(Green, 1923)
Diagnosis
In life, scale cover of adult female 0.8-1.2 mm long, irregularly elongate, fairly flat, dirty white with yellow or orange terminal exuviae MERHAL1.jpg . Second instar exuviae of the female with a distinctive reddish-brown spot at the posterior end, like L. gloverii. Male scale cover similar to female's but smaller MERHALL.jpg . Body of adult female yellowish (Gill, 1997).
Body of slide-mounted adult female elongate, mostly membranous but head sometimes becoming sclerotized with maturity MERHALS.jpg . Pygidium with median lobes only, these well separated, not zygotic, with a pair of gland spines present between their bases; lobes without any basal scleroses; perivulvar pores absent; gland spines occurring singly. Pygidium with 4 or 5 enlarged marginal macroducts on each side; and submarginal and submedian macroducts few, small, arranged in rows MERHALP.jpg .
Host range
Mercetaspis halli has been recorded from hosts belonging to the plant family Rosaceae (Borchsenius, 1966); in California it prefers deciduous fruit and nut trees in the genus Prunus (Gill, 1997). Hosts include species of: Cydonia, Malus, Prunus, Pyrus, Spiraea and other Rosaceae.
Affected plant stages: vegetative growing, flowering and fruiting stages
Affected plant parts: on the trunk and branches MERHAL1.jpg , particularly in bark crevices; in heavy infestations, may be found on the fruit also (Gill, 1997).
Biology and ecology
In California, there are one to two generations per year and the insect overwinters as adult females (Gill, 1997). In Israel, there are three generations per year and overwintering takes place at the egg stage; males are rare, and the scales preferentially settle and develop under buds that are tightly adpressed to the twigs (Berlinger et al., 1996).
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
Heavily infested winter buds fail to open in spring. Infested nectarines develop red spots under the scales that become gradually darker over time, whereas in peach fruits the marks do not develop until closer to harvest (Berlinger et al., 1996).
Economic impact
Mercetaspis halli is a serious pest of fruit trees (Gill, 1997), and was listed as a pest of stone fruits of great regional importance in the southern Palaearctic region by Kozár, 1990b. It has been mentioned as a pest of almond (Prunus dulcis) (Chua and Wood, 1990). The development of red spots on infested nectarine and peach fruits would reduce their value or render them unmarketable.
Detection and inspection methods
Examine the bark of Rosaceae and the hosts listed above, for irregularly elongate, fairly flat, dirty white scale covers, each with yellow or orange terminal exuviae MERHAL1.jpg .
Natural enemies
Predators:
- Haplothrips cahirensis, in Egypt, Sudan
- Hemisarcoptes coccophagus
Distribution
See Mercetaspis halli distribution.
Microscopic examination of slide-mounted adult females is required for authoritative identification to species.
Comments
Members of the genus Mercetaspis are thought to originate form an area inclucing Central Europe, eastern Mediterranean and the Middle East as far as Pakistan. Mercetaspis halli has been eradicated in California, so it is now thought not to occur in the Western Hemisphere, Australia, or from the Pacific islands.
Europe
Cyprus: present, no further details (Danzig and Pellizzari, 1998)
Former USSR
Tadjikistan: present, no further details (Nakahara, 1982; Ramaseshiah, 1985)
Turkmenistan: present, no further details (Nakahara, 1982)
Uzbekistan: present, no further details (Nakahara, 1982)
Transcaucasus: present, no further details (Danzig and Pellizzari, 1998)
Middle Asia: present, no further details (Danzig and Pellizzari, 1998)
Hungary: The Natural History Museum collection, London, UK
Greece: present, no further details (Nakahara, 1982; Danzig and Pellizzari, 1998)
Asia
Afghanistan: present, no further details (Nakahara, 1982)
Iran: present, no further details (Seghatoleslami, 1977; Danzig and Pellizzari, 1998)
Iraq: present, no further details (Nakahara, 1982; Danzig and Pellizzari, 1998)
Israel: present, no further details (Nakahara, 1982; Danzig and Pellizzari, 1998)
Pakistan: present, no further details (Nakahara, 1982; Danzig and Pellizzari, 1998)
Saudi Arabia: present, no further details (Danzig and Pellizzari, 1998)
Syria: present, no further details (Nakahara, 1982)
Turkey: present, no further details (Nakahara, 1982; Danzig and Pellizzari, 1998)
Africa
Egypt: present, no further details (Nakahara, 1982; Danzig and Pellizzari, 1998)
Libya: The Natural History Museum collection, London, UK