(Kuwana, 1923)
Diagnosis
In life, scale cover of adult female mussel-shell shaped, 2.5-3.6 mm, slightly convex, blackish-brown with a paler margin; exuviae terminal, brownish-yellow UNYANL4.jpg and UNCITL3.jpg . Scale cover of male smaller than that of female, 1.3-1.6 mm, white and conspicuous, elongate oval, with two or three longitudinal ridges and yellow-brown terminal exuviae (Davidson and Miller, 1990) UNYANL1.jpg and UNYANL.jpg .
Body of slide-mounted adult female membranous, elongate, more than twice as long as wide UNYANS.jpg . Pygidium with median lobes not zygotic, with a pair of setae present between their bases; dorsum of pygidium with 130-150 scattered dorsal macroducts present UNYANP.jpg .
Host range
Unaspis yanonensis has been recorded from hosts belonging to 4 genera in two plant families (Davidson and Miller, 1990), including members of the genera Citrus and Poncirus. In Japan, it is found on all types of Citrus except on the specifically Japanese hybrids known as Natsudaidi and on Citrus junos (Ohkubo, 1980). Hosts include species of: Citrus deliciosa, Citrus sinensis, Citrus unshiu, Citrus reticulata, Citrus limon, Citrus x paradisi.
Affected plant stages: vegetative growing, flowering, fruiting and post-harvest stages
Affected plant parts: leaves, small branches and (in heavier infestations) fruits UNYANL2.jpg
Biology and ecology
In south-east Asia, U. yanonensis has three generations per year, and overwinters as fertilized adult females (Nohara, 1962). Each generation has two population peaks, and the duration of these is much affected by sunshine-hours and temperature. The first and second instar stages last about 22 days and the adults live for about 34 days, but these times tend to be longer for the second instars and adults of the second and third generations. In Japan, the third generation is only seen in southern regions (Ohkubo, 1980). Unaspis yanonensis survives best in shade but prefers high temperatures. Natural mortality is high on the upper part of the canopy, which receives most sunlight. In France, attacks are mainly observed on the north side of trees, the south side remaining practically free from the pest (Bénassy and Pinet, 1972).
Unaspis yanonensis has a low dispersal potential. As in other diaspidids, the main dispersal stage is the first instar, which may be naturally dispersed by wind and animals. Internationally, U. yanonensis is liable to be transported by man on Citrus plants for planting or on Citrus fruits.
Symptoms
Infested plants show inhibited growth, yellow blotches and necrosis of leaves, leaf fall, shortened or dead branches and small deformed fruits. Large masses of white male scales may be seen on twigs, together with darker, curved female scales. In cases of severe attacks, tree mortality has been observed. The cause of the dieback is not yet understood but it has been suggested that the insect may inject toxic saliva into the tissues.
Economic impact
Unaspis yanonensis is the most important pest of Citrus in Japan (Rosen, 1990b). Leaves and small branches are attacked, but not large branches or trunks; only the second and third generations are found on fruits (Ohkubo, 1980). Attacked fruits lose their commercial value because of the feeding punctures of the pest, but this has little further consequence for the tree. Attacks on branches and leaves lead to leaf fall, and possibly to complete dieback. Leaves and branches begin to die back at a density of 1.1 females per leaf (Ohkubo, 1980), while a density of 8 females per leaf in spring is likely to lead to complete dieback of the tree within the year (Ohgushi and Nishino, 1968).
In Europe, U. yanonensis usually does not occur in commercial Citrus-growing areas, and its economic impact has been negligible. However, Danzig and Pellizzari, 1998, describe this species as a dangerous pest, and Foldi, 2001, lists it as an economically important pest in France; it causes widespread damage to Citrus in the French Riviera (Kreiter et al., 1998).
Phytosanitary risk
Unaspis yanonensis is liable to be transported by man on Citrus plants for planting or on Citrus fruits. It is a quarantine pest for CPPC and OIRSA. In view of its establishment in southern France and northern Italy, it was felt that the pest could present a risk to Citrus-growing throughout the Mediterranean area, and it was therefore at one time listed as an EPPO A2 quarantine pest (EPPO/CABI, 1997). However, no spread has been observed in 25 years in the Mediterranean region, so its quarantine pest status is under revision.
Detection and inspection methods
Aerial parts of potential host-plants, especially leaves and twigs, should be thoroughly inspected for stunted growth, and yellowing, necrosis and dropping of the leaves. Fruit should be examined for the dark female scale covers UNYANL2.jpg . The conspicuous white male scale covers are easily detected, but the dark females are less easily seen UNYANL1.jpg .
