviviparous and produce 35-50 young (Kosztarab, 1963; Kosztarab, 1996).
Comments
Diaspidiotus ostreaeformis originated in the Palaeartic Region (Kozár, 1990b) but is now widely distributed (Kozár, 1990a; Zahradník, 1990a). In the 1970s it was observed spreading in the Central European part of the former Soviet Union (Kozár and Konstantinova, 1981). It has not been recorded from most of the Pacific islands.
Europe
Austria: present, no further details (Kosztarab and Kozár, 1988; Danzig and Pellizzari, 1998)
Belgium: present, no further details (Danzig and Pellizzari, 1998)
Bulgaria: present, no further details (Kosztarab and Kozár, 1988; Danzig and Pellizzari, 1998)
Finland: present, no further details (Gertsson, 2001)
Former Czechoslovakia: present, no further details (Kosztarab and Kozár, 1988; Danzig and Pellizzari, 1998)
Former USSR
Armenia: present, no further details (Danzig, 1993)
Central European Territory: present, no further details (Danzig and Pellizzari, 1998)
East Serbia: present, no further details (Danzig and Pellizzari, 1998)
Far East: present, no further details (Danzig and Pellizzari, 1998)
Georgia, Republic of: present, no further details (Danzig, 1993; Aleksidze, 1995)
Kazakstan: present, no further details (Danzig, 1993; Danzig and Pellizzari, 1998)
Kirgizia: present, no further details (Danzig, 1993)
Middle Asia: present, no further details (Danzig and Pellizzari, 1998)
North European territory: present, no further details (Danzig and Pellizzari, 1998)
Russian Federation: present, no further details (Danzig, 1993)
Russian Far East: present, no further details (Danzig, 1993)
Siberia: present, no further details (Danzig, 1993)
South European Territory: present, no further details (Danzig and Pellizzari, 1998)
Tajikistan: present, no further details (Danzig, 1993)
Ukraine: present, no further details (Borchsenius, 1966)
Uzbekistan: present, no further details (Danzig, 1993)
Former Yugoslavia: present, no further details (Kosztarab and Kozár, 1988)
France: present, no further details (Danzig and Pellizzari, 1998; Foldi, 2001)
Corsica: present, no further details (Borchsenius, 1966)
Germany: present, no further details (Kosztarab and Kozár, 1988; Danzig and Pellizzari, 1998)
Greece: present, no further details (Danzig and Pellizzari, 1998)
Hungary: present, no further details (Kosztarab and Kozár, 1988; Danzig and Pellizzari, 1998)
Italy: present, no further details (Longo et al., 1995; Danzig and Pellizzari, 1998)
Sardinia: present, no further details (Longo et al., 1995)
Sicily: present, no further details (Longo et al., 1995)
Malta: present, no further details (Borchsenius, 1966)
Moldova: present, no further details (Borchsenius, 1966)
Norway: present, no further details (Gertsson, 2001)
Portugal: present, no further details (Danzig and Pellizzari, 1998)
Poland: present, no further details (Kosztarab and Kozár, 1988; Danzig and Pellizzari, 1998)
Romania: present, no further details (Kosztarab and Kozár, 1988; Danzig and Pellizzari, 1998)
Spain: present in Almería, Barcelona, Grenada, Madrid and Toledo (Amparo Blay Golcoechea, 1993)
Sweden: present in Uppland (Danzig and Pellizzari, 1998; Gertsson, 2001)
Switzerland: present, no further details (Kozár et al., 1994; Kosztarab and Kozár, 1988)
United Kingdom: present (C.P. Malumphy, Central Science Laboratory, UK, pers. comm.)
