Whiteflies are small hemipteran that typically feed on the undersides of plant leaves they belong to kingdom Animalia, phylum Arthropoda, class Insecta, order Hemiptera, suborder Sternorrhyncha, superfamily Aleyrodoidea, family Aleyrodidae, having three subfamilies Aleurodicinae, Aleyrodinae, and Udamoselinae (Martin and Mound, 2007). There are more than 1550 species that have being described, where 33 species are considered common and economically important. The ability to recognise one of these species with confidence can aid in determining specie for a particular crop or for further identification (Hodges and Evans, 2005). They are sap-sucking insect which include excrete sticky honeydew and cause yellowing or death of leaves. They derive their name from the mealy white wax covering the adult wings and body. The adult have yellowish bodies and whitish wings although some specie have distinctive wings markings while others specie are most readily distinguish in the last nymphal (immature) stage which is wingless. Whitefly normally laid their tiny, oblong eggs on the underside of leaves; the eggs hatch and the young whitefly gradually emerge passing through four nymphal stages called instar. All stages feed by sucking plant juice from leaves and excretory excess liquid as drops of honey dew as they feed. This causes leaves to turn yellow, appear dry or fall of plants. Generally plants losses do not occur unless there is significant population of whitefly nymphs
Trialeurodes vaporariorum (Greenhouse Whitefly) is a common pest of house plants and greenhouse adult is about 0.9 to 1.1mm; wings are white held nearly parallel to the leaf and cover the abdomen when at rest. Eggs are oblong, smooth, and initially yellow but darken before hatching, occasionally laid in circular patterns on the plants with smooth leaves. 4th instar nymphs have very long waxy filaments and marginal fringe. Host plants include more than 200 plant species, cucumber tomato, grape, bean, ageratum, poinsettia, hibiscus are mostly infested (Cranshaw, 2013).
Siphoninus phillyreae (Ash whitefly) is a pest of numerous ornamental crops and fruit crops like ash, citrus, apple, Bradford pear, and pomegranate. 4th instar nymph have a very thick band of wax down, the back and a fringe of tiny tube each with a liquid droplet at the end. Heavy infestation causes leaf wilt, early leaf drop and smaller fruit (Bellows et al., 2002). It is found in Florida, Europe, Africa, Asia and North America (Stocks and Hodges 2010).
Trialeurodes abutilonea (bandedwinged Whitefly) is a pest of cotton, cucurbits, hibiscus, poinsettia, geranium and other vegetables. The adults are bigger than silverleaf and green house whiteflies and are recognised by irregular shaped (zigzag pattern) grey bands on the front pair of wings. Eggs are laid in irregular or meat circle on the leaves, depending on the host plant species, 4th instar have short, waxy, filaments around their edges. Adults have brownish bands across the wings and their body is grey.
Dialeurodes citri (Citrus Whitefly) is a pest of citrus plants, gardenia, ash, ficus, green ash and pomegranate. Adults are similar to adult greenhouse whiteflies but have broader wings and feed mainly on shrubs and trees. The eggs are yellow with a surface which is nearly smooth. 4th instar nymphs have no fringe around theory edges but have distinctive Y shape in their back.it is found in Africa (Algeria), Asia, Central, North and South America, Europe and Caribbean (Fasulo and Brooks, 2010).
Aleurodicus dugesi (Giant Whitefly) is a pest found only in southern California in which their host plants include Begonia, hibiscus, orchid tree, banana, mulberry, vegetable. Adult is 0.19inch long leaving spirals of wax on leave. Nymphs and pupae secrete long cylindrical strands of wax extending up to 2inch from the leaf surface and nymphs have long filament of wax that can be up to 2inch long and give leaves a bearded appearance. Accumulation of these wax strands resembles fluffy-white hair (Bellows et al., 2002).
Aleyrodes spiraeoides (Iris Whitefly) adult have dot on each wings and quite waxy. 4th instar nymphs have no fringe or waxy filaments but are located near distinctive circle of wax where egg laying took place. Feed on plant they infest, but the nymphs do more damage by withdrawing sap. In some species the last instar nymphs secrete white wax plumes, ribbon or filament, forming fringe around their bodies that protect them from parasitoids and predator. Both nymphs and adult Plant host include iris, cotton and herbaceous plants (Bryant, 2006).
Bemisia argentifolii and Bemisia tabaci (Silverleaf and Sweet potatoes) host plant include cotton, cassava, tomatoes, Cole crops and hibiscus. Adults have white wings and yellow body; they hold their wings slightly titled on surface or substrate. 4th instar nymphs have no waxy filaments or marginal fringe. It takes 40-50 days to reach adulthood, during moulting the files shed silver skins which are left on the leaves (De Barro et al., 2011).