Phytosanitary measures
Import of Citrus plants for planting and Citrus fruits from countries where U. yanonensis occurs can be restricted to prevent any introduction or spread. Fumigation treatments have been developed to control U. yanonensis on consignments of Citrus fruits (Mizobuchi et al., 1995). Unaspis yanonensis is mentioned on quarantine lists (Burger and Ulenberg, 1990).
Natural enemies
Unaspis yanonensis is attacked by numerous parasitoids, mycoparasites and predators (USDA, 1984). Only natural enemies originating from China have proved to be able to control this scale insect.
Parasitoids:
- Aphytis yanonensis, attacking: nymphs, adults, in China; introduced: Japan; Argentina
- Coccobius fulvus, attacking: nymphs, adults, in China; Introduced: Japan, France
- Encarsia citrina, in Japan
Predators:
- Chilocorus kuwanae, attacking: nymphs, adults, in China, Japan
Distribution
See Unaspis yanonensis distribution.
Unaspis yanonensis should be distinguished from U. citri (Brooks, 1977), which also occurs in south-east Asia and Australia. In general, U. citri is mainly found on shoots and has less tendency to attack fruits than U. yanonensis. Authoratative identification requires microscopic study of slide-mounted adult females; in U. yanonensis there are twice as many dorsal pygidial macroducts (130-150) UNYANP.jpg as there are in U. citri (which has 60-75 of these ducts) UNCITP.jpg .
Unachionaspis bambusae (Cockerell) UNABS.jpg is a species not included in the key, which could be mistaken for Unaspis yanonensis. However, Unachionaspis bambusae is found only on species of bamboo; the female scale cover is white UNCHIBL2.jpg; the (relatively few) dorsal macroducts are arranged in segmental rows, and there are perivulvar pores present UNABP.jpg. Unaspis yanonensis UNYANS.jpg occurs on species of Citrus, never on bamboo; the female's scale cover is dark brown UNYANL4.jpg; the numerous dorsal macroducts are scattered and perivulvar pores are absent UNYANP.jpg. Unachionaspis bambusae is known from former USSR (Far East), China (Anhui, Jiangsu, Fujian, Sakhalin) and Japan (Honshu) on the lower leaf surfaces of species of Phyllostachys and Sasa (Tao, 1999; Danzig and Pellizzari, 1998; Kawai, 1980). The male scale cover is much smaller and narrower than that of the female, parallel sided, with longitudinal ridges UNCHIBL1.jpg. This species is a pest of bamboo in China (Anhui), where there are three generations per year (Wu, 1981). See also genus Unachionaspis, Background.
Unaspis euonymi (Comstock) (euonymus scale, cochenille du fusain) UNEUL1.jpg could be misidentified as U. yanonensis but differs by the female scale cover being dark brown and the male scale covers being white and conspicuous UNEUL5.jpg; lacking perivulvar pores UNEUP.jpg, and the prosoma remains membranous throught life UNEUS.jpg. In U. yanonensis, the female scale cover is light tan and there are no white male scale covers; perivulvar pores are present, and the prosoma becomes sclerotized at maturity. Unaspis euonymi is known from China (Guangdong, Hong Kong, Inner Mongolia, Jiangsu, Shandong, SE China), Japan (Hokkaido, Honsu, Kyushu, Shikoku), Korea, Austria, Bulgaria, England, former USSR (Armenia, Azerbaijan, Caucasus, Crimea, Georgia, Krasnodar Territory, Ukraine, Uzbekistan), France, Germany, Greece, Hungary, Italy, Poland, Sardinia, Sicily, Malta, Portugal, Romania, Spain (mainland and Canary Is), Switzerland, former Yugoslavia, Turkey, Israel, Algeria, Morocco, Canada (British Colombia), Egypt, Iran, Israel, China, Japan, Korea, South-East Asia, Canada, USA (Alabama, Arkansas, California, Connecticut, Delaware, District of Colombia, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Maryland, Massachussetts, Michigan, Mississippi, Missouri, New England, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee (under glass), Texas, Virginia, Wisconsin and West Virginia), Mexico, Honduras, Argentina (Buenos Aires, Córdoba, Cuyo, Jujuy, Santa Fe) and Bolivia on aerial parts (usually stems and leaves) of hosts from 18 genera in 7 plant families, although it is rarely found on hosts other than Euonymus (Squire, 1972a; Davidson and Miller, 1990; Amparo Blay Golcoechea, 1993; Labanowski and Soika, 1997; Schmutterer, 1998). Unaspis euonymi has been recorded on aerial parts of species of