Most known insect vectors of phytoplasmas are classified in the Order Hemiptera. This Order contains insects that possess piercing/sucking type of mouthparts. The mouthparts form stylets, narrow tube-like structures. Phytoplasma vectors use the stylets to pierce plant tissues and to feed upon contents of phloem cells, during which they acquire phloem-inhabiting phytoplasma cells.

The phytoplasma vectors collectively possess several characteristics that make them efficient vectors of phytoplasmas: (a) Nymphs and adults feed similarly and are in the same physical location\u2014often both immature insects and adults can transmit phytoplasmas. (b) They feed specifically on phloem sap. (c) They have a propagative and persistent relationship with phytoplasmas; that is, phytoplasmas multiply in the insect body, and vector insect species remain infected by phytoplasma for life. (d) The insect vectors contain obligate symbiotic prokaryotes that are passed to their offspring by transovarial transmission; in some cases the same mechanisms may allow transovarial transmission of phytoplasmas.

Phytoplasmas are phloem-limited; therefore, only phloem-feeding insects can potentially acquire and transmit the phytoplasmas. However, among phloem-feeding insects, relatively few species have been confirmed as vectors of phytoplasmas. Phytoplasma vectors include diverse leafhoppers, four families of planthoppers, and two genera of psyllids.

As noted above, phloem-feeding insects acquire phytoplasmas passively during feeding in the phloem of phytoplasma-infected plants. The insects must feed for an extended period of time to acquire a sufficient titer of phytoplasma to establish infection in the body of the insect vector. This time period is called the acquisition access period (AAP) and can be minutes to hours long.

The time that elapses, from initial acquisition (of phytoplasma during feeding) to the time when the insect is able to transmit phytoplasma to a plant upon which the insect feeds, is known as the latent period (LP) and is sometimes called the incubation period.

During the LP the phytoplasma cells, obtained during feeding on phloem cells, establish infection in insect vector gut cells, move through gut cells into the insect's hemolymph in which the phytoplasma cells circulate, and eventually infect and replicate in many tissues of the insect vector's body. To be transmitted to plants, phytoplasmas must penetrate specific cells of the salivary glands, which accumulate a high titer of phytoplasma cells and from which phytoplasma cells become incorporated into saliva that is injected into plant phloem tissue during feeding.

Human activities have introduced vector species into previously unoccupied geographical regions, sometimes resulting in very damaging phytoplasma-caused plant diseases. Management of plant diseases caused by phytoplasma has often focused on controlling the insect vector populations by applications of insecticides, but mitigation of disease is slowly shifting toward habitat management and the use of genetic methods to produce naturally disease-resistant plants.

A new and potentially powerful/effective tool is being studied, for controlling transmission of phytoplasmas by insect vectors through the manipulation of symbiotic bacteria in the insects. This approach exploits the fact that many arthropods carry symbiotic microorganisms that are required for life functions of the arthropod host. The hypothesis being tested is that an insect's symbiotic bacteria can be genetically modified to prevent the transmission of pathogens (including phytoplasmas) by the insect. Another possibility relates to the fact that phytoplasma vectors obtain nutrients through feeding on phloem tissue; thus, it may be possible to utilize the carbohydrate-binding properties of compounds such as plant lectins to interfere with the insect's nutrition, hindering the vector's capabilities.

Weintraub P.G., and Beanland L. 2006. Insect vectors of phytoplasmas. In: Ann. Rev. Entomology 51:91-111.

Weintraub, P.G. 2007 Insect vectors of phytoplasmas and their control - an update. In: Bull Insectol. 60:169-173)

For more information about phytoplasma vectors please refer to references listed elsewhere in this website.