Chapter 5 - Analysis of Noncirculative Transmission by Electrical Penetration Graphs

Abstract

Electron microscopy techniques have been used extensively to localize virus particles in their insect vectors. Transmission electron microscopy combined with immunogold labeling has provided information on the specific sites where helper components or virions are attached and retained inside their insect vectors. The use of cDNA technology has also helped in elucidating the mechanisms of plant virus transmission by their insect vectors. One technique that has become indispensible in transmission mechanism studies is electronic monitoring of insect probing and feeding behavior, also called the electrical penetration graph (EPG) technique. This technique has been applied to behavioral studies of insect vectors during plant virus transmission. This, in part, has been possible because of the development of an improved electronic device based on the direct current (DC) amplifier. This chapter deals with the analysis of electrically recorded probing and feeding activities of insect vectors associated with noncirculative transmission of plant viruses. Noncirculative transmission is a term that was first used by Harris to describe aphid-transmitted viruses that are not able to circulate through the hemocoel and salivary system of their vector. This type of virus–vector interaction has only been described for the insects in the order Homoptera. Noncirculative viruses have been subdivided into two main groups according to their persistence in vectors, which are nonpersistent and semipersistent.