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Abstract
INTRODUCTION
Ornamental plants play an important role in the national economy as a large amounts of these plants are frequently exported to foreign countries. Trees and shrubs form a large part of ornamental plants. In former times trees have been used as ornamental plants. More than 4000 years ago, the ancient Egyptians wrote about trees being transplanted with a ball of soil around their roots. Some trees were moved up to 2400 km by boats.
Trees represent one of the most important components of every terrestrial ecosystem and are a part of nature’s precious gifts. Some are deciduous; others are evergreen. Some have beautiful flowers; others have beautiful fruits or foliage. Some are scented; others are ugly but economically very important. The welfare of humankind is affected not only by their density and diversity but also by their direct and indirect values, which are beyond estimation. In fact, each letter of the plural word “TREES” has a logical meaning (Seth, 2002):
T- Timber, the first and the foremost use of trees.
R- Restoration, reclamation and rejuvenation of denuded and disturbed soils by using trees to control soil erosion and desertification, protect watersheds, improve soil nutrient status (by growing nitrogen-fixing trees) and retain moisture in the soil.
E- Ecological, ecodevelopmental and environmental use of trees for effective and efficient purification of the environment because trees act as oxygen banks and eliminate air pollutants; for abating or moderating temperature, noise and wind by planting trees as environmental screens, thus affecting the microclimate; for harboring wildlife; for maintaining biodiversity; and for conserving energy.
E- Educational and recreational value in gardening, landscaping, bioesthetic planning, art, culture and religion.
S- Source of sustenance; i.e., food, fuel, fodder, fertilizer, fibre, medicine, tannin, dyes, oils, etc.
Shrubs are planted for farming the doorway; as foundation or base plantings, corner and boundary plantings, screens; for dividing the property, seasonal beauty of flowers, leaves, fruits and twinges; as accent points or background for flower borders, for making the entrance to the drive-way, banking along curves of walks and drives, covering steep or rugged banks, and forming naturalistic or formal enclosures or for partial out lining of turn court area as hedges and enhancing tree planting when they are arranged in well-placed groups, because they supply the intermediate height (Shoemaker and Teskey, 1955).
Climbers are plants with soft stems that grow only with a support. They rely on something else for support; another plant, a wall or trellis. Light spreading climbers can be grown on trellises or coir mesh to form effective screens to hide potting shed, kitchen, garden or to enclose the veranda. Creepers can be grown along the top of the compound wall or as a cover for walls, or at the entrance as an arch.
Insect pests are regarded as one of the important injurious factors responsible for deterioration of ornamental plants in Egypt. Amongst, scale insects constitute one of the common insect pests of ornamental plants which are extensively cultivated in Egypt and play an important role in the national economy (Moursi et al., 1991).
Scale insects (Hemiptera: Coccoidea) are sap feeding pests of many agricultural crops and ornamental plants (Miller et al. 2005). They are common on ornamental trees and shrubs. Occasionally they build up in large enough numbers to cause serious damage or death to the host tree. Scales do not resemble typical insect pests, so they often go unnoticed until a large population has developed and caused damage. The main harmfulness of scale insects consists in sucking the plant sap what affects the growth, leads to defoliation, withering of shoots or the entire plant. A secretion of honeydew which coats the plant surface impedes the assimilation and photosynthesis. Honeydew accumulates different dust and pollutants but first of all it is a perfect medium for sooty mould which covers plants with a black film (Dziedzicka 1988; Kosztarab 1996; Ben-Dov and Hodgson 1997).
One of the most common groups of scale insects attacking ornamental plants is called mealy bugs. Mealy bugs are prevalent pests in greenhouses and interior plants capes such as shopping malls, conservatories, hotels and office buildings. Mealy bugs cause great losses to growers and retailers as millions of pounds per year for control costs and crop damage or loss. Damage is caused due to feeding of mealy bugs on host tissues and injecting toxins or plant pathogens into host plant. In addition to the secretion of a waste product, honeydew, which is a syrup, sugar liquid that falls on the leaves, coating them with a shiny, sticky film. Honeydew serves as a medium for the growth of sooty mold fungus that reduces or inhibits the plant’s photosynthetic abilities and ruins the plant’s appearance. Feeding by mealy bugs can cause premature leaf drop, dieback, and may even kill plants if left unchecked (CUES, 2008).
In this concern Orthezia insignis is a mobile scale insect, which can do considerable damage to Lantana sp. (Holloway, 1964). O. insignis produces copious amounts of honeydew (Williams & Williams, 1988). While yellow sage (Lantana camara) is occasionally sold as a houseplant and may also be planted outdoors in the summer. All parts of the plant are quite toxic, and poisoning may occur year-round but is most common in summer and fall. The fruit of L. camara may poison humans if ingested, occasionally resulting in death (Everist, 1981; Swarbrick et al., 1998). Shepherd (2004) also indicated that the leaves of L.camara were poisonous. Children who ingested green berries became ill and died. Care should be taken to keep children as well as family pets away from this plant (Wolfson and Solomons 1964, McLennan and Amos 1989, Spoerke and Smolinske 1990). Sheep, cattle, horses, and humans are sensitive to the effects of the plant. Vice versa it is widely used as a traditional medicine for the treatment of infectious diseases.
Beeson and Chatterjee, 1940; Essig, 1948 and Thomas and Ellison (2000) reported that Lantana camara and Lantana aculeata are major weeds in many regions of the Palaeotropic. They used Orthezia insignis in the biological control programme for the control of these weeds.