Aphids and mosaic virus
Aphids feed through their mouth parts, the labium and proboscis. The labium is is a long tubular organ housing the stylets within a groove. These stylets together are known as the proboscis. The stylets are well adapted to piercing plant tissue because of their fine tips and broad bases, which then penetrate the tissue effortlessly. A food channel opens between the maxillary stylets enabling feeding through a fabricated straw. Interestingly, the aphids rely on turgor pressure within the plan to aid in sap flowing in to them.
Aphids can cause stunting in various plants through the transmission of viral diseases. These are transmitted through sucking sap from plants as the protein receptors within the aphid mouthparts enable retention of the viroid. A good example of an Aphid transmitted virus is mosaic virus.
Mosaic virus has the biggest plant host range of any viroid including cucurbits, cucumbers, celery, lettuce, delphiniums, primulas, aquilegias, daphne, cyclamen, anemone, tomatoes, tulips, and many more. Primary virus spread is the result of aphid vectors. The infection starts in the parenchyma tissue in leaves through proboscis penetration and finds its way to the phloem, where it may infect the whole host. Infected cells are harnessed, utilising their protein synthesis systems to create further virus particles, which, in number are estimated to be between 100,000 and 10 million in each infected cell. Externally, CMV can be seen as small yellow specks on young leaves initially, followed by yellow or green patches or mottling, giving the host an obvious mosaic appearance. The leaves, fruit, and main plant may then become stunted and distorted, and the leaves may then crinkle.
Resistant cultivars can be selected, and cultural practices such as disposing infected plant matter, and keeping areas weed free can minimize spread, along with good sanitation practices. Unfortunately, aphid control isn’t possible outdoors. However, inside glass houses pest control measures can be implemented.