(Targioni Tozzetti, 1892)
Taxonomic note
The morphological similarity of P. blanchardi to other Parlatoria species, and its wide distribution and host range, have perhaps contributed to the misidentifications that have occurred over the past century.
Diagnosis
Scale cover of adult female in life subcircular, 1.0-1.2 mm long, light to dark brown with a pale, slightly off-centre exuviae PABLAL4.jpg and PABLAL.jpg . Scale cover of male smaller than that of female, white, elongate with parallel sides, with pale, terminal exuviae PABLAL.jpg . Males tend to aggregate in clusters. Both winged and wingless forms of adult male have been recorded (Ghauri, 1962).
Body of slide-mounted adult female pyriform to elongate pyriform, membranous, with two-bar ducts; fringed plates extending as far forward as abdominal segment 2; and submarginal duct tubercles absent from prosoma PABLAS.jpg . Pygidium with three pairs of unilibulate lobes; 3 plates present between third and fourth lobes on each side; and without any submedian macroducts within the frame formed by the perivulvar pores PABLAP.jpg .
McKenzie, 1945, gives a detailed morphological description, illustrations and a key to the many species of Parlatoria.
Host range
Parlatoria blanchardi has been recorded from date palm and other hosts belonging to the plant family Palmae (Borchsenius, 1966). Palms are the preferred hosts. Hosts include species of: Hyphaene, Jasminum, Latania, Phoenix spp., Pritchardia, Vinca and Washingtonia.
Affected plant stages: vegetative growing, flowering, fruiting and post-harvest stages
Affected plant parts: entire plant, especially leaf undersides PABLAL3.jpg and young fruit
Biology and ecology
Reproduction is sexual and oviparous throughout the year (Bénassy, 1990). Each female lives 5-25 days and lays 4-13 eggs in a cluster underneath her scale cover (Abivardi, 2001). Upon completion of egg-laying, the female dies leaving the eggs protected under her cover. The reddish crawlers emerge in about 2 weeks and settle on leaflets. Parlatoria blanchardi prefers to settle on the lower surfaces of the leaves in the lowest part of the canopy. Highest numbers are found near the base of the leaves. It prefers to feed on the white succulent tissue, protected by layers of other tissue and fibre.
The development period for this species differs depending upon the geographical region. In Iran, female development ranged from 85 to 100 days in the spring and 120 to 150 days for the winter generation (Gharib, 1973). Bénassy, 1990, gives the life cycle duration as about 75 days in summer to 150-180 days in winter. Upon reaching adulthood, males live 2-3 days. This species is recorded to have three to five overlapping generations annually (Gharib, 1973; Abdul Ahad and Jassim, 1983; Bénassy, 1990; Khoualdia et al., 1993). In Iran, P. blanchardi has 3-4 generations per year (Abivardi, 2001). The sex ratio favours females, with males generally forming less than 25% of the population (Bénassy, 1990).
Infestations become more intensive over time, with the heaviest concentrations occurring on the leaf surfaces near the leaf base, especially on the lower surfaces of leaves in the lower portion of the canopy (Dabbour, 1981; Al Hafidh et al., 1981). The incidence of scales on the pinnae had a significantly negative correlation with average maximum temperature and relative humidity (Swaminathan and Verma, 1991). As numbers increase, specimens settle on all parts of the plant and fruit. In areas with high humidity levels (>50%), P. blanchardi was found on palms together with Palmaspis phoenicis Rao (Asterolecaniidae) in Iran (Gharib, 1974).
The dispersal stage is the first instar crawler, but this can only walk a short distance; in Niger, infestations spread only 30-90 cm per month, depending on the season (Stansly, 1984). High temperatures combined with wind and low humidity cause high crawler mortality (Bénassy, 1990). Dissemination to new hosts is the result of several factors including movement by wind, birds, insects and the transportation of infested plants from one area to another. Movement of P. blanchardi into new areas has commonly been due to the importation of infested date offshoots.
