Sat Sep 23, 2017 9:08 am

Togribase

TOspovirus aGRIcultural DataBASE

Mode of transmission of Tospoviruses

     Tospoviruses are transmitted by several species of thrips in a circulative and propagative manner. Similarly, single species of thrips can transmit several viruses. Among the 5500 thrips species, twelve are known vectors of tospoviruses. Adult thrips feeding on an infected plant can acquire the virus but cannot transmit. For an adult thrips to be capable of transmitting the virus (=transmitter, infective or viruliferous), the virus has to be acquired by the first or second larval stages. It then multiplies in the larvae, survives through the later developmental stages and the emerging adult thrips become infective. It is important to note that once thrips acquire the virus, they remain viruliferous (infected with virus) throughout their life span.

     The scientific reason for the ability of the adult thrips to become viruliferous only if they acquire the virus during their larval stages is that, in the first instar larva the small head capsule contains large groups of cibarial muscles that displace the supra-oesophageal ganglion far into the thorax and push the salivary glands against the mid-gut. In this stage, cells of the salivary glands fuse with the mid-gut and visceral muscle cells. In the late second instar larva the brain starts to be repositioned into the head, and so the intimate contact between the cells of the salivary glands and visceral muscles is lost. During metamorphosis large groups of wing muscles develop, and this leads to a final separation of the salivary glands from the mid-gut. As a consequence, further virus movement into the salivary glands is prevented, although subsequently there is an accumulation of virus in the malpighian tubules. Mechanical transmission through excrement and oviposition by adults is a possible alternative mode of virus transmission that requires investigation.


Transmission of multiple tospviruses by Frankliniella occidentailis and Thrips palmi

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Frankliniella occidentailisThrips palmi
Chrysanthemum stem necrosis virus
Groundnut ringspot virus
Impatiens necrotic spot virus
Tomato chlorotic spot virus
Tomato spotted wilt virus
Calla lily chlorotic spot virus
Capsicum chlorosis virus
Melon yellow spot virus
Peanut (groundnut) bud necrosis virus
Watermelon bud necrosis virus
Watermelon silver mottle virus

Virus transmission depends on the following factors: acquisition of virions, retention of acquired virions in specific sites, release of virions from retention sites upon salivation/ regurgitation and delivery of virions to site of infection.