An understanding of aphid movement between and within fields helps to explain the patterns that can be seen. aphids move by flying or walking.

Flying generally means migrations or long distance movement into fields from areas outside or from one field to another. This movement establishes individual aphid colonies and introduces BYDV into a field. These will generally be the oldest BYD infections and will exhibit the most definite symptoms.

Flitting is short distance flight, usually within a single field. "Flitting" aphids are usually the offspring from an aphid colony already established in the field. This flight may result in new aphid colonies and therefore additional BYD infection sites. These infections will be younger than the initial infection sites.

Walking is short distance movement. It results in aphid colonies spreading out from a central location. If BYDV is present the circle of infected plants will grow larger. Often the central plants in these spots will show much more obvious symptoms, with the outer plants being less vivid.

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