Symptoms
The primary feeding site of P. blanchardi is the succulent white tissue at the base of the leaf stalk (Boyden, 1941). A discolored area of injured tissue develops where individuals settle and feed. If the population is allowed to develop unchecked, P. blanchardi may become a serious pest. Left uncontrolled, the pest may infest the fruits over successive generations (Carpenter and Elmer, 1978; Bénassy, 1990). This species may infest all parts of the date palm, with heaviest infestations at the leaf bases and crown (Khoualdia et al., 1993). Significant damage to the leaves results in the pinnae withering and eventually dying PABLAL2.jpg . Heavy infestations weaken the tree by increasing transpiration, depleting nutrients and destroying chlorophyll, so impairing photosynthesis and productivity (Bénassy, 1990). Infestations often produce discoloration of the leaves and may cause yellowing and premature leaf drop; fruit may be stunted, distorted or shrivelled, and the vigour of the tree may be reduced PABLAL1.jpg . In heavy infestations, encrustations of scales on the host tissue appear dirty white or greyish due to the dark colour of the exuviae against the white background of the developing individuals (Stickney et al., 1950; Bénassy, 1990).
Economic impact
Parlatoria blanchardi is a pest of commercial dates and other palms (Gill, 1997). In 1920, it killed about 100, 000 date palms at one oasis in Algeria (Rosen, 1990b). It causes problems in south-western Asia (India and Pakistan), Iran, the Middle East (Israel, Saudi Arabia) and Africa (Sudan, Mauritania and other countries on the Mediterranean coast of Africa including Egypt, Libya, Tunisia, Algeria and Morocco) (Bénassy, 1990). Danzig and Pellizzari, 1998, described the species as a pest. Parlatoria blanchardi is presently recorded from most date-growing countries in the world except the USA (Bénassy, 1990).
The pest damages date palms by covering infested parts so thickly that transpiration, respiration and photosynthesis are impaired, causing withering of foliage, hinderance of growth and reduction of yield of mature trees and death of young palms (Bénassy, 1990; Abivardi, 2001) PABLAL1.jpg . Infestation of the fruit causes shrivelling, distortion, small size and may make them unmarketable; under favourable conditions, severe infestations in Morocco have damaged 70-80% of the crop (Smirnoff, 1957; Bénassy, 1990).
Detection and inspection methods
Initial infestations by invading specimens are difficult to see; P. blanchardi tends to hide in branch axils and beneath fibrous sheaths, where it can go undetected. Examine palm leaves and leaf bases for discolourations that may be associated with feeding scales, and for developing white scale covers. Heavy infestations give encrusted surfaces a dirty white appearance.
Natural enemies
The use of natural enemies against P. blanchardi is especially valuable in those areas where chemical control cannot be used. Although the initial build-up of the scale is rapid and poses a serious threat to the host plant, introduction of parasitoids and predators have consistently been found to reduce the pest population to acceptable levels (Smirnoff, 1957; Carpenter and Elmer, 1978). The occurrence of natural enemies is influenced by climatic conditions. Some 28 species of parasitoids and predators have been documented attacking this pest. Of 13 species of beneficial agents observed attacking P. blanchardi, Bitaw and Ben Saad, 1990, found the predators to be more common and abundant than the parasitoids, especially in parts of southern Libya.
Parasitoids:
- Aphytis mytilaspidis, in Iraq
- Aphytis phoenicis, in Israel
- Pteroptrix arabicus, in Saudi Arabia and Israel
Predators:
- Chilocorus bipustulatus var. iranensis, attacking: nymphs, adults, in Iran. Introduced: Mauritania, Niger, Tunisia
- Chilocorus nigrita, attacking: nymphs, adults, in India
- Chilocorus stigma, attacking: nymphs, adults
- Cybocephalus mesopotamicus
- Cybocephalus nigriceps nigriceps, attacking eggs, nymphs, in Israel
- Cybocephalus nigriceps palmarum, attacking: nymphs, adults, in North Africa
- Cybocephalus rufifrons, attacking: nymphs, adults
- Nephus quadrimaculatus
- Pharoscymnus horni, attacking: nymphs, adults, in India (Rajasthan)
- Pharoscymnus setulosus, in Mauretania
- Pharoscymnus numidicus, in Algeria, Israel, Morocco, Niger
- Pharoscymnus ovoideus, attacking: nymphs, adults, in Iran, North Africa
- Pharoscymnus simmondsi, attacking: nymphs, adults, in Pakistan
Distribution
See Parlatoria blanchardi distribution.
Microscopic examination of slide-mounted adult females is required for authoritative identification to species.
