ARTHROPOD RELATIONSHIPS WITH VIRUSES 31 
fact is no longer significant for virus transmission because the beetle 
vectors and their larvae lack salivary glands, and the mechanism of 
transmission, as previously mentioned, is probably by regurgitation 
of infected material from the crop. This supposition is further 
strengthened by the apparent inability of lepidopterous larvae, which 
do not regurgitate, to transmit the virus. 
When non-viruliferous leaf-hoppers are inoculated in the abdomen 
with the virus of which they are the natural vectors, they become 
viruliferous and transmit the virus because the virus enters the blood 
and later the saliva. But when the beetle larvae vectors of turnip 
yellow mosaic virus are inoculated in the abdomen, they do not 
become viruliferous. In this case presumably the virus simply passes 
outside the body with the faeces; it cannot pass upwards into the 
crop and be regurgitated because of the valve situated at the posterior 
end of the crop (Markham and Smith, 1949). 