Buxus, Celastrus, Citrus, Daphne, Euonymus, Fraxinus, Hedera, Hibiscus, Ilex, Jasminum, Lagerstroemia, Ligustrum, Lonicera, Magnolia, Olea, Pachysandra, Pachystigma, Prunus, Syringa and Viscum (CIE, 1970a; Seghatoleslami, 1977; Kawai, 1980; Nakahara, 1982; Carnero Hernandez and Perez Guerra, 1986; Kosztarab and Kozár, 1988; Davidson and Miller, 1990; Kozár et al., 1994; Longo et al., 1995; Miller, 1996; Gill, 1997; Danzig and Pellizzari, 1998; Tao, 1999; Foldi, 2001; Claps et al., 2001a). The species probably originated in eastern Asia (Longo et al., 1995). It is a major pest of Euonymus (Davidson and Miller, 1990); bark may become distorted and leaves may develop chlorotic spotting as a result of infestation (Kosztarab, 1990; Kosztarab, 1996) and unchecked infestations can kill Euonymus japonica (Davidson and Miller, 1990; Gill, 1997). In Hungary, it is one of the most important scale insect pests of ornamental trees and shrubs (Ripka, 1999). Danzig and Pellizzari, 1998, describe this species as a dangerous pest in the Palaearctic region, and Foldi, 2001, lists it as an occasional pest in France. In life, adult female scale cover 1.5-2.2 mm long, mussel-shaped, slightly convex, dark brown with yellowish-brown terminal exuviae; male scale cover elongate, white, strongly tricarinate, with brown-yellow terminal exuviae. The males are very common and easily seen. Exposed body of living female orange yellow (Kosztarab and Kozár, 1988).There are 2-3 generations per year and overwintering is mainly as adult females (Davidson and Miller, 1990). Each female lays 30-50 eggs (Kosztarab and Kozár, 1988). This species is a 'B'-rated pest in California (Gill, 1997). The extensive literature on U. euonymi is indicative of the importance of this insect. Colonies UNEUL1.jpg ; UNEUL4.jpg ; male and female scale covers UNEUL3.jpg ; male scale covers UNEUL6.jpg
Comments
Unaspis yanonensis originates from mainland China (Rosen, 1990b), and has been accidentally introduced into limited areas in southern France (Provence-Alpes-Côte d'Azur) and northern Italy (Liguria) (CABIIE, 1988; CABI/EPPO, 1998b). The species is not present in Switzerland or the United Kingdom, and has been eradicated from Taiwan (EPPO, 1999). Unaspis yanonensis has been reported from India and Malaysia, but its presence in these countries has not been confirmed (EPPO, 1999). It has also been recorded from Australia, Myanmar, Pakistan, the Philippines, Indonesia, Thailand and Vietnam, based on old unsubstantiated records, but these are now considered to be erroneous (EPPO, 1999). Unaspis yanonensis has not been recorded from Africa, the Western Hemisphere, or from Australia.
Europe
France: restricted distribution (only in Alpes-Maritimes; not in Corsica) (CABIIE, 1988; Foldi, 2001)
Italy: present, few occurrences (Western Liguria only) (EPPO, 1999)
Asia
China
Fujian: present, no further details (Tao, 1999)
Gansu: present, no further details (Tao, 1999)
Guangdong: present, no further details (CABIIE, 1988)
Guangxi: present, no further details (Tao, 1999)
Guizhu: present, no further details (Tao, 1999)
Hebei: present, no further details (CABIIE, 1988)
Henan: present, no further details (CABIIE, 1988)
Hubei: present, no further details (Tao, 1999)
Hunan: present, no further details (CABIIE, 1988)
Inner Mongolia: present, no further details (Tao, 1999)
Jiangsu: present, no further details (Tao, 1999)
Jiangxi: present, no further details (Tao, 1999)
Shaanxi: present, no further details (Tao, 1999)
Shandong: present, no further details (CABIIE, 1988)
Shanxi: present, no further details (Xie, 1982)
Sichuan: present, no further details (Tao, 1999)
Xizhang: present, no further details (EPPO, 1999)
Yunnan: present, no further details (Tao, 1999)
Zhejiang: present, no further details (Tao, 1999)
Japan: present, no further details (Kawai, 1980; Tao, 1999)
Honshu: widespread (Danzig and Pellizzari, 1998)
Kyushu: widespread (CABIIE, 1988; Danzig and Pellizzari, 1998)
Shikoku: widespread (Danzig and Pellizzari, 1998)
Korea: present, no further details (CABIIE, 1988; Danzig and Pellizzari, 1998)
Korea, DPR: present, no further details (EPPO, 1999)
Korea, Republic of: present, no further details (EPPO, 1999)
Ryukyu Archipelago: present, no further details (EPPO, 1999)
Tibet: present, no further details (CABIIE, 1988)
Oceania
Fiji: present, no further details (EPPO, 1999)