Channel Is, Jersey: The Natural History Museum collection, London, UK
England: The Natural History Museum collection, London, UK
Asia
China: present, no further details (Danzig and Pellizzari, 1998)
Anhui: present, no further details (Tao, 1999)
Heilongjiang: present, no further details (Tao, 1999)
Inner Mongolia: present, no further details (Tao, 1999)
Liaoning: present, no further details (Borchsenius, 1966)
Shaanxi: present, no further details (Tao, 1999)
Shanxi: present, no further details (Xie, 1982)
Xinjiang: present, no further details (Tao, 1999)
India: present, no further details (Nakahara, 1982)
Iran: present, no further details (Danzig, 1993; Danzig and Pellizzari, 1998)
Iraq: present, no further details (Nakahara, 1982)
Israel: present, no further details (Danzig, 1993; Danzig and Pellizzari, 1998)
Japan: present, no further details (Nakahara, 1982; Tao, 1999)
Hokkaido: present, no further details (Danzig, 1993)
Korea: present, no further details (Nakahara, 1982; Tao, 1999)
Korea, DPR: present, no further details (Danzig, 1993)
Korea, Republic of: present, no further details (Nakahara, 1982)
Nepal: present, no further details (Nakahara, 1982)
Pakistan: present, no further details (Nakahara, 1982)
Turkey: present, no further details (Nakahara, 1982; Danzig and Pellizzari, 1998)
Africa
Algeria: present, no further details (Danzig, 1993; Danzig and Pellizzari, 1998)
Egypt: present, no further details (Danzig, 1993; Danzig and Pellizzari, 1998)
Western Hemisphere
?Argentina: not recorded since 1938 (Danzig, 1993; Claps et al., 2001a)
?Buenos Aires: present, no further details (Claps et al., 2001a)
?Mendoza: present, no further details (Claps et al., 2001a)
?Rio Negro: present, no further details (Claps et al., 2001a)
Canada: present, no further details (Davidson and Miller, 1990; Danzig, 1993)
British Columbia: present, no further details (Kosztarab, 1996)
Ontario: present, no further details (Kosztarab, 1996)
Central America: present, no further details (Danzig and Pellizzari, 1998)
South America: present, no further details (Danzig and Pellizzari, 1998)
USA: present in all the continental states except Wyoming (Gill, 1997)
Colorado: present, no further details (Nakahara, 1982)
Connecticut: present, no further details (Nakahara, 1982)
Iowa: present, no further details (Nakahara, 1982)
Idaho: present, no further details (Nakahara, 1982)
Indiana: present, no further details (Nakahara, 1982)
Kansas: present, no further details (Nakahara, 1982)
Massachusetts: present, no further details (Nakahara, 1982)
Maine: present, no further details (Nakahara, 1982)
Maryland: present, no further details (Kosztarab, 1996)
Michigan: present, no further details (Nakahara, 1982)
Minnesota: present, no further details (Nakahara, 1982)
Montana: present, no further details (Nakahara, 1982)
New Hampshire: present, no further details (Nakahara, 1982)
New York: present, no further details (Nakahara, 1982)
Ohio: present, no further details (Nakahara, 1982)
Oregon: present, no further details (Nakahara, 1982)
Pennsylvania: present, no further details (Nakahara, 1982; Kosztarab, 1996)
Rhode Island: present, no further details (Nakahara, 1982; Kosztarab, 1996)
South Dakota: present, no further details (Nakahara, 1982)
Utah: present, no further details (Nakahara, 1982)
Washington: present, no further details (Nakahara, 1982)
West Virginia: present, no further details (Nakahara, 1982)
Wisconsin: present, no further details (Nakahara, 1982)
Wyoming: present, no further details (Nakahara, 1982)
Oceania
Australia: present, no further details (Danzig and Pellizzari, 1998)
Tasmania: present, no further details (CSIRO, 2001; The Natural History Museum collection, London, UK)
Victoria: present, no further details (CSIRO, 2001; The Natural History Museum collection, London, UK)
South Australia: The Natural History Museum collection, London, UK
New Zealand: present, no further details (Kosztarab and Kozár, 1988; Charles and Henderson, submitted)