Vector transmission processes are usually complex,
even for the seemingly simple mechanical transfer of
plant viruses to plants on the tips of vectors’ stylet-like
mouthparts (similar to a hypodermic needle) during
feeding. In many other cases, the plant parasites transmitted by insect vectors must multiply and circulate
throughout the body of the vector to be transmitted.
The most fundamental characteristic by which to
classify or categorize vector transmission is that of
transmission efficiency (also called vector competence),
or how often a vector transmits a pathogen over time
or per transmission opportunity. Transmission efficiency can increase or decrease over time after a vector
first acquires a pathogen, usually by feeding, but some
pathogens are transmitted from a mother vector to her
offspring via her eggs or embryos. Generally, vector
acquisition of pathogens increases with time spent
feeding on infected plant sources of the pathogen.
Transmission is called nonpersistent if the rate of
transmission drops to near zero within a short time
(hours). Nonpersistent transmission of viruses also differs from other types of vector–pathogen relationships
in that acquisition generally decreases rather than
increases with sustained feeding on infected plants.
Semipersistent transmission persists for, at most, a
few days after acquisition. Persistent transmission
describes situations in which the vector can transmit
over many days, in some cases, for weeks or months