A great number of plant pathogens depends on upon arthropod vectors in order to be transmitted. Like human and animal pathogens, plant pathogen can also be transmitted through active and passive mechanisms.
Plant pathogenic bacteria cause many different kinds of symptoms that include galls and overgrowths, wilts, leaf spots, specks and blights, soft rots, as well as scabs and cankers (Sarah, et al 2008).These pathogens are easily spread from infected plant to uninfected plant by different insects vectors such as flies, aphids, ants, beetles, whiteflies, etc., that land on the plant and come in contact with bacteria and carry them physically to another plant.
Viruses are the second important arthropod-borne plant pathogen. As viruses that affect humans and animals, plant virus is obligatory intracellular parasites and are able to spread systemically. Many insects vectors can transmit viruses. The most important are Aphids (Aphididae), whiteflies (Aleyrodidae), leaf hoppers and plant hoppers (Fulgoroidea) (Alexander, 2005).
Phytomonas are flagellate protozoa of the family trypanosomatidae. They affect more than 100 plant species in about 12 families (Magán, 2004), and can cause more than 600 diseases (Kirkpatrick, 1992; McCoy et al., 1989). An example of disease transmitted by phytomonas is the palm tree “harrot” called the lethal yellowing of palm. Planthoppers and leafhoppers are the major insect vectors of phytomonas to plant. These pathogenic agents are found in tropical and subtropical zones, although they have been described in all continents except the Antarctic (Camargo, 1994).
Fungi are the most important plant pathogens transmitted by insects. Most of them are parasitic and microscopic organisms that reproduce mainly by spores. Plant infections with fungi occur through wounds produced by insects. Any insect vector can thus potentially spread fungi or their spores between plant, producing diseases like stem rust, corn smut, brown rot and many others, thus the transmission being mainly mechanical.
Nematodes interactions with insects have evolved many times , but few species are known to be plant pathogens (Giblin-Davis, 2003).The most tough is the pine wood nematode Bursaphelenchus xylophilus,which is vectored to the pine tree by a beetle of the family Cerambycidae in a symbiotic association with fungal pathogen (Agrios 1997) The cycles of the disease is very complex, with the immature nematodes multiplying within plant tissues and enter the spiracles of the newly molted adult beetles, which then carry it from plant to plant.