Tetraleurodes mori (Mulberry Whitefly) is a pest in central and South America Caribbean; nymphs are blackish, oval bodies with white waxy fringe. Hosts plants include citrus, mulberry and sycamore (Flint, 1998)
Aleurodicus rugioperculatus (Rugose Spiralling Whitefly) host plant include, coconut (Coco nucifera), palm (Dypsis lutescens), mango (Mangifera indica), copperleaf (Acalypha wilkesiana), gumbo limbo (Bursera simaruba), and Brazilian pepper (Schinus terebinhthifolius). They are closely related to giant whitefly which is about three times larger than other whiteflies but are slower. The female whitefly lays her eggs in a spiral pattern on the leaves and also deposits a white waxy substance on theggs.it is found in Florida and Central America.
Aleurodicus dispersus Russel (Spiralling Whitefly) is a major pest devouring agricultural crops as it spread with extraordinary speed across tropics. Adults resemble tiny moths with four wings, covered by a white dusty of mealy material that resembles the wings scales in butterflies and moths. Their name is derived from silken spirals that the female produces when laying her eggs on foliage and fruits. Spiralling whitefly develops as colonise of individuals on the underside of the leaves where by the nymphs and adult suck the sap from the leaves. The polyphagy of the white spiralling white fly is the major reason it is able to spread so quickly from one crop to another across the tropics (Gungah et al., 2005).
Due to its high reproduction and dispersal rate spiralling white fly is found in USA (southern Florida), south America, Africa (west Africa) and canary island, it is reported in Hawaii, India, Thailand Vietnam , Singapore, Taiwan as well as Indonesia, Malaysia, Torres straits and Queensland in Australia (Botha et al., 2000).Spiralling whitefly is a threat to many plant, important host plant include; banana (Musa sapientum) citrus spp, coconut (Cocos nocifera) guava (Psidium quajava), tomato (Lycopersicon esculentum), pawpaw (Carica papaya), Indian almond (Terminalia catappa) (Saminathan and Jayaraj, 2001). Also Ocimum gratissimum and Manihot esculenta are host plant. Ocimum gratissimum is an herbeous perennial grass belonging to family Lamiaceae, it is generally knowns African basil, clove basil. It hails from Africa and spread throughout Hawaii and other region. The plant has reputable health benefits such as antibacterial activity, antidiabetic properties, and anthelmintic activity. A. dispersus has invaded this plant hereby reducing its medicinal benefits.
Genetic variability is important for biodiversity because without variability it is difficult for a population to adapt to its environmental changes and makes it’s to be prone to extinction (Sousa et al., 2011). This also helps to know the genetic makeup of an organism. Genetic variability of A. dispersus is being discovered using molecular techniques based on polymerase chain reaction, the RAPD-PCR. This method is widely used in applied entomology (Harry et al., 1998)
Random Amplification of Polymorphic DNA (RAPD) reaction is a PCR reaction whereby the segments of DNA that are amplified are random. In RAPD analysis the target sequence(s) to be amplified is unknown. A primer with arbitrary sequence will be designed. Polymerase Chain Reaction (PCR) is biochemical technology in molecular biology to amplify a single or few copies of a piece of DNA across several orders of magnitude, generating thousand to millions of copies of particular DNA sequence (Bartlet and Stirling 2003). Deoxyribonucleic acid (DNA) is the hereditary material in human and almost all other organism. It is a molecule that encodes the genetic instruction used in the development and functioning of all known living organism (Bruce et al., 2002). DNA are double stranded helices, consisting of two long biopolymers of simpler units called nucleotides, each nucleotides is composed of nucleobase (Guanine, Adenine, Thymine and Cytosine), as well as a backbone made by alternating sugars (deoxyribose) and phosphate group with the nucleobase (G,A,T,C) attached to the sugars (Ghosh and Bansal 2003).
1.1 STATEMENT OF THE PROBLEM
A. dispersus has the ability to cause severe damage to agricultural crops, hereby having ability to infest the lower (abaxial) surface of every plant. It is found to infest the lower (abaxial) of Citrus aurantifolia, thus increasing its infestation and adverse effect on its host plant. It is also found as a new insect pest inhabiting Ocimum gratissimum hereby reducing the economic importance of this plant.
1.2 SCOPE OF STUDY
The scope of this study covers the genetic variability of A.dispersus of C.aurantifolia and O.gratissimum using RAPD-PCR analysis technique.
1.3 SIGNIFICANCE OF STUDY
This study will enlighten researchers that genetic diversity of the species of A.dispersus which infest crops such as Citrus auarntifolia and Ocimum gratissimum. Also it will help farmers in identification of insect (Spiralling Whitefly), knowledge of the effects and how to control in Nigeria.
1.4 JUSTIFICATION OF STUDY
A.dispersus is becoming more prominent in Africa evading different plant species.it has also become new pest to some crops such as Mulberry and Africa basil, thus reducing the its economic importance. Biodiversity of these pests has being studied and genetic variability of this insect pest has being done in the recent years using different PCR analysis but little has been done in West Africa (Nigeria).
This research is to find out whether A.dispersus is found inhabitng Ocimum gratissimum are of the same genetic composition with the population found on the lower (abaxial) surface of Citrus aurantifolia using RAPD-PCR method and research was carried out in Nigeria (Ago-Iwoye, Ogun state).