Comments
Parlatoria blanchardi originated in the oases of Mesopotamia (Bénassy, 1990) but was accidentally introduced from the Middle East into many tropical and subtropical date-growing countries, through the propogation and replanting of infested date palm offshoots. It was accidentally introduced to the USA and was found in Arizona, California and Texas. It was successfully eradicated in 1914 in Arizona, 1919 in Texas and in the 1930s in California (Boyden, 1941; Bénassy, 1990; Gill, 1997). The pest has been reported from Asia, the Mediterranean region, the Middle East, North Africa and South America. Parlatoria blanchardi has not been recorded from the Pacific islands.
Europe
Former USSR
Turkmenistan (Gharib, 1973; Abivardi, 2001)
France: present, no further details (Foldi, 2001)
Italy: restricted distribution, Liguria only (Longo et al., 1995)
Spain: restricted distribution (Madrid) (Amparo Blay Golcoechea, 1993)
Asia
Afghanistan: present, no further details (CIE, 1962c; Nakahara, 1982)
Bahrain: The Natural History Museum collection, London, UK
India: restricted distribution (Gharib, 1973; Nakahara, 1982; Abivardi, 2001)
Andhra Pradesh: The Natural History Museum collection, London, UK
Delhi: present, no further details (CIE, 1962c)
Gujarat: present, no further details (Murlidharan et al., 1992; Murlidharan, 1993; Murlidharan, 1994)
Punjab: present, no further details (Batra and Sohi, 1974)
Rajasthan: present, not further details (Sachan, 1976; Swaminathan and Verma, 1991)
Iran: present, no further details (Gharib, 1973; Gharib, 1974; Seghatoleslami, 1977; Abivardi, 2001)
Iraq: present, no further details (Al Hafidh et al., 1981; Abivardi, 2001)
Israel: present, no further details (Kehat et al., 1976; Nakahara, 1982; Danzig and Pellizzari, 1998)
Jordan: present, no further details (CIE, 1962c; Nakahara, 1982)
Oman: present, no further details (Elwan, 2000)
Pakistan: restricted distribution (Gharib, 1973; Rafiq Ahmad and Ghani, 1973; Abivardi, 2001)
Palestine: present, no further details (Abivardi, 2001)
Qatar: present, no further details (Al Azawi, 1986)
Saudi Arabia: restricted distribution (Gharib, 1973; Basalah, 1987; Abivardi, 2001)
Syria: present, no further details (Gharib, 1973; Nakahara, 1982; Abivardi, 2001)
Trucial States: The Natural History Museum collection, London, UK
Turkey: present, no further details (Gharib, 1973; Abivardi, 2001)
Africa
Algeria: restricted distribution (Boyden, 1941; CIE, 1962c; Danzig and Pellizzari, 1998)
Chad: present, no further details (Nakahara, 1982)
Egypt: present, no further details (Gharib, 1973; El-Minshawy et al., 1974; Abivardi, 2001)
Eritrea: The Natural History Museum collection, London, UK
Kenya: The Natural History Museum collection, London, UK
Libya: restricted distribution (Bitaw and Ben Saad, 1990; Danzig and Pellizzari, 1998)
Mali: present, no further details (Nakahara, 1982)
Mauritania: restricted distribution (Montaigne and Maouloud, 1986)
Mauritius: restricted distribution (Iperti et al., 1970; Nakahara, 1982)
Morocco: restricted distribution (Iperti, 1970; Leghtas, 1970; Danzig and Pellizzari, 1998)
Niger: restricted distribution (Popov et al., 1984; Stansly, 1984; Abivardi, 2001)
Somalia: present, no further details (Nakahara, 1982)
Sudan: present, no further details (Siddig, 1975; Nakahara, 1982; Popov et al., 1984)
Tunisia: restricted distribution (Khoualdia et al., 1997; Danzig and Pellizzari, 1998)
Western Hemisphere
Argentina: present, no further details (Nakahara, 1982)
La Rioja: present, no further details (Claps et al., 2001a)
Brazil: present, no further details (Nakahara, 1982)
Pernambuco: present, no further details (Claps et al., 2001a)
Rio de Janeiro: present, no further details (Claps et al., 2001a)
Sao Paulo: present, no further details (Claps et al., 2001a)
Bolivia: restricted distribution (Squire, 1972a; Nakahara, 1982)
Central America: present, no further details (Danzig and Pellizzari, 1998)
Jamaica: The Natural History Museum collection, London, UK
Montserrat: restricted distribution (Boyden, 1941)
Oceania
Australia: present, no further details (CSIRO, 2001; Abivardi, 2001)